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 EG: Nuclear Structure A=100-140 |
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Chair: Kathrin Wimmer, The University of Tokyo Room: Hilton King's 3 |
Thursday, October 25, 2018 7:00PM - 7:15PM |
EG.00001: Precise αK and αT Internal Conversion Coefficients Measurements of 39.752(6)-keV E3 Transition in 103mRh: Test of Internal Conversion Theory N. Nica, J. C. Hardy, V. Horvat, V. E. Iacob, H. I. Park, T. A. Werke, K. J. Glennon, C. M. Folden III, M. B. Trzhaskovskaya We used the γ- to x-ray ratio method to measure αK and αT for the 39.752(6)-keV E3 transition in 103mRh, which we populated by both the β- decay of 103Ru and the ε decay of 103Pd. Based on the particularities of the two level schemes, from 103Ru decay one can extract both αK and αT, while the 103Pd decay provides a relationship between αK and αT, which is useful as a consistency check. Sources of 103Ru and 103Pd were prepared by neutron activation, and measured for about four months. From 103Ru decay we extracted αK = 140.8(39) and αT = 1428(29); then, using this value of αK, we obtained αT = 1438(37) from 103Pd decay. All the results are preliminary. When compared with Dirac-Fock calculations, these results are in statistical agreement with the version of the theory that incorporates the effect of the K-shell atomic vacancy, αK = 135.3(1) and αT = 1404(1), and disagree with the version that does not, αK = 127.5(0) and α = 1388(2). This is consistent with the results from the series of three E3 and six M4 transitions that we measured previously, and extends our measurements to the lowest Z we have studied so far. |
Thursday, October 25, 2018 7:15PM - 7:30PM |
EG.00002: Chiral vibrations and collective bans in 104,106Mo Brooks M Musangu, Enhong Wang, Joseph H Hamilton, Stefan Frauendorf, Gowhar Bhat, Javid Sheikh, Christopher J Zachary, Jonathan M Eldridge, Akunuri V Ramayya, John Rasmussen, Yixiao Luo, Gurgen M Ter-Akopian, Yuri Oganessian, Shengjiang Zhu New theoretical calculations of 104Mo and 106Mo have been conducted. Reduced transition probabilities for the proposed chiral bands in both isotopes have been calculated from TPSM and are found in good agreement with the experimental data. High spin states of the neutron-rich triaxial 104Mo nucleus have been reinvestigated by analyzing both γ-γ-γ and γ-γ-γ-γ coincidence data in the spontaneous fission of 252Cf with Gammasphere. A new ΔI=1 band was discovered. The new band is proposed to have a tentative 5− band head and form a class of chiral doublets with another 4− band previously found by our group. Angular correlation measurements have been performed to determine spin and parity of the 4− chiral band head. The energies of the two sets of chiral bands are very similar to the chiral bands observed in 106Mo, e.g. the two 5− levels in 104Mo are at 2211.9 and 2276.8 keV with ΔE=65 keV and in 106Mo, 1952.4 and 2090.6 keV with ΔE=138 keV. Now at every spin 5−, 6−, 7−, 8−, the separation energies of the same spin states are about a factor of two smaller than in 106Mo. This indicates even better agreement with expectations for two sets of chiral bands. |
Thursday, October 25, 2018 7:30PM - 7:45PM |
EG.00003: Identification of the s1/2 band in 109Ru Enhong Wang, Joseph H Hamilton, Akunuri V Ramayya, Christopher J Zachary, Jonathan M Eldridge, Brooks M Musangu, Acan Dai, Furong Xu, Jae-Kwang Hwang, Yixiao Luo, John Ramussen, Shengjiang Zhu, Yuri Oganessian, Gurgen M Ter-Akopian The 109Ru nucleus has been studied from the spontaneous fission of 252Cf by using Gammasphere at LBNL. A total of 11 new transitions have been observed in the γ-γ-γ and γ-γ-γ-γ coincidence data. These new transitions form a band structure in this nucleus similar to 111Ru. Potential energy surface calculations are performed for this nucleus. The calculations and systematic comparison with the neighboring Ru nuclei indicate that this new band is possibly originating from the neutron s1/2 orbital.
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Thursday, October 25, 2018 7:45PM - 8:00PM |
EG.00004: Study of neutron emission properties after muon capture on palladium isotopes Takeshi Y Saito, Megumi Niikura, Teiichiro Matsuzaki, Hiroyoshi Sakurai, Shoichiro Kawase, Yoshitaka Kawashima, Takuma Koiwai, Michael K Kubo, Keishi Matsui, Satoru Momiyama, Yoshiharu Mori, Akihiro Nambu, Kazuhiko Ninomiya, Hideaki Otsu, Akira Sato, Xiaohui Sun, Akihiro Taniguchi, Dai Tomono, He Wang, Yasushi Watanabe, Kathrin Wimmer The nuclear muon capture reaction is an analogue process of electron capture decay. Contrary to the electron capture, the daughter nucleus of the muon capture can be excited up to around 50 MeV owing to the muon rest mass of 106 MeV/c2, and thus decays by emitting neutrons and γ rays. The properties of excited states created by the muon capture, such as excitation energies and neutron emission probabilities, have not been well understood. In this study, we measured the neutron energy distribution and multiplicity after muon capture reactions on palladium isotopes. A liquid scintillator array named SEAMINE was newly designed and constructed. SEAMINE consists of 21 liquid scintillators and seven BaF2 scintillators in order to measure the neutron time-of-flight. A digital data acquisition system enabled the n – γ discrimination by the pulse shape of the liquid scintillators. The experiments on five isotopically enriched palladium targets (A = 104, 105, 106, 108 and 110) were conducted on February 2017 and January 2018 at the MuSIC beamline, RCNP, Osaka University. We will report on the experiments and show preliminary results. |
Thursday, October 25, 2018 8:00PM - 8:15PM |
EG.00005: Penning trap mass spectrometry Q value determinations for investigating ultra-low Q value β-decays Matthew Redshaw, Georg Bollen, Fritz Buchinger, Jason A Clark, Martin Eibach, Nadeesha D Gamage, Kerim Gulyuz, Alec S Hamaker, Christopher J Izzo, Rodney Orford, Daniel J Puentes, Ryan J Ringle, Rachel Sandler, Guy Savard, Kumar Sharma, Isaac Yandow Ultra-low Q value (ULQ) β-decays, in which the parent decays to an excited state of the daughter with a Q<∼1 keV, are of interest because they can provide a testing ground for atomic interference effects in nuclear β-decay, and because of their potential as candidates for direct neutrino mass determination experiments. The lowest known Q value β-decay is that of 115In to the 3/2+ state in 115Sn with Qβ = 155(24) eV. Additional candidates, such as 115Cd and 135Cs have been identified by evaluating atomic mass and nuclear energy level data. We have also identified 112,113Ag, 89Sr and 139Ba as potential candidates. Current atomic mass data for the parent and/or daughter isotopes in these cases are not precise enough to determine whether the ULQ decay branches are energetically allowed. Here we present preliminary Q value measurement results for 112,113Ag, 115Cd, 89Sr and 139Ba using Penning trap mass spectrometry with the CPT mass spectrometer at Argonne National Lab and LEBIT at the National Superconducting Cyclotron Lab. |
Thursday, October 25, 2018 8:15PM - 8:30PM |
EG.00006: Proton resonance scattering of a shape-coexistence nucleus 118Sn Rieko Tsunoda, Nobuaki Imai, Takashi Teranishi, Masanori Dozono, Kotaro Iribe, Noritaka Kitamura, Satoshi Sakaguchi, Hidemitsu Sakai, Kazuki Ueno It is well known that shape coexistence was observed in stable even-even Sn(Z=50) nuclei, and the even-odd neighbouring nucleus may have a hint of the structure. So far, some single-particle like states in 119Sn were observed by measuring (d,p) reaction on 118Sn. Though the isobaric analog resonances corresponding to the low-lying states in 119Sn were already measured for the spectroscopic information on 119Sn, there are some missing resonances expected from (d,p) reaction. It is necessary to measure the excitation function of proton-elastic resonance scattering with the wide energy range to understand the structure of 119Sn. The proton resonance elastic scattering on 118Sn yields the spectroscopic information of the single particle state coupled to the ground state of 118Sn. In addition, the inelastic channels will also tell the fruitful information. The experiment was carried out at the tandem accelerator facility in Kyushu Univ. An enriched 118Sn target was irradiated by a proton beam while varying the beam energy from 7 to 10 MeV. The reaction channel was identified by the outgoing angle and energy of scattered protons measured by single-sided silicon strip detectors placed at 140-160°lab. We will present the details of the experimental setup and the preliminary result. |
Thursday, October 25, 2018 8:30PM - 8:45PM |
EG.00007: Decay Spectroscopy of Neutron-rich 129Cd with the GRIFFIN Spectrometer Yukiya Saito, Nikita Bernier, Iris Dillmann, Reiner Kruecken Nuclei around doubly magic 132Sn are of particular interest in nuclear structure as well as nuclear astrophysics. Their properties provide important input for the r-process as waiting-point nuclei. For example, their shell structures and half-lives affect the shape of the second r-process abundance peak at A∼130. In terms of nuclear structure, the evolution of single-particle levels near shell closures is ideal for testing the current nuclear models far from stability. There have been two studies on 129Cd, however, the level schemes of 129In have large discrepancies [1,2]. Also, many of the spins of the excited states remain unclear. Therefore, the main purpose of the present study is to resolve the disagreements in the reported level schemes and to determine the properties of the energy states. The experiment was performed at the ISAC facility of TRIUMF, Canada. The data was collected with the GRIFFIN spectrometer, along with the β-particle detector SCEPTAR. The high statistics and the high sensitivity of the detectors allowed us to perform a detailed and precise spectroscopy. The results of the analysis, including 29 new transitions and 5 new excited states, will be discussed. [1] Acta Phys. Pol. B 40, 437 (2009). [2] PRC 91, 054324 (2015). |
Thursday, October 25, 2018 8:45PM - 9:00PM |
EG.00008: Neutrinoless double-beta decay rates around mass 130 in the nuclear shell model Ai Uehara, Naotaka Yoshinaga, Kota Yanase, Chinatsu Watanabe The double beta decay is a second order process of the weak interaction which converts two neutrons into two protons. There are possibly two modes of the double-beta decay. The 0ν mode (0νββ), in which no neutrinos and only two electrons are emitted, can only take place if the neutrino is a massive Majorana particle. It demands an extension of the Standard Model since it violates the lepton number conservation. Thus, the observation of the 0νββ decay is considered as one of the best probes for physics beyond the Standard Model. Despite intensive experimental efforts the 0νββ decay has not yet been observed. The 0νββ decay half-life is given by a phase-space factor, the effective mass of the electron neutrino, and the nuclear matrix element (NME). Our attention is focused on calculating the NMEs. Many theoretical attempts have been made to calculate the NMEs and the resulting half-lives. We carry out the nuclear shell model calculations for nuclei with mass 136 and 130. Energy levels and transition rates are compared with the experimental data. Using the wave functions thus obtained, nuclear matrix elements for the neutrinoless double-beta decay are estimated. It turns out that the nuclear matrix elements are sensitive to the ground state correlations. |
Thursday, October 25, 2018 9:00PM - 9:15PM |
EG.00009: Studies of the Stable Xe Isotopes from Inelastic Neutron Scattering and Shell Model Calculations Erin E Peters, Benjamin P Crider, Andrew E Stuchbery, Pieter Van Isacker, Steven W Yates
The nuclear structure of the stable Xe isotopes is of interest for multiple reasons. First, these isotopes span a transitional region and, in general, have been poorly studied. Moreover, these nuclei play prominent roles in the ongoing searches for neutrinoless double-beta decay (0νββ). 136Xe is a candidate in the search for 0νββ, 134Xe is a contaminant in these experiments, and 130Xe is the daughter in the double-β decay of 130Te. Comprehensive structural information provides crucial tests for the nuclear structure models used in calculating the nuclear matrix element for 0νββ and the neutrino mass.
We have studied 130,132,134,136Xe at the University of Kentucky Accelerator Laboratory using inelastic neutron scattering (INS) from enriched solid XeF2 samples. The γ-ray angular spectroscopic measurements yielded new information, which allowed the determination of reduced transition probabilities.
In addition to these measurements, shell model calculations were performed for the positive-parity states in 132,134,136Xe. The comparison with experimental data is quite good overall. |
Thursday, October 25, 2018 9:15PM - 9:30PM |
EG.00010: Nucleosynthesis of “light” heavy elements in neutrino-drive winds. Role of (a,n) reaction rates. Almudena Arcones, Julia Bliss, Fernando Montes, Jorge Pereira Neutrino-driven winds following core-collapse supernovae explosions have been proposed as a possible scenario where the synthesis of the so-called “light r elements” (between Fe and Ag) might occur. Steady-state model calculations, combined with nucleosynthesis reaction networks indicate a substantial sensitivity of the element abundances to (a,n) reaction rates and the astrophysical conditions (e.g. alpha-to-seed and neutron-to-seed ratios). In this presentation, I will summarize the most relevant aspects of our study, emphasizing the (a,n) nuclear reactions that need to be measured. Preliminary experimental results on some of these reactions will be briefly discussed.
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