Nuclei in the Cosmos - IX

CERN, Geneva

CERN, Geneva

International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX
    • 17:00 20:00
      Registration Restaurant #1

      Restaurant #1

      CERN, Geneva

      Registration will commence at 17.00h and end at 20.00h. This
      will take place in the Main Restaurant No 1 at CERN. We will
      be offering one refreshment and you will be able to purchase
      drinks from the bar. You will be given your conference bag
      and envelope with your detailed information pack.

      The CERN Restaurant will be open until 19.30h this evening
      and will be serving items from their grilled menu.

    • 09:00 09:30
      Introduction CERN Main Auditorium

      CERN Main Auditorium

      CERN, Geneva

      Convener: Alberto Mengoni (IAEA, Vienna/CERN n_TOF)
      • 09:00
        Welcome 10m
        Speaker: Jos Engelen (CERN CSO)
      • 09:10
        In memory of Al Cameron 10m
        Speaker: John Cowan
      • 09:20
        In memory of John Bahcall and Ray Davis 10m
        Speaker: Peter Parker
    • 09:30 11:00
      1 Stars: observations, evolution & nucleosynthesis
      Convener: Michael Wiescher (U Notre Dame)
      • 09:30
        Nuclear astrophysics with gamma-ray line observations 30m
        Gamma-ray spectrometers with high spectral resolution are operating in space since 2002: RHESSI and SPI on INTEGRAL. Understanding the instrumental response and backgrounds is major effort but a prerequisite of detailed science interpretations. While 44Ti from core collapse supernovae could not be detected, this still adds constraints to Cas A 44Ti ejection. Diffuse nucleosynthesis is studied through 26Al, 60Fe, and positron annihilation gamma-ray measurements. With SPI on INTEGRAL, the gamma-ray line from decay of radioactive 26Al could be measured at unpredecented spectroscopic precision. This made possible a new determination of the total mass of 26Al produced by stellar sources throughout the Galaxy, and an analysis of the properties of the interstellar medium around 26Al sources. 60Fe is clearly detected with SPI, its intensity ratio to 26Al is confirmed to be on the lower side of theoretical predictions. Nucleosynthesis sources are probably minor contributors to Galactic positrons, as deduced from the bulge-centered spatial distribution of the annihilation gamma-ray emission.
        Speaker: Roland Diehl (MPE Garching)
      • 10:00
        From massive stars to supernovae 30m
        I will give a review on the evolution of massive stars and their paths to supernovae. Depending on their initial parameters, e.g., initial mass, metalicity, mass loss, and rotation, different kinds of supernovae are the result: normal core collapse supernovae, collapsar-powered supernovae like gamma-ray bursts, or even pair-instability supernovae. Similarly varied are the possible remnants of these supernovae and their nucleosynthesis. While the lowest mass stars may have only very little ejecta, the most massive pair-instability supernovae may eject as much as hundred solar masses in metals, out of which up to half can be radioactive nickel 56. I will present recent results of extended grids of nucleosynthesis of stars of low metallicity.
        Speaker: Alexander Heger (Los Alamos/UC St Cruz)
      • 10:30
        The rp-process and X-ray bursts 30m
        Accreting neutron stars in X-ray binaries provide a unique laboratory for thermonuclear burning at extreme temperature and density conditions. A range of newly discovered, and largely puzzling, observables needs to be understood and interpreted. A key in this endeavor is the understanding of the underlying nuclear physics of unstable nuclei that span the entire range from the proton drip line to the neutron drip line. X-ray bursts and the rp-process play a central role in this context. I will discuss recent advances in our unserstanding of these systems from the observational, theoretical, and the experimental side. Concerning the latter, particular attention is payed to advances in the capabilities of radioactive beam facilities such as the National Superconducting Cyclotron laboratory at Michigan State University, where indirect methods have been developed to better constrain thermonuclear reaction rates at X-ray burst conditions.
        Speaker: Hendrik Schatz (National Superconducting Cyclotron Laboratory, MSU)
    • 11:00 11:45
      break 45m
    • 11:45 13:15
      2 Experiments in nuclear astrophysics I
      Convener: Alan Shotter (TRIUMF)
      • 11:45
        Underground Nuclear Astrophysics 30m
        Cross section measurements for quiescent stellar H and He burning are hampered mainly by extremely low counting rate and cosmic background. Some of the main reactions of H-burning phase have been measured at the LUNA facility (Laboratory for Underground Nuclear Astrophysics) taking advantage of the very low background environment of the Underground Gran Sasso National Laboratory in Italy. An overview of the adopted experimental techniques will be given together with the latest results on the 14N(p,)15O reaction and the status of the ongoing experiments. Furthermore a brief summary of possible future experimental methods coupling low background environment and detector techniques will be presented.
        Speaker: Heide Costantini (U Genova/Notre Dame U)
      • 12:15
        The 26gAl(p,g)27Si reaction in Novae 20m
        The strength of the 188 keV resonance in the 26gAl(p,g)27Si reaction has been measured directly in inverse kinematics using the DRAGON recoil separator at TRIUMF-ISAC. Radioactive 26Al beams with peak intensities of 5 x 10^9 ions/sec were utilised in conjunction with a windowless, recirculating hydrogen gas target. Recoil 27Si ions were separated and detected with a double-sided silicon strip detector in coincidence with capture gamma-rays at the target position in a highly efficient BGO detector array. Background from random coincidence was separated using time-of-flight through the length of the separator. Measured silicon charge state distributions using a 28Si beam, combined with stopping power information measured in the gas target allowed determination of the strength of this resonance at the level of <20% error. In addition, the resonance energy was measured via the distribution of gamma-ray hits in the BGO array, leading to the conclusion that it is lower than previously thought. The 188 keV resonance dominates the reaction rate at typical Oxygen-Neon Nova temperatures and the formation of 26Al in Novae depends sensitively on the value of this rate. We have found a value of resonance strength differing from the only existing unpublished measurement that has been used in the reaction networks so far in Nova nucleosynthesis models. The results of the experiment will help determine the importance of Novae as originators of Galactic 26Al compared to other sources, and we discuss the implications of the measurement in this context.
        Speaker: C Ruiz (TRIUMF, Vancouver, BC V6T 2A3, Canada)
      • 12:35
        Direct measurement of the 18F(p,a)15O reaction for application to nova gamma-ray emission. 20m
        The 18F nucleus is one of the radioactive isotope produced during nova explosions. It is of particular interest since it is the main responsible for the 511 keV gamma-ray emission of novae that could be detected with the INTEGRAL satellite or future gamma-rays telescope. The amount of 18F synthesised still suffers from large uncertainties coming from missing nuclear information concerning the destruction reaction of 18F: 18F(p,alpha)15O. In particular, the interference sign between three 3/2+ resonances in 19Ne, situated slightly above the proton threshold (8 keV and/or 38 keV) and at higher energy (665 keV), is unknown. The maximum effect of these interferences is lying in the energy range corresponding to the Gamow peak region, having a strong impact on the 18F(p,alpha)15O reaction rate. We report here on the direct measurement at low energy (down to 400 keV in the center of mass) of the 18F(p,alpha)15O total cross section that we performed at the Louvain-la-Neuve CRC-RIB facility with the high intensity and purity 18F radioactive beam (T1/2 = 110 min). Total cross-section for the different incident energies will be presented and compared to previous experimental data, followed by a R-matrix analysis aiming at the determination of the interference sign of the relevant resonances.
        Speaker: Nicolas de Sereville (Universite catholique de Louvain)
      • 12:55
        Measuring Difficult Reaction Rates Involving Radioactive Beams: A New Approach 20m
        Rates of sub-barrier, radiative capture reactions involving radioactive reactants, needed for understanding various astrophysics explosive scenarios, are often quite difficult to measure directly at relevant stellar temperatures. In general relatively intense radioactive beams (>1011/s) are needed for these inverse kinematic studies, as cross sections are very low. A new production approach is proposed herein that would supply such required intensities in a relatively straightforward fashion. While this system may have many applications, one area could be increasing our understanding of classical novae and X-ray bursts. 25Al (p,g), 30P(p,g), and 15O(a,g)19Ne are key reactions in our understanding of nova outbursts and/or X-ray bursts and their nucleosynthetic imprints in the Galactic abundances. The first one is important for the synthesis of 26Al, since it determines the amount of nuclear flow that bypasses 26Al synthesis through the isomeric state, 25Al(p,g)26Si(b+)26mAl. Hence, reliable predictions of the contribution of novae to the Galactic 26Al content depend critically on this rate. In turn, 30P(p,g) determines the path through the Si-Ca region in nova outbursts, and therefore, is crucial in the synthesis of these intermediate-mass elements, and for the location of the nucleosynthesis endpoint in such explosions. Moreover, competition between 30P(p,g) and 30P(b+) determines the final amount of 30Si, an important signature that helps to identify presolar meteoritic grains of a likely nova paternity. The 15O(a,g)19Ne reaction is believed to be the breakout path of the hot CNO cycle in an X-ray burst leading to the rp process. It is important to our understanding of ignition temperatures for the rp process to know the absolute value of this rate, rather than an upper limit. In this presentation a new approach to the production of required radioactive beam intensities is described which may lead to measurements of the rates of these key reaction.
        Speaker: Mats Lindroos (CERN)
    • 13:15 14:30
      lunch 1h 15m
    • 14:30 16:10
      3 Nuclei far from stability
      Convener: Karlheinz Langanke (GSI, Darmstadt)
      • 14:30
        Nuclear-physics data for modeling of the r-process 30m
        Nucleosynthesis theory predicts that about half of the chemical elements above iron are formed in explosive stellar scenarios by the r-process, i.e. a combination of rapid neutron captures, inverse photodisintegrations, and slower beta-decays, beta-delayed processes, as well as fission and possibly interactions with neutrinos. A correct modelling of this process, therefore, requires the knowledge of nuclear properties very far from stability and a detailed description of the astrophysical environments. With respect to nuclear data, after an initial period of measuring ''waiting-point'' nuclei with magic neutron numbers, recent investigations have paid special attention to shape transitions and the erosion of classical shell gaps with possible occurrence of new magic numbers. The status of experimental and theoretical nuclear data on masses and beta-decay properties will be briefly reviewed, and consequences on the overall r-process matter flow up to the cosmochronometers Th-232 and U-238 will be discussed.
        Speaker: Karl-Ludwig Kratz (Institut für Kernchemie, Universität Mainz)
      • 15:00
        Progress in the investigation of nuclei approaching the r-process waiting point A=195 20m
        The complete understanding of the r-process still remains a challenge not only because of the identification of the possible astrophysical sites but also because of the interpretation of the observed abundances. With respect to this latter point, one of the main problems we have to overcome to fully understand the observed r-process abundances is the lack of information on the nuclei participating in this process, in particular for the heaviest ones. The main reason for this is that the heavy nuclei involved in the r-process are so neutron-rich that until now they have been far from any experimental access. During the last years promising results have been obtained investigating the properties of medium-mass neutron-rich nuclei close to the waiting point A=130 [1] while the waiting point around A=195 remains a completely unexplored territory. Nevertheless, the possibility to accelerate heavy ions at relativistic energies has allowed the investigation of reactions mechanisms leading to the production of heavy neutron-rich nuclei such as cold-fragmentation reactions [2]. In this work we report on an experiment performed with the FRS at GSI to explore the production of heavy neutron-rich nuclei close to the neutron shell N=126 and to measure their beta half-lives. We used cold-fragmentation reactions induced by a 208Pb beam at 1 AGeV impinging a Be target to produce heavy neutron-rich nuclei south of lead. The isotopic identification of the projectile residues was achieved by determining both the atomic number and the mass-over-charge ratio of each nucleus by measuring their magnetic rigidity, time-of-flight and energy loss. The identified nuclei were implanted in an active catcher made of four 5x5 cm2 Double- Side Silicon Strip Detectors 1 mm thick. The position and time correlations between the implanted nuclei and the subsequent beta decay allowed the determination of the beta half-lives. In this measurement we were able to identify for the first time around 30 new neutron-rich nuclei approaching the neutron shell N=126. In addition, the half-life of some of them has been determined. These half-lives have been compared with model calculations [3,4] which in general do not reproduce the measured values. This work opens new perspectives for further detailed spectroscopic investigations coupling with gammas that will allow us better understand the structure and decay properties of the A=195 waiting point nuclei. [1] Dillmann I., Kratz K.-L., et at Phys. Rev. Lett. 91, 162503 (2003) [2] Benlliure J., et al. Nucl. Phys. A 660, 87, (1999) [3] Tachibana T. et al. Proc. Int. Conf. on Exotic Nuclei and Masses, A 660, Arles, 763 (1995) [4] P. Möller et al. Atomic Data and Nuclear Data Tables, 66, 131 (1997)
        Speaker: Teresa Kurtukian-Nieto (Universidad de Santiago de Compostela,Spain)
      • 15:20
        Building nuclei from the ground up 20m
        Investigations of rare isotopes in the laboratory are opening the way to understand and clarify the properties of all nuclei and bulk nuclear matter. In this talk I will assess where we stand today in solving the nuclear problem and how future rare isotope facilities will impact our understanding of nuclei and our ability to predict nuclear properties in stellar and other environments. The first part of the nuclear problem concerns our ability to describe complex nuclei from the ground up using as input the basic interactions among protons and neutrons. Indeed, our community is on the verge of discovering how light nuclear systems are built from bare nuclear interactions that have their roots in QCD. I will describe this exciting frontier of research through illustrating recent progress in the nuclear implementation of coupled-cluster methods, a quantum many-body technique that enjoys great success in quantum chemistry. After describing the basic coupled-cluster ideas, I will illustrate their power by reporting on results of ground- and excited state calculations for Oxygen and Calcium nuclei. This research is supported by the Office of Nuclear Physics, Office of Science of the U.S. Department of Energy under Contract Number DE-AC05-00OR22725 with UT-Battelle, LLC (Oak Ridge National Laboratory).
        Speaker: Gaute Hagen (ORNL)
      • 15:40
        Mass measurements of exotic nuclei and their role in stellar nucleosynthesis 30m
        The mass of nuclides far from stability provides information on decay and reaction energies that is crucial for modeling stellar nucleosynthesis. Low production rates, short half-lives, and the inherent precision required make masses perhaps the most difficult nuclear quantity to measure. The minuteness of the binding energy has also contributed to confounding attempts at reliable theoretical mass predictions. This talk will introduce the role played by masses in astrophysics and then quickly review and compare the (growing) multitude of mass-measurement programs now active worldwide. The evaluation process that links reaction, decay and binding energies is also described with its production of a benchmark for the development of the the mass models required by nucleosynthesis networks.
        Speaker: David Lunney (Université de Paris Sud)
    • 16:10 17:10
      break + poster session 18

      Poster sessions will be held outside the Main Auditorium, in the CERN Main building.

      No oral presentation of poster contributions is schduled.

      Poster session 18
    • 17:10 18:20
      4 Big-bang nucleosynthesis
      Convener: Carmen Angulo (Université catholique de Louvain)
      • 17:10
        Recent results in Big-Bang Nucleosynthesis 30m
        Primordial nucleosynthesis (BBN) has been used for the determination of the baryonic density of the universe. It has now been superseded, for this purpose, by the more precise determination provided by the analysis of the CMB anisotropies by WMAP. Nevertheless, BBN is still very interesting as when we look back into the history of the universe, this is the last era for which, in principle, we know all the physics. Deviation from BBN predictions can hence give hints on non-standard Big Bang models. It is thus important that nuclear reactions involved in BBN be known with a good accuracy. Two recent nuclear physics experiments have improved the reliability of lithium calculated yields in standard big-bang nucleosynthesis. The cross section for the 7Be(d,p)2alpha reaction has been directly measured at BBN energies at Louvain-la-Neuve. A coulomb break-up experiment has provided a better determination of the D(alpha,gamma)6Li cross section over a wide energy range. Nevertheless, the discrepancy between the primordial 7Li abundance deduced from halo stars observations and BBN remains and the BBN 6Li production is still orders of magnitudes below the reported 6Li observations in some halo stars. Now that the baryonic density is accurately provided by the analysis of the CMB anisotropies, BBN can be used to constrain non-standard models: scalar-tensor theories of gravity for instance.
        Speaker: Alain Coc (CSNSM,CNRS/IN2P3 and Universite Paris Sud)
      • 17:40
        Is Deuterium Cosmological? 20m
        All the astronomical observations of deuterium are consistent with a cosmological origin of D. Deuterium has been extensively studied because it is not produced via stellar nucleosynthesis and is thought to be primarily produced via the big-bang so its abundance will only decrease with time unless there are additional sources of D. The D/H ratio is an important prediction of standard and non-homogeneous big-bang models because the abundance of D depends critically on the temperature and baryonic density during the epoch of nucleosynthesis (first 1000 seconds). In homogeneous inflationary or other flat models, the D/H ratio gives the amount of dark matter and an upper limit to the number of neutrino families. Any Galactic source of D would undermine its use to estimate the baryonic density of the universe and place constraints on big-bang nucleosynthesis models. D nucleosynthesis models have included supernovae, supernovae shock-waves, cosmic-ray spallation reactions, accretion disks around neutron stars or black holes, gamma-ray photospallation reactions, stellar flares, and a large proton flux during an early active phase of the Galaxy as possible sources for deuterium. If D is produced via any stellar or Galactic nucleosynthesis process, then its abundance would be a maximum value in the Galactic Center (which is the most active and heavily processed region of the Galaxy). We review observations of deuterium in the Galaxy, external galaxies, active galaxies, and in quasar absorption systems, including our own observations. D has been detected in molecular clouds, diffuse clouds, HI regions, and HII region from observations of deuterated molecules, Lyman lines, Balmer lines, QSO absorption lines, and the DI 92-cm hyperfine-structure line. The Galactic D/H ratios range from 2 ppm in the Galactic Center to 23 ppm towards the anticenter (12 kpc from the GC). The QSO D/H ratios range from 20 – 30 ppm. Deuterium has not been detected in planetary nebulae, SNRs, or AGN. Because the D/H ratio is lowest value in the Galactic Center yet increases with distance from the Galactic Center, D is not produced via stellar or galactic activity (massive stars and star formation, cosmic rays, or stellar flares). Thus the observed D is cosmological with the observed D abundances reduced by astration, infall, mixing, and depletion onto grains.
        Speaker: Donald Lubowich (Hofstra University, Hempstead, New York)
      • 18:00
        New measurement of the cross section of the Big Bang nucleosynthesis reaction D(a,g)6Li and its astrophysical impact 20m
        The recent observations of non-negligible amounts of 6Li in old halo stars [1] have renewed interest in the Big-Bang Nucleosynthesis (BBN) of 6Li. The deduced primordial 6Li abundance was found to be unexpectedly large compared to the BBN predictions. One important ingredient in the BBN predictions is the low-energy D(a,g)6Li cross section. Up to now, the only available experimental result [2] for this cross section introduced an error of about a factor of 20 in the 6Li abundance at the energies of astrophysical interest (Ecm<300 keV). This uncertainty arises from the discrepancy between the theoretical low energy dependence of the S-factor and the experimental data. Accordingly, new measurements of the cross section of the D(a,g)6Li reaction using Coulomb dissociation (CD) of 6Li at 150 A MeV have been performed recently at GSI. The preliminary GSI results, which indicate a drop of the S-factor as predicted by theory [3] will be presented as well their impact on the calculated 6Li abundance as a function of the baryon-to-photon ratio eta. [1] M. Asplund et al., astro-ph/0510636, Astrophys J. in press [2] J. Kiener et al., Phys. Rev. C 44, 2195 (1991) [3] A. Kharbach et al., Phys. Rev. C 58, 1066 (1998)
        Speaker: Fairouz Hammache (IPN-Orsay)
    • 18:50 20:50
      Convener: Mats Lindroos (CERN)
    • 08:30 10:30
      5 Element production and stellar evolution: MP/UMP and Novae
      Convener: André Maeder (Geneva Observatory)
      • 08:30
        r-Process Enhanced Metal-Poor Stars 30m
        Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities -- which disappears with increasing metallicity or [Fe/H] -- suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture ( i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of the Galaxy, and hence the Universe.
        Speaker: John Cowan (University of Oklahoma)
      • 09:00
        The First Nova Explosions 20m
        Classical nova outbursts are powered by thermonuclear runaways (hereafter, TNRs) that take place in the hydrogen-rich accreted envelopes of white dwarfs in close binary systems. Extensive numerical simulations of nova outbursts have shown that the accreted envelopes attain peak temperatures ranging between 100 and 400 MK for about several hundred seconds, and therefore, their ejecta is expected to show signatures of a significant nuclear activity, Indeed, it has been claimed that novae can play a certain role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes 17O, 15N and 13C, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution in a number of other species with A < 40, such as 7Li, 19F, or 26Al. Estimates of the contribution of novae to the Galactic abundances usually rely on poorly known quantities, and implicitly assume that novae have been the same sort of objects during the whole Galaxy's history: that is, an explosion on a particular white dwarf, of a given mass and luminosity, is today similar to those contaminating the interstellar medium in the early epochs of the Galaxy. In this presentation, we analyse the first nova explosions and demonstrate that these objects were more important contributors to the Galactic abundances in the past.
        Speaker: Jordi Jose (Institut d'Estudis Espacials de Catalunya/UPC)
      • 09:20
        Mass loss at very low metallicity: impacts on nucleosynthesis and GRB progenitors 20m
        Massive stars with no or very little amount of metals are generally considered as having very weak stellar winds. We reconsider here this question through stellar models accounting for the effects of axial rotation and show that rotating models of massive stars might lose a significant fraction of their initial mass through mass loss. The physical mechanisms triggering these mass losses and the chemical composition of the stellar winds will be discussed. Consequences of these models for nucleosynthesis and the nature of the GRB progenitors will be presented.
        Speaker: Georges Meynet (Geneva Observatory)
      • 09:40
        Chemical Compositions Derived from Near Ultra-Violet Observations of Low-Metallicity Stars: New Insights into the Sites of Neutron-Capture Nucleosynthesis Processes 30m
        Numerous signatures of r- and s-process nucleosynthesis can be observed in the photospheres of stars. To date, however, the stellar abundance determinations of many of the elements have been scarce because a large portion of the dominant atomic transitions reside in the UV. To be reported in the context of other recent results of neutron-capture studies, are the abundances (or upper limits) of Nb, Pd, Ag, Yb, Hf, Pt, Pb, and other neutron-capture elements for a sample of stars observed with the near-UV sensitive detector on the High Resolution Echelle Spectrometer of the Keck I telescope.
        Speaker: Inese Ivans (Carnegie Observatories & princeton university)
      • 10:10
        The Frequency of Carbon-Enhanced Stars in HERES and SDSS 20m
        Recent large surveys of metal-poor stars in the Galaxy have revealed that a surprising fraction of them are enhanced in their carbon-to-iron ratios by factors of from 10-10,000 relative to the solar ratio. Although most of the stars in the metallicity interval -2.7 < [Fe/H] < -2.0 are likely to have arisen from Asymptotic Giant Branch processing (and subsequent dumping via mass transfer to a surviving companion), there exist many stars with [Fe/H] < -3.0 (including the two lowest [Fe/H] stars known, with [Fe/H] < -5.0) that cannot be accounted for by this process. Rather, primordial (or nearly primordial) progenitors are implicated. We report on the existing information from present surveys, including cool giants from the recently completed HERES (Hamburg/ESO R-process Enhanced Star) survey, and from warm turnoff stars from SDSS-I. We will also describe the results that will come from the recently-funded extension of the SDSS, which includes the program SEGUE = Sloan Extension for Galactic Understanding and Exploration. SEGUE will identify some 20,000 stars with [Fe/H] < -2.0, several thousand of which are expected to be carbon enhanced. New carbon-enhanced models have been used in the analyses of these spectra, and we consider the impact of these models on the derived [Fe/H], [C/Fe], and in some cases, [N/Fe], that are derived.
        Speaker: Timothy Beers (Michigan State University and JINA)
    • 10:30 11:30
      break + poster session 19

      Poster sessions will be held outside the Main Auditorium, in the CERN Main building.

      No oral presentation of poster contributions is schduled.

      Poster session 19
    • 11:30 13:30
      6 Evidence of nucleosynthesis in stars and presolar grains
      Convener: Roberto Gallino (Universita' di Torino/INFN Torino)
      • 11:30
        Heavy elements in presolar grains: constraints on conditions in asymptotic giant branch stars 30m
        Presolar SiC grains come from a variety of kinds of stars, but the most common type, the mainstream grains, are believed to have formed in the outflows of low mass, carbon-rich asymptotic giant branch (AGB) stars. Measurements of the isotopic composition of the s-process elements Sr, Zr, Mo, Ru and Ba in individual mainstream SiC grains allow constraints of the range of conditions used in stellar models of AGB stars.
        Speaker: Andrew Davis (University of Chicago)
      • 12:00
        On the stellar sources of presolar graphite in primitive meteorites 20m
        Primitive meteorites contain graphite spherules whose anomalous isotopic compositions indicate a stellar origin [1]. Because the isolation of presolar graphite grains is difficult, they have been less well studied than presolar SiC and presolar oxide grains. It has been known that the isotopic compositions of presolar graphite grains depends on their density, but detailed isotopic measurements have been made only on low-density (<2 individual grains [2]. The NanoSIMS ion microprobe has enabled us to measure O and Si isotopic ratios in graphite grains with a range of densities from the carbonaceous chondrites Murchison and Orgueil [3-5]. These measurements confirm that low-density grains originated from supernovae and indicate that most high-density (>2 grains come from C-rich AGB stars of low metallicity. Low-density grains and a few grains of higher density are characterized by large 18O and 28Si excesses that are signatures of Type II supernovae. Many high-density grains have high 12C/13C ratios (>300) and large excesses in 30Si and smaller ones in 29Si. These are best explained by low-metallicity AGB stars. In these stars the enrichments of the envelope in the heavy Si isotopes and in 12C, products of nucleosynthesis in the He shell, are much larger than those expected for solar-metallicity parent stars. The high 12C/13C ratios imply also high C/O ratios, which cause the preferential condensation of graphite grains over SiC grains. The Ne-E(L) component, almost pure 22Ne, which is characteristic of presolar graphite and led to its discovery [6], apparently has two sources [7]. In SN grains it is due to the decay of short-lived (T1/2 = 2.6 yr) 22Na, which condenses into the grains, whereas in AGB grains it is due to the abundant 22Ne in the He shell, produced by α-captures on 14N, the result of previous H burning in the CNO cycle. [1] Hoppe P. et al. (1995) Geochim. Cosmochim. Acta 59, 4029-4056. [2] Travaglio C. et al. (1999) Astrophys. J. 510, 325-354. [3] Amari S. et al. (2004) Meteorit. Planet. Sci. 39, A13. [4] Amari S. et al. (2005) Meteorit. Planet. Sci. 40, A15. [5] Jadhav M. et al. (2006) New Astron. Rev. submitted. [6] Amari S. et al. (1990) Nature 345, 238-240. [7] Amari S. (2006) New Astron. Rev. submitted.
        Speaker: Ernst Zinner (Washington University)
      • 12:20
        Isotopic Composition of Presolar Spinel Grain OC2: Constraining Intermediate-Mass Asymptotic Giant Branch Models 20m
        Presolar spinel (MgAl2O4) grains have been recently discovered in meteorites and represent the most abundant type of presolar oxides. The O, Mg and Al isotopic compositions of the vast majority of presolar oxide grains indicate that these grains originated in red giant and asymptotic giant branch (AGB) stars of masses lower than approximately 3 solar masses. Grain OC2 has a unique composition, showing most extreme O and Mg isotopic ratios among presolar oxide grains: O17/O16 three times higher than solar, O18/O16 26 times lower than solar, and excesses in Mg25 and Mg26 of (43+/-1)% and (117+/-1)%, respectively, with respect to solar. Its origin has thus been tentatively attributed to an AGB star of intermediate mass, around 5 solar masses. In intermediate-mass AGB stars the heavy Mg isotopes are produced in the He intershell by alpha-capture reactions on Ne22, while the O and Al compositions are mostly determined by proton captures at the base of the convective envelope (hot bottom burning). Using detailed models of AGB stars of different masses and metallicities that include Vassiliadis & Wood mass-loss rates and time-dependent convective mixing during the nucleosynthesis postprocessing, we analyse the O, Mg and Al compositions in AGB stars and discuss them in the light of the extremely precise measurements of the composition of grain OC2.
        Speaker: Maria Lugaro (University of Utrecht)
      • 12:40
        Ne22 a primary source of neutron for the s-process and a major neutron poison in CEMP AGB stars 20m
        In AGB stars of low mass and very low metallicity, [Fe/H]<-2, a large abundance of C12 is mixed with the envelope by each third dredge up episode. The further activation of the H burning shell at the bottom of the envelope converts almost all CNO nuclei into N14. Thus the H-burning ashes contain N14 from the original CNO nuclei, plus an increasing amount of primary N14. During the subsequent convective thermal instability in the He shell, all N14 nuclides present in the He intershell are converted to Ne22 by double alpha capture on N14 during the early development of the thermal instability. At the peak temperature reached at the base of the thermal pulse, the Ne22(alpha,n)Mg25 reaction is partly activated, giving rise to an efficient neutron exposure feeding the s-process. At the same time, although the neutron capture cross section of Ne22 is very small (MACS(Ne22,30Kev)=0.059+-0.0057 mbarn, Beer et al. 1991), Ne22 acts as a major poison against the s-process. This poison effect is substantial also in case of addition of a C13-pocket with a range of neutron exposure efficiencies. Some fraction of primary O16 is also made in the thermal pulse by alpha capture on C12 (with mass fraction X(O16) = 0.04, while X(C12) = 0.20). Besides C12 and Ne22, a number of light isotopes are largely produced in a primary way, among which F19 (from neutron capture on O18, and other channels as well), Ne21, Na23, some Mg24, Mg25, Mg26. An effort should be devoted to the measurement of the MACS of all the light isotopes involved with improved accuracy, in order to better constrain both the s-process efficiency and the production of light isotopes in these stars.
        Speaker: Roberto Gallino (University of Torino)
      • 13:00
        Accelerator Mass Spectrometry and Nuclear Astrophysics 30m
        Accelerator Mass Spectrometry (AMS) is an extremely sensitive method for determination of rare ions. Besides ongoing applications in quite different scientific fields it is still a rather new tool in nuclear astrophysics. In this presentation I will show the reasons for this unique sensitivity and where are the limits: from the table top machine too a large facility. Applications in nuclear astrophysics range from direct determination of nuclear synthesis in the past until measurements of relevant cross sections. Examples of recent and also ongoing measurements will be discussed.
        Speaker: Gunther Korschinek (Fachbereich Physik, Technische Universität München)
    • 13:30 14:30
      lunch 1h
    • 14:30 16:30
      7 Experiments in nuclear astrophysics: indirect methods
      Convener: Claudio Spitaleri (Universita' di Catania/INFN Catania)
      • 14:30
        Indirect techniques in nuclear astrophysics - ANCs and THM 30m
        A puzzle in gamma ray astronomy has been the lack of a signal from the decay of 22Na in novae sites. The isotope should be produced in the Ne-Na cycle following the proton capture reaction 21Na(p,gamm)22Mg and then the beta decay of 22Mg to 22Na. A reaction that could play a role in understanding the lack of a signal gamma-ray astronomy is 22Mg(p,gamma)23Al. Depending on the stellar conditions, this reaction could reduce the amount of 22Na that occurs in a novae. Little is known about the reaction rate for proton capture on 22Mg. Furthermore there is a question about the spin-parity of the ground state of 23Al which can change the reaction rate by more than an order of magnitude depending on whether the ground state is 1/2+ or 5/2+. Two separate experiments have been carried out at the Texas A&M University Cyclotron Institute to better understand this reaction rate. We have obtained the asymptotic normalization coefficient for 22Mg+p to 23Al using the 13C(22Ne,23Ne)12C reaction and mirror symmetry. We also have determined the spin-parity for the ground state of 23Al by observing its beta decay to 23Mg. With this new information, we can now determine the direct capture rate for this reaction which fixes the stellar reaction rate and provides a basis for evaluating the importance of the capture reaction in depleting 22Na in novae.
        Speaker: Robert Tribble (Texas A&M University)
      • 15:00
        Reaction rate of 15O(alpha,gamma)19Ne via indirect measurements 20m
        15O(alpha,gamma) is one of the main breakout reactions from the hot CNO cycles, which triggers the thermonuclear runaways or X-ray bursts occurring in accreting neutron stars. A recent study has shown that this reaction is critical for the burst amplitude and periodicity of X-ray bursters. However, a direct measurement of this reaction rate at astrophysically relevant temperatures is not feasible yet due to the lack of very high intensity radioactive 15O beams. There has been considerable effort in the past to investigate this reaction rate indirectly by obtaining gamma and alpha decay widths of the alpha-unbound states in 19Ne. While this approach has been successful for investigating higher energy resonances, the critical level at 4.03 MeV remains unknown. This leaves the reaction rate largely uncertain since previous attempts have only provided limits on its gamma width and its alpha decay branching ratio. In this talk we present new experimental work conducted at the University of Notre Dame. Lifetimes of the 4.03 MeV state and other relevant states in 19Ne have been measured successfully using the 17O(3He,n-gamma) reaction. We will also present the results of our recent measurement of the alpha-decay branching ratios. Alpha-unbound states in 19Ne were populated via the reaction 19F(3He,3H-alpha) and triton-alpha coincidences were observed using a low energy particle detection Silicon array and the TWINSOL facility. The experimental results and the astrophysical implications will be discussed in the presentation.
        Speaker: Wanpeng Tan (University of Notre Dame)
      • 15:20
        Study of astrophysically important resonant states in 26Si by the 28Si(4He,6He)26Si reaction 20m
        The emission of 1.809 MeV gamma-ray from the first excited state of 26Mg followed by beta-decay of 26Al in its ground state (26Alg.s.) has been identified by gamma-ray telescopes such the Compton Gamma-Ray Observatory (CGRO). To resolve controversy over the possible sources of the observational 1.809 MeV gamma-rays, one needs accurate knowledge of the production rate of 26Al. The 25Al(p,gamma)26Si reaction which is the competition reaction for production of 26Alg.s. is one of the important subjects to be investigated. Illiadis et al. suggested that the 25Al(p,gamma)26Si reaction is dominated by the 3+ unnatural parity state under explosive Hydrogen burning conditions. Recent studies of 28Si(p,t)26Si, 24Si(3He,ngamma)26Si, and 29Si(3He,6He)26Si reduced the uncertainties in the 26Si levels above the proton threshold and identified new states as a candidate for the unnatural parity state. However, for the candidate, they could not make any spin assignment directly using the angular distribution measurement. In this work, the astrophysically important 26Si states were studied via the 28Si(4He,6He)26Si reaction which can excite unnatural parity state directly, which is contradictory to the (p,t) reaction that can not excite unnatural parity state. We have preformed an angular distribution measurement using the high resolution QDD spectrograph (PA) at Center for Nuclear Study (CNS), University of Tokyo. The experimental results and data analysis will be presented.
        Speaker: Young Kwan KWON (Department of Physics, Chung-Ang University, Seoul 156-756, Republic of Korea)
      • 15:40
        Influences on the triple alpha process beyond the Hoyle state 20m
        The triple alpha process, the fusion of three alpha particles, is responsible for the main stellar production of 12C. It is known that the rate of this process is dominated by the 7.65 MeV resonance predicted by Hoyle and identified in 1953 [1]. At present two reaction rates are widely employed [2,3]. Work is ongoing to improve these rates both at the most important temperature range [4], and for temperatures where other natural parity resonances in 12C play a role [5] which is where the two existing rates actually differ. To clarify the latter, we present a detailed experimental analysis of the 0+ and 2+ strength in the triple alpha continuum above the Hoyle state and investigate their influence on the triple alpha process. Since the 0+ and 2+ states in question show a strong coupling to the triple alpha continuum, they are broad and not easily distinguished among the other states in this 12C energy region. Our approach is to selectively fed the states through the beta decay of 12N and 12B, and we detect the subsequent triple alpha breakup to identify the states. A new experiment (IG301) with improved detector setup has been performed at the IGISOL separator, Finland, to allow a detailed analysis of the properties of the states. We use a setup of segmented silicon detectors to measure triple alpha coincidences with a sufficient detection efficiency in most regions of three particle phase space. This has for example permitted us to observe previously unknown breakup channels involving the 8Be 2+ exited state. Since the 12C states overlap in energy and some have the same spin and parity they interfere. This is evident from the data and our analysis takes this into account. In this way we determine: properties of the states; their interference; and their coupling to the possible breakup channels 8Be(0+)+alpha and 8Be(2+)+alpha. With this knowledge we investigate the influence from these states and breakup channels on the reaction rate of the triple alpha process, and thus explore the influences on the triple alpha process beyond the Hoyle state. References: 1. F. Hoyle, Astrophysical Journal Supplement Series 1, 121 (1954) 2. G.R. Caughlan and W.A. Fowler, Atomic Data and Nuclear Data Tables 40, 283 (1988) 3. C. Angulo et al., Nuclear Physics A 656, 3 (1999) 4. S.M. Austin, Nuclear Physics A 758, 375c (2005) 5. H.O.U. Fynbo et al., Nature 433, 136 (2005)
        Speaker: Christian Aa. Diget (Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark)
      • 16:00
        Experimental determination of reaction rates via Coulomb dissociation 30m
        Intermediate-energy Coulomb dissociation using fast radioactive-isotope (RI) beams has been employed to study astrophysical (p,gamma) reactions. This method has an advantage of large cross sections and high experimental efficiency. Several experiments have been performed so far at fragmentation-based RI-beam facilities like, GSI, MSU and RIKEN. The most studied case is for the 7Be(p,gamma)8B reaction, which is important in estimating high-energy neutrino flux from the sun. Coulomb dissociation experiments provide an opportunity to determine the cross section independent to direct capture measurements. To extract accurate results, possible contributions of nuclear breakup, higher order process, possible mixture of different multiplicity contribution mixed into the dominant E1 contribution are being investigated both experimentally and theoretically.
        Speaker: Tohru Motobayashi (RIKEN Nishina Center for Accelerator-Based Science)
    • 16:30 17:00
      break 30m
    • 17:00 19:00
      8 Experiments in nuclear astrophysics II
      Convener: Yasuki Nagai (Osaka University)
      • 17:00
        Beta decay of highly charged ions 30m
        Ion storage rings and ion traps have provided for the first time the opportunity to investigate beta decay of highly charged atoms, i.e. with only a few or even none bound electrons. The impact of this new field of research for nuclear astrophysics and, in particular, for s-process nucleosynthesis in hot stellar plasmas is obvious. In this talk an overview is given on the activities in this field during the last decade at the ion storage-cooler ring ESR of GSI, with the emphasis on bound-state beta decay and its astrophysical implications. Moreover, first results of a new technique, single-ion decay spectroscopy, will be presented and analyzed, i.e. the direct observation of two-body beta decays (bound-state beta decay and orbital electron capture) of single, stored and cooled ions at well-defined atomic charge states.
        Speaker: Fritz Bosch (GSI Darmstadt, Germany)
      • 17:30
        Alpha-induced reactions in stellar burning 30m
        Alpha-induced reactions play an important role in a variety of astrophysical environments. They provide the neutron sources for the main s-process which takes place in highly convective AGB stars and for the weak process during core Helium burning in massive stars. In addition, alpha induced reactions on 15O and 18Ne provide a break-out from the CNO cycle which is important for the dynamics of explosive Hydrogen burning. To illuminate experimental difficulties in determinating reaction rates results of recent and ongoing experiments will be presented and future developments at the Nuclear Structure Laboratory at Notre Dame will be discussed.
        Speaker: Joachim Goerres (University of Notre Dame and Joint Institute for Nuclear Astrophysics)
      • 18:00
        Measuring 12C(alpha,gamma)16O with ERNA 15m
        The fusion of carbon and helium via $^{12}$C$(\alpha,\gamma)^{16}$O in the helium burning phase of red giant stars is generally accepted to be a key reaction of nuclear astrophysics. Although there exist several direct and indirect measurements, the cross section in the Gamow peak is still not known sufficiently well. A new measurement of the $^{12}$C$(\alpha,\gamma)^{16}$O reaction cross section has been done using the European Recoil separator for Nuclear Astrophysics ERNA. \par In ERNA the reaction is performed in inverse kinematics, i.e. guiding a $^{12}$C beam on a $^{4}$He gas target. In the recoil separator the high intensity beam is filtered from the oxygen recoil nuclei using velocity and momentum filters. ERNA also needs to provide the necessary acceptances in angle and energy needed to cover the kinematics governed by the gamma ray emission. At the end of the separator the recoil nuclei are freely (i.e. without coincidence conditions) detected in a $\Delta$E-E ionisation chamber telescope. Assuming full acceptances for the choosen charge state one therefore measures the total cross section. Additional measurement of the coincident gamma rays will provide information on the different capture amplitudes.\par The key parameters of the recoil separator like acceptance of the recoil nuclei and suppression of the incoming beam are discussed. The results of the measurements of the total cross section of $^{12}$C$(\alpha,\gamma)^{16}$O in an energy range of 1.9-5 MeV are presented and compared to R-Matrix calculations.
        Speaker: Daniel Schuermann (Ruhr-Universitaet Bochum)
      • 18:15
        Measurement of the cascade cross section to the 6.049-MeV state in 16O in 12C(a,g)16O 15m
        The cascade through the 6.049-MeV J(pi)=0+ state 16O of has rarely been discussed as contributing to the 12C(a,g)16O cross section at low energies largely due to experimental difficulties in observing this transition. We report here first measurements of this transition in 12C(a,g)16O using the DRAGON recoil separator facility at TRIUMF. The experiment was performed in inverse kinematics with an incident 12C beam on a windowless 4He gas target, covering center of mass energies between 2.2 MeV and 5.42 MeV. The coincidence setup included a BGO array around the gas target and a DSSS Detector for the detection of 16O recoil particles at the focal plane of DRAGON. To derive actual cross sections, the acceptance of DRAGON including the BGO array has been simulated in GEANT. The transition strength has been derived and analyzed in the R-matrix formalism. Information on the 6.92-MeV cascade transition and the ground state transition were also obtained from the same data set. We derived the 12C(a,g)16O total cross section and found it in good agreement with a recently reported measurement
        Speaker: C. Matei (Ohio University, Athens, OH)
      • 18:30
        The supernova-nucleosynthesis 40Ca(alpha,gamma)44Ti reaction 15m
        The 44Ti(t1/2= 59 y) nuclide is considered an important signature of core-collapse supernova (SN) nucleosynthesis and has recently been observed as live radioactivity by gamma-ray astronomy from the Cas A SN remnant. We investigated in the laboratory the major 44Ti production reaction, 40Ca(alpha,gamma)44Ti (Ecm ~0.6-1.2 MeV/u), by off-line counting of 44Ti nuclei using accelerator mass spectrometry [1]. The observed yield is significantly higher than inferred from previous prompt-gamma spectroscopy experiments. The present data strongly support the BRUSLIB statistical model [2] which incorporates a microscopic model of nuclear level densities and of the gamma-ray strength function, and a global alpha-nucleus optical-model potential. Comparison of the data with the statistical model confirms the strong suppression in yield expected for (alpha,gamma) reactions on self-conjugate (N=Z) nuclei. The derived astrophysical rate of the 40Ca(alpha,gamma)44Ti reaction is a factor 5-10 higher than calculated in current models. We will present results of stellar calculations in spherical hydrodynamics, as those described in [3] but using this reaction rate, showing an increase of the calculated SN 44Ti yield by a factor ~2 over current estimates. An increase by a factor of ~2 in 44Ti is found also in the calculated fall back material. The yields calculated by multi-dimensional SN explosion calculations proposed to explain the observed 44Ti yield of Cas A, in which parts of deeper layers can be ejected while some of the outer layers fall back, are expected to be enhanced in 44Ti as well. This work was supported in part by the US- DOE, Office of Nuclear Physics, under Contract No. W-31-109-ENG-38, the DOE Program for Scientific Discovery through Advanced Computing (SciDAC; DE-FC02-01ER41176), by DOE contract W-7405-ENG-36 to the Los Alamos National Laboratory, and by the USA-Israel Binational Science Foundation (BSF). [1] H. Nassar et al., Phys. Rev. Lett., to be published. [2] M.Arnould and S.Goriely, Nucl. Phys. A, to be published. [3] T.Rauscher et al., Astrophys. J., 576, 323 (2002).
        Speaker: Hisham Nassar (Hebrew University, Jerusalem, Israel 91904)
      • 18:45
        Study of the 40Ca(alpha,gamma)44Ti reaction at stellar temperatures with DRAGON 15m
        44Ti (60.0 yr half-life) is one of the few short-lived radionuclides which has been detected in space by gamma-ray astronomy and thus confirm ongoing nucleosynthesis. Since it is produced predominantly in supernovae during the alpha-rich freezeout, its measured abundance can be used to constrain supernova models. The 40Ca(alpha,gamma)44Ti reaction plays a key role in 44Ti production. It has been studied partly in the past by prompt gamma-ray measurements. A recent integral measurement over a larger temperature regime by off-line counting of 44Ti nuclei with AMS showed a significantly larger 44Ti yield compared to previous results from prompt gamma-ray measurements. We have measured this reaction in inverse kinematics at the recoil mass spectrometer DRAGON, located at the ISAC facility at TRIUMF (Vancouver, Canada). High-purity 40Ca beam (less than 0.5% 40Ar contamination) was accelerated to energies of 0.8 – 1.2 MeV/amu impinging on a windowless He gas target surrounded by a high-efficiency BGO gamma-ray detector array. 44Ti recoils are then separated from the 40Ca beam by the recoil mass spectrometer and identified in an ionization chamber. The advantage of direct detection of 44Ti recoils and prompt gamma rays allows a detailed study of this reaction over a large energy range with sufficient resolution to resolve individual resonances. In this presentation, we report on the status of our investigations, which begins at the strong isospin triplet around E_x = 9.2 MeV and continues from here to lower energies covering a temperature regime of T_9 ~ 1.5 – 2.5 relevant for supernova nucleosynthesis.
        Speaker: Christof Vockenhuber (TRIUMF, Vancouver, BC, Canada)
    • 19:00 20:30
      Big Poster-Session [all posters]
      All posters
    • 08:30 10:10
      9 Element production, stellar evolution, and stellar explosions
      Convener: Verne V Smith (NOAO, Tucson)
      • 08:30
        New Ideas in the Theory of Core-Collapse Supernova Explosions 30m
        Core-collapse supernova explosions are fundamentally aspherical and require multi- dimensional radiation/hydrodynamical tools to address them. Recent simulations have hinted that the inner core of the protoneutron star executes vigorous g-mode oscillations that damp by the emission of acoustic power. I will present results from our recent 2D simulations that explore such core pulsations, the generation of sound, neutrino emissions, and explosion. The sound pulses radiated from the core steepen into shock waves that merge as they propagate into the outer mantle and deposit their energy and momentum with high efficiency. All models we address explode with the aid of such acoustic power, but what the ultimate role of sound may be in the supernova phenomenon remains to be seen. I will address the implications of the new simulations for the mechanism of supernova explosions, the r-process, pulsar kicks, supernova blast morphology, and the gravitational radiation signatures of the deaths of massive stars and I will provide a roadmap for future theoretical explorations to test, verify, or refute the new ideas that are emerging.
        Speaker: Adam Burrows (University of Arizona)
      • 09:00
        The Role of Neutrinos in Explosive Nucleosynthesis 20m
        A new nucleosynthesis process, that we denote $\nu p$-process, will be presented. It occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers $A>64$. Making this process a possible candidate to explain the origin of the solar abundances of the light p-nulcei (such as $^{92,94}$Mo and $^{96,98}$Ru). This process also offers a natural explanation for the large abundance of Sr seen in an hyper-metal-poor star.
        Speaker: Carla Frohlich (University of Basel)
      • 09:20
        Neutrinos and Nucleosynthesis in Gamma Ray Bursts 20m
        Gamma-ray bursts, while rare, may be important contributors to galactic nucleosynthesis. Here we consider the types of nucleosynthesis that can occur as material is ejected from a gamma-ray burst accretion disk. We calculate the composition of material within the disk as it dissociates into protons and neutrons and then use a parameterized outflow model to follow nuclear recombination in the wind. From the resulting nucleosynthesis we delineate the disk and outflow conditions in which iron peak, r-process, or light p-process nuclei may form. In all cases the neutrinos have an important impact on the final abundance distributions.
        Speaker: Rebecca Surman (Union College)
      • 09:40
        Presupernova Evolution and Explosive Nucleosynthesis of Massive Stars 30m
        I will review the presupernova evolution and the associated explosive nucleosynthesis of massive stars with mass loss in the mass interval between 11 and 120 Msun. For the solar metallicity models i will address the following topics: 1) the evolutionary properties of Wolf-Rayet stars and their comparison with observations; 2) the chemical yields provided by a generation of core collapse supernovae; 3) the contribution of these stars to the production of Al26 and Fe60 in the Galaxy. For the zero metallicity models i will mainly disucuss their chemical yields and their connection with "normal" and C-rich extremely metal poor stars.
        Speaker: Alessandro Chieffi (INAF-Osservatorio Astronomico di Roma)
    • 10:10 11:00
      break + poster session 20

      Poster sessions will be held outside the Main Auditorium, in the CERN Main building.

      No oral presentation of poster contributions is schduled.

      Poster session 20
    • 11:00 13:00
      10 Element production & stellar evolution II
      Convener: Robert Hoffman (LLNL, Livermore)
      • 11:00
        Globular clusters : Ideal laboratories to test hydrogen-burning nucleosynthesis and hydrodynamics in stars? 30m
        Galactic globular clusters (GC) stars exhibit abundance patterns which are not shared by their field counterparts, e.g. the well-documented O-Na and Mg-Al anticorrelations. Recent observations provided compelling evidence that these abundance anomalies were already present in the intracluster gas from which the observed stars formed. A widely held hypothesis is that the gas was polluted early in the history of the GC by material processed through H-burning at high temperature and then lost by stars more massive than the presently observed long-lived stars. However the "polluters" have not been unambiguously identified yet. Most studies have focused on AGB stars, but rotating massive stars present an interesting alternative. In this talk we try to answer to the following question : "Are GC ideal laboratories to test hydrogen-burning nucleosynthesis and hydrodynamics in stars?" We critically analyse the pros and cons of both potential stellar polluters. We discuss the constraints that the observational data bring on the stellar nucleosynthesis and hydrodynamics as well as on nuclear reaction rates.
        Speaker: Corinne Charbonnel (Geneva Observatory & CNRS)
      • 11:30
        Neutron-capture elements in globular cluster M15 20m
        We report on observations of six giants in the globular cluster M15 (NGC 7078). The Subaru/HDS was used to measure neutron-capture elemental abundances. Previous studies have reported a significant star-to-star variation in the neutron-capture elemental abundances of M15, and deduced that their origin was from the r-process. Our abundance analyses based on high-quality blue spectra confirm the scatter in the abundances of heavy neutron-capture elements (e.g., Eu). Observed [La/Eu] ratios indicate there are no significant s-process contributions. We have found, for the first time, that there are anti-correlations between the abundance ratios of light to heavy neutron-capture elements ([Y/Eu] and [Zr/Eu]) and heavy ones (e.g., Eu). This indicates that light neutron-capture elements in these stars cannot be explained by only a single r-process, but another process that has significantly contributed to the light neutron-capture elements is required to have occurred in M15. We will also discuss possible r-process enrichment model to explain our results.
        Speaker: Kaori Otsuki (University of Chicago)
      • 11:50
        Chemical evolution of C-Zn and r-process elements produced by the first generation stars 20m
        Metal-poor stars record enrichment history of the Galaxy at the early epoch. Abundance analysis of these stars reveals large star-to-star scatters in r-process elements. This may be interpreted as a result of incomplete mixing of the interstellar medium (ISM) at the beginning of the Galaxy. However, recent studies also show considerable small dispersions for abundance ratios of C-Zn (Cayrel et al. 2004). We construct an inhomogeneous chemical evolution model, assuming supernova induced star formation. Then we discuss whether inhomogeneity of the ISM consistently accounts for observed differences between r-process and lighter elements, using several latest sets of supernova yields for metal-poor stars. If metal-poor stars are enriched by only one or a few supernovae, huge dispersions in r-process elements possibly imply that their yields are highly dependent on supernova progenitor masses. However, the site of r-process is still uncertain even from nucleosynthesis studies. We, then, attempt to determine the site of r-process, using an inhomogeneous chemical evolution model. In our previous study, we have shown that values of [Eu/Fe] of three metal poor stars given by Subaru observation strongly support the model where the r-process site is assumed as the low mass-end of supernova progenitors, such as 8-10 solar mass stars. On the other hand, a large dispersion has been found in [Sr/Ba] at lower metallicity (e.g., Ryan et al. 1996; Honda et al. 2004), suggesting that lighter elements such as Sr does not come from a universal process, which produces Ba and Eu, but from `weak' r-process. We show that this scenario well explains observations, when weak r-process produces ~60% of Sr but only ~1% of Ba in metal- poor stars. Intermediate mass elements between Sr and Ba must provide clues to understand the nucleosynthesis of weak r-process. We estimate Pd abundances of very metal-poor stars, using Subaru and also show that weak r-process pattern gradually decreases with atomic mass from Sr to Ba.
        Speaker: Yuhri Ishimaru (Academic Support Center, Kogakuin University)
      • 12:10
        Reaction rate uncertainties and the operation of the NeNa and MgAl chains during HBB in intermediate-mass AGB stars 20m
        We study the effect of uncertainties in the proton-capture reaction rates on nucleosynthesis due to the operation of the NeNa and MgAl chains during hot bottom burning (HBB) in intermediate-mass asymptotic giant branch (AGB) stars. This kind of nucleosynthesis is associated with the production of sodium, of the radioactive nucleus Al26 and of the heavy magnesium isotopes, and it is possibly responsible for the O, Na, Mg and Al abundance anomalies observed in globular cluster stars. We model HBB with an analytic code based on full stellar evolution models. In this way we can calculate a very large number of stars in a relatively quick time (e.g. 10^6 stars in 12 hours). We have computed stellar models at two different metallicities (0.02 and 0.004) and two masses (5 and 6 solar masses). We vary in turn each of the p-capture rates involved in the NeNa and MgAl chains of factors corresponding to their current uncertainties in the range of temperatures relevant for HBB (T_9 ~ 0.06 - 0.1 K). We find large uncertainties, variations of up to one order of magnitude, in the final yields of Na23 and Ne22, Al26, Al27, and Mg24, because of uncertanties in the Ne22(p,g)Na23, Mg25(p,g)Al26, Al26(p,g)Si27, Mg26(p,g)Al27 and Na23(p,g)Mg24 reaction rates. The uncertainty ranges increase with decreasing metallicity and increasing mass of the star, because the temperature at the base of the convective envelope increases in these cases, making HBB more efficient. We are in the process of modelling stars of lower metallicity (0.0001), where the effect of HBB is even greater. Current work also involves the computation of models in which we vary all the reaction rates in the same model. We then calculate the variation of each isotopic yield due to the uncertainties associated with all the reaction rates involved in the NeNa and MgAl chains.
        Speaker: Robert Izzard (University of Utrecht)
      • 12:30
        The new solar chemical composition: Does the Sun have a sub-solar metallicity? 30m
        In the Sun, the convection zone reaches up to the solar atmosphere and can thus directly influence the emergent spectrum. Traditionally, the effects of convection has been modelled with the local mixing length theory in 1D hydrostatic model atmospheres for stars like the Sun. In a different approach, we have performed realistic time-dependent, 3D, radiative-hydrodynamical simulations of the outer layers of the solar convection zone, including the atmosphere. Both the different mean stratification and the presence of atmospheric inhomogeneities in 3D impact the spectral line formation. We have applied this 3D solar model atmosphere to the problem of the solar chemical composition while adopting the best possible atomic and molecular line data and taking into account departures from LTE in the line formation when necessary. The inferred C, N, O and Ne abundances are all significantly lower than estimated from previous 1D modelling by 0.2-0.3 dex. These results have significant implications for a range of topics in contemporary astrophysics, including causing a severe headache for helioseismology. In this review talk I will present an overview of our analysis, give arguments why our results are trustworthy and discuss some of their ramifications.
        Speaker: Martin Asplund (Australian National University)
    • 13:00 14:00
      lunch 1h
    • 14:00 18:30
      Excursions Varius locations

      Varius locations

      You should have already chosen one of the events that you
      would like to attend and received a ticket for this event
      during registration. Please bring this ticket with you and
      hand this to one of the organizers before getting on to the
      coach. Coaches will be leaving CERN at 14.00h and returning
      to CERN at 19:30. Organizers will direct you to the coaches.

      There will be a limited number of prepared lunch bags which
      are being provided for us by the restaurant staff this lunch
      time. These will cost 6.00CHF each (can please have the
      correct money). There are vegetarian bags available too.

    • Event 1 : A guided tour of Geneva Town. The tour includes a general visit of the International Organizations and some of the parks of Geneva, and afterwards about a 45 min walking tour of the old town.
    • Event 2 : A visit to the National Park Haut Jura, which includes a visit of the Exhibition centre. Followed by a short walk and afterwards we sample the local cheese and wine.

      Note: For both events we recommend good walking shoes and perhaps a rain coat.

    • 08:30 10:30
      11 Nuclear theory in astrophysics
      Convener: Friedrich-Karl Thielemann (Basel University)
      • 08:30
        Direct Reactions in/for Nuclear Astrophysics 30m
        Precise nuclear reaction rates are needed for a detailed description of the production of elements in primordial nucleosynthesis and during the hydrostatic burning of stars to constrain the astrophysical models. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies [1]. In recent years several indirect methods have been developed and applied to extract low-energy astrophysical S factors. Here, the methods of Coulomb dissociation, of the asymptotic normalization coefficient (ANC) and the Trojan-Horse method will be discussed. The application of these indirect methods requires a combination of experimental and theoretical efforts. This contribution focuses on the underlying reaction theories that have to be understood well in order to assess the precision and limitations of the various approaches [2]. Studying nuclear structure and nuclear reactions within a consistent approach is a complicated issue in nuclear physics. Here I will report on an attempt to reconcile structure and reactions in the No-Core Shell-Model (NCSM). The principal foundation of the NCSM is the use of effective interactions appropriate for the large, but finite, basis spaces employed in the calculations. These effective interactions are derived from the underlying realistic inter-nucleon potentials by a unitary transformation in a way that guarantees convergence to the exact solution as the basis size increases. It is a challenging task to extend ab initio nuclear structure approaches to the description of nuclear reactions. I will present the first calculations of the $^{7}$Be(p,$\gamma$)$^{8}$B S-factor starting from the ab initio NCSM wave functions of $^{7}$Be and $^{8}$B bound states [3]. These wave functions were obtained in basis spaces up to 10$\hbar\omega$ and used to calculate channel cluster form factors (overlap integrals) of the $^{8}$B ground state with $^{7}$Be+p. Due to the use of the harmonic oscillator (HO) basis, the overlap integrals have incorrect asymptotic properties. We fix this problem in two alternative ways. First, by a Woods-Saxon potential solution fit to the interior of the NCSM overlap integrals. Second, by a direct matching with the Whittaker function. The corrected overlap integrals are then used for the $^{7}$Be(p,$\gamma$)$^{8}$B S-factor calculation. \vspace{12pt} \parindent=0pt \textbf{References} [1] C.A. Bertulani, Phys. Lett. B 585 (2004) 35 [2] C.A.Bertulani, Phys. Rev. Lett. 94, 072701 (2005) [3] P. Navratil, C.A. Bertulani, and E. Caurier, Phys. Lett. B 634 (2006) 191; Phys. Rev. C, in press.
        Speaker: Carlos Bertulani (Department of Physics, University of Arizona, Tucson, AZ)
      • 09:00
        Cross sections of light-ion reactions calculated from ab initio wave functions 20m
        I will discuss present attempts to employ many-body nuclear structure information in nuclear reaction calculations. The foundation of our approach is the ab initio no-core shell model (NCSM), which is a well-established theoretical framework aimed at an exact description of nuclear structure starting from high-precision interactions between the nucleons. We are now able to extract translationally invariant cluster form factors from the NCSM many-body wave functions, and subsequently use them in cross section calculations. I will show some of our first results from studies of the radiative capture reactions 3He(a,g)7Be and 10Be(n,g)11Be. The former reaction corresponds to the most important uncertainty in solar model predictions of neutrino fluxes, while the latter represents a possible breakout from the standard primordial nucleosynthesis in inhomogeneous Big Bang scenarios. This work was partly performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. Support from the LDRD contract No. 04-ER-058 is acknowledged.
        Speaker: Christian Forssén (Lawrence Livermore National Laboratory)
      • 09:20
        Nuclear models for light systems 30m
        First we present general properties of low-energy reactions between light nuclei. Different theoretical approaches are briefly described. We present recent results on the 18F(p,a)15O reaction, obtained in a microscopic cluster model. We point out that some 1/2+ resonances, generally disregarded, may play a role. The spectroscopic properties of 19Ne, and charge symmetry between 19Ne and 19F are also discussed. Another application deals with the 14C(n,g)15C reaction, where we use the Asymptotic Normalization Constant (ANC) method. By using recent data on 14O+p elastic scattering, we show that some indirect results on 14C(n,g)15C are inconsistent with charge symmetry.
        Speaker: Pierre Descouvemont (Physique Nucléaire Théorique et Physique Mathématique)
      • 09:50
        Modified Nuclear Lifetime in Hot Dense Plasmas 20m
        In hot dense plasmas, the electronic environment in the immediate vicinity of the nucleus is modified, and thus, the plasma conditions influence key processes driving the lifetime of a nuclear level [1]. A correct lifetime prediction requires every deexcitation process to be evaluated jointly with its corresponding excitation process. For heavy nuclei, the nuclear lifetime of discrete levels is often strongly dependent on internal conversion which involves bound electrons. In plasma, many of these electrons are no longer in a bound state and the internal conversion rate can be significantly reduced. Its coupling with its inverse process, Nuclear Excitation by Electron Capture (NEEC), can lead to greatly increased nuclear lifetimes. In some cases, an atomic transition can be coupled with a nuclear transition in a process called Nuclear Excitation by Electron Transition (NEET) if their energies are closely matched [2]. This can accelerate the deexcitation of the excited nuclear level, and reduce its lifetime. We developped a model able to deal with these processes in plasma under thermodynamic equilibrium. It evaluates internal conversion, NEEC and NEET rates in plasma. Depending on the particular situation, we use either an average atom description or a Multi Configuration Dirac Fock (MCDF) approach to describe the electronic environment of the atom. Large variations of several excited nuclear level lifetimes have been predicted. A complete description of the nuclear lifetime must also include some other nuclear levels through which indirect nuclear excitation or deexcitation may occur. This particular situation may provide a fast method to populate or depopulate nuclear isomers [3]. [1] M. R. Harston and J. F. Chemin, Phys. Rev. C59, 2462 (1999) [2] P. Morel, V. Meot, G. Gosselin, D. Gogny and W. Younes, Phys. Rev. A69, 063414 (2004) [3] G. Gosselin and P. Morel, Phys. Rev. C70, 064603 (2004)
        Speaker: Gilbert GOSSELIN (Comissariat a l'energie atomique (CEA))
      • 10:10
        Enhanced electron screening in nuclear reactions and radioactive decays 20m
        In recent years, an enhanced electron screening in metallic environments has been demonstrated by many groups in experimental investigations of low-energy nuclear reactions. Similarly, first radioactive decay experiments in metallic materials have been performed to possibly observe an alteration of the decay constant due to electron screening. Both kinds of experiments are of fundamental importance for nuclear astrophysics since the metallic quasi-free electrons represent a model for dense astrophysical plasmas and thus the corresponding theories can be experimentally verified. Here, the self-consistent dielectric function theory will be applied to determine electron screening energies in different metallic materials. The results will be compared with the experimental values obtained for different nuclear reactions and some predictions for radioactive decay experiments will be presented. Furthermore, several solid state effects which can lead to an increase of the screening energy will be discussed. Special interest will be devoted to the temperature dependence of the electron screening effect.
        Speaker: Konrad Czerski (Institute of Physics, University of Szczecin, Szczecin, Poland)
    • 10:30 11:30
      break + poster session 21

      Poster sessions will be held outside the Main Auditorium, in the CERN Main building.

      No oral presentation of poster contributions is schduled.

      Poster session 21
    • 11:30 13:30
      12 Cosmology and BBN
      Convener: Richard N Boyd (National Science Foundation, USA)
      • 11:30
        Dark matter, dark energy & particle physics 30m
        Speaker: John Ellis (CERN)
      • 12:00
        Type Ia Supernovae as Standard Candles 30m
        Type Ia supernovae are believed to be thermonuclear explosions of carbon-oxygen white dwarf stars. Observationally they show a wide range of light curve shapes and peak luminosities at optical wavelengths. Fortunately their peak brightness correlates with the decline rate of their light curve making them "standardizable" candles with a precision of 7 to 10% in distance. At near infrared wavelengths, type Ia supernovae appear to be closer to true standard candles and also less susceptible to dust extinction. Observations between 1 and 3 microns may be the ideal way to use type Ia supernovae as accurate cosmological probes. The origin of the diversity in type Ia supernovae remains an interesting problem. The peak brightness is controlled by the mass of radioactive nickel produced in the explosion, but what determines the nickel yield? Possibilities include the heavy metal content of the progenitor star or the mass of the star that produced the white dwarf. Both possibilities are examined by studying the characteristics of the galaxies that host type Ia events.
        Speaker: Peter Garnavich (University of Notre Dame)
      • 12:30
        When Stars Attack! Live Radioactivities as Signatures of Nearby Supernovae 20m
        Supernovae are critical for life in many ways, e.g., their nucleosynthesis is the dominant cosmic source of heavy elements essential for planet formation and ultimately for biology. Yet supernovae take a more sinister shade when they occur closer to home, because an explosion inside a certain "minimum safe distance" would pose a grave threat to life on Earth. We will discuss these cosmic insults to life, and ways to determine whether a supernova occurred nearby over the course of the Earth's existence. We will then present recent evidence that a star exploded near the Earth about 3 million years ago. Radioactive iron-60 atoms have been found in ancient samples of deep-ocean material, and are likely to be debris from this explosion. Recent, high-quality data confirm this radioactive signal, represent a major step forward for this field. We will present simulations of the supernova impact on the solar system and delivery of ejecta into Earth's orbit. We will show how sea sediments can be used for nuclear astrophysics "archaeology": terrestrial samples of supernova debris allow direct laboratory probes of nucleosynthesis products from an individual explosion.
        Speaker: Brian Fields (University of Illinois)
      • 12:50
        Electron capture reactions in neutron star crusts: deep heating and observational constraints 20m
        Many neutron stars accrete H- and He-rich matter from a stellar companion. Over the lifetime of the binary, enough matter can be transferred to replace the crust of neutron star. As the material is compressed, the rising electron Fermi energy induces electron captures. We calculate the evolution of a fluid element being compressed to neutron drip under conditions appropriate for the crust of an accreting neutron star. We consider different initial distributions of nuclei (X-ray burst and superburst ashes) and allow for electron captures into excited states. The heating from these reactions sets the temperature of the neutron star crust at depths where explosive burning of carbon (observed as a superburst) occurs, thus providing a possible constraint on the heating from these captures. A second constraint comes from neutron stars that accrete intermittently; when the accretion halts, the surface is detectable with X-ray telescopes such as Chandra and XMM. We calculate the evolution of the X-ray luminosity following the end of an accretion outburst using our new crust models.
        Speaker: Edward Brown (MIchigan State University/Joint Institute for Nuclear Astrophysics)
      • 13:10
        Early Star Formation, Nucleosynthesis, and Chemical Evolution in Proto-Galactic Cloud 20m
        We present numerical simulations to describe the nucleosynthesis and evolution of pre-Galactic clouds in a model which is motivated by cold dark matter simulations of hierarchical galaxy formation. We adopt a SN-induced star-formation mechanism within a model that follows the evolution of chemical enrichment and energy input to the clouds by Type II and Type Ia supernovae. We utilize metallicity-dependent yields for all elements at all times, and include effects of finite stellar lifetimes. We derive the metallicity distribution functions for stars in the clouds, their age-metallicity relation, and relative elemental abundances for a number of alpha- and Fe-group elements. The stability of these clouds against destruction is discussed, and results are compared for different initial mass functions. We find that the dispersion of the metallicity distribution function observed in the outer halo is naturally reproduced by contributions from many clouds with different initial conditions. The scatter in metallicity as a function of age for these stars is very large, implying that no age-metallicity relation exists in the early stages of galaxy formation. Clouds with initial masses greater than that of presently observed globular clusters are found to survive the first 0.1 Gyr from the onset of star formation, suggesting that such systems may have contributed to the formation of the first stars, and could have been self-enriched. More massive clouds are only stable when one assumes an initial mass function that is not biased towards massive stars, indicating that even if the first stars were formed according to a top-heavy mass function, subsequent star formation was likely to have proceeded with a present-day mass function, or happened in an episodic manner. The predicted relative abundances of some alpha- and Fe-group elements show good agreement with the observed values down to metallicities below [Fe/H] = -4 when the iron yields are reduced relative to stellar models. The observed scatter is also reproduced for most elements including the observed bifurcation in [alpha/Fe] for stars with low [Fe/H]. However, the predicted dispersion may be too large for some elements (particularly alpha elements) unless a limited range of progenitor masses contributing to the abundances of these elements is assumed. The contributions to the abundances from supernovae with different progenitor masses and metallicity are discussed. The results suggest that the low-mass end of SNeII was probably absent at the very lowest metallicities, and that the upper mass limit for the first stars that contributed to nucleosynthesis may be < 40 solar masses.
        Speaker: Grant Mathews (Center for Astrophysics (CANDU), Department of Physics, University of Notre Dame, Notre Dame,)
    • 13:30 14:30
      lunch 1h
    • 14:30 16:10
      13 Experiments in nuclear astrophysics III
      Convener: Björn Jonson (Chalmers U of Technology)
      • 14:30
        AMS measurements of stellar cross sections across the nuclear chart 20m
        Accurate and precise cross-section data are the key ingredients to our understanding of stellar nucleosynthesis. Common techniques for these data comprise online time-of-flight measurements of reaction cross sections as well as offline methods like the activation technique. In cases of longer-lived nuclides or nuclides with an unfavourable decay scheme, counting atoms directly rather than their decay rates, is the far more sensitive method. Accelerator mass spectrometry (AMS) offers a powerful tool to measure cross sections independent on half-lives of reaction products. At the Vienna Environmental Research Accelerator (VERA) we are pursuing a program to study cross sections relevant to nuclear astrophysics. In this context, various samples are irradiated in a quasi-stellar neutron spectrum of kT = 25 keV produced with the 7Li(p,n)7Be reaction at the 3.7MV Van de Graaff accelerator of Forschungszentrum Karlsruhe. The subsequent AMS measurements are performed at VERA. The main challenge in AMS is to discriminate isotopic and isobaric interferences. By extensive background studies the required sensitivity for cross section measurements has been demonstrated for various isotopes prior to the AMS measurements. So far, the reactions 9Be(n,g)10Be, 13C(n,g)14C, 40Ca(n,g)41Ca, 54Fe(n,g)55Fe, and 209Bi(n,g)210Bi have been investigated. For some of these reactions no experimental results exist up to now. The implications of measured cross sections for various nucleosynthesis scenarios will be discussed.
        Speaker: Anton Wallner (Institut für Isotopenforschung und Kernphysik, VERA, Univ. Wien)
      • 14:50
        Proton resonance scattering of 7Be 20m
        We have studied the proton resonance scattering of 7Be by using a pure 7Be beam produced at CRIB (CNS Radioactive Ion Beam separator; CNS stands for Center of Nuclear Study, University of Tokyo). The excitation function of 8B was measured up to the excitation energy of 6.8 MeV, using the thick-target method. The excited states of 8B higher than 3.5 MeV were not known by the past experiments. This proton elastic scattering is also of importance in relation with the 7Be(p,gamma)8B reaction, which is a key reaction in the standard solar model. The latest results of our measurement will be presented.
        Speaker: Hidetoshi Yamaguchi (CNS, Univ. of Tokyo)
      • 15:10
        Improving the rate of the triple alpha reaction 20m
        The rate of the triple alpha process, which plays a central role in the production of 12C in stars, is known with an accuracy of about 12%. Variations within the +/-12% errors can cause significant changes in the determination of the mass of the iron core in core-collapse supernovae (type II) and the composition of the material later ejected in the interstellar medium, as well as a factor of two change in the surface abundance of 12C in light ABG stars. The present triple alpha experiment aims therefore at reducing the uncertainty on the knowledge of this rate to about 6% by measuring more accurately than has been done in the past the pair branch for the 7.654 MeV state in 12C. This state is excited by inelastic proton scattering, taking advantage of a strong resonance at an excitation energy of 10.6 MeV and a scattering angle of 135 degrees in the lab. The protons are produced by using the Tandem accelerator at Western Michigan University. A reduction in the gamma ray background is achieved by a coincidence requirement between a thin scintillator tube and the large block of plastic scintillator surrounding it. The pair branch is then given by the ratio of the number of electron-positron pairs detected in the plastic scintillators in coincidence with the protons scattered at 135 degrees to the total number of such scattered protons. The experimental status will be presented.
        Speaker: Clarisse Tur (Michigan State University / NSCL)
      • 15:30
        High-precision mass measurements for reliable nuclear-astrophysics calculations 20m
        The nuclear mass is an important parameter in nuclear physics and astrophysics. The experimental determination of precise and accurate values is a challenge, especially for short-lived radionuclides far away from the valley of stability with low production yields as well as half-lives down to the millisecond time scale. However, these mass values are required for testing and modelling nucleosynthesis theories that describe how elements and nuclides are formed in stellar evolution, e.g., violent processes like supernovae explosions. For the calculations of the various pathways from hydrogen to the heavier elements the nuclear properties of a large number of nuclides need to be known [1,2]. Especially in the case of the r-process, where elements heavier than iron are formed by rapid neutron capture, nuclear structure data of neutron-rich nuclides far from the valley of stability are required. The path of the r-process is determined by and reflects nuclear structure. For example at the neutron shell N=50 it crosses through the waiting point nuclide 80Zn. Slight deviations in the nuclear physics parameters can lead to large discrepancies in the modeling of the subsequent nucleosynthesis processes. One crucial parameter is the mass of the nuclides, which enters the determination of neutron separation energies and the Q-values for the beta decays as well as interaction cross-sections. They are thus essential for the study of the r-process and other astrophysical aspects. With the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN very precise and accurate mass measurements with relative mass uncertainties down to dm/m=8x10-9 can be achieved. Recently, the atomic masses of the neutron-rich zinc isotopes 71-81Zn have been measured. For the first time the masses of 79Zn and 81Zn have been determined. The new experimental data allow the investigation of nuclear structure at the neutron shell N=50 for low Z. The possible impact on nuclear astrophysics and further examples are discussed. [1] M. Mukherjee et al., Phys. Rev. 93, 150801 (2004) [2] D. Rodriguez et al., Phys. Rev. Lett. 93, 161104 (2004)
        Speaker: Alexander Herlert (European Organization for Nuclear Research (CERN))
      • 15:50
        Alpha-capture reactions and the alpha-Nucleus Optical Potential for p-process nucleosynthesis 20m
        The p process is the production mechanism for a certain number of proton-rich, stable nuclei, that cannot be produced by neutron captures. These 35 nuclei, lying between Se and Hg, are referred to as p nuclei. The most favoured scenarios for the p process involve the photodisintegration of intermediate and heavy elements at high temperatures (2-3 billion degrees Kelvin) that can be achieved only during the explosive burning phases of massive stars. One of the persistent puzzles of the current abundance calculations, is the underproduction of the Mo-Ru region. These discrepancies could be due to uncertainties in the astrophysical models or in the nuclear physics data used. During the photodisintegration process, neutron, proton and alpha emission compete with one another and with beta decays. A p-process network calculation involves almost 20000 reactions. However, only very few of these reactions can or have been measured in the laboratory, so the network calculations rely largely on theoretical estimates of the relevant reaction rates. Considerable effort has been devoted in the recent years to determine the nuclear properties entering the theoretical calculations of reaction rates. One such property is the alpha-nucleus optical model potential (OMP) which is poorly known at low energies close to the Coulomb barrier. The uncertainties in the alpha OMP, lead to large uncertainties in the alpha-induced reaction cross sections and inverse processes (up to a factor 10), and can therefore affect the p-process network calculations. This has motivated us to carry out a systematic investigation of low-energy alpha-induced reactions on nuclei of relevance to the p process. Experiments have been carried out at the Dynamitron accelerator of the University of Bochum. At the same time, we have updated a recent global, alpha-nucleus OMP based on the double-folding method, on all existing data on alpha-nucleus reactions. In this paper, we shall report on our new measurements and present detailed comparisons with calculations using the improved alpha-nucleus OMP. The impact on p-nuclei abundances and perspectives will also be discussed.
        Speaker: Sotirios Harissopulos (Institute of Nuclear Physics, NCSR "Demokritos")
    • 18:45 23:00
      Banquet Lac Léman

      Lac Léman


      The conference dinner/cruise will embark at 18:45 and the
      boat will leave at 19:00. For those of you who have
      accommodation in France and are taking a car we recommend
      that you allow at least one hour for your journey time into

      The boat Lausanne
      will leave from the pier "Genève Pâquis", downtown Geneva.

      If you are taking a car: Park in the Mont Blanc car park and walk (10 minutes) across the bridge or park in the Grand Casino (Noga Hilton Hotel) car park, the CGN boat called Lausanne is moored at the pier Paquis. Organizers will be there to meet you.

      Bus no. 9 from CERN or no.29 from Meyrin stops at the end of the route de Mont Blanc, turn left and you walk for 5 minutes along the Quai du Mont blanc where you will find the boat.

      If you are staying in French Hotels or the Hostel and you require transport to the boat: We will be providing coaches from CERN to the boat, coaches will leave the CERN car park at 17.45h and return at approximately 22.45h. Please bring your dinner/cruise ticket with you and give this to one of the organizers when you embark on to the boat.

      General information on Compagnie Générale de Navigation sur le lac Léman here.

    • 08:30 10:35
      14 Experiments in nuclear astrophysics IV
      Convener: Shigeru Kubono (CNS, University of Tokyo)
      • 08:30
        Neutron capture cross section measurements for nuclear astrophysics at n\_TOF 30m
        The neutron time of flight (n\_TOF) facility at CERN is a neutron spallation source with a flight path of 187 m. A proton beam from the CERN PS with an energy of 20 GeV, an intensity of $7 \times 10^{12}$ protons/pulse and a pulse width of 6 ns is focused on a lead spallation module. A white neutron beam is produced which covers fully the energy range of interest for capture cross section measurements relevant in nuclear astrophysics, in particular for $s$-process nucleosynthesis. The measuring station at 187 m from the spallation module allows for time-of-flight measurements with very high energy resolution in a low-background environment. The extremely high instantaneous neutron flux and the low repetition frequency of the proton beam is best suited for capture cross section measurements on radioactive samples. This contribution gives an overview of the neutron capture measurements on isotopes of Mg, Zr, La, Sm, Os, Pb, and Bi relevant for nuclear astrophysics.
        Speaker: Michael Heil (Forschungszentrum Karlsruhe, Institut f\"ur Kernphysik)
      • 09:00
        Measurements of the (n,γ) and (n,n') reaction cross sections on 186,187,189Os and 187Re-187Os cosmochronology 15m
        187Re-187Os pair is known as the most promising nuclear cosmochronometer with considerable potential. This is because 187Re beta decays with the half-life of 42.3+/- 1.3 Gyr,187Re is produced only by the rapid neutron capture process nucleosynthesis, and both 186Os and 188Os are produced only by the slow neutron capture process nucleosynthesis. However, there remains a non-trivial problem related to an excited neutron capture reaction of 187Os at a stellar temperature. Namely, 187Os is produced and depleted by the slow process nucleosynthesis. Hence, it is necessary to obtain both the production and depletion rates of 187Os to derive the excess abundance of 187Os, which can be attributable to beta-decay from 187Re. While, 187Os is depleted not only by its ground state neutron capture reaction but also by an excited state neutron capture reaction of 187Os. Note that 187Os has a low-lying excited state at Ex = 10 keV, and the state could be significantly populated at a stellar temperature kT ~ 30 keV [1. Hence, it is necessary to know the excited state neutron capture cross section for 187Os* to estimate the depletion rate of 187Os [2]. In order to deduce neutron capture cross section for 187Os*, it has been suggested to measure the neutron inelastic scattering cross section for 187Os off the ground state of 187Os to its excited 10 keV state. The measurement of the inelastic scattering cross section of the ground state in 189Os has been also suggested to derive the neutron capture cross section for the first excited state of 187Os*, since the spin-parities of the ground state in 189Os is the same as that of the first excited in 187Os. In the present study, we have measured the neutron capture reaction cross sections for 186Os, 187Os and 189Os accurately and neutron inelastic scattering reaction cross-section for 187Os in the neutron energy range from 10 to 100 keV. The measurements of the neutron capture reactions have been carried out by detecting a prompt γ-ray from the reaction by means of an anti-Compton NaI(Tl) spectrometer. The (n, n’) reaction cross section for 187Os has been measured by means of 6Li- glass scintillation detectors. Theses results will be discussed. [1] D. D. Clayton, Astrophys. J. 139, 637 (1964) [2] W. A. Fowler, Revs. Mod. Phys, Vol. 56, No2. Part1. April 1984.
        Speaker: Mariko Segawa (Research Center for Nuclear Physics, Osaka University, Japan)
      • 09:15
        Experimental challenges for the Re/Os clock 15m
        The stellar neutron capture cross sections of 186Os and 187Os are fundamental for the Re/Os cosmo-chronometer for defining the s-process abundance of 187Os. Subtraction of the s component from the solar 187Os abundance yields the radiogenic contribution to 187Os due to the beta-decay of 187Re (t1/2=42.3 Gy) since the onset of r-process nucleosynthesis. The laboratory cross section of 187Os requires a significant correction for the effect of low-lying excited state at 9.75 keV, which is strongly populated under stellar conditions. This theoretical correction can be improved by an experimental cross section for inelastic scattering to the 9.75 keV state. High resolution time-of-flight measurements of (n,gamma) cross sections of 186,187,188Os from 1 eV to 1 MeV at CERN n_TOF facility are reported. The inferred stellar cross sections differ from previously recommended values. In addition, the inelastic scattering cross section has been measured at 30 keV neutron energy via time-of-flight at the Karlsruhe 3.7 MV Van de Graaff. The implications of these results for the Re/Os clock are discussed
        Speaker: Marita Mosconi (Forschungszentrum Karlsruhe GmbH (FZK))
      • 09:30
        Electromagnetic Excitations in Nuclei: From Photon Scattering to Photo-dissociation 15m
        In explosive nucleosynthesis temperatures are high enough for photo dissociation reaction to occur, e.g. leading to the production of p-process nuclei. In order to understand the details of element production and element disruption we started an experimental program at the new bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ-Rossendorf, Dresden. The bremsstrahlung facility and the detector setup are designed such that the scattering of photons from nuclei and the photo dissociation of nuclei around the particle separation energies can be studied under optimized background conditions. The results of photon scattering experiments from the Z=42 nuclei 92,98,100-Mo and the N=50 nuclei 88-Sr, 89-Y,´and 90 Zr will be shown and compared to calculations based on a random-phase approximation method for deformed nuclei. In activation measurements with bremsstrahlung at end point energy from 10.5 to 16 MeV (gamma, p), (gamma, n) and (gamma,alpha) reactions of 92,100-Mo. have been studied. The results are compared to recent astrophysical network calculations to investigate if the underproduction of Mo, Ru isotopes in the p- process is due to incorrect nuclear reaction rates.
        Speaker: A.R. Junghans (Institut für Kern- und Hadronenphysik Forschungszentrum Rossendorf)
      • 09:45
        Photodissociation as a Tool for Nuclear Astrophysics 15m
        Photodissociation cross sections play an important role in our understanding of nucleosynthesis in the mass region above A > 60. The bulk of these heavy nuclei is produced by neutron capture reactions during the s- and r-process. The so-called branching points of the s-process have typical half-lives of the order of a few days up to a few hundred years. The direct measurement of neutron capture cross sections of the short-living is not feasible. However, some of the long-living ones were measured successfully [1,2]. We try to constrain theoretical predictions of the capture cross section by measuring the inverse ($\gamma$,n) cross section directly above the neutron threshold. A current result, the cross section of $^{186}$Re(n,$\gamma$) will be shown and its influence on the Re/Os-chronometer will be discussed [3]. About neutron deficient nuclei with masses A > 60 cannot be produced by neutron capture reactionS. These so-called p-nuclei are produced by photodisintegration reactions during the p-process. The p-process takes place at temperatures of about 2.5GK. At this temperature the photons stemming from the thermal photon bath induce ($\gamma$,n), ($\gamma$,$\alpha$), and ($\gamma$,p) reactions. We can emulate thermal photon spectra in the needed energy range to deduce directly the ground state reaction rates [4]. We will show recent results for neutron deficient nuclei with Z > 78 [5]. One of the remaining puzzles is the abundance of the neutron deficient Molybdenum isotopes. These abundances are underestimated by all network calculations by at least one order of magnitude. We measured the coulomb dissociation cross section of $^{92,93,94,100}$Mo at the LAND setup at GSI. This cross section can be converted into a photodissociation cross section. For comparison, the photodisscociation cross section of $^{100}$Mo will be measured at the S-DALINAC using real photons. The last part of this presentation will be about the status of the quasi-monochromatic photon source NEPTUN at the S-DALINAC. The high resolution photon tagger NEPTUM at the S-DALINAC is designed to measure ($\gamma$,n) cross sections with an energy resolution of about 0.25% in the energy range between 8 MeV and 20 MeV. [1] K. Wisshak, F. Voss, F. Käppeler, M. Krtcka, S. Raman, A. Mengoni, and R. Gallino, Phys. Rev. C 73, 015802 (2006) [2] U. Abbondanno et al. Report CERN-SL-2002-053 ECT, CERN (2003) [3] S. Müller, A. Kretschmer, K. Sonnabend, A. Zilges and D. Galaviz, Phys. Rev. C, in press [4] P. Mohr, K. Vogt, M. Babilon, J. Enders, T. Hartmann, C. Hutter, T. Rauscher, S. Volz and A. Zilges Phys. Lett B 488, 127 (2000) [5] K. Sonnabend, K. Vogt, D. Galaviz, S. Müller and A. Zilges, Phys. Rev. C 70, 035802 (2004)
        Speaker: Sebastian Müller (Institut fuer Kernphysik, TU Darmstadt)
      • 10:00
        Photodisintegration of Ta-181 leading to the isomeric state Ta-180(m) 15m
        Photoneutron cross sections for $^{180}$Ta$^{m}$ were determined from simultaneous measurements of total cross sections ($\sigma^{tot}$) and ground-state cross sections ($\sigma^{gs}$) for $^{180}$Ta in photodisintegration of $^{181}$Ta with laser Compton-backscattered $\gamma$ rays. Techniques of direct neutron counting and photoactivation were used for the measurement of $\sigma^{tot}$ and $\sigma^{gs} $, respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of $^{180}$Ta. Implications for the p- and s-process nucleosynthesis of $^{180}$Ta$^m$ are given.
        Speaker: S Goko (Konan University)
      • 10:15
        Neutron capture measurements on the s-process termination isotopes lead and bismuth 20m
        Resonance cross sections relevant for the termination of the s-process reaction path have been determined for 204,206,207Pb and 209Bi at the CERN neutron time-of-flight spectrometer n_TOF. The measurements were carried out in the neutron energy range from 1 eV up to 500 keV. By using a system of C6D6-detectors with optimized neutron sensitivity, the main corrections of previous measurements related to neutron scattered backgrounds could be practically eliminated. Other corrections were thoroughly treated by control measurements with additional samples for determination of the ambient background and of background from in-beam g-rays as well as by detailed analyses via Monte Carlo simulations. The final resonance parameters of the four isotopes and the Maxwellian averaged cross sections will be reported and their implications for the s-process abundance contributions in the Pb/Bi region will be discussed. * This work has been partially supported by the EC (contract FIKW-CT-200000107) and by the National Institutions partners in the n_TOF Collaboration.
        Speaker: Dr Cesar Domingo Pardo (Instituto de Fisica Corpuscular (IFIC) UV-CSIC)
    • 10:35 11:30
      break + poster session 22

      Poster sessions will be held outside the Main Auditorium, in the CERN Main building.

      No oral presentation of poster contributions is schduled.

      Poster session 22
    • 11:30 13:00
      15 Galactic and stellar evolution
      Convener: Michael Smith (ORNL)
      • 11:30
        Early galactic chemical evolution: the Milky Way in a cosmological context 30m
        I will present an overviw of recent work on the early chemical evolution of galaxies. Available information on the early Milky Way (derived from observations of abundances, abundance ratios, metallicity distributions etc.) will be compared to information about the distant Universe (derived from e.g. metallicity, star formation rate, supernova rates, abundance patterns, etc. as a function of redshift).
        Speaker: Nikos Prantzos (IAP, Paris)
      • 12:00
        Neutron-Capture Processes in the Early Galaxy 30m
        High resolution spectroscopy for very metal-poor stars have revealed that some fraction of objects have large excesses of neutron-capture elements, whose abundance patterns agree very well with that of the r-process component of solar-system material (e.g. Sneden et al. 1996, ApJ, 467, 819). However, recent abundance studies show the existence of objects that have quite different abundance patterns. One is the class of objects that have very large enhancement of light neutron-capture elements. Although the nucleosynthesis process responsible for such chemical composition is still unknown, observational studies for this process have made substantial progresses in the past few years: (1) Such objects appear even in the extremely low metallicity range ([Fe/H]~<-3.0), while the stars having large excesses of heavy neutron-capture elements appear in the metallicity range of [Fe/H]>~-3.0. (Aoki et al. 2005, ApJ 632, 611). A large excess of the light neutron-capture element Sr is found even in the most iron-deficient star HE1327-2326 (Frebel et al. 2005, Nature 434, 871). (2) An evidence of this process is found in metal-poor globular cluster stars (Otuski et al. 2006, ApJL, in press). These observational facts indicate that the process was efficient in general in the very early Galaxy. (3) The detailed elemental abundance pattern (Sr-Yb) was determined for the metal-poor star HD122563, a star that might well preserve the yields of this process (Honda et al. 2006, ApJ, in press). The abundances of elements between the 1st and 2nd abundance peaks of neutron-capture elements continuously decrease in this object. This result provides strong constraints on modeling the process responsible for production of light neutron-capture elements in the early Galaxy, which is presumably related to early generation supernovae. Another is the class of carbon-enhanced metal-poor stars that exhibit large excesses of Eu as well as s-process elements (e.g. Ba, Pb). Although contributions of nucleosynthesis in AGB stars are assumed because of the excesses of s-process elements, standard s-process models cannot explain the Eu enhancement. Our recent study determined the abundances of Os and Ir for one star in this group (CS31062-050), confirming the excesses of r-process elements. Discovery of such objects and measurements of their detailed abundance patterns have impact on the studies of the origins of r-process elements.
        Speaker: Wako Aoki (National Astronomical Observatory of Japan)
      • 12:30
        AGB stars evolution and nucleosynthesis 30m
        AGB stars are the nuclear production phase of low- and intermediate mass stars. The double-shell burning of He and H around the electron degenerate core drives a rich pattern of nucleosynthesis, including the slow neutron capture process, as well as the formation of neutron rich isotopes. This nucleosynthesis is now observationally accessible in extremely metal poor stars, in particular the carbon enhanced s- process rich stars in binaries. Models of AGB star evolution and nucleosynthesis include a wide range of approaches: parameterized s-process post-processing, stellar evolution models with various assumptions on stellar mixing as well as, more recently, hydrodynamic simulations of He-shell flash convection. New studies have been caried out to investigate the sensitivity of mixing and element production to nuclear reaction rates. (LA-UR-05-0900, LA-UR-05-8084, LA-UR-04-5295)
        Speaker: Falk Herwig (Theoretical Astrophysics Group, LANL)
    • 13:00 14:00
      lunch 1h
    • 14:00 15:00
      16 Evolution and evidence of nucleosynthesis in stars: AGBs
      Convener: Richard Azuma (Toronto U)
      • 14:00
        3D Hydrodynamical Models of the Core Helium Flash 20m
        We present fully three dimensional models of the core helium flash in low mass stars. These hydordynamical models show that the simple 1D hydrostatic models are not too misleading! New results, for rotating models, will be reported.
        Speaker: John Lattanzio (Monash University)
      • 14:20
        The s-process in massive stars: the Shell C-burning contribution 20m
        In massive stars evolution the s-process is activated at different temperatures, during He-burning and during C-burning. In the convective C Shell, the s-process affects the previous Core He-burning s yields, and the final results carry the signature of both the two following neutron capture processes. A detailed analysis of the s-process in massive stars is presented, in particular at the end of the Shell C-burning when the local temperature could rapidly increase with the s-process efficiency.
        Speaker: Marco Pignatari (Universita' di Torino)
      • 14:40
        Light and heavy elements nucleosynthesis in low mass AGB Stars 20m
        We present a new set of low mass AGB Stars models having the same mass (2 Msun) and different metallicities (Z=1e-4, Z=e-3 and Z=1.5e-2, corresponding to the most recent evaluation of the solar metallicity). For each mass we present the evolution from the Pre Main Sequence up to the end of the Thermally Pulsing AGB Phase. The introduction of an exponential decay of the convective velocities at the inner border of the convective envelope allows the formation of a tiny 13C pocket after Third Dredge Up episodes, whose extension in mass decreases along the AGB path. Detailed pulse by pulse surface enrichments and final yields at different metallicities, using a full nuclear network directly incorporated in the FRANEC stellar evolutionary code, are presented and discussed in detail. We follow the production of both light and heavy elements describing nuclear chains responsible of their production and show new results for the synthesis of radioactive isotopes such as 26Al and 60Fe.
        Speaker: Sergio Cristallo (Osservatorio Astronomico Teramo (INAF, Italy))
    • 15:00 15:30
      break 30m
    • 15:30 17:00
      17 Experiments and theory in nuclear astrophysics
      Convener: Thomas Rauscher (Universität Basel)
      • 15:30
        Role of the fission in r-process nucleosynthesis 30m
        Fission can have an important influence on the termination of the r-process and on the abundances of long-lived actinides, which are relevant for determinating the age of the Universe. Fission can also influence the abundances of nuclei in the region A~90 and 130 due to the fission cycling. In order to quantitatively understand the fission role in the r process, two important pieces of information are needed: the fission-barrier heights and mass- and charge-distributions of the fission fragments. Unfortunately, experimental information is only available for nuclei in a limited region of the nuclide chart, and for heavy r-process nuclei one has to rely on theoretical predictions. Recently, important progress has been made in developing full microscopic approaches to nuclear fission. Nevertheless, due to the complexity of the problem, this type of calculations is still difficult to apply to heavy nuclei and, moreover, the precission of these models is often still low. In this contribution we will concentrate on macroscopic-microscopic approaches that could help us understanding the contribution of fission to the r process. Firstly, using available experimental data on saddle-point and ground-state masses, we will present a detailed study on the predictions of different models concerning the isospin dependence of saddle-point masses [1]. It will be shown that several models yield unrealistic barriers for very neutron-rich nuclei. Secondly, we will present a model for calculating mass- and charge-distributions of fission fragments, that can correctly predict the transition from double-humped to single- humped distributions with decreasing mass of the fissioning system and increasing excitation energy in the light actinides. This model has recently [2] been used to calculate fission-fragment distributions in neutrino-induced fission of r-process nuclei. [1] A. Kelic and K.-H. Schmidt, accepted by Phys. Lett. B [2] A. Kelic et al, Phys. Lett. B 616 (2005) 48
        Speaker: Aleksandra Kelic (GSI)
      • 16:00
        Nucleosynthesis in neutrino heated matter 30m
        Independently of the still unclear explosion mechanism for core-collapse supernovae there will be matter ejected under strong neutrino fluxes. Depending of the spectral properties of both neutrinos and antineutrinos the composition of the matter goes from proton rich to neutron rich. Current supernova simulations suggest that the early ejecta is proton rich while at latter times we expect neutron-rich ejecta. Proton-rich ejecta constitute the site a new kind of rp-process that is catalyzed by antineutrino absorptions in protons and that we denote as vp-process. The combination of proton-rich ejecta and mildly neutron-rich ejecta could explain the production of several light p-nuclei in particular 92,94Mo and 96,98Ru and at the same time explain the elemental abundances of Sr, Y and Zr seen in metal poor stars. The r-process is expected to occur in neutron rich ejecta. Depending in the conditions even the heavier r-process elements can be produced. In this case fission can play a major role in understanding the production of r-process elements. In this talk I will discuss the current theoretical and experimental uncertainties related to nucleosynthesis in neutrino heated matter and in particular the role of fission (neutron induced, neutrino induced and beta-delayed) in r-process nucleosynthesis.
        Speaker: Gabriel Martínez Pinedo (GSI Darmstadt))
      • 16:30
        Studies of radioactive nuclei and their role in the cosmos 30m
        Radioactive nuclei play an important role in many astrophysical phenomena, particularly in stellar explosions where the rates of nuclear reactions can be much faster than the lifetimes of most radioactive isotopes. Accelerated beams of radioactive ions are being used to address uncertainties in some key reaction rates. We will review recent progress in the field, focusing on results from the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. The production of gamma-rays from electron-positron annihilation in novae is particularly sensitive to the rate of the 18F(p,alpha)15O reaction. Uncertainties have remained in the 18F(p,alpha)15O reaction rate due to the uncertain contributions of low-energy resonances and the nature of interferences between resonances. We will report on recent measurements of the 18F(p,alpha)15O cross section at the HRIBF using an experimental approach similar to previous measurements. [1] The new data provide some of the first constraints on the nature of interferences between resonances in the 18F(p,alpha)15O reaction. We will present a novel experimental technique that we have developed to allow improved sensitivity for studies of low energy (p,alpha) resonances. In this new approach a heavy ion beam bombards a large, windowless chamber filled with hydrogen gas. Alpha particles and recoiling heavy ions are detected in coincidence in arrays of silicon strip detectors operating inside the hydrogen gas. While each element of the detector array simultaneously views reaction products over a wide range of angles, the relative kinematics of the two reaction products allows the vertex of the reaction to the accurately determined on an event-by-event basis. We will present results from a measurement applying this technique to the 183-keV resonance in the 17O(p,alpha)14N reaction that was first reported using a more conventional approach last year. [2] The strength of this resonance is also crucial for understanding the production of 18F in novae as well as the Galactic origins of the rare 17O isotope. This approach will next be applied to low energy resonances in 18F(p,alpha)15O. Results from recent measurements using 7Be beams at the HRIBF will also be presented. Accurate measurements of the neutrino flux originating from the decay of 8B in the solar core provide a powerful probe of the properties of the solar interior and neutrinos themselves. [3] While recent measurements have substantially improved our understanding of the 7Be(p,gamma)8B reaction rate that impacts the interpretation of solar neutrino observations [4], the experimental situation is less than completely resolved. We are performing direct measurements of the 7Be(p,gamma)8B cross section in inverse kinematics, using a radioactive 7Be beam on a windowless hydrogen gas target. This alternative approach at direct measurement of the 7Be(p,gamma)8B cross section is interesting since it provides an independent check on potential systematic uncertainties. We will present results from the first measurements at the HRIBF that have demonstrated the advantages and limitations of the approach, though not yet competitive statistically with 7Be target experiments. We will also present measurements of 7Be+p elastic and inelastic scattering cross sections at center-of-mass energies ranging between 0.5 to 3.4 MeV that provide new information on the properties of excited states in 8B and 7Be+p s-wave phase shifts, which can influence extrapolations of the 7Be(p,gamma)8B cross section to solar energies in some models. [5] *for the RIBENS Collaboration. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. [1] D.W. Bardayan et al., Phys. Rev. Lett. 89, 262501 (2002). [2] A. Chafa et al., Phys. Rev. Lett. 95, 031101 (2005). [3] S.N. Ahmed et al., Phys. Rev. Lett. 92, 181301 (2004). [4] A.R. Junghans et al., Phys. Rev. C 65, 065803 (2003), and references therein. [5] P. Descouvemont, Phys. Rev. C 70, 065802 (2004).
        Speaker: Jeff C Blackmon (for the RIBENS Collaboration, Oak Ridge National Laboratory)
    • 17:00 17:30
      Convener: Alberto Mengoni (IAEA Vienna/CERN n_TOF)
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