ISOLDE Workshop and Users meeting 2006/2007

Europe/Zurich
Council Chamber, 503/1-001 (CERN)

Council Chamber, 503/1-001

CERN

Karsten Riisager
Description
The purpose of the ISOLDE workshop is to gather together the ISOLDE community. The workshop is combined with the yearly users meeting taking place at EU recognised large scale facilities in Nuclear Physics.
    • 2:00 PM 3:40 PM
      Opening Session Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Kris Heyde (Gent)
      • 2:00 PM
        Welcome and Announcements 10m
        Speaker: Karsten Riisager (CERN)
        Slides
      • 2:10 PM
        Atomic Physics Goes Online: the Role of ISOLDE in the Past and in the Future 30m
        Speaker: Prof. Heinz - Juergen Kluge (GSI)
        Slides
      • 2:40 PM
        Nuclear Mixed-Symmetry States as Probes for the Proton-Neutron Effective Valence-Shell Interaction 30m
        Considerable efforts are currently being made to improve our understanding of the structural evolution of heavy nuclei, in particular, those with neutron excess. This evolution as a function of nucleon number is dictated by the dynamics of the valence shell. Since quantitative theoretical predictions from first principles are not yet possible, experimental constraints and input on key quantities, such as the proton-neutron quadrupole-quadrupole interaction, are highly desirable. The proton-neutron interaction in the nuclear valence shell dominates the formation of collective structures at low excitation energy, e.g., nuclear quadrupole deformation. The properties of proton-neutron non- symmetric excitation modes of the valence shell, so-called mixed-symmetry states (MSSs), are particularly sensitive to certain parts of the effective valence- shell interaction. MSSs of stable nuclei have, therefore, been studied for over 20 years with electron-, photon-, and neutron-scattering reactions. We have recently demonstrated [1,2] a technique for investigating MSSs based in Coulomb excitation reactions in inverse kinematics, a method applicable to neutron-rich radioactive ion beams. MSSs in vibrational nuclei such as 96Ru and 138Ce near N=50 and 82 neutron shell closures have been studied with this method. We will give an overview over these results and we will address the potential research on MSSs with modern RIBs. [1] N. Pietralla et al., Phys. Rev. C 64, 031301(R) (2001). [2] G. Rainovski et al., Phys. Rev. Lett. 96, 122501 (2006).
        Speaker: Prof. Norbert Pietralla (IKP, Technische Universität Darmstadt)
        Slides
      • 3:10 PM
        Exotic Nuclear Shapes: Probing the Limits of Nuclear Stability 30m
        With the recent advent of Radioactive Ion Beams facilities, entire regions of the nuclear chart have become accessible in experiments. Moreover, the on-going developments of e.g. new generations of segmented gamma arrays will also allow to explore low-statistic reaction channels. This large and constant supply of new data puts severe constraints on nuclear models. In particular, the shape and geometrical symmetries of atomic nuclei are very sensitive to variations of the particle number (going to the drip-lines), angular momentum (high-spin physics) or temperature (hot nuclei). The nuclear shape is therefore a convenient tool to investigate the underlying mechanisms that govern nuclear stability. I will describe two phenomena to illustrate this point. On the one hand, nuclear states corresponding to a shape with tetrahedral symmetry have been investigated in the framework of various mean-field approaches, where it is interpreted as a manifestation of the spontaneous symmetry breaking. The challenge, both for theorists and experimentalists, now resides in the observation of the signatures of such states. On the other hand, nuclear hyper-deformed states have been predicted for some time, but it is only recently that the importance of the Jacobi transition in the population of such states was recognized. Hyperdefomation represents a rare case of a nucleus at the limit of deformation and spin, and thus is invaluable for theorists. The experimental challenge consists in being able to populate such a weakly-populated channel. I will conclude by mentionning some of the directions explored by theorists to address such issues.
        Speaker: Dr Nicolas Schunck (Universidad Autonoma de Madrid)
        Slides
    • 3:40 PM 4:10 PM
      Coffee 500/R-203 - Foyer

      500/R-203 - Foyer

      CERN

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    • 4:10 PM 6:15 PM
      Physics 1 Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Kris Heyde (Gent)
      • 4:10 PM
        High-precision mass measurements of exotic nuclides: The 2006 harvest of ISOLTRAP 25m
        In 2006 the mass measurements at the tandem Penning trap spectrometer ISOLTRAP investigated short-lived nuclides relevant for superallowed beta decays, nuclear structure, and nucleosynthesis. After the installation of a new detector [1] and a temperature stabilization system, which improved respectively the precision and the accuracy of the experiment, a new excitation scheme has been successfully applied. Furthermore, for the first time mass selected iron nuclides have been directly studied at ISOLDE. To contribute to the test of the unitarity of the CKM quark mixing matrix, a mass uncertainty below 1 keV is required. For the 38Ca and 26Al nuclides a new excitation scheme has been applied in order to reach a better precision within the given beam time period. Instead of the quadrupolar radiofrequency (rf) excitation, time separated oscillating fields, known as Ramsey technique, have been used resulting in a reduction of the uncertainty in the cyclotron frequency measurement by a factor of 3 compared to the standard technique within identical experimental conditions and beam time. For the first time, refractory neutron-rich iron nuclides 61-63Fe were produced in the preparation Penning trap of ISOLTRAP by use of the in-trap decay technique [2]. Mass-selected manganese nuclides 61-63Mn from the ISOLDE target were stored in the preparation trap, waiting for the beta decay towards their iron daughter nuclide. After additional cooling the neutron-rich iron ions were transferred to the precision trap for precise mass determination dm/m in the order of 10-8. The new techniques developed for high-precision mass experiments and the associated results will be presented together with outcomes from beam times dedicated to the investigation of neutron-rich Cd and Ag nuclides. [1] C. Yazidjian et al., accepted in Hyp. Int. [2] A. Herlert et al., New J. Phys. 7, 44 (2005)
        Speaker: Dr Chabouh Yazidjian (GSI, Atomic Physics Group, Darmstadt, Germany)
        Slides
      • 4:35 PM
        In-source Laser Photoionization Spectroscopy of Pb, Bi and Po Isotopes at ISOLDE 20m
        Shape coexistence at low excitation energy in nuclei has continuously shown much interest on both experimental and theoretical fronts. The region around the neutron mid-shell (N = 104) and closed proton shell (Z = 82) is of special interest. For example, in Pb at N = 104, it has been found that the three lowest lying states have 0+ as spin and parity values, these states have been associated with different shapes in the nucleus: spherical and deformed (prolate and oblate). Significant mixing of the deformed states into spherical ground state would result in an increased nuclear charge radius. At ISOLDE laser spectroscopy studies of neutron deficient isotopes (and isomers) of Pb and Bi have been extended to N=100-107 (Pb) and N=106,108 (Bi). The measured values of the mean charge radius variations and nuclear magnetic moments will be presented and compared with the recent theoretical calculations (for Pb isotopes: IBM and beyond mean field calculations). Our data support the predominantly spherical shape of the ground state of the Pb isotopes near the neutron mid-shell (N=104). The results of the first tests of photoionization schemes for Po will also presented.
        Speaker: Dr Maxim Seliverstov (Institut fuer Physik, Johannes Gutenberg Universitaet, Mainz)
        Slides
      • 4:55 PM
        Laser pumping of ions in a cooler-buncher 20m
        Collinear laser spectroscopy measurements of nuclear moments and mean-square charge radii at JYFL have benefited from the introduction of an ion beam cooler. The reduced energy spread of the emerging beam increases the spectral resolution while the smaller emittance allows a narrower waist of the laser-ion overlap, thus requiring less laser power. A lower background from the decreased continuous scattering of laser light is further improved by pulsing the release of the ions from the cooler. The installation of ISCOOL at ISOLDE will couple these advantages with the higher beam intensities offered. Axial confinement of the slowly traveling cooled ions at the end of the cooler provides an opportunity to excite transitions and redistribute the electronic level populations. This may be done using broad band lasers which can readily access a wide range of wavelengths. Manipulation of state population in such a way extends the number of transitions available for study by collinear techniques. Transitions may be chosen on the basis of strength, preferred spins or hyperfine structure and hindered less by the lower state population.
        Speaker: Bradley Cheal (The University of Manchester)
        Slides
      • 5:15 PM
        33Mg: determination of a negative parity intruder ground state via nuclear moments 20m
        Since introduced in nuclear physics, the concept of shell structure and magic numbers has governed our understanding of nuclear matter in atomic nuclei close to stability. Experimental research in 30Ne, 31Na and 32Mg, systems with a closed neutron sd shell (N=20), provided evidence for a ground state deformation in these nuclei. The observed phenomenon is understood as an inversion of the normal spherical ground state configuration, expected according to the traditional shell model, with deformed states governed by particle-hole excitations over the N=20 shell gap. The properties of nuclei in the “Island of inversion” are of particular importance for the theoretical modelling of the region. The research taking place at the collinear laser spectroscopy setup COLLAPS at ISOLDE - CERN makes an intriguing contribution in this aspect. For the first time an unambiguous determination of the nuclear ground state spin and parity of 33Mg will be reported. A measurement of the hyperfine structure and the nuclear g-factor will be presented, illustrating the importance of the technique of nuclear magnetic resonance in combination with laser spectroscopy. The results will be discussed in the frame of the spherical shell model, showing the intruder nature of the ground state, associating it with negative parity. Inconsistencies in the interpretation of former experimental studies will be discussed and based on the firm ground state spin-parity assignment a new set of spins and parities for the lowest excited states will be proposed. The coexistence of different particle-hole excitations in the low lying energy spectrum of 33Mg will be demonstrated. A parallel interpretation will be given within the deformed shell model. A review of recent results, obtained at COLLAPS, in the vicinity of the island of inversion will be given and future prospects will be discussed. Supported by the German Federal Ministry for Education and Research (BMBF) and the Belgian Fund for Scientific Research (FWO - Vlaanderen).
        Speaker: D. T. Yordanov (Instituut voor Kern- en Stralingsfysica)
        Slides
      • 5:35 PM
        The WITCH experiment: campaign 2006 and perspectives 20m
        The WITCH experiment aims to study a possible admixture of a scalar or tensor type interaction in beta decay by determining the beta-neutrino angular correlation from the shape of the recoil energy spectrum. The experimental set-up couples a double Penning trap system to form a scattering-free radioactive source and a retardation spectrometer to probe the recoil ion energy. The intensive commissioning of the set-up is ongoing at ISOLDE (CERN). The layout of the WITCH set-up and results of commissioning tests performed until now will be presented. Results of the data taken during 2006 (two beam times with 124In) will be shown as well, presenting the first recoil ion spectrum obtained. Finally, perspectives of the physics program will be discussed.
        Speaker: Dr Valentin Kozlov (Instituut voor Kern- en Stralingsfysica)
        Slides
      • 5:55 PM
        Laser spectroscopy of radioactive copper isotopes 20m
        The evolution of nuclear structure with neutron excess in the copper isotope chain is currently under investigation by the COLLAPS collaboration. This experiment uses high-resolution laser spectroscopy, which unambiguously measures the nuclear spin and provides model-independent measurements of nuclear moments. It is therefore an ideal tool to study the nuclear structure. In the isotopes 69,71,73Cu, strong evidence of a migration of the pi f5/2 level with increasing neutron number was observed in beta-decay studies of 68-74Ni [1,2]. It is predicted that the pi p3/2 ground state will be replaced by the pi f5/2 level at N=46. Two-neutron separation energies from ISOLTRAP mass measurements, show a signature for the onset of deformation in this same region of the copper chain [3]. This project aims to chart the onset of deformation and to confirm a pi f5/2 ground-state configuration at N=46. It also aims to measure the spin/parity of 72Cu, and thus resolve the inconsistency between recent results from in-source spectroscopy and beta-decay studies [4,5]. An initial on-line run was carried out in September 2006. The hyperfine structures of 64,66,67,68g,68m,69,70gCu were resolved and the magnetic dipole and electric quadrupole moments, nuclear spins and isotope shifts subsequently extracted. These results and future prospects for this project in 2007 will be presented and discussed. [1] S. Franchoo et al., Phys. Rev. C 64, 054308 (2001). [2] J. Van Roosbroeck et al., Phys. Rev. C 71, 054307 (2005). [3] C. Guenaut et al., submitted to Phys. Rev. C. [4] J.-C. Thomas et al., Phys. Rev. C 74, 054309 (2006). [5] U. Koster, Private Communication, 2005.
        Speaker: Dr Kieran Flanagan (KU-University of Leuven)
        Slides
    • 9:00 AM 10:40 AM
      News from other Laboratories Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Peter Butler (Liverpool)
      • 9:00 AM
        SPIRAL/GANIL latest news 30m
        The first accelerated exotic beam of the SPIRAL (“Production System of Radioactive Ion and Acceleration On-Line”) facility at GANIL at Caen has been delivered for experiments in September 2001. After working for almost 5 years, 32 experiments were performed in the facility using exotic isotopes of helium, oxygen, neon, argon and krypton. The intensities of the radioactive beams increased since the first beam was delivered. Nominal intensity values are achieved for most of noble gas beams. Developments of new beams as well as the increasing of present intensities for a number of isotopes are being undertaken. Together with highlights of physics results, this contribution will also present the first results obtained for the production of light alkali beams. Other developments are also envisaged in the close future.
        Speaker: Dr Antonio Villari (GANIL)
      • 9:30 AM
        EXCYT: the RIB Facility at INFN-LNS 30m
        EXCYT (EXotics with CYclotron and Tandem) is a ISOL facility located at INFN-LNS to produce and accelerate radioactive ion beams. The primary heavy ion beam provided by the K-800 Superconducting Cyclotron (up to 80 MeV/amu, 1 pµA) generates, in a target-ion source complex (TIS), the required nuclear species which will be post-accelerated by the 15 MV Tandem. For some ion beam such as for Li, the higher extraction efficiency from the TIS is obtained by positive ionisation. Then the injection into the Tandem is suitable only after a charge exchange (CEC) to obtain negative ions. The commissioning of the facility has been concluded by delivering a 8Li beam to the BigBang experiment at 28.1 MeV and 10.2 MeV. The production of the radioactive lithium (8,9) beams were performed by injecting a 13C4+ primary beam of 45 MeV/amu on a graphite target up to a beam power of about 150W, while the ionisation was achieved by using a Tungsten positive surface ioniser. The maximum 8Li yield obtained was about 1×107 pps, however the need of the charge exchange and an unexpected low transmission in the tandem coupling line and through the tandem decrease this maximum yield at the experimental point to a few 104 pps. We are confident to decrease such losses matching the design calculations by adding more diagnostics and with a fine realignment of the magnetic elements. However, the tandem transmission efficiency will be always affected by the terminal voltage: values ranging between 10-37% have been obtained during the commissioning by changing the terminal voltage between 2.5 to 7MV. The charge exchange process has been characterised off-line and the results obtained at the EXCYT facility confirm our previous observations and expectations such as the efficiency at different beam energies and the isotopic shift effect. Since the CEC showed an increase of efficiency by decreasing the lithium beam energy, we decided to lower the TIS extraction. The best operating point was found experimentally at 10 kV permitting to obtain higher CEC efficiency (3.6% circa) with negligible beam losses over the HV platforms with respect to higher Li beam energy. Finally, a presentation of the facility will be given with particular concern to the TIS, to the CEC and to the results of lithium beams production together with the future improvements and plan.
        Speaker: Dr Luigi Celona (INFN-LNS)
        Slides
      • 10:00 AM
        Exploring the nuclear physics along the rp process path 20m
        Type I X-ray bursts, thermonuclear runaways on the surface of an accreting neutron star in a binary system, are one of the known sites for the rapid proton capture process (rp-process)[1,2]. After accumulation of material, mainly hydrogen and helium, on the surface of the neutron star, the triple-alpha reaction triggers a series of fast (a,p) and (p,g) reactions, with subsequent beta decays, that drive the process along the proton-rich side of the valley of stability. The process stops around the Sn-Te region [3], and after ther hydrogen is depleted, the produced nuclei decay B+ and fall onto the surface of the neutron star. Proton capture rates are a key ingredient in the description of the energy release curve associated to X-ray bursts, as well as in the determination of the final isotopic abundance distribution [4]. In order to reduce the uncertainties in the determination of (p,g) reaction rates, several experiments were performed at the National Superconducting Cyclotron Laboratory (NSCL) at the Michigan State University, using radioactive beams, to determine precisely the level structure above the proton threshold of rp process nuclei. This work presents the experimental approach and the set-up at the NSCL, which involves the S800 Spectrograph and the Segmented Germanium Array (SeGA), as well as the first results obtained with this technique. Implications of the new results in the astrophysical rp process are also discussed. [1] R. K. Wallace, and S. E. Woosley, Astrophys. J. (Suppl.) 45, 389 (1981) [2] H. Schatz et al., Phys. Rep. 294, 167 (1998) [3] H. Schatz et al., Phys. Rev. Lett. 86, 3471 (2001) [4] J. L. Fisker et al., Astrophys. J. Lett. 608L, 61 (2004)
        Speaker: Mr Daniel Galaviz Redondo (CSIC)
      • 10:20 AM
        Structure of neutron-rich Fe nuclei near N = 40 from studies at ISOLDE and ATLAS 20m
        New results will be presented for the structure of neutron-rich Fe nuclei based on data from deep inelastic scattering studies with GAMMASPHERE and beta decay of Mn nuclei at ISOLDE isolated with the Resonance Ionization Laser Ion Source. In particular, the low-energy levels in 64Fe are found to be well described by shell-model calculations using pf –shell neutrons and protons. The main yrast sequence in the odd-mass Fe nuclei will be presented and interpreted as the weak coupling of a g9/2 neutron to two f7/2 proton holes.
        Speaker: Dr William Walters (University of Maryland)
        Slides
    • 10:40 AM 11:00 AM
      Coffee 500/R-203 - Foyer

      500/R-203 - Foyer

      CERN

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    • 11:00 AM 12:50 PM
      Physics 2 Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Peter Butler (Liverpool)
      • 11:00 AM
        Evolution of nuclear shell structure with neutron excess in the fp-shell 30m
        The evolution of properties of atomic nuclei with respect to increase in neutron richness is one of the crucial issues in the modern nuclear structure studies. In particular, neutron-rich nuclei above the doubly magic 48Ca have recently attracted a lot of interest due to an N=32 subshell closure that was evidenced in 52Ca, 54Ti and 56Cr. This phenomenon was attributed to the strong proton f7/2 - neutron f5/2 monopole interaction, which causes an increase in energy of the f5/2 single particle orbital with respect to the p3/2 and p1/2 levels as protons are subtracted from the f7/2 shell. However, the magnitude of this increase, particularly in Ca isotopes, is difficult to detect as the states involving the neutron f5/2 orbital in such nuclei like 51-53Ca are very hard to reach. In our recent experiments we studied neutron-rich species close to Z=20 using deep inelastic processes occurring in heavy ion collisions of a 48Ca beam on a 238U target. In one measurement, a thick target technique was applied and the gamma coincidence data were collected with GAMMASPHERE at Argonne NL. In the second experiment, the same reaction was studied employing the PRISMA+CLARA detection system at LNL in Legnaro. With A and Z reaction fragment identifications obtained from PRISMA, we were able to assign the observed (with CLARA) gamma transitions to a given product. These transitions were subsequently used as “starting points” in the analysis of thick target gamma coincidence data. Among many findings, yrast structures in the N=31 isotones, 52Sc and 51Ca were located - these structures include excitations involving f5/2 neutrons. The presentation will discuss new results in light of shell model calculations and theoretical predictions for the f7/2 – f5/2 monopole interaction strength arising from the tensor component of the nucleon-nucleon interaction.
        Speaker: Prof. Bogdan Fornal
        Slides
      • 11:30 AM
        Coulomb excitation of neutron-rich 44Ar at SPIRAL 20m
        A low-energy Coulomb excitation experiment on neutron-rich 44Ar has been performed at the SPIRAL facility of GANIL. The primary question addressed by the experiment was the possible weakening of the N=28 shell closure in neutron-rich nuclei and, closely connected to that, the development of deformation and shape coexistence in this region of the nuclear chart. A beam of 44Ar was produced by fragmentation of a primary 48Ca beam at 60 A MeV on the carbon production target of SPIRAL. The Ar44 fragments were re-accelerated in the CIME cyclotron to 2.7 and 3.7 MeV/nucleon and Coulomb excited on 109Ag and 208Pb targets, respectively. The scattered projectiles and recoiling target nuclei were detected in a highly segmented double-sided silicon detector and the gamma rays were detected with the EXOGAM germanium detector array. Apart from the first excited 2+ state, at least one higher-lying level was populated. The level of statistics is sufficient to determine the gamma-ray yields for several ranges of scattering angles and for the two different target materials. Although the analysis is still in progress, it is anticipated that the collected data will allow extracting the transition probabilities between the observed states, as well as the static quadrupole moment of the first 2+ state. It is anticipated to continue in this experimental program with the Coulomb excitation of 46Ar.
        Speaker: Magda Zielinska (CEA Saclay)
        Slides
      • 11:50 AM
        Level densities and gamma strength functions 20m
        The Oslo group has developed a technique to measure with high precission the level density from the ground state up to the neutron binding energy. The method provides simultaneously the level density and gamma-ray strength function in one and the same experiment. After establishing the level density as a function of excitation energy, the entropy is known and we can explore various thermodynamical parameters of the nucleus. The caloric curve, derived within the framework of the micro-canonical ensemble, shows structures, which we associate with the break up of nucleon pairs. And the nuclear heat capacity deduced within the framework of the canonical ensemble exhibits an S-shape as function of temperature, indicating a phase transition. Nuclear level densities and gamma strength functions are input parameters in large network calculations of stellar evolution, and in the simulation of accelerator-driven transmutation of nuclear waste. I will discuss the evolution of the level density and radiative strength function as one moves from the well deformed Dy, Er and Yb nuclei to the close to spherical Sm nuclei. A pygmy resonance at around 3 MeV has been observed in several deformed rare earth nuclei and vanishes for the spherical nuclei. This is as expected for a scissors mode pygmy resonance. Results from Oslo combined with a thermal neutron capture experiment analysing two-step cascades finally establish the M1 multipolarity of this pygmy resonance. Preliminary result for Sm will also be shown and a discussion of what happens to the level density and the radiative strength function of samarium isotopes as one approaches and crosses the N=82 closed shell.
        Speaker: Dr Sunniva Siem (University of Oslo)
        Slides
      • 12:10 PM
        Lattice location studies of the "anti-site" impurities As and Sb in ZnO and GaN 20m
        The group V impurities As and Sb are of interest as possible acceptor dopants in the II-VI semiconductor ZnO and as isoelectronic impurities in the III-V semiconductor GaN. Since the chemical valence of As and Sb is closer to O or N than to Zn or Ga, it is in in both cases often assumed that As and Sb substitute for the anions of the compound semiconductor, i.e. for O in ZnO and for N in GaN. However, these simple arguments do not take into account the ionic size of these impurities and there exist theoretical predictions that both foreign atoms are more stable on cation (i.e. Zn or Ga) sites. We report here on recent lattice location experiments of 73As (80.3 d) and 124Sb (60.3 d)in ZnO and GaN by means of the emission channeling method. While it is found that As is in its large majority incorporated in cation sites in ZnO (i.e. replacing Zn), it turns out that it is amphoteric in GaN, occupying substitutional Ga and N sites roughly in a ratio 1:1. The experiments with 124Sb are still ongoing but preliminary results indicate the substitutional incorporation of Sb in Zn and Ga sites. As and Sb are thus interesting cases of "anti-site" impurities, where the lattice position is to a large extent dominated by atomic size rather than chemical valence. Some consequences of this unusual behaviour will be discussed.
        Speaker: Dr Ulrich Wahl (Instituto Tecnológico e Nuclear ITN)
      • 12:30 PM
        Lattice site location of implanted Fe in SrTiO3 and lattice damage recovery studies 20m
        We report on the lattice site location of Fe in SrTiO3 single crystals using the emission channeling technique. Following the room temperature 60 keV implantation of the precursor isotope 59Mn(t1/2=0.71s) to a dose of 2E13 at./cm2, the angular distribution of β- particles emitted from 59Fe(t1/2=44.6d) was recorded around the <100>, <111>, <211> and <110> axis in the as- implanted state and following 10min in-situ vacuum annealing steps at 300ºC, 600ºC, 750ºC and 900ºC. The results provide direct evidence that Fe occupies substitional sites to a large extent already in the as implanted state and as well octahedral interstitial sites to a considerable fraction of 20%. However, following annealing at 300°C the interstitial fraction of Fe atoms is converted preferentially to Ti substitutional sites, which is 86% in the last annealing step at 900ºC. In order to study the 900ºC annealing efficiency regarding the lattice damage recovery induced by implantation, Rutherford backscattering/channeling spectroscopy was performed for SrTiO3 56Fe- implanted to doses of 1E15 and 5E15 at./cm2. Preliminary magnetic moment measurements from these samples will be briefly introduced as a further point to study in Fe doped SrTiO3 crystals.
        Speaker: Ana Claudia Lourenco Santana Marques (Centro de Física Nuclear da Universidade de Lisboa CFNUL)
        Slides
    • 12:50 PM 2:15 PM
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      CERN

    • 2:15 PM 4:10 PM
      Technical Developments Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Dr Mats Lindroos (CERN)
      • 2:15 PM
        Target developments at ISOLDE 30m
        Speaker: Dr Thierry Stora (CERN)
        Slides
      • 2:45 PM
        The LARIS lab 25m
        The LARIS (LAser Resonance Ionization Spectroscopy) laboratory is a new facility at the Meyrin site. The lab is located in building 252. The main purpose of the laboratory is to provide the RILIS laser system with new data on atomic ionization pathways. For each radioactive ion beam to be produced on-line with RILIS, the most efficient ionization schemes can be derived from off-line experiments with corresponding stable isotopes. At LARIS, high-lying atomic states of stable isotopes will be examined using three wavelength tunable laser systems at low pulse repetition rate (10 Hz). In particular, new data will be provided for the future upgraded solid-state RILIS system. This is important, since the wavelength coverage of the new solid-state based RILIS will differ from the present one. The main focus of the lab will be on the characterization of autoionizing states of atoms by resonance ionization spectroscopy of atomic beams, produced either through laser ablation of metal targets or using effusive oven techniques. Development and testing of ion sources could be one of the activities. The LARIS lab is expected to be fully operational, with three tunable lasers, in summer 2008. Technical details of the experimental setup in construction will be discussed in the presentation.
        Speaker: Dr Olli Launila (Royal Institute of Technology)
        Slides
      • 3:10 PM
        ISCOOL: cooled and bunched beams for ISOLDE 20m
        The increasing need for cold and bunched radioactive beams for nuclear physics experiments has motivated the development of new methods, instrumentation and devices for ion beam manipulation. A radio frequency quadrupole ion cooler and buncher is an example of such devices, presenting features that make it suitable for many radioactive ion beam facilities. The ISOLDE ion cooler (ISCOOL), in particular, was tailored to be a general purpose device. It is planned to be integrated with the existing beam optics equipment at the High Resolution Separator (HRS), in order to deliver better quality beams in terms of emittance and energy spread, both in continuous and bunched modes. Prior to its on-line installation the cooler is being intensively tested to assess its performance and reliability. The off-line results presented here strongly suggest that ISCOOL will meet the standards necessary for on-line operation. Some physics experiments should soon directly or indirectly benefit from its capabilities.
        Speaker: Mr Ernesto MANE (Dept.of Phys.&Astronomy,SchusterLab - University of Manchester)
        Slides
      • 3:30 PM
        Negative ion sources 20m
        Halogen ion beams can be produced either positively or negatively charged, depending on the employed ion source. At CERN-ISOLDE, although positively charged fluorine and astatine can be produced from a hot plasma ion source, they are often contaminated by isobars and molecular sidebands. This has generated a request from the scientific community for fluorine and astatine negative ion beams free of contaminants. Here we report our research on the development of new surface ion sources suitable for the production of negative halogen beams
        Speaker: Mariano Menna (Unknown)
      • 3:50 PM
        SiC targets at ISOLDE 20m
        The On-Line Isotope Separation (ISOL) method is used at ISOLDE for the production of intense radioactive ion beams of 70 different chemical elements with the best possible beam purity. Within EURISOL, direct targets are expected to operate for at least 3 weeks at 100kW of primary proton beam power. To fabricate such targets many issues have to be addressed, which includes the ones related to diffusion in the target, effusion at the surface, heat removal, temperature distribution, ageing and an efficient target and ion-source combination to form a selective system. This presentation will be focused on the development of a new SiC target. Off-line release studies were done at ISOLDE using Rabit (Rapid p-Beam Irradiation Transport) and ion-implantation techniques to estimate the diffusion coefficient of selected isotopes. Online tests were then performed with the best target material candidate. I will finally briefly introduce the ongoing TARPIPE experiment within EURISOL DS, which aims the investigation of the target’s ageing at high temperature under proton irradiation, which starts at PSI in spring 2007.
        Speaker: Sandrina Fernandes (CERN)
        Slides
    • 4:10 PM 4:25 PM
      Coffee 500/R-203 - Foyer

      500/R-203 - Foyer

      CERN

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    • 4:25 PM 6:05 PM
      Student Session (mixed) Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Dr Mats Lindroos (CERN)
      • 4:25 PM
        Production of short lived carbon and nitrogen isotopes 20m
        Within the EU-RTD project TARGISOL the most suitable materials for the target and ion source unit at ISOL (Isotope Separation On-Line) facilities for the production of beams of short-lived radioactive carbon isotopes with half-lives of minutes down to milliseconds have been investigated. On-line and off-line experiments have been performed at ISOLDE, Paul Scherrer Institute (Villigen, Switzerland) and GANIL (Caen, France) during three years. The individual steps during the in-target production, diffusion out of the target, through the transfer line and the final ionization before extraction to experiments have been investigated. The achieved results are showing promising possibilities for ameliorations of the production yields of short-lived carbon and nitrogen isotopes from an ISOLDE target unit coupled to the MiniMono ECR ion source.
        Speaker: Hanna Franberg (CERN)
        Slides
      • 4:45 PM
        Local Ordering of Oxygen in High-Tc Superconductors 20m
        Lattice sites and collective ordering of highly oxygen doped samples of HgBa2Can-1CunO2n+2+δ (n=2, 3, Hg-1212 and Hg-1223) were investigated using the Perturbed Angular Correlation (PAC) technique by measuring the electric field gradients at 199mHg nuclei. The experiments in these compounds were performed at different annealing conditions, under Ar flow or O2 pressure up to 152 bars. In comparison with the data and calculations already published for the fluorine doping in Hg-1201 (n=1) [1], the preliminary analysis hints that at high concentrations oxygen atoms order in different way, other than the atomic-like stripes found for fluorine. In addition, these experiments have been performed at different temperatures, above and below the superconducting transition, which have revealed further differences in the charge distribution of the Hg surroundings. A full set of PAC, magnetic and X-ray diffraction data has been obtained that is now being analyzed to be further compared to first principle calculations of charge density in these materials obtained for different oxygen configurations. [1] J. G. Correia, H. Haas, V. S. Amaral, A. M. L. Lopes, J. P. Aráujo, S. Le Floch, P. Bordet, E. Rita, J. C. Soares, W. Troger and the ISOLDE collaboration, Physical Rev. B 72 (2005) 1.
        Speaker: Tania Melo Mendonca (Departamento de Física, Instituto Tecnológico e Nuclear, ITN, E.N. 10, 2686-953 Sacavém, Portugal)
        Slides
      • 5:05 PM
        Charge breeding ions for nuclear physics with the Phoenix Booster ECRIS 20m
        At ISOLDE, CERN, an online test bench is dedicated to charge breeding experiments with the Daresbury Phoenix booster ECR ion source. The investigation of the 1+ --> n+ scenario for next generation ISOL post- accelerators is ongoing for one more year, with charge breeding of stable and radioactive elements. Many technical developments have been undertaken to improve the flexibility of operation (60kV upgrade), as well as to reduce the background (vacuum improvement, calculations for an isotopic separator). Whether the ECR test bench will evolve towards a permanent setup still remains an open question. An overview of what has been achieved up to now with the ECR will be given, and possibilities for physics with the charge breeder will be discussed.
        Speaker: Ms Melanie Marie-Jeanne (Universite Joseph Fourier de Grenoble)
        Slides
      • 5:25 PM
        Investigations on Isolated Eu Atoms in ZnO and on Pd Surfaces 20m
        The valences of isolated Eu impurities at Pd surfaces and in ZnO semiconductor crystals are intended to be determined from the oscillation patterns of the perturbed angular correlation technique. After the production and the implantation of appropiate precursor isotopes, the 11/2-isomeric levels in Eu- 149 and Eu-147 have been utilized. After annealing procedures, first successful measurements could be done to determine the quadrupolar interactions of Eu in the top layer of a Pd single crystal and in non-cubic ZnO. Applying an external magnetic field in addition, the measured combined interactions are found to be in agreement with the assumption of bivalent Eu in ZnO.
        Speaker: Przemyslaw Imielski (Freie Universität Berlin)
        Slides
      • 5:45 PM
        LOCAL PROBING OF ELECTRIC AND MAGNETIC ORDER COEXISTENCE IN MANGANITE SYSTEMS 20m
        The Mn3+/Mn4+ mixed valence manganite systems have very rich phase diagrams [1] exhibiting charge, orbital, magnetic and dielectric competing orders depending on doping, magnetic and electric applied fields, temperature and pressure. The recent interest in multiferroic materials, displaying coexistence of ferroelectricity and magnetic order has triggered further research in manganites, where phenomena such as the switching of the electric polarization by a magnetic field in TbMnO3 [2] were reported. Recently, a new mechanism that combines magnetic order and ferroelectricity was proposed by Efremov et al [3]. This mechanism is based on the charge order state that occurs in manganites, such as Pr1-xCaxMnO3, and conciliates the site versus bond-centred charge order models, which brought up much debate during the last years [4, 5, 6]. We have studied the Electrical-Field Gradients (EFG), via 111mCd/111Cd Perturbed Angular Correlations (PAC), in the Pr1-xCaxMnO3 system to achieve a better understanding on the charge ordered state (CO) and, in particular, to find out about the existence of ferroelectric order in the Pr1-xCaxMnO3 system using local probe information. The existence of a local paraelectric-to- ferroelectric discontinuous phase transition, decoupled by a few degrees from the charge order transition, is reported. Moreover, our data suggest that the charge order transition is driven by the softening of vibration modes. Finally, the preliminary PAC experimental results on RMnO3 (R, rare-earth) multiferroic systems will be presented. References [1] B. Raveau et al. Phys. Rev. B, 60, 12191 (1999) [2] T. Kimura, Nature 426,55 (2003) [3] D.Efremov et al, Nature Materials, 3,853 (2004) [4] P. G. Radaelli et all. Phys. Rev.B 55, 3015 (1997) [5] Daoud-Aladine et al, Phys Rev. Lett 89, 97205 (2002) [6] M. Coey, Nature 430,155 (2004)
        Speaker: A.M. Lima Lopes (Dep. Física and CICECO, University of Aveiro)
        Slides
    • 9:30 AM 10:50 AM
      Physics 3 Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Reiner Kruecken (Munich)
      • 9:30 AM
        Coulomb Excitation of 80Zn 20m
        In the summer of 2003, the first Coulomb excitation experiment with post- accelerated and laser ionized even-even Zn isotopes was performed at REX- ISOLDE. Originally the aim was to measure the B(E2) strength to the first excited 2+ state in 74 and 76Zn. In 2006 though, these B(E2) values have been measured up to the "magic" neutron number 50 in the even-even Zn isotopes. In addition, the first excited 2+ state has been fixed in both 78 as 80Zn. These measurements shed light on the evolution of collective behavior in neutron rich Zn isotopes. In this presentation, an overview will be given of the production methods and the physics results obtained on all isotopes. The emphasis will be on the isobaric beam contamination and the evolution of the nuclear structure towards the N=50 line.
        Speaker: Van De Walle Jarno (KU-University of Leuven)
        Slides
      • 9:50 AM
        A New Setup for Transfer Reactions at REX-ISOLDE 20m
        Transfer reactions yield important spectroscopic information about isotopes, including spin and parity assignments to nuclear levels and spectroscopic factors. The corresponding information is still lacking for many nuclei far from stability, e.g. in the region of the ``island of inversion'' [1]. A previous experiment [2], studying the d($^{30}$Mg, $^{31}$Mg)p reaction with MINIBALL at REX-ISOLDE, has shown the need to cover an extended angular range in order to unambiguously determine the transferred angular momentum. Therefor a new setup for transfer experiments in inverse kinematics at REX-ISOLDE was designed which consists of two segmented annular detectors and a barrel of position sensitive strip detectors. The status and the results of first tests of this new setup as well as simulations will be presented. [1] C. Thibault et al., Phys. Rev. C 12, 644 (1975) [2] M. Pantea, PhD Thesis, TU Darmstadt, Germany (2005) *supported by BMBF 06MT190 and 06MT238
        Speaker: Vinzenz Bildstein (Physik-Department E12, TU München)
        Slides
      • 10:10 AM
        Coulomb Excitation of Neutron-rich Isotopes around A~140 20m
        Recent studies on isotopes around the shell closure at N=82 have shown that despite decreasing excitation energy $E(2^{+}_{1})$ the B(E2;$0^{+}_{1} \rightarrow 2^{+}_{1}$) = B(E2$\uparrow$) values for Te and Sn isotopes above N=82 are lower than expected from a general systematics established as "Grodzins' rule". The aim of the experiment IS411 is to measure the B(E2$\uparrow$) values of neutron-rich even-even nuclei in the mass region of $A\approx140$. As a continuation of our experimental campaigns in 2004 and 2005, where the $2^{+}_{1}\rightarrow0^{+}_{g.s.}$ gamma transitions following Coulomb excitation of $^{122,124}$Cd and $^{138,140,142}$Xe beams have been measured with the gamma detector array MINIBALL, in 2006 we measured the respective transitions in $^{144}$Xe and $^{124,126}$Cd. We show preliminary results on B(E2$\uparrow$) values of $^{144}$Xe and $^{126}$Cd for the first time. Perspectives for future experiments will be discussed. This work was supported by BMBF 06MT238 and RII3-EURONS (506065).
        Speaker: Mr Thomas Behrens (Physics Department E12, TU München)
      • 10:30 AM
        Coulomb excitation of odd-A nuclei 67,69,71,73Cu with Miniball and Rex-Isolde 20m
        The low-energy levels in the radioactive neutron-rich odd-A isotopes 67,69,71,73Cu were studied by Coulomb excitation. The results allow a study of the systematic trend across the N=40 subshell closure and the residual proton-neutron interaction when neutrons start filling the g9/2 orbital.
        Speaker: Ms Stefanescu Irina Stefania (Instituut voor Kern- en Stralingsfysica - KU-University of Leuve)
        Slides
    • 10:50 AM 11:10 AM
      Coffee 500/R-203 - Foyer

      500/R-203 - Foyer

      CERN

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    • 11:10 AM 12:55 PM
      Instrumentation and RIB handling Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Reiner Kruecken (Munich)
      • 11:10 AM
        Performance and results of the Prisma spectrometer 30m
        Prisma is a spectrometer that unites a large solid angle and momentum acceptance with a satisfactory mass resolution. Such a performance is accomplished by "trajectory reconstruction", which requires detecting the entrance and exit X,Y position, time of flight and energy loss. It has been designed for the study of two-body reactions and is actively used together with the clover gamma-array Clara to investigate moderately neutron rich nuclei. This seminar provides an overview of the spectrometer and discuss a few examples of recent experimental results.
        Speaker: Dr Fernando Scarlassara
        Slides
      • 11:40 AM
        The new vacuum mode separator at JYFL 30m
        In order to extend our research activities towards lighter elements and to diminish the workload on RITU at JYFL, our team has designed a new vacuum separator. The new separator is ideally suited to investigations of nuclei in the A = 50-150 mass region produced in (near) symmetric or inverse reactions. An electromagnetic mass separator was chosen to fulfil these requirements. The design for this new separator will be an energy and angle focussing recoil mass spectrometer. The ion optics code GIOS has been used to design the configuration of magnetic and electric elements. Two bending elements will be used and ordered with an electric dipole (E) followed by a magnetic dipole (M). The EM structure is augmented with a quadrupole triplet (QQQ) lens system to increase the solid angle and to improve the final angular focus. In these simulations a maximum angular acceptance better than 10 msr was achieved and a mass resolving power better than 1/350 (with 5 msr acceptance) was attained.
        Speaker: Dr Uusitalo Juha (University of Jyväskylä, Department of Physics)
        Slides
      • 12:10 PM
        REX operation and development in 2006 25m
        The operational experiences from the 2006 measurement campaign with REX- ISOLDE will be presented. This year a number of new beams were accelerated; a record beam energy of 3.1 MeV/u was achieved; successful charge breeding of elements with A>200 was demonstrated; the ion pulse could be extracted slowly from the EBIS; isobaric separation inside the REXTRAP was proven feasible with a new cooling and excitation scheme; the electron beam current inside the EBIS reached a record value of 460 mA; and the transverse emittance after the linac was accurately measured among other development efforts. The first phase of the REX upgrade is well underway. The Miniball experiment is moved into the new hall extension and modifications of the beamline layout are carried out in order to improve beam quality and measurement conditions at the experimental targets. This is the first step towards a more ambitious upgrade program including a possible superconducting linac for higher beam energies in the framework of HIE Isolde.
        Speaker: Didier Voulot (Ludwig-Maximilians-Universitat Munchen)
      • 12:35 PM
        A mass-purification method for REX beams 20m
        The Penning trap ion cooler REXTRAP has been upgraded with a mass-separation technique to clean REX beams from isobaric impurities. The system was lately demonstrated to work with stable beams. It showed a maximum resolution of about 30 Hz in the case of 40K/40Ca, corresponding to a mass resolving power of M/dM ~40000, enabling to resolve many radioactive isobars from stable and radioactive contaminations. The technique will be briefly introduced and the possibilities and limitations will be dicussed.
        Speaker: Sven Sturm (CERN/ISOLDE)
        Slides
    • 12:55 PM 2:15 PM
      Lunch Restaurants

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      CERN

    • 2:15 PM 3:40 PM
      Physics 4 Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Mark Huyse (Leuven)
      • 2:15 PM
        Exotic diffusion phenomena in II-VI semiconductors 25m
        Understanding and control of diffusion profiles of intrinsic and extrinsic defects in semiconductors is of central importance for developing electronic and optoelectronic devices. Usually, diffusion profiles in all materials are characterized by a depth profile decreasing monotonously from the source of the diffusing species. In some compound semiconductors for certain dopant atoms, however, completely different diffusion profiles can be obtained. Depending on the external vapor pressure during Ag diffusion in CdTe, for identical conditions of temperature and time very different concentration profiles can be observed. E.g. after diffusion at 800 K for 60 min under Cd pressure a peak-shaped profile and under Te pressure a U-shaped profile was observed [1]. In compound semiconductors, like CdTe or ZnTe, large concentrations of intrinsic point defects can be obtained by inducing slight deviations from stoichiometry by exposing the respective material to external vapor pressures of one of its constituents. It turned out that variations of the deviation from stoichiometry during the diffusion process strongly influence the diffusion profile of fast diffusion elements like e.g. Ag or Cu in CdTe. The observed unusual diffusion profiles can be described quantitatively by a model based on defect reactions of the Ag dopant with intrinsic defects [2]. In a semiconductor, intrinsic as well as extrinsic defects can assume different charge states and, in addition, an inhomogeneous distribution of charged defects causes an internal electric field. The model, therefore, considers the presence of different charge states of the participating defects and a drift force acting on the charged defects due to the internal electric field. It turned out that, e.g. in case of Ag diffusion in CdTe, the flux of the Ag atoms essentially is determined by its positively charged interstitial fraction. In addition, the Ag profile essentially reflects the actual distribution of intrinsic defects. A principal question arising from the observation of the unusual diffusion profiles described above is the possible formation of such profiles for other combinations of compound semiconductor and dopant. The formation of diffusion profiles for different dopant atoms in different II VI semiconductors was investigated at ISOLDE using the short-lived isotopes 24-Na, 43-K, 65-Ni, and 56-Mn. In case of 24-Na in CdS and CdTe some features of unusual diffusion profiles similar to Ag in CdTe have been observed but for a quantitative description the model mentioned above might to be modified to some extent. In case of 65-Ni in CdZnTe a different type of an unusual diffusion profile has been observed, which most probably reflects some atypical inhomogeneities of the used host crystal. [1] H. Wolf, F. Wagner, Th. Wichert, and ISOLDE Collaboration, Phys. Rev. Lett. 94 (2005) 125901. [2] H. Wolf, F. Wagner, Th. Wichert, R. Grill, and E. Belas, J. Electr. Mat. 35 (2006) 1350
        Speaker: Dr Herbert Wolf (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany)
        Slides
      • 2:40 PM
        Electronic Configurations of sp-Element Atoms at Nickel Surfaces and Interfaces 20m
        By elaborate preparation techniques radioactive cadmium and selenium probes are positioned at different sites at surfaces of ferromagnets and in interfaces. Magnetic and quadrupolar hyperfine interactions are measured by angular correlation spectroscopy. At the nickel surface, the measured magnetic fields correlate with the number of neighbouring host atoms. Band structure calculations confirm these findings and predict magnetic fields for various sp- elements from the local level structure of the condution s-electrons. The measured quadrupolar interaction is determined by the occupation of the p- sublevels at the impurity atom. The results contribute to understand mechanisms in which scattering of electrons in crystals play a major role.
        Speaker: Wolf-Dietrich Zeitz (Hahn-Meitner-Institut)
        Slides
      • 3:00 PM
        Gamma Spectroscopy of the superdeformed shape isomers in 237Pu 20m
        While so far spectroscopic studies of fission isomers concentrated on even-even nuclei, high-resolution spectroscopy of odd-N fission isomers will allow to identify Nilsson orbitals in heavy actinide nuclei. As the first case ever studied for odd-N nuclei, the fission isomer in 237Pu (t1/2 = 110ns/1.1 ?s) was investigated using the 235U(alpha,2n) reaction with a pulsed alpha beam (Ealpha =24 MeV, pulse distance 400 ns) from the Cologne Tandem accelerator. A self-supporting thick metallic 235U target (3.7 mg/cm2) was used, where the 237Pu reaction products were stopped and fission products were emitted in opposite directions. The rare -rays from the second potential well in delayed coincidence with fission products were measured with the MINIBALL spectrometer. Due to the small population cross section of about 2 ?b a large solid angle coverage both for the -rays as well as for the fission fragments was required. A very compact 4Pi parallel plate detector array (diameter ca. 15 cm) was used for the fission fragment detection, allowing for a discrimination between the dominant prompt fission products and the rare isomeric fission events. Results, such as the identification of rotational bands, isomeric lifetimes and angular distributions etc., will be presented. *Supported by DFG under contract no. HA1101/12-1
        Speaker: Thomas James Morgan (Ludwig Maximilians University)
        Slides
      • 3:20 PM
        Shape coexistence in exotic nuclei studied by low energy coulomb excitation 20m
        The study of the shape coexistence in exotic nuclei provide important benchmarks for modern nuclear theories. Shape-coexisting states in neutron-deficient krypton isotopes have been studied by low-energy multi-step Coulomb excitation of radioactive 74Kr and 76Kr beams at GANIL. Thanks to a large statistic, both transitional and diagonal matrix elements were extracted up to high spins using the GOSIA code. The final result shows a complex coupling between prolate, oblate and vibrational configurations. All experimental values are compared with HFB+GCM theoretical calculations underlining the necessity to treat all quadrupole degrees of freedom to describe these nuclei. Finally, the investigation of shape coexistence between a highly deformed prolate configuration and a spherical state in neutron-rich nuclei around N=60 at REX-ISOLDE will be presented. The future Coulomb excitation experiment (IS451) of a radioactive 96Sr beam at MINIBALL will be discussed.
        Speaker: Dr Emmanuel Clement (European Organization for Nuclear Research (CERN))
    • 3:40 PM 4:00 PM
      Coffee 500/R-203 - Foyer

      500/R-203 - Foyer

      CERN

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    • 4:00 PM 5:20 PM
      Physics 5 Council Chamber, 503/1-001

      Council Chamber, 503/1-001

      CERN

      Convener: Prof. Mark Huyse (Leuven)
      • 4:00 PM
        New techniques for probing nuclear shape around A=70 30m
        The presence of large shell gaps at N=Z=34 and 36 at both oblate and prolate shape has long been predicted to lead to a coexistence of shapes in this region. Recent results are beginning to challenge whether such oblate shapes can indeed be located. We present two complementary approaches to investigating such shape coexistence. The first is the reorientation effect in low energy Coulomb excitation, a well-established technique which has been reinvigorated by the availability of intense radioactive beams. We discuss this in the context of 70Se where a Coulomb excitation experiment using MINIBALL at REX-ISOLDE has shown that this nucleus has a weakly-deformed prolate shape for the first 2+ state, in contrast to the oblate shape suggested by many theories. The second approach is the previously neglected impact of shape changes on Coulomb energy differences in isospin multiplets. In investigating the latter, we have focussed on the properties of odd-odd N=Z nuclei in the A=70-80 region, and have devised the new technique of recoil-beta-tagging. This makes use of the high energy positrons emitted in the decay of odd-odd N=Z nuclei as a tag at the focal plane of the recoil separator RITU at the University of Jyvaskyla. In this manner, we have extended knowledge on the excited states of 74Rb and discovered the location of the T=1 states in 78Y for the first time. Coulomb energy differences (CED) may then be evaluated for the T=1 pairs: 70Br/70Se, 74Rb/74Kr, 78Y/78Sr. While, in general, for sd and fp-shell T=1 pairs, the CED trend uniformly increases as a function of spin, the behaviour of the A=70-80 pairs is rather different. In particular, the trend for A=78 is flat and near-zero, while the A=70 trend strongly decreases as a function of spin. A simple treatment within the deformed liquid drop model shows that such a dramatic effect on the Coulomb energies can be well-explained for A=70 if 70Br and 70Se are evolving from weakly-deformed prolate to strongly- deformed prolate as a function of spin. The combination of this analysis and the Coulomb excitation result strongly questions the presence of oblate shapes in the light selenium nuclei. Ideas for the continuation of both of these complementary experimental techniques in answering questions relating to nuclear shape will be presented. It is a pleasure to acknowledge the strong contribution of colleagues in the MINIBALL and REX-ISOLDE collaborations and in the RITU-GAMMA group at the University of Jyvaskyla.
        Speaker: Dr David Jenkins (University of York)
        Slides
      • 4:30 PM
        Evolution of single-particle strengths towards the island of inversion 20m
        The replacement of the N=20 spherical shell gap in nuclei of the island of inversion by the N=14,16 gaps can be explained by the tensor monopole interaction between the proton and neutron Fermi levels. The next step in understanding the evolution of shell structure is to measure the strengh of this interaction, which is present throughout the nuclear chart. The ideal tool for this are transfer reactions where single-particle energies and spectroscopic factors can be extracted. While accurate determination of single-particle strengths remains out of reach for the more exotic isotopes, it would be particularly interesting to explore the less exotic 28Mg(d,p)29Mg reaction in inverse kinematics. This reaction will be possible at Rex-Isolde after the energy upgrade to 5 MeV/u, necessary to ensure the conditions of a direct reaction mechanism. A new highly segmented silicon-pad detector called Trace that could be used for this kind of experiments is under development at Legnaro and Orsay.
        Speaker: Serge Franchoo (Institut de Physique Nucleaire (IPN))
        Slides
      • 4:50 PM
        Super-allowed 0+ to 0+ beta decay at ISOLDE and elsewhere 30m
        Results from a recent ISOLDE experiment, where the half-life of Ca38 and the beta-decay Q value were measured, will be presented and put into the contexte of world-wide efforts in this field. Possible new measurements at ISOLDE will be proposed.
        Speaker: Dr Bertram Blank (CEN Bordeaux-Gradignan)
        Slides