Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session MB: Nuclear Structure of Neutron-rich Exotic Nuclei III |
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Chair: Daniel Bazin, National Superconducting Cyclotron Laboratory Room: Kohala 2 |
Saturday, October 11, 2014 2:00PM - 2:15PM |
MB.00001: Production of rare isotopes at RIKEN RI Beam Factory: summary of search for neutron-rich new isotopes Naoki Fukuda, Daisuke Kameda, Hiroyuki Takeda, Hiroshi Suzuki, Deuksoon Ahn, Yohei Shimizu, Daichi Murai, Naohito Inabe, Toshiyuki Kubo We report production of rare isotopes (RI) at the RIKEN RI Beam Factory (RIBF), focusing on the progress of search for neutron-rich new isotopes, which have been conducted since the commissioning in 2007. The experiments were performed with the BigRIPS fragment separator by using the in-flight fission of $^{\mathrm{238}}$U beam at 345 MeV/nucleon. Thanks to the large ion-optical acceptances and excellent performance in particle identification of the BigRIPS, more than 120 new isotopes have successfully been observed so far. In this talk, the summary of new-isotope search experiments will be presented along with the capability of the BigRIPS separator. We will also sum up various types of experiments, which were carried out with a variety of RI beams produced at the BigRIPS. [Preview Abstract] |
Saturday, October 11, 2014 2:15PM - 2:30PM |
MB.00002: Identification of 25 new neutron-rich isotopes produced in the EURICA uranium beam campaign at RIKEN RIBF Yohei Shimizu, Toshiyuki Kubo, Naoki Fukuda, DeukSoon Ahn, Naohito Inabe, Daisuke Kameda, Hiromi Sato, Hiroshi Suzuki, Hiroyuki Takeda, Koichi Yoshida The EUROBALL RIKEN Cluster Array (EURICA) collaboration aims to conduct isomer and $\beta $-delayed $\gamma $-ray spectroscopy of several hundred nuclei far from stability. In 2012 and 2013, at the RIKEN Nishina Center RI Beam Factory, the EURICA uranium beam campaign was been conducted to investigate isomeric decays from very neutron-rich nuclei and their $\beta $ decays. In the EURICA uranium beam campaign, the nuclei of interest were produced by the in-flight fission of 345 MeV/nucleon $^{238}$U beam colliding with a Be target. Fission fragments were identified by using the superconducting in-flight separator BigRIPS. The particle identification was performed using the $\Delta $E-TOF-B$\rho $ method. We observed 25 new neutron-rich isotopes: $^{116}$Nb, $^{118}$Mo, $^{121,122}$Tc, $^{125}$Ru, $^{127}$Rh, $^{129,130,131}$Pd, $^{132}$Ag, $^{134}$Cd, $^{136,137,138}$In, $^{139,140}$Sn, $^{141,142,143}$Sb, $^{144,145}$Te, $^{146,147}$I, $^{149}$Xe, and $^{154}$Ba. In this contribution, details of the measurement and analysis will be presented. [Preview Abstract] |
Saturday, October 11, 2014 2:30PM - 2:45PM |
MB.00003: Observation of new $K$ isomers among neutron-rich rare earth nuclei produced by in-flight fission of 345 MeV/nucleon $^{238}$U Daisuke Kameda, Toshiyuki Kubo We have performed search for new $K$ isomers for a wide range of neutron-rich rare earth nuclei using the BigRIPS separator at RIKEN RIBF. The rare earth nuclei were produced by in-flight fission of a $^{238}$U beam at 345 MeV/nucleon, and isomeric gamma rays were detected using four clover-type germanium detectors. As a result, we have observed a total of 25 new microsecond isomers: $^{\mathrm{158m,159m,160m}}$Nd, $^{\mathrm{158m,159m,161m}}$Pm, $^{\mathrm{160m,161m,162m}}$Sm, $^{\mathrm{163m,164m}}$Eu, $^{\mathrm{162m,164m,165m,166m}}$Gd, $^{\mathrm{164m,165m,166m,167m,168m}}$Tb, $^{\mathrm{167m,168m,169m,170m}}$Dy, and $^{\mathrm{171m}}$Ho, and obtained a wealth of spectroscopic information on these nuclei. The nuclei in this region are predicted to be well deformed with a prolate shape, and $K $isomers are expected to appear due to the $K$ hindrance. In the present measurement, as anticipated, many of the observed new isomers have been interpreted as a $K$ isomer, because we could identify some gamma rays which belong to the grand-state rotational band being fed by isomeric transitions. The systematics of known $K$ isomers, such as those in neighboring higher-$Z $isotones, also help and support the interpretation of isomerism. Here we will report on the details of the experimental results and discuss the possible configurations of deformed orbits for the observed new $K$ isomers. [Preview Abstract] |
Saturday, October 11, 2014 2:45PM - 3:00PM |
MB.00004: Production yield measurement for neutron-rich nuclei around $Z=60$ from in-flight fission of a $^{238}$U beam at 345 MeV/nucleon Daichi Murai, Kazuo Ieki, Toshiyuki Kubo, Naohito Inabe, Daisuke Kameda, Naoki Fukuda, Hiroyuki Takeda, Hiroshi Suzuki, Koichi Yoshida Production yields of the neutron-rich nuclei with the atomic numbers $Z$ around 60 by the in-flight fission of $^{238}$U$^{86+}$ beam was measured at the RIBF in the RIKEN Nishina center. The isotopes were produced by $^{238}$U$^{86+}$ beam at 345 MeV/nucleon with a Be target and separated using the BigRIPS separator. Particle identification was performed by determining of $Z$ and mass-charge ratio $A/Q$ of each isotope using the $B\rho-TOF-\Delta E$ method. Production yields were deduced from the $A/Q$ spectrum of each $Z$ obtained by the detailed analysis with correction of the detector efficiency and the lost events for background rejection in analysis and so on. Deduced yields were over two orders of magnitude larger than prediction given by the LISE$^{++}$ (Ver. 8.4.1), which reproduced production yields at the $Z<50$ region measured in 2008 experiment fairly well. [Preview Abstract] |
Saturday, October 11, 2014 3:00PM - 3:15PM |
MB.00005: Production cross section of neutron-deficient radioactive isotopes produced from a $^{124}$Xe beam at 345 MeV/u by the BigRIPS separator at RIKEN RI Beam Factory Hiroshi Suzuki, Toshiyuki Kubo, Naoki Fukuda, Naohito Inabe, Daisuke Kameda, Hiroyuki Takeda, Hiromi Sato, Yohei Shimizu, DeukSoon Ahn, Yohei Ohkoda, Naohito Iwasa, Daichi Murai The production cross sections of radioactive isotopes (RI) are crucial for designing RI-beam experiments. Systematic measurements of production cross sections are very important to improve models which are used to predict cross sections. In this talk, we will present the cross sections of RIs, which were produced by projectile fragmentation of a $^{124}$Xe beam at 345 MeV/u impinging on a production target of Be. The experiments were performed using the BigRIPS separator at RIKEN RI Beam Factory in 2011 and 2013. We produced neutron-deficient RIs with atomic numbers $Z =$ 34-52 including a double-magic nucleus $^{100}$Sn. Particle identification was performed by the TOF-\textit{Brho}-d$E$ method. The production cross sections were deduced from the measured production yields based on the transmission efficiency of the separator that is calculated by using the LISE$^{++}$ code. The experimental cross sections were compared with the empirical cross-section formulae EPAX3. The measurements of the momentum distributions were also performed, and they were compared with the LISE$^{++}$ calculation. [Preview Abstract] |
Saturday, October 11, 2014 3:15PM - 3:30PM |
MB.00006: Probing the nature of the 2$^+$ excited state in $^{72}$Ni with lifetime measurements Karolina Kolos, David Miller, Robert Grzywacz, Hironori Iwasaki, Mohammad Al-Shudifat, Daniel Bazin, Carol R. Bingham, Thomas Braunroth, Giordano Cerizza, Alexandra Gade, Antoine Lemasson, Sean N. Liddick, Miguel Madurga, Chris Morse, Mostafa M. Rajabali, Francesco Recchia, Lee L. Riedinger, Phillip Voss, William B. Walters, Dirk Weisshaar, Kenneth Whitmore, Kathrin Wimmer We present the results of an experiment to measure the lifetimes of the $2^+_1$ excited state in $^{72}$Ni populated in a proton knockout reaction at intermediate energies using the recoil distance method. This experiment was performed at the NSCL during GRETINA campaign and the array was used for $\gamma$-ray detection. Measured $\gamma$-ray spectra were directly compared with GEANT4 simulations [1] accounting for the geometry of the experiment. The new result does not indicate increased collectivity in nickel isotopes above $N=40$ and is found to be in agreement with the recent MCSM calculations [2]. [1] P. Adrich et al., Nucl. Instrum. and Meth. A598 (2009) 454. [2] Y. Tsunoda, T. Otsuka, N. Shimizu, M. Honma and Y. Utsuno, Journal of Physics: Conference Series 445 (2013) 012028. [Preview Abstract] |
Saturday, October 11, 2014 3:30PM - 3:45PM |
MB.00007: Beta-decay rate and beta-delayed neutron emission probability of improved gross theory Hiroyuki Koura A theoretical study has been carried out on beta-decay rate and beta-delayed neutron emission probability. The gross theory of the beta decay is based on an idea of the sum rule of the beta-decay strength function, and has succeeded in describing beta-decay half-lives of nuclei overall nuclear mass region. The gross theory includes not only the allowed transition as the Fermi and the Gamow-Teller, but also the first-forbidden transition. In this work, some improvements are introduced as the nuclear shell correction on nuclear level densities and the nuclear deformation for nuclear strength functions, those effects were not included in the original gross theory. The shell energy and the nuclear deformation for unmeasured nuclei are adopted from the KTUY nuclear mass formula, which is based on the spherical-basis method. Considering the properties of the integrated Fermi function, we can roughly categorized energy region of excited-state of a daughter nucleus into three regions: a highly-excited energy region, which fully affect a delayed neutron probability, a middle energy region, which is estimated to contribute the decay heat, and a region neighboring the ground-state, which determines the beta-decay rate. Some results will be given in the presentation. [Preview Abstract] |
Saturday, October 11, 2014 3:45PM - 4:00PM |
MB.00008: Reaction cross sections of proton scattering from carbon isotopes: $^{9-22}$C Kaori Kaki Reaction cross sections of carbon isotopes for proton scattering are calculated in large energy region. Density distributions of carbon isotopes are provided from relativistic mean field results. Calculations are based on two procedures: the Glauber theory and elativistic impulse approximation, and are compared with each ther as well as with experimental data. A strong relationship between reaction cross section and root-mean-square radius is clearly hown for $^{12}$C using a model distribution. [Preview Abstract] |
Saturday, October 11, 2014 4:00PM - 4:15PM |
MB.00009: Large-scale shell model calculations for structure of Ni and Cu isotopes Yusuke Tsunoda, Takaharu Otsuka, Noritaka Shimizu, Michio Honma, Yutaka Utsuno We study nuclear structure of Ni and Cu isotopes, especially neutron-rich ones in the $N\sim 40$ region by Monte Carlo shell model (MCSM) calculations in $pfg_9d_5$ model space ($0f_{7/2}$, $1p_{3/2}$, $0f_{5/2}$, $1p_{1/2}$, $0g_{9/2}$, $1d_{5/2}$). Effects of excitation across $N=40$ and other gaps are important to describe properties such as deformation, and we include this effects by using the $pfg_9d_5$ model space. We can calculate in this large model space without any truncation, as an advantage of MCSM. In the MCSM, a wave function is represented as a linear combination of angular-momentum- and parity-projected deformed Slater determinants. We can study intrinsic shapes of nuclei by using quadrupole deformations of MCSM basis states before projection. In doubly-magic $^{68}$Ni, there are oblate and prolate deformed bands as well as the spherical ground state from the calculation. Such shape coexistence can be explained by introducing the mechanism called Type II shell evolution, driven by changes of configurations within the same nucleus mainly due to the tensor force. [Preview Abstract] |
Saturday, October 11, 2014 4:15PM - 4:30PM |
MB.00010: Coulomb Excitation with CARIBU Beams: Octupole Strength in $^{144}$Ba Measured with GRETINA and CHICO2 Brian Bucher, Shaofei Zhu The neutron-rich barium isotopes sit in one of the few mass regions on the nuclear chart observed to display octupole correlations. These isotopes are challenging to study since they lie far from stability and are thus difficult to produce in large quantities. In particular, this region is interesting for studying the evolution of octupole correlations since the enhancement of the E1 strength drops by an order of magnitude from $^{144}$Ba to $^{146}$Ba, where shell corrections appear to play a significant role. To provide unambiguous insight into the octupole correlations, B(E3) strengths have been measured using Coulomb excitation of $^{144}$Ba beams at 650 MeV on a 1 mg/cm$^2$ $^{208}$Pb target. This experiment represents the first successful measurement utilizing re-accelerated CARIBU beams combined with the $\gamma$-ray tracking array GRETINA and the auxiliary charged-particle detector CHICO2. Preliminary results from the experiment will be presented. [Preview Abstract] |
Saturday, October 11, 2014 4:30PM - 4:45PM |
MB.00011: Shell-model description of E1 excitation Noritaka Shimizu, Yutaka Utsuno, Tomoaki Togashi, Takaharu Otsuka, Michio Honma We discuss a microscopic description of E1 excitations based on shell-model calculations. We performed large-scale shell-model calculations for Ca isotopes with Lanczos-strength-function method and $sd$-$pf$-$sdg$ model space allowing up to 3$\hbar\omega$ excitation and obtained their photoabsorption cross sections. It gives a very good description of giant dipole and low-lying pygmy resonances rather independently of smoothing parameter. We also present the feasiblity of the Monte Carlo shell model (MCSM) to study the E1 excitation in order to to treat larger model space. By using the MCSM we discuss some results about light nuclei. [Preview Abstract] |
Saturday, October 11, 2014 4:45PM - 5:00PM |
MB.00012: Multiple-scattering effects in nucleus-nucleus reactions with Glauber theory Shinya Hatakeyama, Shuichiro Ebata, Wataru Horiuchi, Masaaki Kimura A study of new unstable nuclei has become possible in new radioactive beam facilities. In order to understand the relationship between reaction observables and nuclear structure, we need reaction theory which exactly reflects the nuclear structure. The Glauber theory is a powerful tool of analyzing high energy nuclear reactions. The theory describes the multiple scattering processes, whereas the optical limit approximation (OLA), which is widely used, ignores those processes. Those effects are expected to play an important role in the nuclear collision involving unstable nuclei (see for example Phys. Rev. C \textbf{54}, 1843 (1996)). Here we apply the Glauber theory to nucleus-nucleus reactions. The wave functions are generated by the Skyrme-Hartree-Fock method and are expressed in a Slater determinant that allows us to evaluate the complete Glauber amplitude easily. We calculate total reaction cross sections, elastic cross sections and differential elastic cross sections for $^{\mathrm{16\sim 24}}$O, $^{\mathrm{40\sim 70}}$Ca, $^{\mathrm{56,58}}$Ni, $^{\mathrm{100\sim 140}}$Sn, $^{\mathrm{190\sim 214}}$Pb on proton, $^{\mathrm{4}}$He, $^{\mathrm{12}}$C targets and compare with experimental data. The Glauber theory gives much better description than the OLA, especially at larger scattering angles. [Preview Abstract] |
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