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ISOLDE Workshop and Users meeting 2017
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Europe/Zurich
503/1-001 - Council Chamber (CERN)
Gerda Neyens
(CERN)
Description
This workshop aims to bring together the present and prospective ISOLDE user community to review the status of the ISOLDE experimental programme and to discuss future plans and ideas. Prizes, donated by CAEN, will be awarded for the best talks by young researchers as well as the best posters presented at the workshop poster session.
Support
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Convener: Gerda Neyens (CERN)
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WelcomeSpeaker: Gerda Neyens (CERN)
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Thirty years with ISOLTRAP at ISOLDE
Proposed by Heinz-Juergen Kluge in 1980 and installed in 1986, ISOLTRAP was the world's first Penning trap connected to a radioactive beam facility. Since then, ISOLTRAP has pioneered most of the techniques now associated with on-line ion trapping and manipulation for precision measurements of atomic masses. After an introduction of physics motivation, a brief history and description of the ISOLTRAP spectrometer is given, followed by an overview of the numerous developments and scientific results achieved since Juergen's presentation at this workshop 10 years ago. Plans for the next 10 years will also be addressed.
Speaker: David Lunney (Université Paris-Saclay (FR)) -
3
Progress of mass measurements of short-lived nuclides at the heavy-ion storage ring in Lanzhou
Recent commissioning of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou enabled us to conduct high-precision mass measurements at the Institute of Modern Physics in Lanzhou (IMP). In the past few years, mass measurements were performed using the CSRe-based isochronous mass spectrometry employing the fragmentation of the energetic beams of 36Ar, 58Ni, 78Kr, 86Kr, and 112Sn projectiles. Masses of short-lived nuclides of on both sides of the stability valley were measured. Relative mass precision of down to 106 107 is routinely achieved and some issues in nuclear structure and nuclear astrophysics have been addressed. In this talk, the experimental details are presented and the progress and some typical results are briefly introduced. We also outline the plans for future experiments.
Speaker: Yuhu Zhang (Institute of Modern Physics, CAS, Lanzhou) -
4
Structure and beta decay properties of medium-heavy nuclei from the relativistic nuclear field theory
The relativistic nuclear field theory (RNFT) developed throughout the last decade will be featured as an approach to the nuclear many-body problem, which is based on meson-nucleon Lagrangian and connects consistently the high-energy scale of heavy mesons, the medium-energy range of the pion, and the low-energy domain of emergent collective vibrations (phonons). Mesons and phonons build up the effective interaction in various channels, in particular, the phonon-exchange part takes care of the retardation effects, which are of great importance for the fragmentation of single-particle states, spreading of collective giant resonances and soft modes, quenching and beta-decay rates with significant consequences for astrophysics and theory of weak processes in nuclei.
Recent progress on the response theory in the proton-neutron channel has allowed for a very good description of spin-isospin-flip excitations. Spectra of such excitations can serve for probing the nucleon-nucleon interaction in the isovector sector caused by the exchange of pion and rho-meson between nucleons in the strongly-correlated medium. At the same time, such excitations as, for instance, Gamow-Teller and spin-dipole resonances in medium-mass nuclei are of a high astrophysical importance as they are in the direct relation to beta-decay and electron capture rates. Some more exotic isospin-flip excitations studied lately at NSCL facility have been also described very reasonably by the RNFT. Recent developments consider excitation modes in the deuteron transfer channel in view of their role in mediating the proton-neutron pairing and in constraining the delta-meson contribution to the nuclear forces.
Speaker: Elena Litvinova (Western Michigan University) -
5
Perturbed Angular Correlations at ISOLDE: a 40 years young technique
The idea that “new-is-small” is a paradigm propelling industries and research: new materials for new applications and new technologies. Precise and efficient characterization techniques are, therefore, required to make the “new” and the “small”, understandable, applicable, and reliable. Within this concept, Time Differential Perturbed Angular Correlations, TDPAC, appears as one of the most exotic and efficient techniques to characterize materials and is celebrating 40 years at ISOLDE, CERN [1]. In this overview we explore the TDPAC measurement possibilities at ISOLDE-CERN for solid state physics research with a rich potential due to the wide number of available radioactive probe elements, delivered with great purity and high yield.
[1] Juliana Schell, Peter Schaaf and Doru C. Lupascu, Perturbed Angular Correlations at ISOLDE: a 40 years young technique, AIP Advances, Accepted October (2017).
Speaker: Dr Juliana Schell (Universität Duisburg-Essen)
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16:00
Coffee Break 61/1-201 - Pas perdus - Not a meeting room -
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Convener: Maria Garcia Borge (CSIC Madrid)
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Overview of ISOLTRAP's mass measurements (the 2017 edition)
This presentation will focus on the experiments carried out during 2017 with ISOLTRAP, the versatile mass spectrometer situated at ISOLDE/CERN. Highlights of this year's campaign were the precision mass measurements of neutron-rich krypton ($^{98,99}$Kr), argon ($^{48}$Ar) and cadmium ($^{127,129,131,132}$Cd) isotopes addressing, respectively, the onset of deformation in the $A \approx 100$ region and the quenching of the neutron shell gaps at $N = 28$ and $82$ far from stability. Over the course of the year ISOLTRAP performed several tests with ISOLDE beams, including the implementation of the Phase-Imaging Ion-Cyclotron-Resonance Mass Spectrometry to study the $^{88}$Rb - $^{88}$Sr $Q$-value. The value was determined to better then 200 eV precision. Furthermore, by using Multi-Reflection Time-Of-Flight Mass Spectrometry the ISOLTRAP team together with the RILIS and the ISOLDE target and ion-source groups performed a yield study of neutron-rich titanium and scandium. The outcome of these tests as well as preliminary results from the mass measurements will be discussed.
Speaker: Dinko Atanasov (Technische Universitaet Dresden (DE)) -
7
Isomeric decays of N ~ Z nuclei in the vicinity of 100Sn
(On behalf of the EURICA collaboration)
The structure of nuclei in the vicinity of doubly magic $^{100}$Sn offer insight to the interplay between the seniority scheme in closed-shell nuclei and isoscalar proton-neutron interactions which are prevalent in $N \sim Z$ nuclei. Below $^{100}$Sn, information on the excited states of $N \sim Z$ nuclei is accessible by isomeric decays and $\beta$-delayed $\gamma$-ray spectroscopy with limited production rates.
A decay spectroscopy experiment was performed at the RI Beam Factory of RIKEN Nishina Center. A 345-MeV/u $^{124}$Xe beam was fragmented on a $^{9}$Be target, producing record quantities of $^{100}$Sn and other proton-rich isotopes in its vicinity. Ion implantation and $\beta$ decays were measured with the Wide-
range Active Silicon-Strip Stopper Array for Beta and ion detection (WAS3ABi), and $\gamma$ rays were measured with the EUroball-RIKEN Cluster Array (EURICA).Half-lives and transition strengths of many $\gamma$-decaying isomeric states were measured. New isomeric decay information was obtained in $^{92}$Rh, $^{96}$Ag and $^{98}$Cd, consistent with shell-model calculations. As one of the highlights of the experiment, the low-spin structure $^{96}$Cd was revealed for the first time.
Speaker: Joochun Park (Lund University (SE)) -
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Coulomb excitation of doubly-magic 132Sn at HIE-ISOLDE
The vibrational first $2^+$ and $3^-$ states of the doubly-magic nucleus $^{132}$Sn were excited via safe Coulomb excitation (CE) employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The $^{132}$Sn ions were accelerated to an energy of 5.5 MeV/nucleon and impinged on a $^{206}$Pb target. Dexciting $\gamma$ rays from the first excited states of the target and the projectile nucleus were recorded in coincidence with scattered particles. The optimized beam energy, the high-energy resolution and good efficiency of the HPGe spectrometer provide a favourable combination to master the demanding measurement characterized by small CE cross sections of the high lying states with excitation energies above 4 MeV. The reduced transition strengths were determined for the transitions $0^+ \rightarrow 2^+_1$, $0^+ \rightarrow 3^-_1$, and $2^+_1 \rightarrow 3^-_1$ in $^{132}$Sn. In the past first preliminary results for the $B(E2; 0^+ \rightarrow 2^+_1)$ value were obtained with an efficient BaF2 array at ORNL [1]. The results on excited collective states in $^{132}$Sn provide crucial information on cross shell configurations that are expected to be dominated by a strong proton contribution. Large-scale shell model calculations and new mean field calculations are on its way.
[1] R.L. Varner, et al.; Eur. Phys. J. A 25, s01, 391 (2005)Speaker: Mr Dawid Rosiak (University of Cologne) -
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Collinear Resonance Ionization Spectroscopy (CRIS) studies of neutron-rich Indium isotopes
With a proton hole in the Z = 50 shell closure, the indium isotopic chain (Z = 49) offers a
compelling scenario to explore the evolution of nuclear-structure properties in the
neighbourhood of the doubly-magic isotopes 100Sn (Z, N = 50) and 132Sn (N = 82).This contribution will present recent measurements of the hyperfine spectra of the neutronrich
indium isotopes 113-131In using the Collinear Resonance Ionization Spectroscopy
(CRIS) experiment. From these measurements, the spins, electromagnetic moments, and
changes in root-mean-squared charge radii of several ground and isomeric states have been
determined for the first time, extending our experimental knowledge up to N = 82. The
importance of these results, in connection with modern developments of nuclear theory,
will be discussed.The development of the ionization schemes used during the experiment was enabled by the
creation of an ablation ion-source setup, which will also be discussedSpeaker: Adam Robert Vernon (University of Manchester (GB))
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Poster Session 61/1-201 - Pas perdus - Not a meeting room -
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Facilities Session 1 503/1-001 - Council ChamberConvener: Riccardo Raabe (Instituut voor Kern- en Stralingsfysica, K.U.Leuven)
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PHYSICS AVENUE WITH THE SUPER SEPARATOR SPECTROMETER (S3) AT THE SPIRAL2 FACILITY
The LINAG superconducting linear accelerator of the SPIRAL2 project in GANIL (Caen) will produce stable heavy ion beams with very high currents. Their energy ranges from from 2 to 14MeV/u. These stable ion beams will enable us to observe rare events in the fields of nuclear physics, like very heavy and superheavy elements studies, neutron deficient nuclei at the proton drip line, as well as of atomic physics, like beam-beam ion interactions. S3 (Super Separator Spectrometer [1]) is a device designed to handle these high beam currents, combining a high selectivity of the reaction products with a high transmission of the nuclei of interest. The primary target is a fast rotating wheel, able to sustain the high beam current. The S3 line is a two-step, low energy fragment separator. The first step is a momentum achromat for rough rejection of the primary beam and the second step is a mass spectrometer. The backbone of S3 is composed of seven large aperture (r=150mm) superconducting quadrupole triplets. They are combined with sextupole and octupole correctors, in order to ensure a high mass resolution at the final focal plane. It can be equipped with different detection setups. Notably, the SIRIUS [2] spectroscopy station is designed to study proton alpha, electron and gamma decays of the nuclei of interest. Conversely, the REGLIS3 [3] low energy branch can be installed to stop the products in a gas cell for in-gas-jet laser ionisation and spectroscopy and, if required, transmission to other detection systems. In the present contribution, we will present the design and the latest progresses in the construction of the spectrometer. We will show the expected performances for some highlight physics cases.
[1] F. Dechery al., Eur. Phys. J. A 51, 56 (2015).
[2]J. Piot and the S3 collaboration, Acta Phys. Pol. B 43, 285 (2012).
[3]R. Ferrer al., Nucl. Inst. and Meth. B 317, 570 (2013).Speaker: Herve Savajols (GANIL) -
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Exploring the extremes with NUSTAR at FAIR
With the ground breaking in July 2017, the construction of FAIR, the Facility for Antiproton and Ion Research, has officially started. Besides the adaption of the existing SIS18 synchrotron for FAIR operation, the ground works for the new SIS100 synchrotron tunnel is presently pursued. FAIR will host four scientific pillars: APPA, CBM, NUSTAR and PANDA. NUSTAR comprises several experiments aiming at the exploration of nuclear structure, astrophysics and reactions at extremes. The exotic ions of interest will be produced by impinging a primary beam of heavy ions (for example uranium) on a target and will be selected by use of the high resolving power of the Super-FRS fragment separator and distributed to three branches: low-energy, high-energy, and the ring branch.
The low energy branch will house the HISPEC/DESPEC experiments dedicated to high-resolution gamma spectroscopy and decay spectroscopy as well as the stopped-beam experiments MATS and LaSpec, which aim at measuring the masses and perform laser spectroscopy on short-lived ions. In the high-energy branch, the R3B collaboration will perform studies on nuclear reactions at high energy and intensity, employing inverse kinematics. The ring branch couples the Super-FRS with the collector ring CR, where the ILIMA collaboration will mount their detectors for mass and lifetime measurements on stored highly-charged short-lived ions. Furthermore, the Super-FRS itself can be employed as a setup for an experiment by adding supplemental detectors at the focal planes of the separator.
Many of the future detectors and equipment are already available and will be used in a precursor phase prior to the operation at FAIR. This program – called Phase 0 – will take place at GSI but also at other facilities, where NUSTAR experimental equipment can be employed for first tests and physics runs.
An overview of the present status of the FAIR facility and the NUSTAR experiments will be given as well as an outlook on the next years of the project.
Speaker: Alexander Herlert (Facility for Antiproton and Ion Research (FAIR)) -
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HELIOS: New Results and Future Developments
The HELIOS spectrometer was developed to study of light-ion transfer reactions in inverse kinematics, where outgoing ions are transported through a solenoidal field removing the effects of kinematic compression. It operates at ATLAS at Argonne National Laboratory where it can be used with stable beams, light radioactive ion beams produced by the in-flight technique, and fission-fragment beams from CARIBU. HELIOS has been in use for approximately ten years, demonstrating excellent Q-value resolution for studies with beams from mass 10 to 140. I will discuss recent results, including the measurement of transfer reactions induced by an isomer beam, and comment on future developments for HELIOS, and new solenoidal-spectrometer projects.
Speaker: Benjamin Kay (Argonne National Laboratory) -
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An update on the chemical separation of 152Tb and its subsequent application for PET imaging
Terbium is a unique element, as it provides a quadruplet of radionuclides suited for diagnostics and therapy in nuclear medicine [1]. Much success has been gained from the PSI-ISOLDE collaboration, with the collection and purification of 149Tb (α-emitter, T1/2 = 4.1 h – for potential therapy), used for preclinical therapy studies [2] and PET imaging [3], and 152Tb (β+-emitter, T1/2 = 17.5 h – for use in PET imaging), for preclinical [4] and clinical [5] PET imaging, respectively.
Following this success, further upgrades were required for the chemical separation system, as the ALARA (As Low As Reasonably Achievable) radiation safety principle should be adhered to – thereby, minimizing direct manipulation of the nuclides.
In 2017, mass-separated beams of 152Tb were implanted at ISOLDE-CERN into Zn-coated Au foils, using new shielded collection chamber. Collections of 152Tb lasted 4 to 6 hours and up to 600 MBq 152Tb could be shipped to PSI.
At PSI, the chemical separation system was performed using a new set up and manipulators in a hot cell. The foil containing the 152Tb was extracted from the Zn foils by dissolving them in HNO3/NH4NO3. The dissolved nuclides were loaded on to a macroporous strongly acidic cation exchange resin and 152Tb eluted using dilute α-hydroxyisobutyric acid (α-HIBA). As an addition, the product eluent was passed through a second resin, to ensure formulation of the product in chloride form.
152Tb was directly employed for radiolabeling of PSMA-617. PET/CT scans were performed with PC-3 PIP (PSMA-positive) tumor-bearing mice at different time points after injection of 152Tb-PSMA-617.
The successful experimental runs with the updated system has prepared the collaboration well for proposed extended preclinical imaging and therapy experiments in 2018, in the hope of finalizing the preclinical therapy study with 149Tb.
Support by ENSAR2 (EU H2020 project Nr. 654002) is gratefully acknowledged.The authors thank the ISOLDE RILIS team for efficient Dy ionization and the ISOLTRAP-MR-TOF-MS team for beam characterisation.
[1] C. Müller et al., J. Nucl. Med. 53, 1951 (2012).
[2] C. Müller et al., Pharmaceuticals 7, 353 (2014).
[3] C. Müller et al., EJNMMI Radiopharmacy and Chemistry 1,5 (2016).
[4] C. Müller et al., EJNMMI Research 6, 35 (2016).
[5] R. Baum et al., Dalton Transactions, in press (2017).Speaker: Nicholas Philip Van Der Meulen (Paul Scherrer Institut (CH))
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10:50
Coffee Break 61/1-201 - Pas perdus - Not a meeting room -
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Convener: Richard Catherall (CERN)
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Target Developments
As in the previous years, the target and ion source development group (TISD) has been working to push the limits of beam intensity and purity of available beams, and to develop new beams of elements, which are not yet available at any other ISOL facility. Important progress has been made on the LIEBE project, which exploits the forced circulation of a hot Pb-Bi eutectic melt. Here, the prototype is nearing completion and commissioning is planned. We have launched a material development campaign to synthesize and characterize novel low work function materials to increase the efficiency of negative ion sources. The work on an improved proton to neutron converter is progressing fast, as well as the detailed study and optimization of the VADLIS cavity. The status of molecular beam developments as well as an overview of target operation in 2017 will finally be presented.
Speaker: Jochen Ballof (Johannes Gutenberg Universitaet Mainz (DE)) -
15
RILIS developments 2017
The Resonance Ionization Laser Ion Source (RILIS) at ISOLDE is the most frequently used ion source, providing 60% of the ion beams in 2017, and more than 85% in 2016. The ionization mechanism, based on stepwise resonance excitation of an outer electron of the atom, is element selective. For certain elements even isomer-selective ionization can be achieved, enabling the delivery of beams with an enhanced isomer- or ground-state abundance. This year isomeric indium beams were delivered for IDS and CRIS experiments. In the reduced laser linewidth mode, Doppler-broadening becomes the limiting factor in terms of spectral resolution but, for certain atomic transitions, the isotope shifts or hyperfine structures can be resolved. Our ongoing campaign to study these for the lead-region continued this year with bismuth – together with our first use of the ISOLDE Decay Station for this purpose.
The 2017 technical developments and new laser hardware will be presented, along with the resonance ionization scheme developments that have been performed in an attempt to reduce the dependence on dye lasers during standard operation. The generation of high-power blue laser beams by intra-cavity frequency doubling inside the Ti:Sapphire lasers is now routine operation, resulting in an improved laser beam shape and higher power for the blue and deep-UV range. RILIS ionized radiogenic Sc was measured for the first time, representing a new beam to the ISOLDE user’s community. Further attempts to extract laser-ionized Se were made, although suitably efficient and selective Se beam production needs further development. The technical developments of the VADLIS: RILIS ionization inside the ISOLDE FEBIAD have been continuing at the ISOLDE offline separator, with promising progress towards optimizing the RILIS-mode of operation. The advances towards the goal of high-resolution, Doppler-free RILIS ionization making use of two-photon excitation will be presented. If successful, this approach may not only provide the means for high-resolution in-source spectroscopy of exotic nuclei, but also enable selective resonance ionization of elements with high ionization potentials that can so far only be ionized with a plasma ion source.Speaker: Katerina Chrysalidis (Johannes Gutenberg Universitaet Mainz (DE)) -
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Progress towards the commissioning of first stable beams at CERN-MEDICIS
The CERN-MEDICIS laboratory is located in an extension of the CERN-ISOLDE radioactive ion beam facility in Geneva, Switzerland. ISOLDE is able to provide more than 1000 different isotopes by irradiating a thick target with a 1.4 GeV proton beam from the CERN Proton Synchrotron Booster. Since more than 90 % of the proton beam passes through the ISOLDE targets, the MEDICIS targets will be placed immediately behind the HRS one on a dedicated station to produce radioactive isotopes and benefit from the otherwise lost proton beam. The isotope batches will be extracted in the new laboratory thanks to a dedicated electromagnetic isotope mass separator.
With the development of the facility, many innovative radioisotopes will become available. Applications in fundamental studies in cancer research and new imaging and treatment protocols in cell and animal models will follow, possibly extended to pilot trials. On a weekly basis, 500 MBq isotope batches, purified by mass separation combined with chemical methods can be collected.
In this talk we will offer an overview on the current status of the facility and the progress towards the commissioning of the first stable beams at MEDICIS. We will discuss the main requirements for the production of radioactive beams in terms of efficiency, chemical selectivity and reliability/feasibility when dealing with high beam currents.
By joining forces with leading institutes in life and medical sciences within a newly formed translational collaboration, CERN-MEDICIS offers an exciting prospect with its scientific program in the coming years.Speaker: Yisel Martinez Palenzuela (KU Leuven (BE)) -
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Current progress on Offline 2 and the RFQcb ISCOOL.
For many years the RFQcb (Radio-Frequency Quadrupole cooler buncher) has been a vital part of ISOLDE experiments and it has improved the beam optics of the HRS line significantly downstream. However, there is very little time and infrastructure available to test and quantify improvements made to the RFQcb's structure, tuning and bunching methods. The Offline 2 separator was proposed to allow for proper analysis of the RFQcb and many other areas of the ISOLDE beam, such as: target development, laser scheme testing and new beam optics methods. All of these are vital in keeping ISOLDE competitive in the ISOL facilities field. The current status of the ISOLDE RFQcb and progress on the construction of Offline 2 will be presented.
Speaker: Dr Stuart Warren (CERN)
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12:40
Lunch Break
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Convener: Wolfram Korten
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CRIS: A Toolbox for Exploring Quantum Many-body Problems
The Collinear Resonance Ionization Spectroscopy (CRIS) apparatus at ISOLDE-CERN [1] provides a powerful tool to perform highly-efficient and precise hyperfine structure measurements on isotopes produced at rates lower than 100 ions/s [2]. Such measurements allow the extraction of observables that are key for our understanding of the nuclear many-body problem: nuclear ground-state spins, electromagnetic moments, and changes in the root-mean square charge radii. Moreover, a precise knowledge of the interaction between the atomic nucleus and the surrounding electrons offers an important benchmark to test the validity of atomic many-body methods and weak interaction Hamiltonians used in studies of fundamental symmetries [3].
This contribution will present the recent developments that have allowed the extension of collinear resonance ionization spectroscopy in the potassium, copper and indium isotopic chains at extreme regions in the nuclear chart. The relevance of these results in connection with the recent advances in nuclear and atomic theory will be discussed. Future experimental programs focused on studying exotic isotopes around doubly-magic nuclei will be presented.
[1] K.T. Flanagan et al. Phys. Rev. Lett. 111, 212501 (2013).
[2] R.P. de Groote et al. Phys. Rev. C 96, 041302(R) (2017).
[3] R.F. Garcia Ruiz et al. Submitted (2017).Speaker: Dr Ronald Fernando Garcia Ruiz (The University of Manchester) -
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HIE-ISOLDE physics campaign in 2017
HIE-ISOLDE experiments have been focused on two experimental setups in 2017, with the Miniball HPGe array [2] taking most of the beam time alongside experiments at the third beam line. The ISOLDE Solenoidal Spectrometer (ISS) [3] is currently being commissioned on the second beam line with the aim of performing few-nucleon transfer reactions in the magnetic field of a former MRI magnet. As HIE-ISOLDE operation becomes routine, the number of experiments per year is increasing and this year there were 12 experiments in a campaign running from July until November. In addition to Coulomb excitation, this year we have also performed multi-nucleon transfer reactions, utilising the maximum energy of the linac.
In this talk I will present the preliminary status of experiments from the 2017 campaign at Miniball.
References
[1] M. Lindroos, P. Butler, M. Huyse, and K. Riisager, NIM B 266, 4687 (2008).
[2] N. Warr et al., EPJ A 49, 40 (2013).
[3] S. J. Freeman et al., CERN-INTC 031, 099 (2010).Speaker: Liam Gaffney (CERN) -
20
Collectivity of the 4+ states in heavy Zn isotopes and the first HIE-ISOLDE experiment
Shell evolution in the vicinity of $^{68}$Ni has recently attracted many theoretical and experimental investigations. By now it has been clearly established that the presumed subshell closure at N=40 is not very pronounced. While the intruder character of the $1g_{9/2}$ and $2d_{5/2}$ neutron orbital induces collectivity by pair excitations from the $fp$ shell into the $g_{9/2}$ orbital, the parity change hinders quadrupole excitations and therefore mimics the properties of a doubly magic nucleus in $^{68}$Ni, i.e. a high 2$^+_1$ energy and a low B(E2; 2$^+$ $\to$ 0$^+$) value. Adding valence nucleons to the N=40 open shell leads to a rapid increase of collectivity, with an interplay of both collective and single-particle degrees of freedom. Such rapid changes indicate underlying complex effects and make this region ideal for testing theoretical calculations.
While measurements of B(E2; 2$^+$ $\to$ 0$^+$) values are useful to investigate the evolution of collectivity along isotopic chains, even more insight into the collective behavior can be gained by measuring lifetimes of higher-lying states. Almost all stable Zn isotopes present an anomalously low B(E2; 4$^+$ $\to$ 2$^+$)/B(E2; 2$^+$ $\to$ 0$^+$) ratio of 1 or less, which is normally observed only around closed shells. Coulomb excitation studies at REX-ISOLDE ($^{74,76}$Zn [1]) as well as a DSAM lifetime measurement in $^{70}$Zn [2] suggested an important increase of collectivity of the 4$^+$ state for heavy Zn isotopes with a maximum at N=40. However, a recent RDDS lifetime measurement performed with AGATA Demonstrator in Legnaro [3] yielded lifetimes of the 4$^+$ states in $^{70-74}$Zn that are considerably longer and correspond again to B(E2; 4$^+$ $\to$ 2$^+$)/B(E2; 2$^+$ $\to$ 0$^+$) ratio lower than 1. This has been confirmed by the results of another RDDS measurement performed at GANIL [4] for $^{70,72}$Zn.
The ISOLDE facility finished in 2016 the first phase of a major upgrade in terms of the energy of post-accelerated exotic beams, bringing it up from 3 MeV/u to 5.5 MeV/u. The increased beam energy strongly enhances the probability of multi-step Coulomb excitation, giving experimental access to new excited states and bringing in-depth information on their structure. The very first HIE-ISOLDE experiment in October 2015 and its continuation in 2016 have been dedicated to the study of the evolution of the nuclear structure along the zinc isotopic chain. The results discriminate between the two experimental values of B(E2; 4$^+$ $\to$ 2$^+$) in $^{74}$Zn, and the B(E2; 4$^+$ $\to$ 2$^+$) value in $^{78}$Zn has been obtained for the first time.
[1] J. Van de Walle et al., Phys. Rev. C79 (2009) 014309
[2] D. Muecher et al., Phys. Rev. C79 (2009) 054310
[3] C. Louchart et al, Phys. Rev. C87 (2013) 054302
[4] I. Celikovic et al, Acta Phys.Pol. B44, 375 (2013)Speaker: Magdalena Zielinska (CEA Saclay) -
21
High precision laser spectroscopy of Nickel isotopes
Nickel isotopes $^{58-68,70}$Ni were measured using collinear laser spectroscopy at the COLLAPS setup at CERN-ISOLDE. Nickel has magic proton number 28, the first magic number that is caused by the spin-orbit interaction and the isotope chain is state-of-the-art in nuclear structure research. One of these is the sub-shell closure at N=40, which has been intensively studied by various experimental methods [1-5]. In the whole region, $^{68}$Ni is expected to exhibit the strongest sub-shell closures and this is visible in the behavior of the now measured mean-square charge radii crossing N=40.
Furthermore, a tight correlation between neutron-radii, the electric dipole polarizability $\alpha_D$ and the neutron equation of state (EOS) has been intensively discussed first based on Skyrme Hartree-Fock models, linking nuclear properties with the structure of neutron stars. Of particular interest in this respect are also recent ab initio calculations entering into the medium mass region and demonstrating a clear correlation between the charge radius, the neutron radius and $\alpha_D$ in the case of $^{48}$Ca [6].
Indeed, this correlation was exploited to predict $\alpha_D$ based on $^{48}$Ca’s experimental charge radius in reasonable agreement with a recent measurement [7]. Ab initio calculations now become feasible in the Nickel mass region as well. Recent $\alpha_D$ measurements in $^{68}$Ni [8] are now backed up by our experimental value for the mean-square charge radius making this a rare case where both observables are experimentally known and will therefore provide an important new benchmark for ab initio as well as density functional theory.[1] R. Broda et al., Phys. Rev. Lett. 74 , 868 (1995).
[2] H. L. Seifert et al., Z. Phys. A 349, 25 (1994).
[3] O. Sorlin et al., Phys. Rev. Lett. 88, 092501 (2002).
[4] S. Rahaman et al., Eur. Phys. J. A 43, 5 (2007).
[5] C. Guenaut et al., Phys. Rev. C 75, 044303 (2007).
[6] G. Hagen et al., Nature Physics12, 186-190 (2016).
[7] J. Birkhan et al., Phys. Rev. Lett. 118, 252501 (2017)
[8] D.M. Rossi et al., Phys. Rev. Lett. 111, 242503 (2013)Speaker: Simon Kaufmann (Technische Universitaet Darmstadt (DE)) -
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Coulomb excitation of 66Ge
This work pertains to determining the spectroscopic quadrupole moment for the first 2+ state in 66Ge using “safe” Coulomb excitation measurements. Motivation to study 66Ge arises from the anomalous rotational behaviour of the high-lying first 2+ state observed in even-even isotopes in the A ~ 70 region [1]. Low-lying 0+ excited states have been suggested for even-even neutron-deficient nuclei Se [2] and Kr [3] which may be an indication of shape coexistence [4]. The same trend was observed in 198Pt and is interpreted as the result of the presence of an intruder state [4]. The A ~ 70 region near the N = Z line is a region of rapidly changing nuclear shapes due to the shell gaps at proton and neutron number 34 and 36, making this region an excellent testing ground to study the phenomenom of shape coexistence. In addition, macroscopic-microscopic models suggest gamma-softness for 64Ge through oblate-prolate shape coexistence in 68Se and 72Kr to some of the most deformed nuclei at 76Sr and 80Zr.
Our experiment was performed at HIE-ISOLDE during July 2017. A 4 mg/cm2 target of 196Pt was bombarded with 66Ge beams at 4.395 MeV/u. This was the first experiment carried out using accelerated unstable Ge beams. The initial aim was to study 70Se, but the beam was contaminated with 66Ge. At first it was thought not to be a problem, but it became clear that the ratio between 70Se and 66Ge grew in favour of 66Ge. The beam was then tuned to run 66Ge for the rest of the experiement. The gamma rays were detected using the MINIBALL array containing 8 cluster of HPGe detectors. Scattered particles were detected using an annular CD detector placed a distance of 25.74 mm, covering scattering angles from 21 to 57 degrees. Studying the shape of 66Ge may shed light on some of the systematics in this rapidly changing region of nuclear shapes. Preliminary results for the spectroscopic quadrupole moment of the first 2+ state in 66Ge will be presented during the ISOLDE Workshop.
[1] P.J. Davies, A.V. Afanasjev, R. Wadsworth and C. Andreoiu, Phys. Rev. C 75 011302(R) (2007)
[2] J.H. Mamilton et al. Phys. Rev. Lett. 32, 239 (1974)
[3] E. Clement et al. Phys. Rev. C 75, 054313 (2007)
[4] J.L. Wood, K. Heyde, W. Nazarewics, M. Huyse and P. Vn Duppen, Phys Rep. 215, 101 (1992)Speaker: Mr Kenzo Abrahams (The University of the Western Cape)
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16:05
Coffee Break 61/1-201 - Pas perdus - Not a meeting room -
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Convener: Jens Dilling (triumf/UBC)
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Recent developments in gravitational wave science
Recently, the LIGO Virgo Collaboration achieved the first detections of a gravitational waves. A century after the fundamental predictions of Einstein, we report the first direct observations of binary black hole systems merging to form single black holes. The detected waveforms match the predictions of general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. These observations demonstrate the existence of binary stellar-mass black hole systems. Our observations provide unique access to the properties of space-time at extreme curvatures: the strong-field, and high velocity regime. It allows unprecedented tests of general relativity for the nonlinear dynamics of highly disturbed black holes. Last month, the first detection of gravitational waves from the merger of a binary neutron star was reported. This event was also observed by thousands of scientists by using conventional astronomy. We now have realized a global gravitational wave network that allows interdisciplinary studies in (fundamental) physics, astrophysics, astronomy, cosmology and nuclear physics.
The scientific impact of the recent detections will be explained. In addition key technological aspects will be addressed. Attention is paid to Advanced Virgo, the European detector near Pisa, which recently come on-line. The lecture will close with a discussion of the largest challenges in the field, including plans for a detector in space (LISA), and Einstein Telescope (ET), a large underground observatory for gravitational waves science.
Speaker: Jo van den Brand (Nikhef) -
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First Observation of the Low-Spin Structure of 213Fr Populated in the EC/β+ Decay of 213Ra
The level scheme of 213Fr was investigated for the first time through γ-ray spectroscopy at ISOLDE, CERN. An A=232 molecular beam of 213Ra+19F was sent to the ISOLDE Decay Station setup, where γ-rays and charged particles were detected using HPGe clover detectors and DSSSDs, respectively. Low-spin excited states in the semi-magic 213Fr (N=126) were populated in the EC/β+ decay of the 1/2- ground state of 213Ra and the level scheme was constructed starting from the previously reported 498 keV γ-ray depopulating the (7/2-) first excited state and contains over 10 new levels and 20 new transitions. The results will be discussed and compared with neighboring N=126 nuclei.
Speaker: Ms Cristina CLISU (IFIN-HH) -
25
Study of shell evolution around the doubly magic $^{208}$Pb, via a multi-nucleon transfer reaction at MINIBALL
Study the east region around the doubly magic $^{208}$Pb, represents an ideal testing ground to understand the effects related to the effective three-body forces, i.e., if the large calculations are feasible and the seniority scheme provides useful guidance. However, this region of the Segrè chart has been traditionally difficult to access experimentally due to its neutron richness and low cross sections. Even with the new improvements and the new facilities, we still have lack of information around this region.
On the other hand, multi-nucleon transfer reaction has been proved for many years an important tool in order to investigate exotic nuclei with stable beams. With this technique it is possible to excite high spins states, to find new isomers and to understand the band structure of a nucleus. In addition, in one experiment you will be able to investigate different isotopes at the same time.
The aim of this experiment is twofold: i) firstly, it will represent the proof of principle that multi-nucleon transfer reactions with unstable beams is efficient to populate neutron-rich heavy binary partners, and represents a competitive method to cold fragmentation ii) secondly, we aim at populating medium- to high-spin states in $^{212,214}$Pb and $^{208,210}$Hg to elucidate the existence of the 16$^{+}$ isomer in the lead isotopes, and at the same time to disentangle the puzzling case of a very low energy 3$^{-}$ state in $^{210}$Hg not described by any nuclear model.
On this way, the first multi-nucleon transfer experiment with radioactive beam (RIB) was carried out in September of this year. Very preliminary results will be presented.Speaker: Andres Illana Sison (Universita e INFN, Legnaro (IT)) -
26
Investigation of octupole excitations in 207Tl using gamma-gamma angular correlations at the ISOLDE Decay Station
$^{208}$Pb is the heaviest stable doubly-magic nucleus and has been studied in great detail. Its first excited state occurs at 2.6 MeV and corresponds to an octupole vibration, resulting from the collective behaviour of a number of E3 ($\Delta l = \Delta j = 3$) particle excitations across the closed shell. This octupole transition has been observed in several other nuclei around $^{208}$Pb, including the single proton-hole $^{207}$Tl$^{[1]}$. This nucleus has a number of known states; however, below the core-breaking limit$^{[2]}$ only the four states below 2 MeV ($s_{1/2}^{-1}, d_{3/2}^{-1}, h_{11/2}^{-1}, d_{5/2}^{-1}$) are well-known from previous experiments$^{[3]}$. It is expected that, given a $\frac{9}{2}^+$ ground state in $^{207}$Hg and a $Q$-value of 4.8 MeV, $\beta$ decay from $^{207}$Hg should populate many of the states consisting of one of these proton-hole states coupled to the octupole $3^-$ vibration.
One experiment took place in 2014 and a second in 2016, both at the ISOLDE Decay Station (IDS) at CERN. Using the molten lead target on the General Purpose Separator (GPS), $^{207}$Hg was produced at a rate of up to $5 \times 10^{4}$ pps in 2014, and $2 \times 10^{5}$ pps in 2016. This was deposited on the tape at IDS and observed by an array of five HPGe detectors.
A new level scheme, including 9 new levels and 73 new transitions, has been established in this analysis. Using relative transition strengths, $\gamma\gamma$ angular correlations, log$ft$ values and electron conversion coefficients, spin-parities have been deduced for the majority of observed states. Angular correlations of successive gamma rays have been performed successfully for a small number of transitions, and used where possible to guide the assignments. This study has motivated the improvement of the IDS setup for angular correlation studies in the future. The KHM3Y shell model calculation - which gives the most accurate replication of the octupole excitation in this region$^{[4]}$ - was performed, and a good agreement was observed between the predicted and experimental level schemes. The majority of the states correspond to three-particle excitations breaking the neutron core. Six collective octupole-coupled states have been observed: the two states corresponding to $\pi$s$^{-1}_{1/2} \times 3^{-}$, three of the four $\pi$d$^{-1}_{3/2} \times 3^{-}$ states and, tentatively, the $\frac{7}{2}^{+}$ $\pi$h$^{-1}_{11/2} \times 3^{-}$ state.
[1] O. Hansen et al., Nucl. Phys. A 127, 71 (1969).
[2] E. Wilson et al., Phys. Lett. B 747, 88 (2015).
[3] B. Jonson et al., CERN 81-09 2, 640 (1981).
[4] B. A. Brown, Phys. Rev. Lett. 85, 5300 (2000).
Speaker: Thomas Andrew Berry (University of Surrey (GB))
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Workshop Diner
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Facilities Session 2 503/1-001 - Council ChamberConvener: Yorick Blumenfeld (Institut de Physique Nucléaire-Orsay)
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MARA -- from commissioning to experiments
MARA is a new in-flight recoil separator mainly for studies of the exotic isotopes close to the N~Z line and close to the proton-drip line produced in fusion evaporation reactions. MARA consists of a quadrupole triplet followed by an electrostatic deflector and a magnetic dipole. It has two main functions: separate a primary beam from products and give additional mass over charge selectivity among the products. The mass resolving power is roughly from 100 to 300 depending on the experiment. MARA is a complementary device to the gas-filled RITU separator and enables the continuation of the nuclear spectroscopy research program in Jyväskylä to lighter masses.
In this presentation the basic properties of MARA will be presented and compared to RITU. The commissioning campaign and the accomplished experiments will be reviewed and an overview of the experimental conditions based on the reactions performed with MARA will be given. Some of the physics cases will be discussed alongside the spectrum of the accepted proposals.
Speaker: Jan Saren (University of Jyväskylä) -
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New possibilities for nuclear spectroscopy at ILL: the FIPPS instrument and its first experimental campaign
Thermal neutron capture gamma-ray spectroscopy and prompt gamma-ray
spectroscopy of fission fragments are powerful tools to obtain detailed nuclear
structure information for nuclides close to stability and medium mass neutron-
rich isotopes. This nuclear structure information can be used for the test of
nuclear models, as well as for the extraction of quantities important for nuclear
applications. The power of coupling a high-efficiency Ge detector array with an
intense pencil-like neutron beam provided by the ILL reactor, has been recently
demonstrated by the success of the EXILL (EXogam at ILL) campaign. This
success led to the installation of permanent setup at ILL, the new instrument
FIPPS (FIssion Product Prompt Spectrometer). In its first phase, it consists of a
halo-free pencil neutron beam incident on a target surrounded by an array of 8
Ge clovers. This setup has been commissioned in Dec. 2016 and it has recently
been exploited for a variety of (n,gamma) experiments. Also fissile and
radioactive targets will be used. In a second phase it will be complemented
with a recoil spectrometer based on a gas filled magnet. This will increase the
sensitivity and selectivity for nuclear spectroscopy of fission products and
enable fission studies of the correlation between excitation energy, angular
momentum and kinetic energy.
After a review of the most significant physics output of the EXILL campaign, the
FIPPS instrument will be described. The present performance of the setup will
be shown, together with a summary of the results of the first experimental
campaign. Future perspectives and physics opportunities will be discussed.Speaker: Caterina Michelagnoli (ILL) -
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Ion beam analysis of materials with MeV beams at the Ruhr University Bochum
The opportunities and features of the analytical techniques such as Rutherford Backscattering Spectrometry (RBS) or Nuclear Reaction Analysis (NRA) available at the 4MV Dynamitron Tandem accelerator in Bochum will be presented and illustrated with examples from the ongoing research programs. In particular diffusion studies in geological systems will be discussed in more detail. Since such diffusion is strongly correlated to defects in the crystal the potential of future studies of minerals with Perturbed Angular Correlation needs to be explored.
Speaker: Dr Hans-Werner Becker Becker (Ruhr-University Bochum) -
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Reactions with 9Li at HIE-ISOLDE
The increase of energy of the ISOLDE radioactive beams made possible through the HIE-ISOLDE project has opened new possibilities for reactions studies with exotic beams. A particular challenge is presented by the light nuclei where unbound final states play an important role and the role of the continuum is by now known to be important. Theoretical work on the reaction mechanisms involved aiming for a detailed description of the reaction processes is ongoing and evolves as new experimental data appear.
I shall report on results from two experiments performed in the Scattering Experimens Chamber (SEC), both using 9Li as reaccelerated radioactive beam. The first experiment ran November 2016 at XT02 at a beam energy of 6.8 MeV/u on a deuterated polyethylene target. The second experiment takes place late October 2017 at XT03 with a beam energy close to 8 MeV/u on a tritium-containing Ti target. Many reaction channels are open at these energies, but the major ones of interest are one- and two-neutron transfer reactions to the isotopes 8Li to 11Li. Particularly interesting are the final channels leading to 10Li and 11Li where knowledge on the detailed structure is still lacking in spite of many earlier experiments at widely different beam energies.
The presentation will give an overview of the experimental set-up used and report on the results that have been extracted so far. A comparison will also be given between the current results and the 9Li+2H experiments carried out earlier at REX-ISOLDE at beam energies of 2.3 MeV/u and 2.8 MeV/u.
Speaker: Jesper Halkjaer Jensen (Aarhus University (DK))
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10:50
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Coffee Break 61/1-201 - Pas perdus - Not a meeting room -
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HIE-ISOLDE Technical Session 503/1-001 - Council ChamberConvener: Yacine Kadi (CERN)
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Operations of the REX/HIE-ISOLDE linac during the 2017 Physics Campaign
The High Intensity and Energy ISOLDE project (HIE-ISOLDE) is a major upgrade of the ISOLDE post-accelerator at CERN. Phase 2A of the project was completed in June 2017 when an additional cryomodule and the third High Energy Beam Transfer line (HEBT) were installed and commissioned. The 2017 Physics campaign started immediately after. Multiple stable and Radioactive Ion Beams (RIBs) were delivered to two different experimental stations and a total of twelve experiments were completed. The main issues and the operational highlights for each of the experiments as well as the reliability of the different subsystems of the linac and possible future improvements and upgrades of the machine will be discussed in this presentation.
Speaker: Jose Alberto Rodriguez (CERN) -
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The HIE-ISOLDE Cryogenic System, its Infrastructure and Considerations for Phase 3
The cryogenic system for the project phases 1 & 2 of HIE-ISOLDE is based on a refurbished helium cryo-plant previously used to cool the ALEPH magnet during the operation of the LEP accelerator from 1989 to 2000. The helium refrigerator is connected to a new cryogenic distribution line, supplying a 2000-liter storage dewar and six interconnecting valve boxes (i.e jumper boxes). Since its implementation, the cryogenic system has been operated with first one cryo-module in 2015, then two in 2016 and three in 2017. During each year the operation of the cryo-plant has required significant technical enhancements and tunings for the compressor station, the cold-box and the cryogenic distribution system in order to reach nominal and stable operational conditions. The commissioning results and the lessons learnt during these three years of operation are presented and the preparatory work for the installation of the fourth cryo-module in early 2018 discussed. Finally, preliminary considerations on a new cryogenic system in view of a potential phase 3 implementation is reported.
Speaker: Olivier Pirotte (CERN) -
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Performance of the HIE-ISOLDE seamless cavity compared with welded series productions
The test result of the newly developed seamless cavity is compared with the series cavities already installed and operated in the cryomodules.
Slow and uniform cool down has been preferred by the series cavities; thus optimized cool-down procedure has achieved performance better than the nominal design.
The off-line test in a dedicated cryostat showed that the seamless cavity did not depend on the cooling down, and resulted in the best performance even without a special care during the cooling down.
Instead, this new cavity was relatively sensitive to the ambient magnetic field such as the earth field.
Comparison between series and seamless cavities will provide information about the thermodynamic environment inside the cryomodule during the RF commissioning 2018.
Also, in order to use the seamless cavity as a spare in the lower energy cryomodules, i.e. CM1 and CM2, a possible modification will be proposed by correcting the beam steering effect.
Finally, possible cavity designs for the low-beta section in Phase3 will be discussed.Speaker: Akira Miyazaki (University of Manchester (GB)) -
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Beam dynamics studies for 10 MHz post-accelerated RIBs in Phase 3 of the HIE-ISOLDE linac upgrade
A ten-fold increase in the bunch spacing of post-accelerated radioactive ion beams has been requested by several research groups at ISOLDE, CERN in order for experiments to use time-of-flight particle identification and background suppression techniques. It is proposed to bunch externally into the existing REX-RFQ at a frequency of 10.128 MHz using a multi-harmonic buncher to produce the desired ~100 ns bunch separation with minimal loss in transmission and, in certain installation scenarios, a significantly reduced longitudinal emittance. A review of the beam dynamics studies, carried out until 2014, will be presented in the framework of the HIE-ISOLDE linac upgrade at CERN.
Speaker: Matthew Alexander Fraser (CERN)
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Lunch Break
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Convener: Karsten Riisager (Aarhus University (DK))
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Engineering defects in diamond
Defects in diamond have great potential for use as quantum sensors and qubits. The negatively-charged nitrogen-vacancy (NV–) center in diamond is established as a leading platform in solid state quantum applications, with potential technologies in sensing, computation and communication enabled by its long spin-coherence time and optical spin polarization. However, NV’s poor photonic properties (Debye-Waller factor ~0.04) have resulted in significant efforts on optical cavities to enhance its coherent emission, and search for alternate color centers with comparable spin properties and superior optical properties.
Currently, the vacancy-impurity family of defects is most promising, with major interest in group IV centers SiV– [1,2], GeV– [3] and SnV– [4,5]. Of these, SiV– is the most-studied, with T2 > 10 ms and single-shot readout demonstrated at 100 mK. Nonetheless, the onerous experimental requirements and low quantum efficiency (~10% [6]) motivate further research on alternative centers. In this presentation, I will discuss recent work alternative color centers, including the neutrally-charged silicon vacancy, SiV0 [7,8], its spin physics and electronic structure.
Full exploitation of their optical and spin properties necessitates that we control the position, orientation and environment of the chose colour centre to optimise all of the desirable properties simultaneously. I will review our understanding of the production of intrinsic defect complexes and present new data on the production of preferentially orientated defect complexes by electron irradiation and/or annealing whilst the sample is subjected to a large uniaxial stress. I will show that near 100 % preferential orientation can be achieved for a number of different defects.This work is supported by EPSRC grants EP/M013243/1, EP/L015315/1, EP/J500045/1, the De Beers Group of Companies, the Gemological Institute of America, the UK Quantum Technology Hub: NQIT - Networked Quantum Information Technologies and the EPSRC Centre for Doctoral Training in Diamond Science and Technology
References
[1] J. N. Becker, J. Görlitz, C. Arend, M. L. Markham, and C. Becher, Nat. Commun. 7, 13512 (2016).
[2] B. Pingault, D.-D. Jarausch, C. Hepp, L. Klintberg, J. N. Becker, M. Markham, C. Becher, and M. Atatüre, Nat. Commun. 8, 15579 (2017).
[3] S. Häußler, G. Thiering, A. Dietrich, N. Waasem, T. Teraji, J. Isoya, T. Iwasaki, M. Hatano, F. Jelezko, A. Gali, and A. Kubanek, New J. Phys. 19, 63036 (2017).
[4] T. Iwasaki, Y. Miyamoto, T. Taniguchi, P. Siyushev, M. H. Metsch, F. Jelezko, and M. Hatano, arXiv 1708.03576 (2017).
[5] S. Ditalia Tchernij, T. Herzig, J. Forneris, J. Küpper, S. Pezzagna, P. Traina, E. Moreva, I. P. Degiovanni, G. Brida, N. Skukan, M. Genovese, M. Jakšić, J. Meijer, and P. Olivero, arXiv 1708.01467 (2017).
[6] A. Sipahigil, R. E. Evans, D. D. Sukachev, M. J. Burek, J. Borregaard, M. K. Bhaskar, C. T. Nguyen, J. L. Pacheco, H. A. Atikian, C. Meuwly, R. M. Camacho, F. Jelezko, E. Bielejec, H. Park, M. Lončar, and M. D. Lukin, Science 354, 847 (2016).
[7] B. L. Green, S. Mottishaw, B. G. Breeze, A. M. Edmonds, U. F. S. D’Haenens-Johansson, M. W. Doherty, S. D. Williams, D. J. Twitchen, and M. E. Newton, Phys. Rev. Lett. 119, 96402 (2017).
[8] B. C. Rose, D. Huang, Z.-H. Zhang, A. M. Tyryshkin, S. Sangtawesin, S. Srinivasan, L. Loudin, M. L. Markham, A. M. Edmonds, D. J. Twitchen, S. A. Lyon, and N. P. de Leon, arXiv 1706.01555 (2017).Speaker: Mark Newton (University of Warwick) -
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Influence of Fermi-level on the lattice location of 27Mg in GaN
During 2017 we focused on investigating the lattice location of 27Mg as a detailed function of implantation temperature, implanted fluence, and fluence rate in different doping types of GaN: undoped GaN, as well as Si-doped n-type, Mg-doped p-type, and Mg-doped as grown.
The amphoteric nature of Mg, i.e. the simultaneous occupation of substitutional Ga and interstitial sites previously reported [1], was fully confirmed: following ultra-low fluence (~2E10 cm-2) room temperature (RT) implantation, the interstitial fraction of Mg was highest (20-25%) in the two samples that were pre-doped with 2E19 cm-3 stable Mg during epilayer growth, and lowest (~8%) in Si-doped n-GaN, while undoped GaN showed an intermediate interstitial fraction of ~12%. However, while for implanted fluences up to 4E12 cm-2 hardly any change at all was observed in the interstitial fraction in undoped and in n-GaN, in p-type GaN following implantation of 1E12 cm-2 of 27Mg it decreased to the ~12% level found for undoped GaN; in as-grown Mg-doped GaN, a similar decrease occurred but already at a fluence of 2.5E11 cm-2, i.e. around four times faster.
Raising the implantation temperature above RT, the amount of interstitial 27Mg initially increased in all types of samples, most pronounced in both Mg pre-doped samples, where interstitial fractions around 30% were reached for ultra-low fluence implantation at 400°C.
Finally, implanting at temperatures above 400°C progressively converted interstitial 27Mg to substitutional Ga sites in all doping types; detailed Arrhenius curves were measured, from which for all four sample types the activation energy for migration of interstitial Mg was estimated between 1.3 and 2.1 eV.
These results are being interpreted within the framework of Fermi-level dependence of the formation of interstitial vs substitutional Mg. The amount of interstitial Mg formed is highest when the Fermi level is low in the band gap, i.e. in p-type material. However, with increasing fluence the implantation-related defects push the Fermi level towards the middle of the band gap, which reduces the amount of interstitial Mg to levels which are identical to undoped material. The fact that this also happens in Mg-predoped samples that were not previously activated indicates that these were actually also p-type, however, with smaller hole concentration since the effect was faster. The observation that the amount of interstitial Mg initially increases with temperature can be explained by the fact that implantation at elevated temperatures creates less defects so that damage-related shifts of the Fermi level are less pronounced. We also have indications that the amount of interstitial Mg is influenced by changes in the Fermi level due to positive charges building up on the GaN surface during implantation.[1] U. Wahl, L.M. Amorim, V. Augustyns, A. Costa, E. David-Bosne, T.A.L. Lima, G. Lippertz, J.G. Correia, M.R. da Silva, M.J. Kappers, K. Temst, A.Vantomme, and L.M.C. Pereira: “Lattice location of Mg in GaN: A fresh look at doping limitations”, Physical Review Letters 118 (2017) 095501.
Speaker: Ulrich Wahl (Universidade de Lisboa (PT)) -
37
Insight into the amorphous-to-crystalline phase transition in GeTe thin films
The unique method of 57Fe emission Mössbauer spectroscopy (eMS), as performed at the large-scale facility of ISOLDE at CERN, was employed to reveal, at the most atomic-scale, important aspects governing the amorphous-to-crystalline phase transition in GeTe thin films, of importance for phase change memory (PCM) applications. By following dilute implantation of 57Mn (T½ = 1.5 min) decaying to 57Fe, we investigated the changes of the electronic charge distribution and local environment occurring around Fe probe substituting Ge (Fe@Ge), across the phase transition. The local structure of as-sputtered amorphous GeTe turned out to be a combination of tetrahedral and defect-octahedral sites. Upon crystallization a large conversion from tetrahedral to defect-free octahedral sites occurred. We discovered that only the tetrahedral fraction in amorphous GeTe participates to the change of the Fe@Ge-Te chemical bonds, with a net electronic charge density transfer of ~ 1.6 e/a0 between Fe@Ge and neighboring Te atoms. The observed atomic-scale chemical-structural changes resulted to be directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.
Speaker: Roberto Mantovan (CNR-IMM Agrate Unit (IT)) -
38
Results of IS601: β-asymmetry and relaxation time of 35Ar
Within the Standard model, the CKM matrix is predicted to be unitary. Testing this unitarity is therefore important to put limits on Beyond Standard Model physics contributions. The dominant matrix element for this test, Vud, is traditionally obtained from the corrected ft-values of superallowed pure Fermi beta transitions [1]. Another sensitive way to address Vud is through measuring the β-asymmetry parameter of the decay of 35Ar (Z=18) [2] which would help to further decrease the experimental uncertainty. To this end, a campaign (IS601) is ongoing at the VITO beamline at ISOLDE-CERN to determine this parameter.
For the first phase of the project, 35Ar was optically polarized and implanted in different stopper hosts (crystals). This phase functions as a design study for the final setup, detailing the efficiency of the laser polarization scheme and studying the performance of several crystal hosts for maintaining the ensemble polarization. This is done by verifying the accuracy of the optical pumping simulations and determining the relaxation time of the implanted polarized ensemble in the different crystals used.
This contribution will focus on the results obtained for the behavior of the relaxation time, including temperature and magnetic field dependency of the host crystals.[1] Towner & Hardy, PR C 79 (2009) 055502
[2] O. Naviliat-Cuncic & N.S., Phys. Rev. Lett. 102 (2009) 142302Speaker: Wouter Anton M Gins (KU Leuven (BE)) -
39
Study of β-delayed proton decays at IDS: the cases of 33Ar and 31Ar
$^{31}Ar$ isotope is one of the most exotic β-delayed particle precursors, near the proton drip-line, with high Q-value and low proton separation energy. Due to these two factors, many channels are opened and β-delayed protons are emitted in the decay of this nucleus (one-proton, two-proton and even three-proton emission) [1].
Taking advance of the ISOLDE Decay Station (IDS) [2], the decay of $^{31}Ar$ was measured in the IS577 experiment, becoming the first of its kind (multi-particle emission) performed successfully at this installation. The aims of this experiment were the study of β2p and β3p channels, the identification of the β3pγ-decay, as well as to provide important information on the resonances of 30S and 29P (proton daughters), important for the astrophysical rp-process [3].
The set-up used consisted of 5 Double Sided Si Strip Detectors (DSSSD) backed by un-segmented Si-pad detectors in ΔE-E telescope configuration (Fig. 1). This Si-array is located inside the new MAGISOL Si-Plugin Chamber, installed by our collaboration at the permanent station IDS, devoted to β-decay measurements. In addition, there are 4 HPGe clover-detectors surrounding the chamber for gamma detection.
This set-up is very compact with both high efficiency (47% of 4π) and good energy resolution (25 keV) over a wide energy range for particle emission.The decay of $^{33}Ar$ was also measured in the experiment, since this isotope is well suited for the energy calibration of the silicon detectors; it emitts β-delayed protons and their energies are well known. However, new low energy proton peaks are seen for the first time in this kind of β-decay works [4]. Thanks to the possibility of detecting p-ϒ coincidences with this set-up, the identification of these new peaks in the level scheme has been done.
Finally, new results in $^{31}Ar$ will be presented here too, such us the identification of proton emission from levels near the threshold in $^{30}S$ (β2p channel). These levels show competition between gamma and proton emission and their study is really important to understand some astrophysical processes.
[1] Proposal to the ISOLDE and Neutron ToF Committee, INTC-P-386, September 2013
[2] http://isolde-ids.web.cern.ch/isolde-ids/
[3] G.T. Koldste et al. Phys. Letters B 737 (2014) 383-387.
[4] N. Adimi et al. Phys. Review C 81, 024311 (2010)Speaker: Irene Marroquin Alonso (Consejo Superior de Investigaciones Cientificas (CSIC) (ES)) -
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Closing RemarksSpeaker: Gerda Neyens (CERN)
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