Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session DB: Mini-Symposium on CAGRA |
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Chair: Nori Aoi, RCNP Osaka University Room: Hilton Kohala 1 |
Thursday, October 25, 2018 9:00AM - 9:30AM |
DB.00001: Overview of the CAGRA Collaboration Invited Speaker: Michael P Carpenter The collaboration, Clover Array Gamma-Ray Spectrometer at RCNP/RBIF for Advanced Research (CAGRA), was first conceived as a collaboration between institutions in the U.S. and Japan to build a gamma-ray detector array for use at accelerator facilities in Japan. The concept was to utilize funding from the Department of Energy (DOE) to build a digital data acquisition system, a LN-fill system, and support structure to instrument sixteen Compton-suppressed Ge Clover detectors where the inventory of detectors would come from both U.S. and Japanese institutions. In the first campaign at RCNP, detectors from the U.S., Japan and China were used in experiments on the EN-course. Six experiments were performed with three of the six experiments utilizing radioactive beams developed using the in-flight technique. In the second campaign, CAGRA was coupled to the high-resolution spectrometer Grand Raiden. Physics topics addressed included: (i) characterization of the Pygmy Dipole Resonance (PDR) as a function of Z and N with both proton and alpha probes, (ii) measurement of the GT response function using the (6Li,6Li’ + g) reaction and (iii) search for rare decay and shapes in 28Si and 40Ca using light-ion scattering. While the collaboration initially included only U.S. and Japanese institutions, the number of participating countries has grown and the collaboration in now international in scope. Future campaigns are being considered at RCNP, JAEA, and RBIF. In this talk, I will give a brief history of the collaboration, update on the current status, and discuss possible future directions. |
Thursday, October 25, 2018 9:30AM - 9:45AM |
DB.00002: The (6Li,6Li*[3.56 MeV]) reaction at 100 MeV/u as a probe of Gamow-Teller transition strengths in the inelastic scattering channel R. G.T. Zegers The (6Li,6Li∗[T = 1, Tz= 0, 0+, 3.56 MeV]) reaction at 100 MeV/u was developed as a probe for isolating the isovector spin-transfer response in the inelastic channel from which the Gamow-Teller transition strengths from nuclei of relevance for inelastic neutrino-nucleus scattering cross sections can be extracted. By measuring the 6Li ejectile in the Grand Raiden magnetic spectrometer and selecting events in which the 3.56 MeV γ ray from the decay of the 6Li*[3.56 MeV] state is detected, the isovector spin-transfer selectivity is obtained. HPGe clover detectors in the CAGRA array served to detect the γ rays. In the study of the 12C(6Li,6Li∗[3.56 MeV]) reaction, the isovector spin-transfer excitation-energy spectrum in the inelastic channel was successfully measured. For heavier target nuclei, the extraction of the isovector spin-transfer response was hampered by the background in the γ-spectra from isoscalar excitations. |
Thursday, October 25, 2018 9:45AM - 10:00AM |
DB.00003: The Proton and Neutron Quadrupole Collectivity in 32Si Thi Ha Hoang, Tetsuya Yamamoto, Nori Aoi, Eiji Ideguchi, Hooi Jin Ong, Shumpei Noji, T. Leung Tang, Yasutaka Yamamoto, Yongde Fang, Dinh Trong Tran, Yohei Matsuda, Nobuaki Imai, Shin'ichiro Michimasa, Takashi Hashimoto, Jenny Lee, Junki Tanaka, Yassid Yayyad, Takeshi Ito, Tomokazu Suzuki, Azusa Inoue, Taras Lokotko The collective excitation is an important characteristic of nuclear structure. Proton and neutron collectivity are the same in most of stable nuclei; however, it has been found out that this can be broken for some of nuclei around magic number, such as 16C and 38Si. In this work, we investigate the collective property in the ground state of 32Si, which has Z=14 semi-magic number and N=18 close to magic number 20, by 32Si (d, d') reaction in inverse kinematics. The experiment was performed at RI beam facility (EN course) RCNP. The 32Si beam at the average energy of 18.5 AMeV bombarded a solid deuterium target. The final states of 32Si were selected from the measurement of de-excitation γ rays using Clover Ge detector array CAGRA, in coincidence with the scattered 32Si identified by ΔE-E method using Silicon telescope. The quadrupole collectivity was deduced from the angular distribution of differential cross section of the (d, d') reaction to the first 2+ state. By combining with proton quadrupole collectivity deduced from the known B(E2) value, proton and neutron quadrupole parameters were determined separately. |
Thursday, October 25, 2018 10:00AM - 10:15AM |
DB.00004: Gamma-ray spectroscopy of 40Ca through light ion reactions Kumar Raju Mukhi, Eiji Ideguchi, Atsushi Tamii, Nori Aoi, Yongde Fang, Takeshi Koike, Nobuyuki Kobayashi, Johann Issak, Michael P Carpenter, Hoang Thi Ha, Chris Sullivan, Yasutaka Yamamoto, Farhan S Babra, James J Carroll, Guillaume Gey, Li Guangshun, Natsumi Ichige, Chihiro Iwamoto, Azusa Inoue, Wang Jianguo, Minliang Liu, Md. Sazedur R Laskar, Shumpei Noji, P. von Neumann-Cosel, CAGRA colloboration
The study of high-spin states through in-beam γ-ray spectroscopy provides valuable information about the level structures and properties of nuclei. The 40Ca, being doubly-magic and spherical in its ground state, has multiple deformed band structures based on excited state configurations [1, 2]. In this work, light-ion scattering reactions are used to populate the level structures in 40Ca, employing particle-γ coincidence technique which is one of the powerful spectroscopic probe to study weak reaction channels. An experiment was performed at RCNP, Osaka University to study the yrast and non-yrast states in 40Ca using inelastic scattering reaction 40Ca(6Li, 6Li*) 40Ca* with incident beam energies of 130 MeV and 600 MeV. The de-excited γ-rays were detected using the CAGRA HPGe detector array in coincidence with the scattered particles detected with the Grand Raiden spectrometer. The progress of the analysis and also the future planned experiment to explore the nuclear shapes in 40Ca will be introduced. [1] E. Ideguchi et al., Phys. Rev. Lett. 87, 222501 (2001). [2] C. J. Chira et al., Phys. Rev. C67, 041303 R (2003). |
Thursday, October 25, 2018 10:15AM - 10:30AM |
DB.00005: Study of shape coexistence and shape evolution by using RI beam induced fusion reaction combined with CAGRA Atsuko Odahara Study of shape evolution as a function of spin and isospin, as well as shape coexistence is one of the most important subjects to understand the competition between single-particle-like and collective-like modes in various deformed nuclear systems. To investigate shape evolution as an increase of spin, we have searched isomers which are caused by large difference of nuclear shapes for excited states below and above the isomer. Experiments were performed by using low-energy (around 10 MeV/u) RI beam induced fusion reaction at RCNP secondary beam line (EN beam line) combined with g-ray detector array, such as CAGRA and so on. Low-energy RI beam induced fusion reaction enables to extend the limit of mass region to study high-spin states which it is difficult to populate by using stable beam and stable target. Although RI beam has very small intensity of around 105 pps, high-S/N measurement has been carried out by event-by-event analysis which can select events correlating RI beam. In my talk, I will present some results of our CAGRA experiment with the low-energy 17N RI beam induced fusion reaction at EN beam line. |
Thursday, October 25, 2018 10:30AM - 10:45AM |
DB.00006: In-beam γ-ray spectroscopy of the odd-odd nucleus 186Re Filip Kondev Excited states in 186Re were investigated in two separate experiments using 186W(d,2n) reactions at beam energies of 12.5 MeV and 14.5 MeV. Two- and three-fold γ-ray coincidence data were collected using the CAESAR and CAGRA spectrometers, respectively, each composed of Compton-suppressed HPGe detectors. Analysis of the data revealed rotational bands built on several two quasiparticle intrinsic states, including a long-lived Kπ=(8+) isomer. The excitation energies of the observed intrinsic states were compared with results from multi-quasiparticle blocking calculations, based on the Lipkin-Nogami pairing approach, that included contributions from the residual proton-neutron interactions. |
Thursday, October 25, 2018 10:45AM - 11:00AM |
DB.00007: Study of deformed structure in mass 40 region using CAGRA gamma-ray spectrometer Eiji Ideguchi, Yong-De Fang, Michael P Carpenter, Rin Yokoyama, Shin'ichiro Michimasa, Takeshi Koike, Hooi Jin Ong, Yassid Ayyad, Shumpei Noji, Nori Aoi, Dinh Trong Tran, Azusa Inoue, Chihiro Iwamoto, Hoang Thi Ha, Phaikying Chan, Tomokazu Suzuki, Atsushi Tamii, Yasutaka Yamamoto, Rikuto Yanagihara, Atsuko Odahara, Shinnosuke Kanaya, Hiroki Nishibata, Hiroshi Kanaoka, Shaofei Zhu, CAGRA collaboration In mass 40 region of atomic nuclei, onset of various structures, such as superdeformation, shape co-existence, cluster structure, etc., is expected. In order to clarify such structure, we are pursuing a systematic study of high-spin states by in-beam gamma-ray spectroscopy. In the previous studies, superdeformed rotational band was observed at 36,40Ar, 40Ca, and 44Ti. Among them, it is not yet well understood at 44Ti and high-spin states are known up to 12+ level. To understand the deformed structure of 44Ti and also neighboring isotopes, we performed gamma-ray spectroscopy using 24Mg+24Mg reaction. Experiment was performed at cyclotron facility in RCNP, Osaka University. A 104MeV 24Mg beam was irradiated on the 24Mg target of 0.5mg/cm2 thickness. Gamma rays and charged particles were measured by CAGRA gamma-ray spectrometer and Si-Ball charged particle filter, respectively. CAGRA is an array of 16 Clover type Ge detectors with BGO Compton suppression shield, constructed by international collaboration between Japan, the US and China. Recent analysis results on high-spin states of mass 40 region will be presented. |
Thursday, October 25, 2018 11:00AM - 11:15AM |
DB.00008: Nuclear structure studies of the heaviest actinides and super-heavy elements with the CAGRA array at the JAEA Tandem Riccardo Orlandi, Eiji Ideguchi, Michael P Carpenter, Hiroyuki Makii, Katsuhisa Nishio, Kentaro Hirose, Masato Asai, Kazuaki Tsukada, Nori Aoi, Yong-De Fang, Minliang Liu, Shaofei Zhu, Dariusz Seweryniak, Filip G Kondev, Torben Lauritsen, Guangshun Li The search for the “island of stability” (IoS) and the production of super-heavy elements is one of the main goals of nuclear research. Different models disagree on the location and extent of the spherical IoS, and a way to obtain information on the single-particle orbitals near the IoS is to study well-deformed, lighter nuclei around fermium and nobelium, which are poorly known. The deformation causes in fact the spherical single-particle states to split and states originating from high-lying spherical orbitals come close to the Fermi surface in these systems. The exceptional availability of a radioactive 254Es target at the JAEA Tandem Accelerator in Tokai, Japan, provides an excellent opportunity to investigate the structure of these nuclei. By irradiating 254Es with heavy-ion beams, via Coulex and multi-nucleon transfer reactions, the γ-ray spectroscopy of neutron-rich isotopes of einsteinium (Z=99), fermium (Z=100), mendelevium (Z=101) and nobelium (Z=102) will be attempted. The γ-rays emitted by these isotopes will be detected using a compact array of 8 clover detectors from the CAGRA collaboration. |
Thursday, October 25, 2018 11:15AM - 11:30AM |
DB.00009: Nuclear structure studies of 254Es region by Coulomb excitation gamma-ray spectroscopy Rikuto Yanagihara, Eiji Ideguchi, Katsuhisa Nishio, Riccardo Orlandi, Hiroyuki Makii, Masato Asai, Kentaro Hirose, Kazuaki Tsukada, Atsushi Toyoshima, Tetsuya K. Sato, Pham Thanh Tung, Nori Aoi, Kumar Raju Mukhi, Yasutaka Yamamoto, Hoang Thi Ha, Asahi Kohda, Shigeru Kubono, Shinichiro Michimasa, Takeshi Koike, Naohito Iwasa, Michael P Carpenter, Krzystof Rykaczewski, Fang Yong-De, Partha Chowdhury, CAGRA collaboration What is the limit of high Z nucleus, where is the island of stability, is one of the focus of nuclear In order to access such shell structure, we are focusing on the deformed nucleus of the heavy mass region including Es isotopes. By studying the excited states, spin and parity, and deformation, we will be able to access the single-particle orbital which is supposed to generate new shell structure at Z=114, 120, N=184 and try to investigate nuclear shell structure in the super-heavy mass region. Coulomb excitation experiment at the Tokai Tandem Accelerator Laboratory of JAEA is planned to measure B(E2) values of low-lying states in 254Es and to deduce the deformation. Unknown high-lying states of 254Es will be also investigated for further understanding of nuclear structure in this region. We obtained 254Es via an international collaboration with ORNL. CAGRA will be used to measure the gamma rays from 254Es. Experimental plan and preparation progress will be presented. |
Thursday, October 25, 2018 11:30AM - 11:45AM |
DB.00010: CAGRA + Grand Raiden campaign at RCNP Nobuyuki Kobayashi, on behalf of CAGRA+GR collaboration CAGRA + Grand Raiden campaign-type experiments were performed at the Research Center for Nuclear Physics (RCNP) in October-December, 2016. The clover array CAGRA was located at the target position of the high-resolution spectrometer, Grand Raiden (GR), for coincidence measurement between a particle and gamma rays. In order to realize low-background gamma-ray detection at the target position in coincidence with light ions scattered at forward angles, we combined CAGRA with the Grand RAiden Forward mode (GRAF) beam line. The experiments aimed at studying a) the nature of the pygmy dipole resonances, b) isovector spin-flip responses of nuclei for astrophysical neutrino-nucleus inelastic scattering, c) gamma-transitions in the super-deformed band-head, and d) excitation of high-spin states via light-ion reactions. In this talk, we will present the summary of the experiments and discuss recent results from the CAGRA+GR collaboration.
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