[RIBF-ULIC-Symposium-007] E(U)RICA International Workshop

23 May 2011, 09:40 → 24 May 2011, 17:10 Asia/Tokyo

RIBF Building 2F Conference Room (RIKEN Nishina Center)

Pieter Doornenbal (RIKEN), Shunji Nishimura (RIKEN)

The primary objective of this workshop is to bring the nuclear structure community together in order to establish the collaboration and to define and decide on the scientific program arising from coupling the Cluster detectors with the BigRIPS fragment separator. We would like to focus on experiments for a stopped beam configuration employing the techniques of isomer and beta-delayed gamma-ray spectroscopy. The presented ideas and discussions are expected to lead into scientific proposals for the RIBF NP-PAC at the end of this year. In case there is an interest by the community for other techniques, these ideas are welcome to be presented and discussed during the workshop.

Application to ULIC App_ulic-sym-007.pdf

Report final-reportPieter.pdf

Workshop Group Photo WorkshopGroupPhoto.JPG

Monday, 23 May

09:40 → 10:00 Coffee

10:00 → 12:00 Opening

10:00 Opening

Speaker: Hideyuki Sakai

10:10 Overview of the RIBF

Speaker: Hiroyoshi Sakurai (RIKEN Nishina Center for Accelerator-Based Science)

10:30 Overview of the BigRIPS fragment separator

Speaker: Toshiyuki Kubo (RIKEN Nishina Center)

Slides Kubo_EURICA_May2011.pdf

10:50 E(U)RICA introduction

Speakers: Pieter Doornenbal (RIKEN), Shunji Nishimura (Researcher)

Slides presentation.pdf

11:10 First results of beta-gamma spectroscopy for neutron-rich nuclei around A=110 at RIBF

A drastic shape evolution is predicted in neutron-rich nuclei around A=110 [1]. For the Zr isotopes, a deformation may reach a maximum by a deformed shell-closure. Energies of low-lying states which are known up to N=64 show the increase of the deformation from N=60 to 64. However, the maximization of the deformation has not been observed as a function of neutron numbers. Furthermore, a spherical shape may appear around 110Zr due to a possible sub-shell closure at N=70 [2]. For neutron-rich isotopes with Z > 40, a shape transition from prolate to oblate shapes is predicted around A=110 [1] and an oblate-shape isomer may appear. In addition, beta-decay half-lives of this neutron-rich region are required to study the r-process nucleosynthesis. We performed a first beta-gamma spectroscopy experiment with stopped beams at RIBF for neutron-rich A~110 nuclei. In this workshop, I'll show an experimental overview and first results related to the shape evolution of the Zr and Nb isotopes [3,4], and beta-decay half-lives [5]. [1] J. Skalski et al., Nucl. Phys. A 617, 282 (1997). [2] M. Bender et al., Phys. Rev. C 80, 064302 (2009). [3] T. Sumikama et al., Phys. Rev. Lett. to be published. [5] H. Watanabe et al., Phys. Lett. B 696, 186 (2011). [4] S. Nishimura et al., Phys. Rev. Lett. 106, 052502 (2011).

Speaker: Kenta Yoshinaga (Tokyo University of Science)

Slides First_Result_of_Beta_decay_Exp.pdf

11:35 Spectroscopy of the doubly magic nucleus 100Sn and its neighbourhood with RISING

The investigation of the shell structure far from the valley of stability is a major task in modern nuclear structure physics, especially close to the drip lines. By fragmentation of a 1.0 A GeV 124Xe beam from the GSI accelerators 100Sn and neighbouring nuclei have been produced, separated in the FRS and identified by multiple deltaE, Brho and ToF measurements. The nuclei were stopped in an implantation detector with high spatial resolution in order to correlate implantations with succeeding decays. The device was surrounded by the "Stopped Beam Rising" array of 15x7 Ge-detectors in close geometry. In this configuration the setup enabled us to do nearly 4Pi spectroscopy of the emitted gamma and particle decay radiation. With a photo peak efficiency of about 10% (E=1MeV) for gamma ray detection and nearly 100% for full energy detection of decay particles up to 5MeV, this high resolution setup allowed for a maximum use of the secondary beam. The presentation will focus on the decay spectroscopy of the doubly magic nucleus 100Sn which decays by a super Gamow Teller spin flip transition populating mostly a single final state in the daughter nucleus. New and more precise values of the half life, the beta endpoint energy and the Gamow Teller strength in the decay of 100Sn have been determined in order to address the question of the Gamow Teller quenching in 100Sn. First insight into the nuclear structure of excited states in 100In was obtained from beta-coincident gamma ray spectroscopy. Also new results concerning the particle stability of exotic nuclei in the vicinity of 100Sn will be presented. Isomer spectroscopy in these nuclei will be discussed with a focus on the first observation of the 6+ to 4+ transition from the already known 102Sn isomer.

Speaker: Christoph Hinke (Physik Department E12 TU Muenchen, Germany)

Slides CHINKE_RIKEN_2011_170511.pdf

12:00 → 13:30 Lunch Break

13:30 → 15:30 Isomer and beta-gamma spectroscopy of light and proton-rich nuclei

13:30 Decay Spectroscopy in Proton-Rich Nuclei

Speaker: Shunji Nishimura (Researcher)

Slides nishimu_sn100_posted.pdf

13:50 Beta Decay Studies Near N=28

The nuclear structure in the region of nuclei around N=28 depends strongly on the filling of both proton and neutron orbitals. In the present proposed experiment, we plan to make systematic study the low lying energy levels for those nuclei as well as the following daughter nuclei via the b-decay and lifetime measurements. We observe the b rays using plastic scintillators. The b-delayed g rays and neurons are measured using the Ge detectors and neutron wall, respectively. In addition, the lifetime of the excited states are measured by two fast LaBr3 counters using time-delayed bgg(t) measurement. The deduced level schemes and the lifetimes of the excited states in these nuclei will help us to understand shell evolution around N=28.

Speaker: Zhihuan Li (RIKEN)

Slides zhli-ppt.pdf

14:10 Studies of the Beta Decays of very neutron-deficient nuclei and a comparison with Charge Exchange reactions.

Studies of the Tz = -1 → 0 beta decays of 42Ti, 46Cr, 50Fe and 54Ni to the self-conjugate nuclei 42Sc, 46V, 50Mn, and 54Co respectively (P.h.D Thesis,Francisco Molina- Univ. Valencia) will be presented. The nuclei of interest were produced in the fragmentation of a 58Ni beam of 680 MeV/nucleon at GSI. The ions were separated using the Fragment Recoil Separator (FRS) and implanted into a set of DSSSD detectors surrounded by the RISING CLUSTER array. The recorded number of implanted ions of the nucleus of interest was typically 3-6 x106 in total. With this large number we were able to make correlations between the Heavy Ion implants and the subsequent beta or beta-gamma decays that follow and thus to a) measure the beta-decay half-lives with one order-of-magnitude better accuracy than the values existing in the literature, b) establish decay schemes, c) determine the direct ground state to ground state feeding in the decays, d) measure the decay intensity to the 1+ states populated in the daughter and hence the absolute B(GT) values for the Gamow-Teller beta decays. The B(GT) values are of importance in terms of the comparison with the analogous Charge Exchange (CE) reactions on the mirror nuclei (Fujita et al.,PRL95(2005)212501), which populate the same levels. One interesting observation in these experiments is that the T=0, 1+ states populated in the beta decay predominantly by M1 transitions to the T=1, 0+ g.s. No M1 gamma transitions were observed to any other T=0, 1+ excited states. This is the result of a selection rule, called a “Quasi-rule” by Warburton and Weneser (D.H. Wilkinson “Isospin in Nuclear Physics”, 1969, SBN 7204 0155 0) and it is observed for the first time in the fp shell nuclei. Encouraged by this success we have now pursued experiments at GANIL, studying the Tz=-1 58Zn and Tz=-2 56Zn beta decays. However these nuclei are more difficult to produce because they are further from stability, ie from the stable nucleus used as a beam to produce them. The high intensity beam at RIKEN would allow us to extend these studies to higher masses and more exotic cases. This would facilitate a comparison of the beta decay and charge exchange reactions in heavier mass systems. Amongst the cases of interest are the very neutron-deficient 63,64 and 66Se isotopes. The first two would allow us to extend our comparison with the mirror CE process on 64Zn and 63Cu. The 66Se case is of particular interest from several viewpoints, a) to study the evolution of the B(GT) strength in the fp shell, b) to study if the “Quasi-rule” for the M1 transitions persists and c) to study a possible proton-neutron condensate. These experiments could be carried out using the fragmentation of 78Kr and could be carried out in tandem with the experiment proposed by B. Blank and collaborators, which is focussed on two proton radioactivity and is already approved.

Speaker: Berta Rubio (CSIC Valencia)

Slides Eurica_2011.pdf

14:30 Study of the N=34 subshell gap (and abstract Ids 12,13,16)

Shell closures are a fundamental concept in nuclear physics and most of our knowledge of effective nucleon-nucleon interactions comes from the study of nuclei with few valence particles around doubly-magic cores. There are by now a wealth of data coming from the study of exotic nuclei showing that the relative energies of the shell-model orbitals are not immutable but can change and evolve as a function of neutron number. This leads to the disappearance of well established magic numbers or to the appearance of new ones. For example, the presence of a $N=32$ subshell closure has been recently derived from various experiments on neutron-rich nuclei from Ca to Cr. The existence of this energy gap at N=32 around Z=20 arises from a large energy spacing between the neutron p3/2 orbital and the higher lying p1/2 and f5/2 orbitals. Otsuka and collaborators have also predicted that the N=34 isotones around Z=20 could exhibit characteristics of a shell closure due to the proton f7/2 - neutron f5/2 monopole tensor interaction. This effect could be revealed by measuring the first excited states involving the f5/2 neutron single particle orbital in the 55Sc nucleus. The most direct evidence of the subshell at N=34 would be the high energy of the first $+ state in 54Ca, not accessible today. However, the low-lying excited states of 55Sc, populated via the beta decay of 55Ca (g.s. 5/2-), involving the f5/2 neutron single particle orbital will help to elucidate the gap at N=34 and this will represent a crucial test for theoretical calculations predicting a new shell clousure at N=34 around Z=20. This nucleus will be produced in a fragmentation reaction at relativistic energies, using a 86Kr primary beam at 350MeV.A. The BigRIPS fragment separator in combination with some of the Euroball Cluster detectors will be used for this study. Probably a total of 7 days of beam time would be enough to perform this experiment with final relevant results.

Speaker: Jose Javier Valiente Dobon (LNL-INFN)

Slides EURICA2011-pubblicato.pptx.pdf

15:10 Study of mid-shell nuclei based on the beta-gamma spectroscopy method

Speaker: Atsuko Odahara (Department of Physics, Osaka University)

Slides EURICAーOdahara.pdf

15:30 → 16:00 Coffee break

16:00 → 18:00 Isomer and beta-gamma spectroscopy of neutron-rich nuclei

16:00 Study of the N=50 major shell effect towards 78Ni : contribution from beta-decay studies at IPN Orsay

The PARRNe ISOL device has been operating at IPN Orsay since 10 years. Originally conceived as a test bench for R&D studies in the framework of SPIRAL2, the performance of the setup has proven suitable to undertake a physics research program on the evolution of N=50 towards 78Ni by beta-decay studies. During the past decade, several experiments were realized using either the Tandem as a deuteron driver or ALTO as an electron driver. Physics results from these experiments will be presented as well as the way they connect to other results obtained elsewhere (and for other observables) in this mass region. Most of the data obtained were largely pioneering at their time and a parallel effort on the theoretical side had to be undertaken in order to provide a correct description and global understanding.

Speaker: David Verney (Institut de Physique Nucleaire - IN2P3-CNRS / University Paris Sud-11)

16:20 Decay Spectroscopy in the vicinity of 78Ni

Study of doubly-closed-shell and neighboring nuclei provides great opportunities for testing of nuclear models and expanding our knowledge of nucleosynthesis processes. Especially, the region around 78Ni (Z=28, N=50) has attracted great interests because of its extreme neutron-to-proton ratio in the region far from the valley of stability. Despite of a great deal of theoretical activity devoted to the 78Ni, a little is known for 78Ni itself and nothing beyond because of their extremely low production yield in the experiment. RIBF facility has started providing very neutron-rich nuclei with the world’s highest intensity uranium beam. Recent discovery of very neutron-rich nuclei including 79Ni [1] assures that systematic study of decay properties (half-lives, beta-delayed gamma) of nuclei around 78Ni becomes feasible eventually. Here, our proposal of decay spectroscopy in the vicinity of 78Ni will be presented together with possible scientific program with a combination of our high efficiency beta-counting system and high efficiency euroball cluster (E(U)RICA). [1] T.Ohnishi, et al., JPSJ 79, 073201 (2010).

Speaker: Shunji Nishimura (Researcher)

Slides nishimu_Ni78_posted.pdf

16:40 Spectroscopy of neutron-rich nuclei around 110Zr

Shape evolution around 110Zr attracts much attention because shape transition from prolate to oblate, spherical or more exotic tetrahedral shapes has been predicted by many authors. 110Zr is expected to be a spherical shape due to a possible subshell closure at N=70 [1]. Furthermore, the transition to an oblate shape may appear in more neutron-rich region [2]. We performed the experiment around 110Zr with stopped beams as a first decay experiment at RIBF [3, 4, 5]. The observed low-lying states of 106, 108Zr indicate that these two nuclei are well deformed, and the deformation reaches maximum at N=64 by deformed subshell closure at N=64 [3]. By combining a higher intensity expected for 238U beam and a high-efficiency-gamma-ray array E(U)RICA, we will be able to approach more neutron-rich Zr and Mo isotopes around N=70. We also expect a detailed spectroscopy of the 108Zr isomer which is a candidate to search for the tetrahedral shape [3]. In this workshop, I will show the results of $^{106, 108}$Zr at the first decay experiment and a future plan of the decay experiment with EURICA around 110Zr. [1] M. Bender et al., Phys. Rev. C 80, 064302 (2009). [2] J. Skalski et al., Nucl. Phys, [3] T. Sumikama et al., Phys. Rev. Lett. to be published. [4] H. Watanabe et al., Phys. Lett. B 696, 186 (2011). [5] S. Nishimura et al., Phys. Rev. Lett. 106, 052502 (2011).

Speaker: Toshiyuki Sumikama (Tokyo University of Science)

Slides Spectroscopy110Zr.pdf

17:00 b-decay spectroscopy study of neutron rich nuclei around the N=82 shell closure including the r-process waiting points 128Pd

The b-decay study of the region around the N=82 shell closure is critical for r-process models. The experiment that we intend to perform with the addition of the EURICA spectrometer aims to study the decay of the N=82 nuclei 128Pd and 129Ag that are expected to be waiting points for the the r-process in most r-process models, and therefore their study will dramatically improve the reliability of the r-process calculations. New half-lives will also be measured for more than 30 isotopes with N<82 including the r-process nuclei 124Ru, 113Nb that are predicted to be waiting points in some r–process models. Our experiment will also extend the E(2+) systematics of the Pd isotopic chain to 122,124Pd. These nuclei are the first isotopes that are affected by the rapid decrease in deformation predicted by the FRDM model that for more exotic nuclei leads to pronounced changes in the r-process path. E(2+) will also be measured for 116,118Ru and 112Mo, three important nuclei in a region where deformation is the focus of intense theoretical and experimental efforts. The nuclei of interest will be produced by fission of a 345 A/MeV 238U beam colliding with a 9Be target. Fission fragments will be selected by the BigRIPS spectrometer, and implanted in a stack of Si detectors surrounded by g detector setup such as the EURICA detectors. With our experimental apparatus we will be able to measure half–lives, b–delayed g rays as well as photons from the decay of microsecond isomers. The results will have implications for nuclear structure studies by providing data to improve the parametrization of mass formulas, and will reveal new insights into important open questions such as shell quenching and the neutron pairing interaction. The use of the EURICA spectrometer will be highly beneficial for this experiment due to the g-detection efficiency that is up to five times higher than compared to the efficiency of the Clover detectors setup available at the RIBF.

Speaker: Giuseppe Lorusso (RIKEN)

Slides ERICA.pdf

17:20 Beta decay of the neutron-rich 132,134Cd isotopes and search for 6+ isomers in 136,138Sn

Speaker: Pieter Doornenbal (RIKEN)

Slides eurica-SnCd.ppt

17:40 Probing neutron-rich isotopes around doubly closed-shell 132Sn and doubly mid-shell 170Dy by combined beta-gamma and isomer spectroscopy

I will present possible decay spectroscopy experiments using the E(U)RICA array at RIBF, aiming at studying neutron-rich nuclei in the vicinity of the doubly magic nucleus 132Sn and the doubly mid-shell nucleus 170Dy

Speaker: Hiroshi Watanabe (RIKEN Nishina Center)

Slides Watanabe_EURICAWS.pdf

18:00 → 20:00 Party at Cafeteria

Tuesday, 24 May

10:00 → 12:05 RISING and other gamma-ray measurement techniques

10:00 Achievements of the RISING Fast Beam Campaign

Speaker: Hans-Jürgen Wollersheim (GSI Helmholtzzentrum)

Slides RISING-hjw-pdf.pdf

10:35 Scientific Achievements of the Stopped Beam RISING Campaign at GSI

Some of the science highlights for the Stopped Beam RISING experimental campaigns at GSI will be reviewed using both passive and active stopping materials. These include isomer and beta-decay studies along the N=Z line from 56Ni up to 100Sn; isomer spectroscopy of shell-model configurations around the doubly magic systems 132Sn and 208Pb; and the use of beta-delayed gamma-ray spectroscopy for studies of the transition from shell-model to deformed collective systems in heavy, neutron-rich nuclei with A>180.

Speaker: Patrick Regan (University of Surrey)

Slides regan-rising-RIKEN-MAY2011.pdf

11:10 Achievements with g-RISING

Within the RISING collaboration a g-factor campaign has been performed on magnetic moment measurements of isomeric states in neutron-rich Sn isotopes and in the neutron-deficient Pb-region. For the first time the experimental technique has been successfully applied at relativistic energies for radioactive isotopes produced by 238U fission and 136Xe fragmentation on 9Be targets and traversing the FRS spectrometer. An overview of the experimental campaign together with its major achievements will be presented during the workshop.

Speaker: Radomira Lozeva (IPHC, CNRS, IN2P3)

Slides RLozeva_E(U)RICA.pdf

11:45 g-factor measurements for highly spin-aligned isomeric states

The nuclear spin alignment in an excited state results in anisotropy of angular distribution in Gamma-ray emission, which provides us a chance to measure nuclear observables through various spectroscopic techniques. Especially the time-differential perturbed angular distribution (TDPAD) method is one of the major techniques to determine a g-factor of an isomeric state with a lifetime of ns - ms order, where the g-factor is determined from a time dependence of anisotropy of de-excitation Gamma rays emitted from spin-aligned nuclei precessing in an external magnetic field. In this study, we have developed a novel method to produce an RI beam with high spin-alignment, that is the two-step fragmentation method with a technique of momentum-dispersion matching. The experiment to apply the new method to study of 32Al was carried out with BigRIPS in RIKEN RIBF. The isomeric states of 32Al was produced by two-step fragmentation of a primary beam of 48Ca via 33Al, then its g-factor was determined for the first time using the TDPAD method. The experimental results will be given in the presentation.

Speaker: Yuichi Ichikawa (RIKEN Nishina Center)

12:05 → 13:30 Lunch Break

13:30 → 15:00 Other gamma-ray measurement techniques II

13:30 In-Beam Gamma-ray Spectroscopy at the RIBF

Speaker: Nori Aoi (RIKEN Nishina Center)

14:05 Gamma spectroscopy and B(E2) measurements to study shape transitions in neutron rich Mo and Tc isotopes

We plan to perform an experiment at the BigRIPS fragment separator at RIKEN to study prolate-oblate shape transitions in neutron rich Mo and Tc nuclides. Existing mean field calculations predict dramatic changes in the ground-state shape in this part of the nuclide chart. To test the validity of the theoretical model framework in the regime, new experimental data in the form of energies of excited states and transition rates are of fundamental importance. Studying shell effects in this region could also shed more light on the astrophysical scenarios along the r-process path. Our proposed experiment aims at, using gamma-ray spectroscopy, measuring B(E2;0+→2+) values in the nuclides 110,112Mo as well as identifying excited states for the first time in A>111 Tc isotopes. CNS GRAPE will be used for gamma-ray measurements and ejectile from the secondary target will be identified by using the ZeroDegree spectrometer.In addition, E(U)RICA spectrometer at final focal plane (F11) will be used to perform life-time measurement of short-lived isomer in these nuclei.

Speaker: Eiji Ideguchi (CNS, University of Tokyo)

14:25 Development of Energy-degraded RI beams at RIBF

Low-energy nuclear reactions such as fusion-evaporation, multi-step Coulomb excitation, transfer reactions, etc. are important probes to investigate exotic structure of unstable nuclei. While RIBF provides world's most intense RI beams, an energy of about 250 MeV/A is much higher than required energies for low-energy reactions. At the last NP-PAC meeting, we proposed the development of energy-degraded RI beams at RIBF. We will produce RI beams with 2–10 MeV/u at the final focal plane F11 of ZeroDegree spectrometer in order to perform gamma-ray spectroscopy. In this development beam time, we plan to use the 110Mo beam as a test case. In order to produce the required low energy RI beams, we will develop a momentum-bunched and achromatic RI beam, which is achieved by the combination of the momentum bunching degrader and new optics mode at the second stage of BigRIPS. With this new method, the beam energy will be pre-degraded from 250 MeV/u to 100 MeV/u, while the momentum spread will be reduced from 6% to 2.4% after the second stage. At the final focal plane, the beam energy is degraded by flat-plate degraders. The beam energy with 0–15 MeV/u and spot size of ~35 mm (FWHM) will be achieved. By considering the transmission and the requirement for energy range and beam spot size at F11, 41% of RI beams produced at F3 can be used for the low energy reactions. In this workshop, I will show the proposed experiment to develop the energy-degraded RI beams.

Speaker: Toshiyuki Sumikama (Tokyo University of Science)

Slides DegradedBeamEURICA.pdf

14:40 Thoughts on the E(U)RICA DAQ

Speaker: Hidetada Baba (RIKEN)

Slides euricababa.pptx

15:00 → 15:30 Coffee break

15:30 → 17:10 Discussions and closing

15:30 Discussions

Speakers: Pieter Doornenbal (RIKEN), Shunji Nishimura (Researcher)

Slides discussion.pdf

17:00 Closing remarks

Speaker: Shunji Nishimura (Researcher)

Slides Closing_Posted.pdf