RIBF ULIC and CNS Symposium on Frontier of Gamma-ray Spectroscopy (Gamma11)

30 Jun 2011, 09:00 → 2 Jul 2011, 18:00 Asia/Tokyo

RIBF conference room

Eiji Ideguchi (CNS, University of Tokyo), Nori Aoi (RCNP/RIKEN)

We are pleased to inform you that the International Symposium on “Frontier of Gamma-ray Spectroscopy (gamma11)” is scheduled to take place at RIKEN Wako campus in Saitama (Japan) on June 30 - July 2, 2011. This symposium is co-hosted by the Center for Nuclear Study of the University of Tokyo (CNS) and the RIKEN Nishina Center. This is the fourth meeting in a series of CNS-RIKEN Joint symposium on frontier of gamma-ray spectroscopy following the last meeting held in 2008 (gamma08). The purpose of the symposium is to discuss recent progress and future perspectives of gamma-ray spectroscopy and recent development of advanced gamma-ray detectors. It is hoped that the symposium will encourage international cooperation and stimulate physicists in the field of nuclear structure studies. Future collaboration for the experimental programs at RIBF will be discussed. The symposium will start in the morning of June 30 and end in the afternoon of July 2. It will be held in the Conference Room of RIBF Building in RIKEN.

Gamma11 photo Gamma11_photo.jpg

Gamma11 poster gamma11poster.png

gamma11 web page TOP http://www.cns.s.u-tokyo.ac.jp/gamma11/

Report report-gamma11-11jul11.pdf

Thursday 30 June

09:30 → 09:50 Welcome address

09:50 → 10:30 Collectivities and shell effects in neutron/proton-rich nuclei

09:50 Recent and near-future activities of in-beam gamma-ray spectroscopy at RIBF

Selected results from the recent experiments and the perspective of the near-future activities of the in-beam gamma-ray spectroscopy at RIBF will be presented.

Speaker: Dr Nori AOI (RCNP, Osaka Univ.)

10:10 Decay spectroscopy of neutron-rich Zr isotopes at RIBF

Neutron-rich Zr isotopes are suddenly deformed at N = 60 and quadrupole deformation $¥beta_2$ reaches around 0.4 [1]. While the deformed sub-shell closure is predicted at N = 60, 62, and 64 [2], the relation between the deformation evolution and the deformed sub-shell closure is unknown, because the deformation evolution beyond N = 64 has not been measured. In the present study, we measured the low-lying state energies of 106Zr and 108Zr to investigate the deformation evolution. The secondary beam of the neutron-rich Zr and Y isotopes was produced as in-flight fission fragments of the 238U beam with 345 MeV/nucleon at RI Beam Factory, RIKEN. We measured the beta-delayed gamma rays from 106Y, which decays to 106Zr, and the gamma rays from a newly-discovered isomer of 108Zr. We will report on experimental results and discuss about the deformed sub-shell closure at N = 64, and also about a possibility of a tetrahedral shape isomer of 108Zr [3]. [1] ENSDF database, NNDC. [2] J. Skalski, S. Miztori and W. Nazarewicz, Nucl. Phys. A 617, 282 (1997). [3] T. Sumikama, et al., Phys. Rev. Lett. (to be published), arXiv:1104.2958.

Speaker: Dr T. Sumikama (Tokyo University of Science)

10:30 → 10:50 Coffee break

10:50 → 12:00 Collectivities and shell effects in neutron/proton-rich nuclei

10:50 Collective modes of excitation in exotic nuclei

Collective modes of excitation unique in deformed neutron-rich nuclei are investigated by the use of the nuclear energy-density functional method. Effects of nuclear deformation and neutron excess on the low-lying dipole excitation and the giant resonances will be discussed.

Speaker: Dr Kenichi Yoshida (Niigata University)

11:20 Gamma-ray Spectroscopy of neutron-rich Mg isotopes by using proton inelastic scattering

The gamma-ray spectroscopy in 34,36Mg(p,p') reactions will be presented in this talk. The experiment has been performed at RIPS beamline in RIKEN facility by using the secondary beam of very neutron-rich sd-shell nuclei. This talk will be focused on the neutron-rich side of 'island of inversion', and will be presented about experimental details and obtained results. We will discuss on evolution of deformation as a function of neutron number.

Speaker: Dr Shin'ichiro MICHIMASA (CNS, Univ. of Tokyo)

11:40 Large-amplitude deformation dynamics in low-lying states of magnesium isotopes around island of inversion

Microscopic mechanism of breaking the N=20 shell gap and nature of deformation in the `island of inversion' is currently under active discussion both experimentally and theoretically. Significant increase of the E(4)/E(2) ratio and the B(E2;2+->0+) value in magnesium isotopes from 30Mg to 34Mg clearly indicate a rapid growth of quadrupole deformation. Experimental data suggest a kind of quantum phase transition taking place around 32Mg and stimulate a microscopic investigation on large-amplitude collective dynamics unique to this region of nuclear chart. In this talk, large-amplitude deformation dynamics in low-lying states of neutron-rich Mg isotopes are discussed using the five-dimensional (5D) quadrupole collective Hamiltonian, which is microscopically derived from the constrained HFB plus local QRPA method. Solving the collective Schroedinger equation with use of the pairing-plus-quadrupole Hamiltonian, we evaluate excitation energies, collective wave functions in the (beta, gamma) deformation plane, E0 and E2 transition properties of excited bands as well as the ground bands in and around the island of inversion. Comparing results of the systematic microscopic calculation with experimental data, we make a critical analysis of the spherical-prolate shape coexistence/mixing picture. In particular, nature of the low-lying excited 0+ states will be discussed including those in 30Mg and 32Mg recently discovered.

Speaker: Dr Nobuo HINOHARA (RIKEN Nishina Center)

12:00 → 13:30 Lunch break

13:30 → 15:20 Single particle properties of exotic nuclei

13:30 Recent physics highlights from MINIBALL at REX-ISOLDE

The MINIBALL Ge-detector array at the REX-ISOLDE post-accelerator has been a workhorse in diverse nuclear structure studies over the past decade. In conjunction with particle detector arrays it has provided excellent in-beam data throughout the chart of nuclei, especially in Coulomb excitation and transfer reaction experiments. This talk is focused on recent physics highlights and will shed light on the future prospects.

Speaker: Dr Janne Pakarinen (CERN-ISOLDE)

14:00 Location of the g9/2 orbit in neutron-rich Ca isotopes studied with the shell model

The tensor force has been regarded as an importance ingredient that causes the evolution of the shell structure in exotic nuclei. From its point of view, the spin-orbit splitting decreases from the L-S closure to the j-j closure. It is thus predicted that a new N=34 magic number would arise in Ca isotopes according to high location of the f5/2 orbit. In Ca isotopes, while the location of the g9/2 orbit is also of great interest because it can be very close to the pf shell due to the tensor-force-driven shell evolution, it has not been determined yet because of lack of direct experimental evidence. In the present study, performing a large-scale shell model calculation whose model space consists of the full sd-pf shell and part of the sdg shell, we propose some excited states in Ca isotopes are highly influenced by the g9/2 orbit, which carries much information on its location. The position of the gap between the pf and sdg shells can be fixed at 51Ti, Z=22, having a 9/2+ state dominated by the g9/2 orbit. Adopting the Hamiltonian whose single-particle energy of the g9/2 orbit is thus determined, the first 3- states in 50,52Ca become in good agreement with experiment. They comprise of strong admixture of proton excitation from the sd- to pf-shell and neutron excitation from the pf- to sdg-shell. On the other hand, they are located too high without g9/2 in a similar way to other sd-pf shell-model calculations. The strong mixing successfully accounts for a large cross section of the 48Ca(t,p)50Ca(3-) reaction as well as the 3- of 52Ca strongly populated by the two-proton knockout reaction of 54Ti. As a result, the g9/2 is predicted to lie ~1 MeV higher than f5/2 in neutron-rich Ca isotopes.

Speaker: Dr Yutaka Utsuno (Japan Atomic Energy Agency)

14:20 Study of Neutron-Rich Mg Isotopes through $\beta$-decay of Spin-Polarized Na Isotopes

The exotic structure of neutron-rich nuclei around “island of inversion” characterized by the disappearance of the neutron magic number $N$ = 20 has been attracting attention. However, most of the information on the excited states of these nuclei, such as spin and parity and so on, has not been known well. We have developed a new method to unambiguously determine the spin-parities of daughter nuclei by taking advantage of asymmetric $\beta$-ray emission in $\beta$-decay of spin-polarized unstable nuclei. We have performed experiments using highly-polarized Na beams to systematically study the shell evolution of neutron-rich Mg isotopes. The $\beta$-ray asymmetry parameters and $\gamma$-ray intensities have successfully assigned spin-parities of levels in $^{28}$Mg and $^{29}$Mg. The level energies, log-$ft$ values and decay properties of all the assigned levels were explained well by assuming sd-shell configurations calculated by using shell model code, NuShell with USD, USDA and USDB interactions.. However, in $^{29}$Mg, two levels at 1.095 and 1.430 MeV associated with large log-$ft$ values could not be reproduced by the sd-shell configurations. The Monte Carlo Shell Model calculation shows the possibility of the states with the intruder configurations predicted 3/2$^-$ and 7/2$^-$ levels around 1 MeV. This fact strongly suggests negative-parity assignment for these two states in $^{29}$Mg. Experiment with spin-polarized $^{30}$Na beam was carried out last year and the data analysis is in progress. Results of $^{28}$Mg and $^{29}$Mg as well as some new findings of $^{30}$Mg will be presented.

Speaker: Mr Kunihiko Tajiri (Dep. of Phys., Osaka Univ., Osaka, Japan)

14:40 Isospin breaking effects in 51Co, 48Fe, and their mirror partners

The measurement of mirror energy differences between excited states in pairs of nuclei, with the same mass but interchanged proton and neutron numbers, provides a unique test of the nucleon-nucleon interaction. The origin of these energy differences lies in the isospin breaking components of the nucleon-nucleon interaction (see for example the review by Bentley and Lenzi [1] and references quoted therein). As protons and neutrons can be considered as different states of the nucleon, differences in energy should be associated with the Coulomb field. However, shell model calculations have demonstrated that the Coulomb interaction cannot account for the measured mirror energy differences. Isospin breaking effects have been studied in the Tz=-3/2 and Tz=-2 nuclei 51Co and 48Fe, respectively, and their isobaric analogue partners. This talk will present new excited states in these nuclei. Shell model calculations in the fp-shell for these nuclei will interpret the results in terms of Coulomb contributions to the isospin breaking effect of the nucleon-nucleon interaction. The importance of the non-Coulomb component of such isospin breaking effects will be discussed. A two step fragmentation process developed by Bentley and Brown et al [2], was employed which allowed access to these highly proton rich nuclei and to produce the mirror via a mirrored fragmentation of a 54Ni beam. The work represents the second time this technique has been used in the study of mirror nuclei and builds on the very successful test case performed by Bentley and Brown et al [2]. [1] M. A. Bentley and S. M. Lenzi, Coulomb energy differences between high-spin states in isobaric multiplets, Prog. Part. Nucl. Phys., 59, 497-561 (2007). [2] J. R. Brown et al., Phys. Rev. C80, 11306 (2009).

Speaker: Dr Paul Davies (University of York)

15:00 Extrapolation method in the Monte Carlo Shell Model and its application to medium heavy nuclei

We recently developed the extrapolation method using the energy variances in the Monte Carlo Shell Model. By using this framework, we can precisely evaluate energy eigenvalues and other physical quantities of the system whose degree of freedom is so large that the conventional diagonalization method is not feasible. It also enables us to perform shell-model calculations in medium heavy nuclei and to study quadrupole collective motion. We would like to report recent achivements of the shell-model study mainly in Ba and Xe isotopes and triaxial deformation. Ref. N. Shimizu, Y. Utsuno, T. Mizusaki, T. Otsuka, T. Abe, and M. Honma Phys. Rev. C82 061305(R) (2010).

Speaker: Dr Noritaka Shimizu (Center for Nuclear Study, University of Tokyo)

15:20 → 15:40 Coffee break

15:40 → 17:10 Single particle motion in isomeric states

15:40 Gamma-ray spectroscopy experiments using RISING with stopped and fast beams

High-resolution gamma-ray spectroscopy used at radioactive beam facilities is a powerful method in the study of exotic nuclei. At GSI the RISING array (Rare Isotopes Spectroscopic INvestigation at GSI) was employed for several years to address a wide range of physical phenomena. RISING was used in different configurations. In the fast beam campaign the Ge detectors placed mainly in the forward direction were used to record transitions following relativistic energy Coulomb excitation and secondary fragmentation. In the stopped beam campaign relativistic radioactive beams were implanted and their subsequent gamma and beta decay investigated. In this case the germanium detectors were arranged in a close geometry around the passive stopper or an array of DSSSD detectors. Highlights from both stopped and fast beam campaigns will be presented.

Speaker: Zsolt Podolyak (University of Surrey)

16:10 g-factor measurement for highly spin-aligned isomeric state of 32Al

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: Dr Yuichi Ichikawa (RIKEN Nishina Center)

16:30 Prolate-oblate shape coexistence and enhanced γ-softness in the neutron-rich N = 68 isotones 109Nb and 110Mo

Shape transitional behavior of atomic nuclei has been one of the major subjects explored in both experimental and theoretical nuclear structure physics. Neutron-rich Z ≈ 40, A ≈ 110 nuclei are predicted to exhibit the phase transitions from prolate, via γ-soft, to oblate shapes with increasing number of neutrons. A major aim of the present research is the spectroscopic study of neutron-rich nuclei in this exotic region, populated using in-flight fission of a 238U beam at 345 MeV/nucleon at the RIBF facility. This presentation focuses on two new results: (1) A new isomer with a half-life of 150(30) ns has been identified at an excitation energy of 313 keV in 109Nb. The strong hindrances observed for the isomeric-decay transitions are interpreted as being ascribed to a significant difference in shape between the isomeric state and the states to which the isomer decays. The results will be discussed in the context of possible shape coexistence, based on configuration-constrained potential energy surface calculations for possible single-proton orbits. (2) For 110Mo, spectroscopic information on the low-lying levels of the γ band built on the Kπ = 2+ state at 494 keV has been obtained for the first time. The experimental finding of the Kπ = 2+ state being lower than the yrast 4+ level suggests that axially-asymmetric γ softness is substantially enhanced in 110Mo, which lies in the proximity of the critical point where prolate-oblate shape transitions occur. The systematics of the low-lying levels in even-even A ≈ 110 nuclei will be discussed in comparison with that in the neutron-rich A ≈ 190 region.

Speaker: Dr Hiroshi Watanabe (RIKEN)

16:50 Gamma-Ray Spectroscopy by Using Low-Energy RI Beam Induced Fusion Reaction

Low-energy (around 5-10 MeV/u) RI beams for in-beam $\gamma$-ray spectroscopy is expected to be one of the effective tools to study high-spin states of nuclei in wider mass region. Although RI beams have a disadvantage in statistics by the low-beam intensity, RI beams have an advantage in significant S/N improvement, such as the selection of the largest cross section of fusion reaction and the event-by-event detection of $\gamma$-rays correlated with the RI beam. Two experiments were performed using the fusion reaction induced by $^{17}$N RI beam at the RCNP fragment separator, EN beam line in RCNP, Osaka University. As the RI beam was produced by the direct reaction of $^9$Be($^{18}$O,$^{17}$N)$^{10}$B using low-energy primary beam, higher beam-energy resolution and smaller beam-spot size were achieved. High-spin states in $^{142}$Pr with $N$ = 83 and in $^{136}$Ba with $N$ = 80 were populated by using $^{130}$Te($^{17}$N,5n) and $^{124}$Sn($^{17}$N,p4n) reactions, respectively. Performance of the RI beam production and the measurement based on the $\gamma$-ray spectroscopy method will be presented in this talk.

Speaker: Dr Atsuko Odahara (Dep. of Phys. , Osaka Univ.)

Friday 1 July

09:00 → 10:10 Collectivities and shell effects in neutron/proton-rich nuclei

09:00 Gamma-ray spectroscopy in the vicinity of 68Ni and 100Sn using the EXOGAM array

EXOGAM is installed at GANIL since 2001 and is extensively used in the various experimental areas. In the last years, we have a performed a serie of experiments using deep inelastic reactions in inverse kinematics. Excited states in neutron rich nuclei around 68Ni have been studied using the EXOGAM array in coincidence with the VAMOS large acceptance spectrometer. The evolution of collectivity has been studied in some details using lifetime measurements performed with the Koln plunger device. New results in iron isotopes toward N=40 will be presented. The discussion on the nature of the low-lying states in this mass region will be extended to odd-A cobalt isotopes where a very rich variety of structures has been observed including collective, single-particle and core coupled states. The observations have been compared to large scale shell-model calculations performed with the available interactions and the results seem to indicate some deficiencies in the current calculations. In another experiment aiming at studying both the prompt and the delayed gamma-rays, we have also obtained new results in the semi-magic 68Ni. These new results will be presented and discussed in some details. On the other side of the Segré chart, the evolution of the level structure as a function of isospin has been studied in detail. The experimental results obtained with EXOGAM coupled to the Neutron Wall and the DIAMANT charged particle array have been compared with shell model calculations. This detailed analysis allows us to discuss the possible role of T=0 pairing in the N=Z=46 palladium nucleus.

Speaker: Dr Gilles de FRANCE (GANIL)

09:30 Pygmy dipole resonance within the fully self-consistent Skyrme-RPA

We have carried out systematic calculations of the electric dipole modes up to mass A=110 region using Skyrme-Hartree-Fock plus RPA approach in fully self-consistent manner. We solved the RPA equation in 3D coordinate space for both spherical and deformed nuclei. We found that the low-angular momentum orbit in neutron-rich nuclei is a key ingredient for emergence of low-lying dipole mode, which is often called pygmy dipole resonance (PDR). The PDRs in light nuclei consist of the single-particle excitations to continuum states. On going to heavier nuclei, the PDRs obtain the collectivity, namely, are made of superposition of the single-particle excitations to loosely bound orbit. We also found that the photoabsorption cross sections cumulated up to 10 MeV has a strong correlation with the neutron skin thickness in all isotope when the PDR grows up. This means that the cross section can be a good indicator to measure the neutron skin thickness.

Speaker: Dr Tsunenori Inakura (RIKEN)

09:50 Pygmy dipole resonance of radio isotopes around r-process

We investigate pygmy dipole resonance(PDR) of radio isotopes systematically with the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory (Cb-TDHFB). The Cb-TDHFB is a new time-dependent method which is derived from TDHFB with a BCS approximation for pairing correlation. The results of this method is a very good approximation of quasi-particle random phase approximation, and they include effects of deformation because we can study with this method in three-dimensional coordinate space representation. We will talk the neutron number dependence of PDR in light radio isotopes(A < 70), then we discuss the heavy nuclei around r-process(A < 150). Especially, we note that the structure of PDR in light nuclei survives in heavy region.

Speaker: Dr Shuichiro Ebata (Center for Nuclear Study, the University of Tokyo)

10:10 → 10:30 Coffee break

10:30 → 12:00 Exotic deformation / new collective motion at low and high spin

10:30 Shape transitions of exotic nuclei

Spectroscopic calculations are carried out for medium-heavy nuclei in terms of the interacting boson model determined microscopically. Recent results relevant to the nuclear shape evolution in various mass region will be presented in comparison with the experiments. The results include the predictions on exotic nuclei.

Speaker: Mr Kosuke Nomura (University of Tokyo)

11:00 Search for Jacobi shape transition in hot rotating 88Mo nuclei through Giant Dipole Resonance decay

The study of the properties of the giant dipole resonance (GDR) at high temperature and angular momentum is one of the central topics in nuclear structure as it provides insight into the behavior of nuclei under extreme conditions. The wealth of experimental data on this subject covers in most cases an interval of temperatures up to 2.5 MeV and is mainly based on the study of the GDR gamma-decay from fusion-evaporation reactions. These data have been shown to provide evidence of relevant physical effects such as damping and shapes, the latter in the liquid drop regime. Of special interest are shape changes induced by temperature and angular momentum, particularly the predicted Jacobi shape transition, seen up to mass 50 and to be confirmed by exclusive experimental data also in heavier nuclei. This phenomenon is predicted as an abrupt change from an oblate to a more elongated triaxial shape occurring at the so called critical value of spin above which the nucleus undergoes scission. An experiment focussing on the 88Mo nucleus was performed in LNL Legnaro using 48Ti beam at 300, 450 and 600 MeV on 40Ca target and producing by fusion evaporation compound nuclei at temperatures of 3, 3.8 and 4.5 MeV. High-energy gamma-rays were measured in coincidence with residues and alpha particles and the data were analysed with the statistical model (CASCADE). The data have allowed to extract the spin and temperature evolution of the GDR width in 88Mo up to at high temperature values, region where information are scarce. A change of the GDR width with angular momentum and temperature was found and this reflects the role played by quantal and thermal fluctuations in the damping of the giant vibrations. In addition, preliminary results deduced from the fit of the measured GDR line-shapes seem to suggest existence of Jacobi shape transition in 88Mo. Future possibilities of similar studies in more exotic nuclei will be discussed in the context of soon available radioactive beam facilities, as e.g. SPIRAL2. Especially the role of a novel detector PARIS in such investigation will be shown.

Speaker: Mr Michal Ciemala (Institute of Nuclear Physics PAN, Poland)

11:20 Two phonon $\gamma$ vibrational bands in $^{103}$Nb

Two phonon $\gamma$ vibrational states in even-even nuclei were observed in a few nuclides in the rare-earth region and stimulated many theoretical studies in the 80s and 90s but those in rotating odd-$A$ nuclei were observed only recently. Distribution of the two phonon $\gamma$ vibrational collectivity in the rotating triaxial neutron-rich odd-$A$ nucleus, $^{103}$Nb, is calculated in the framework of the particle vibration coupling model based on the cranked shell model plus random phase approximation. This nucleus is one of the three for which experimental data obtained by measuring prompt $\gamma$ rays emitted by the spontaneous fission fragments of $^{252}$Cf were reported recently. The present theoretical framework was previously utilized for analyses of the zero and one phonon bands in the rare-earth region and is applied to the two phonon band for the first time. In the present calculation, the zero and one phonon bands are reproduced almost perfectly but the excitation energy of the calculated two phonon band is higher than the observed. The point to be stressed is that three sequences of two phonon bands share collectivity almost equally at finite rotation whereas the $K=\Omega+4$ state is the purest at zero rotation.

Speaker: Prof. Masayuki Matsuzaki (Fukuoka University of Education)

11:40 Two tops model for triaxially strongly deformed bands in 164Lu

For the triaxially strongly deformed bands over odd-A Lu isotopes and 167Ta, we have made a quite good success in explaining both the energy level scheme and the strength of E2 and M1 transitions based on the top-on-top model with the angular momentum dependent moments of inertia, where the Coriolis coupling between the rotating core top and the single-particle top is explicitly considered. We extend this model to tops-on-top model where two nucleons occupying different orbitals coupled to a triaxially deformed core. We introduce three kinds of bosons, one related with the total angular momentum I and two with single-particle angular momenta j1 and j2. In the rough estimtion of B(E2) and B(M1), the transition from I to I-1 gains a factor of [(I-j1-j2)/I]^3 in contrast to [(I-j)/I]^3 in odd case. This makes the observation of the other partner band in even-A nucleus difficult. We have made a calculation on 164Lu, and in future we will apply to even-even nucleus.

Speaker: Prof. Kazuko Sugawara-Tanabe (RIKEN)

12:00 → 13:30 Lunch break

13:30 → 14:30 Collectivities and shell effects in neutron/proton-rich nuclei

13:30 Spectroscopy of 42Si via two-proton removal reaction

Excited states in the 42Si nucleus have been studied via in-beam gamma-ray spectroscopy following two-proton removal reaction to investigate the structure of 42Si, such as the nuclear shape or information on the shell evolution. The experiment was performed at RI Beam Factory operated by RIKEN Nishina Center and CNS, University of Tokyo. The secondary beam of 44S and outgoing particles were identified by the BigRIPS separator and the ZeroDegree spectrometer, respectively. De-excitation gamma rays were detected by the DALI2 gamma-ray detection array in coincidence with 42Si particles. We observed the prominent peak corresponding to the first 2+ state in the gamma-ray spectrum with high statistics and other gamma lines. We will report the experimental results and the candidate of the 4+ state.

Speaker: Dr Satoshi TAKEUCHI (RIKEN Nishina Center (RNC))

13:50 The super-allowed Fermi type charge exchange reaction ($^{10}$C,$^{10}$B$\gamma$) for studies of isovector non-spin-flip monopole resonance

RI-beam induced charge exchange reactions have unique properties which are missing in stable-beam induced reactions and can be used to reveal new aspect of spin-isospin responses in nuclei. We are performing a series of experiments taking advantages of RI-beam induced reactions, by using the SHARAQ spectrometer\cite{Uesaka08} at RI Beam Factory (RIBF). There are some cases where the spectroscopic capability is strengthened by introducing $\gamma$-ray tagging to the reaction studies. In the symposium, result from an experiment as an example of Heavy-ion charge exchange reaction combined with $\gamma$-ray tagging will be reported. Incompressibility of nuclear matter attracts a focus of experimental and theoretical studies because of its fundamental importance to define the equation of state of nuclear matter. Isovector monopole resonances which are oscillation modes of the isovector density $\rho_{IV} = \rho_{n} - \rho_{p}$ are expected to be a key to approach us to asymmetric nuclear matter\cite{colo2003}. A natural way to study isovector excitations is by charge-exchange reactions such as (p,n) and ($^{3}$He,t) reactions. However, not only the $\Delta T = 1, \Delta S = 0$ excitations but also, and even stronger, the $\Delta T = 1, \Delta S = 1$ transitions are excited in such reactions. Thus, the signature of $\Delta T = 1, \Delta S = 0$ excitation is almost invisible. We propose a new probe ($^{10}$C,$^{10}$B$\gamma$) to excite $\Delta S=0$ mode selectively in combination with $\gamma$-ray tagging. Our idea to establish a probe to isovector non-spin-flip states is based on use of a super-allowed Fermi transition between isobaric analog states for the projectile. The analog state of the $^{10}$C ground state is found at $E_{x}$~=~1.740 MeV with 0$^{+}$ spin-parity in $^{10}$B. To identify the 0$^{+}$ $\rightarrow$ 0$^{+}$ transition in the projectile, which is a pure $\Delta S=0$ transition, assures the non-spin-flip excitation in the target. The transition to the 1.740MeV-state in $^{10}$B can be experimentally discriminated by tagging the emitted $\gamma$-ray of 1.022~MeV. The experiment was performed last October using the SHARAQ spectrometer at RIBF. The experimental results and future perspective will be presented. \bibitem{Uesaka08} T. Uesaka et. al., Nucl. Instrum. Meth. in Phys. Res. {\bf B266}, (2008) 4218. \bibitem{colo2003} G. Colo et. al., Phys. Rev. C {\bf 67}, (2003) 044306.

Speaker: Ms Yoshiko Sasamto (Center for Nuclear Study, University of Tokyo)

14:10 Tests of Skyrme energy density functionals in low-energy vibrational states of rare-earth nuclei using QRPA

We present results of Skyrme-QRPA calculations of low-energy vibrational states of well-deformed even-even rare-earth nuclei and compare them with experimental data. The performance of the energy functionals and the QRPA is discussed intending preparation for future massive calculation demanded by nuclear astrophysics. Overall, the energies and the reduced transition probabilities of the gamma-vibrational states are reproduced, however, the detail reveals necessity of many-particle many-hole excitations beyond the QRPA. Skyrme-functional SkM* is better than SLy4. Variation of the pairing energy functional in an acceptable range affects a few nuclei. The QRPA is not as successful for the ``beta-vibrational'' states as for the gamma-vibrational states.

Speaker: Dr Jun Terasaki (University of Tsukuba, Center for Computational Sciences)

14:30 → 14:45 Coffee break

14:45 → 16:15 Development of detectors and experimental methods

14:45 Gamma-ray Energy Tracking Array GRETINA

The gamma-ray energy tracking array GRETINA uses 28 Ge crystals, each with 36 segments, to cover ¼ of the 4pi solid angle. The gamma ray tracking technique requires detailed digital pulse shape information from each of the segments. These pulses are analyzed to determine the energy, time, and three-dimensional positions of all gamma-ray interactions. This information is then utilized, together with the characteristics of Compton scattering and pair-production processes, to track the scattering sequences of the gamma rays. Tracking arrays will give higher efficiency, better peak-to-total ratio and much higher position resolution, and thus increases the detection sensitivity by factors of several hundred compared to current arrays used in nuclear physics research. Particularly, the capability of reconstructing the position of the interaction with millimeters resolution is needed to fully exploit the physics opportunities at current and next generation radioactive beam facilities. GRETINA construction at the 88-Inch Cyclotron at LBNL is completed in March 2011. Currently, Extensive engineering runs were carried out using radioactive sources, and beams from the Cyclotron. The data obtained will be used to optimize its performance. Then scientific runs will start in September 2011. GRETINA will provide world leading opportunities to advance studies in nuclear structure, nuclear reactions, and fundamental symmetries.

Speaker: Dr I-Yang Lee (Lawrence Berkeley National Laboratory)

15:25 Novel design for large position-sensitive HPGe detectors

A novel, large volume, HPGe detector concept capable of providing high efficiency, excellent energy resolution, and extremely fine position sensitivity will be described. The device, referred to as an "Inverted Coaxial" HPGe detector, is based on a non-standard closed-end coaxial geometry and employs point contact technology [1,2]. Experimental characterization measurements have been made using a non-segmented prototype, while detailed electric field and signal generation calculations have been employed in designing a larger, electrically segmented version of the device. The non-segmented prototype has an energy resolution of 1.8 keV FWHM at 1.3 MeV with excellent performance at low energies. A segmentation scheme has been designed for an 80-mm long x 70-mm diameter tapered-cylindrical prototype. This segmentation pattern minimizes the number of readout channels required while providing typical calculated position resolution FWHM values of less than 0.2 mm in three dimensions. Characterization of the non-segmented prototype is ongoing while plans are in place to order a segmented device in the coming months. [1] P.N. Luke et al., Trans. Nucl. Sci. 36 1 (1989) 926 - 930. [2] P.S. Barbeau and J.I. Collar, J. Cosmol. Astropart. Phys. 09 (2007) 009.

Speaker: David Radford (ORNL)

15:55 Digital pulse shape analysis method to extract interaction position for CNS-GRAPE

We are developing a method to extract gamma-ray interaction positions in the segmented planar Ge detector of CNS-GRAPE. The total array of CNS-GRAPE consists of 18 detectors and each of which contains two Ge planer crystals with the effective radius of 30mm and the thickness of 20mm. The cathode of each detector is divided to 3×3, and the anode is common. The pulse shape data from each cathode are taken by 100 MHz Flash ADC. Output pulses from the cathode show the different shapes depending on gamma-ray interaction points and the deposited energy. After analyzing these digitized data, a few parameter set, i.e. centroid and width of pulse shapes, are extracted, which strongly depend on the interaction points of gamma rays. By comparing the experimentally deduced parameters with simulated ones, interaction points in the detector are deduced.

Speaker: Mr Shintaro Go (CNS)

16:15 → 16:30 Coffee break

16:30 → 17:30 Development of detectors and experimental methods

16:30 The EURICA Project: a new proposal at RIBF

A EURICA (Euroball RIKEN Cluster Array) is a project to combine the world's stronget radioactive isotope beam facility (RIBF) and the euroball cluster array used at the GSI (RISING), pending a later decision by the GAMMAPOOL steering committee. The main objective of the EURICA is to perform stopped beam campaigns to study isomer and beta-delayed gamma-ray spectroscopy of very exotic nuclei. There are also possible scientific programs such as fast beams, degraed beams and g-factor measurements, which is also under the discussion. Here, status and some ideas of the EURICA will be presented.

Speaker: Dr Shunji Nishimura (Researcher)

16:50 PARIS: A novel calorimeter for future radioactive beam facilities

Traditionally gamma-ray spectroscopy has gone down two routes: scintillator detectors offering high efficiency but low resolution, while high-purity germanium detectors offer very high energy resolution at the expense of low efficiency. Recently, a third option presents itself in terms of novel scintillators such as lanthanum bromide which offer unprecedentedly high energy resolution and ideal scintillator properties, but at high intrinsic cost. PARIS is a novel 4p calorimeter designed to make extensive use of novel scintillator materials such as lanthanum bromide. PARIS is intended to detect gamma rays in the range from 100 keV to 50 MeV at future ISOL facilities such as SPIRAL2. The challenge is to get the best performance from the novel scintillator while minimising the cost of the project. An attractive avenue of investigation is the phoswich detector where a smaller crystal of e.g. LaBr3 is coupled to a longer crystal of CsI or NaI. Such a design brings with it challenges in terms of choice of photomultiplier tube which must be linear over a very large range, and pulse-shape analysis is mandatory to fully deconvolve the two signals. The present status of PARIS will be given and the principal lessons learned from the ongoing R&D programme will be discussed. The prospects for PARIS will be outlined.

Speaker: Mr Michal Ciemala (Institute of Nuclear Physics PAN, Poland)

17:10 Proposed experiment to measure gamma-rays from O(p,p')O* in relation to O(nu,nu'gamma)X

We are planning an experiment to measure gamma-rays from oxygen using a Grand-Raiden Spectrometer. The purpose is to understand the gamma-ray production in neutral-current neutrino-oxygen interaction in the 20-100 MeV region, in relation to the detection of neutrinos from supernova explosion. We also report on the preparation of gamma-ray detectors (CsI, NaI) and their performance.

Speaker: Prof. Makoto Sakuda (Okayama University)

18:00 → 20:00 Banquet

Saturday 2 July

09:00 → 10:40 Hyper Nuclei

09:00 Gamma-ray spectroscopy of hypernuclei

A series of hypernuclear gamma-ray spectroscopy experiments using a germanium detector array, Hyperball, have accumulated precise data on various p-shell Lambda hypernuclei. We observed "hypernuclear fine structure" in various hypernuclei and extracted the strengths of the spin-dependent parts of the Lambda-N interaction. The obtained strengths allow us to reproduce structure of Lambda hypernuclei quite well, and to test and improve baryon-baryon interaction models. In the J-PARC facility, further experiments of hypernuclear gamma-ray spectroscopy are planned to be performed. In the first experiment (E13), we will extend our study to s-shell and sd-shell hypernuclei and investigate the Lambda-N interaction more in detail. We also plan to study the g factor of a Lambda in a nucleus by measuring a spin-flip B(M1) value in hypernuclei. In future, we will also investigate "impurity effect" of nuclear structure induced by a Lambda, such as the shrinking effect and a possible change of deformation.

Speaker: Prof. Hirokazu Tamura (Deprtment of Physics, Tohoku University)

09:30 Collective excitations of Λ hypernuclei

Many high-resolution γ-ray spectroscopy experiments have been carried out for s-shell and p-shell Λ-hypernuclei in order to understand the nature of Λ-nucleon interaction in nuclear medium and the impurity effect of a Λ on nuclear structure. The J-PARC facility will provide an opportunity to perform hypernuclear γ-ray spectroscopy study with high precision by improving the quality of the secondary mesonic beam. In particular, the J-PARC facility will offer useful tools to study the low-lying states of hypernuclei in medium and heavy hypernuclei. In this contribution, we will present the results of our recent calculations for Λ hypernuclei based on the self-consistent mean-field approaches. We will first discuss the potential energy surfaces for Λ-hypernuclei in the sd-shell region by using both the relativistic mean-field (RMF) and the non-relativistic Skyrme-Hartree-Fock (SHF) methods. We will show that the RMF approach predicts a disappearance of deformation for 13ΛC and 29ΛSi nuclei [1], although the impurity effect of Λ particle is somewhat weaker with the SHF approach [2]. The effect of triaxial deformation can be taken into account much more easily with the SHF method [3]. We will discuss the rotational excitations of 25ΛMg nucleus using the three-dimensional energy surface obtained with the SHF method [4]. 1. Myaing Thi Win and K. Hagino, Phys. Rev. C78 (2008) 054311. 2. H.-J. Schulze, Myaing Thi Win, K. Hagino, and H. Sagawa, Prog. Theo. Phys. 123 (2010) 569. 3. Myaing Thi Win, K. Hagino, and T. Koike, Phys. Rev. C83 (2011) 014301. 4. J.M. Yao, Z.P. Li, K. Hagino, M. Thi Win, Y. Zhang, and J. Meng, arXiv:0909.1741 [nucl-th].

Speaker: Dr Kouichi Hagino (Department of Physics, Tohoku University)

10:00 Hypernuclear gamma-ray spectroscopy at J-PARC and status of Hyperball-J

At the J-PARC facility, several light hypernuclei will be studied via gamma-ray spectroscopy at the K1.8 beam line as a Day-1 experiment (E13). We will study 4{$lambda}He to solve puzzle of charge symmetry breaking and 19{$lambda}F to study spin-dependent {$lambda}N interaction in sd-shell at the initial stage of E13. Gamma rays from the hypernuclei are detected by a new germanium(Ge) detector array, Hyperball-J, for ultra high energy deposit rate. The array consists of 32 coaxial Ge detectors surrounded by PWO counters for background suppression. One of the array’s features is a large absolute photo-peak efficiency, simulated as 6.1% for 1-MeV gamma ray. Other is mechanical cooling of Ge crystal for radiation-hardness. The Ge detector-cooler unit achieved comparable energy resolution with that of the LN2 cooling. PWO counters were introduced for fast background suppression instead of BGO counters used in the past experiments. The dead time due to decay time is shorter. We have also developed a Hyperball-J control system and tested with a few detector units mounted to frame. The construction of the array is at the final stage, and the current status of E13 will be reported.

Speaker: Takeshi Yamamoto (Department of Physics, Tohoku University)

10:20 First results of the HypHI Phase 0 experiment

The HypHI project aims to study relativistic hypernuclei in-flight by means of induced reactions of heavy ion projectiles impinged on a fixed target. The first experiment, so called Phase 0, has been performed at GSI with 6LI projectiles at 2 A GeV on a carbontarget, which has demonstrated the feasibility of the experimental principle of the project. Details of the experiment and first results will be discussed in the talk.

Speaker: Mr Daisuke Nakajima (CNS, University of Tokyo)

10:40 → 11:00 Coffee break

11:00 → 12:10 Exotic deformation / new collective motion at low and high spin

11:00 “Studies of Neutron Rich nuclei with Gammasphere: From Deep Inelastic to CARIBU”.

Over the last decade we have made a number of measurements using both fusion evaporation and deep inelastic reactions to study neutron rich nuclei to high spin. In addition, the ATLAS facility is in the middle of commissioning the CARIBU facility which will provide re-accelerated radioactive ion beams produced from a 252Cf 1Cu fission source. This talk will give some examples of our past Gammasphere studies in the neutron rich N=40 region as well as provide information on the status of CARIBU and the experimental program planned for Gammasphere.

Speaker: Dr Michael Carpenter (Argonne National Laboratory)

11:30 Microscopic analysis of development of deformation in neutron-rich Cr isotopes

We study the development of deformation in low-lying states of neutron-rich Cr isotopes around N=40, where recent experiments suggest the development of deformation. Recently, we have developed a method for determining microscopically the five-dimensional quadrupole collective Hamiltonian, which is a standard tool to describe the quadrupole collective motions. This method consists of the constrained Hartree-Fock-Bogoliubov (HFB) equation and the local QRPA (LQRPA) equations, which is an extension of the usual QRPA (quasiparticle random phase approximation) to non-HFB-equilibrium points, on top of the CHFB states. Therefore, we call this method the CHFB+LQRPA method. The collective Hamiltonian has seven quantities to be determined microscopically: three vibrational and three rotational inertial functions, and the collective potential. One of the advantages of our method is that the inertial functions calculated with this method contain the contributions of the time-odd components of the mean field, which are ignored in the widely-used cranking formula. We have applied the CHFB + LQRPA method to shape phase transition in neutron-rich Cr isotopes. The results of our calculation are in good agreement with available experimental data and suggest the development of quadrupole deformation around N=40.

Speaker: Dr Koichi Sato (RIKEN Nishina Center)

11:50 Collectivity Near 64Cr: A New Region of Deformation

The dominance of intruder configurations in the well-known “island of inversion” surrounding 32Mg has been attributed to a reduced N=20 sd-fp shell gap arising from the tensor monopole component of the effective nucleon-nucleon interaction. At higher masses, a similar mechanism results in a narrowing of the N=40 harmonic oscillator shell closure below Z=28. First evidence for a weakening of the N=40 shell gap, and onset of quadrupole collectivity has been observed in the Cr and Fe isotopes as a steady decrease of the first 2+ energies through N=40. Excited-state lifetime measurements have confirmed collectivity in the Fe isotopes up to N=40, and added to mounting evidence for a new “island of inversion” centered on 64Cr. The collectivity of 66,68Fe isotopes and 64Cr has been recently studied via intermediate-energy Coulomb excitation at NSCL. Secondary beams of 66Fe, 68Fe and 64Cr were excited on a Bi foil at the target position of the S800 spectrograph, in which recoils were identified. De-excitation gamma rays were detected using the scintillator array CAESAR. Preliminary results for the B(E2) of 66, 68Fe and 64Cr will be presented, and discussed in terms of the evolution of collectivity near Z=24 and N=40.

Speaker: Heather Crawford (Lawrence Berkeley National Laboratory)

12:10 → 13:30 Lunch break

13:30 → 15:00 Exotic deformation / new collective motion at low and high spin

13:30 Indian National Gamma Detector Array (INGA) Coupled with a Fast Digital Data Acquisition System for Nuclear Struture and Reaction Studies

Discrete gamma ray spectroscopy using large array of Compton suppressed high purity germanium detectors continues to provide new insights on the structure and dynamics of the nuclear systems. The Indian National Gamma Detector Array(INGA) is set up at TIFR-BARC accelerator facility at Mumbai, as a part of a collaboration between BARC, IUAC, SINP, TIFR, UGC-CSR-KC, VECC and different Universities. The array is designed for 24 Compton suppressed clover detectors providing around 5% photopeak efficiency. INGA along with other ancillary detectors using analogue electronics and CAMAC based data acquisition system has been used for the investigation of variety of nuclear structure phenomena, e.g., shape coexistence, magnetic/anti-magnetic rotation, chiral rotations, coupling of gamma vibration with other modes, high spin states of neutron rich nuclei in sd-shell, and isomers near shell closure. Recently, a PCI-PXI based digital data acquisition system with 96 channels has been implemented for this Compton suppressed clover array. The system has been tested with 64 channels with the event rate up to 125 kHz with 2-fold coincidence rate among any two crystals. Inclusion of a fast timing array and a charged particle array with the INGA is planned. The timing properties of fast scintillator detectors with the existing DDAQ have been investigated. This will facilitate the lifetime measurements of isomeric states from 1 nsec to few microsec during the usual gamma-gamma coincidence measurement. Conventional systems with analog shaping has being replaced by digital system that provides higher throughput, better energy resolution and better stability for the multi-detector Compton suppressed clover array. The results from the initial in-beam experiments of the complete set-up and scope for the future nuclear structure and reaction measurements will be presented.

Speaker: Dr Rudrajyoti Palit (Tata Institute of Fundamental Research)

14:00 Superdeformed Band in Asymmetric N>Z Nucleus, 40Ar, and High-Spin Level Structures in A～40 Nuclei

Nuclear superdeformation is a unique testing ground for the shell structure at extreme deformation. In the light mass region, superdeformed (SD) states were investigated along the N=Z line and a new ‘island’ of SD nuclei was found around A～40 nuclei (i.e., 36Ar[1], 40Ca[2], and 44Ti[3]). Presences of these SD bands indicate the SD shell gaps at N=Z=18, 20, and 22. To clarify the SD shell structures in neutron-rich side, high-spin states in 40Ar were investigated[4], where SD bands associated with asymmetric combination of SD magic numbers, Z=18 and N=22 are expected. High-spin states of other nuclei in A=30～40 region were also studied, including 42Ca associated with the Z=20 and N=22 SD magic numbers and 35S, 36Cl. In the talk, recent experimental results of the SD band in 40Ar and high-spin level structures in A=30～40 will be presented. In order to extend these studies to neutron-rich side, future high-spin studies using energy-degraded RI beams will be also discussed. [1] C.E. Svensson et al., Phys. Rev. Lett. 85, 2693 (2000). [2] E. Ideguchi et al., Phys. Rev. Lett. 87, 222501 (2001). [3] C.D. O'Leary et al., Phys. Rev. C 61, 064314 (2000). [4] E. Ideguchi et al., Phys. Lett. B 686, 18 (2010).

Speaker: Dr Eiji Ideguchi (CNS, University of Tokyo)

14:20 Quantal descriptions of Superdeformed states of Ca and Ar.

By means of angular momentum projection, HFB states corresponding to SD states of Ca and Ar isotopes are quantized. Energy levels are calculated, and the relevant nuclear structure is analyzed from a dynamical point of view.

Speaker: Dr Makito Oi (Senshu University)

14:40 Coexistence of various rotational bands and alpha clustering in 42Ca

Structures of low-lying states in 42Ca have been studied focusing on deformations and clustering using the antisymmetrized molecular dynamics and the generator coordinate method (GCM). Energy variation with constraints on quadrupole deformation parameter and inter-cluster distance between and 38Ar clusters obtain GCM basis, which have deformed and {38Ar cluster structures, respectively. The GCM calculations obtain three rotational bands, which have 6p4h, 4p2h and 8p6h congurations relative to the ground state of 40Ca. The 8p6h states deform largely and those are superdeformed states. Members of ground and 4p2h states contain much 38Ar cluster structure components. The 6p4h rotational band has been conrmed experimentally, but existence of the 4p2h and 8p6h deformed states are theoretical predictions. The ground and 4p2h states contain 38Ar cluster structure components, and those states correspond to the experimental J^pi = 0^+_1 and 0^+_3 states, respectively, because 38Ar(6Li, d) reactions populate the J^pi = 0^+_1 and 0^+_3 states strongly. Unified treatments of deformations and clustering are important for understanding natures of nuclei.

Speaker: Dr Yasutaka TANIGUCHI (RIKEN Nishina Center for Accelerator-Based Science, RIKEN)

15:00 → 15:10 Coffee break

15:10 → 16:10 Discussion

16:10 → 16:20 Closing