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 EM: Nuclear Structure A=6-20 Part II |
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Chair: Frederic Sarazin, Colorado School of Mines Room: Hilton Queen's 6 |
Thursday, October 25, 2018 7:00PM - 7:15PM |
EM.00001: Evidence of enhanced nuclear radius of the α halo states via α + 12C inelastic scattering Makoto Ito, Makoto Nakao In light nuclear systems, it is well known that cluster structures appear in excited states. One of characteristic properties in the cluster states is a prominent extension of the nuclear radius. Typical examples are the 02+ and 22+ states in 12C, which have the developed 3α cluster structure. The radii of these states are expected to be more enhanced by about 60 % than the radius of the ground state but the direct measurement of their radius is completely impossible. In the present study, we focus on the 22+ state and demonstrate that the evidence of the enhanced radius in the 22+ state can be clearly identified in the differential cross section of the α + 12C inelastic scattering. We have performed the microscopic coupled-channel (MCC) calculation for the α + 12C inelastic scattering at the incident energy of E/A= 96.5 MeV. From the MCC calculation, we have found that the angular distribution of 22+ is prominently shrunk in comparison to the 21+ distribution. This shrinkage structure can be attributed to the enhanced nuclear radius in the 22+ state. In the present report, we will discuss the relation of the nuclear radius and the differential cross section in the 3α final channel. |
Thursday, October 25, 2018 7:15PM - 7:30PM |
EM.00002: Coulomb shift in two-center mirror systems Makoto Nakao, Hajime Umehara, Shuichiro Ebata, Makoto Ito The so-called cluster structures appear in the excited states of light nuclear systems, and the structures have been extensively investigated in N = Z self-conjugate systems. In the present report, we focus on a mirror system in non self-conjugate systems (N ≠ Z) and demonstrate that the Coulomb shift of the mirror systems is a new probe to catch the sign of the clustering phenomena. Here we discuss the Coulomb shift in the energy levels of the mirror systems, such as 18O = α + 14C and 18Ne = α + 14O. We have applied the orthogonality condition model (OCM) to these systems. The OCM calculation predicts that the Coulomb shift for the resonant 0+ states is prominently reduced in comparison to the shift for the low-lying bound states. This reduction is induced by the development of the α clustering. Therefore, this result strongly suggests that the Coulomb shift is new probe to identify the cluster degrees of freedom. In this report, we will discuss the enhanced monopole transition, which is another probe to identify the cluster degrees of freedom in detail. |
Thursday, October 25, 2018 7:30PM - 7:45PM |
EM.00003: ``Container'' evolution of nuclear clustering in 16O Yasuro Funaki We introduce the so-called THSR wave function to describe various nuclear states with cluster correlation[1]. Its importance, applicability, and usefulness are extensively discussed in this contribution. The THSR wave function is a promising model to give a comprehensive understanding of cluster states, from the ground states with cluster correlation, ordinary localization of clusters, up to their dilute gaslike configuration. The model wave function explains the evolution of cluster states, from the compact to dilute ones, as an evolution of ``container'' of constituent clusters. This container evolution picture is demonstrated for 16O case by using the THSR ansatz. The ground state with the 4-alpha tetrahedral correlation, alpha+12C cluster states, and the 4-alpha condensate with gaslike configuration are revealed and beautifully explained in the THSR framework[2]. [1] Y. Funaki, H. Horiuchi, A. Tohsaki, Prog. Part. Nucl. Phys. 82, 78 (2015).
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Thursday, October 25, 2018 7:45PM - 8:00PM |
EM.00004: Precision half-life measurement of 18N Shun Iimura, Miki Fukutome, Mariko Hisamatsu, Hajime Umehara, Shinnosuke Kanaya, Hiroki Nishibata, Atsuko Odahara, Tadashi Shimoda, Takafumi Hara, Masaharu Kinoshita, Ryo Nakajima, Rei Shudo, Ryo Wakabayashi Half-life of neutron-rich nuclei is essential for r-process nucleosynthesis in supernova, or neutron star merger, which produces heavy nuclei by neutron capture reaction and β-decay. However, since it is difficult to produce them and to measure short half-life of 〜100 ms, it has not been determined yet for many neutron-rich nuclei. |
Thursday, October 25, 2018 8:00PM - 8:15PM |
EM.00005: Study of neutron unbound states in 18O by β-delayed neutron decay of 18N Hajime Umehara, Shun Iiumra, Shinnosuke Kanaya, Hiroki Nishibata, Atsuko Odahara, Tadashi Shimoda, Masaharu Kinoshita, Rei Shudo, Ryo Nakajima, Takafumi Hara, Ryo Wakabayashi The neutron-unbound states in 18O have been investigated in various types of experiments, however, the data are still in disagreement with each other. The latest β-delayed neutron data in 2005 showed a large missing neutron intensity. We have performed an experiment to measure the β-delayed neutron decay of 18N for the unbound states in 18O with a newly developed TOF detector system consisting of large and small plastic scintillators for a wide neutron energy range (100 keV- 4 MeV), which was designed for spectroscopy of very neutron-rich nuclei far from the stability. The radioactive nucleus 18N was produced at RCNP, Osaka University by the direct reaction of 9Be(18O,18N)9B at 9.4 MeV/u. The secondary 18N beam was isotope-separated by the fragment separater and transported to a gold stopper foil. The 18N beam intensity of ~1300 pps with purity of ~98% was obtained with the primary beam intensity of 3.2 eμA. The β ray and the γ ray were detected by thin plastic scintillators and Ge detectors, respectively. With such system we could find a new low-energy neutron peak (En~355 keV) with large intensity, which may solve the missing neutron intensity problem. Search for other small peaks is in progress. A revised decay scheme of 18N is presented based on β-n-γ coincidence relation. |
Thursday, October 25, 2018 8:15PM - 8:30PM |
EM.00006: Study of 19C using single-nucleon knockout Jongwon W Hwang, Sunji Kim, Yoshiteru Satou, Nigel A Orr, Takashi Nakamura, Yosuke Kondo, SAMURAI Dayone Collaboration For decades, the p-sd-shell nuclei have been a useful tool to study shell evolution toward the dripline. The spectroscopic study of 19C, a one-neutron halo near the neutron dripline, is an important testing ground for the recent shell-model interactions in the p-sd shell space, especially for neutron-rich nuclei. The unbound states of 19C were studied using single-nucleon knockout at RIBF, RIKEN. 19C was produced from 20C (20N) beam by one neutron (proton) knockout. The relative energy spectra and parallel momentum distributions were reconstructed by detecting all decay products, 18C and a neutron, using the SAMURAI spectrometer and NEBULA neutron array. As a result, 5/2+1 was confirmed to locate just above S1n and 1/2-1 was also discovered in the neutron-knockout channel. Additional high-lying resonance over S3n was observed in the proton-knockout channel, which might involve a proton-excited 18C core. In this talk, the details of observed states and the discussion in the context of shell-model calculations will be reported. |
Thursday, October 25, 2018 8:30PM - 8:45PM |
EM.00007: An Analysis of the 18Fg,m(d,p)19F reactions in the Rotational Model. Augusto O Macchiavelli, Heather L Crawford, Christopher M Campbell, Roderick M Clark, Mario Cromaz, Paul Fallon, Michael D Jones, I-Yang Lee, Marco Salathe
In a recent HELIOS[1] measurement, the (d,p) reaction on 18F, from both the ground (1+) and isomeric (5+) states [2] was used to study members of the ground-state rotational band in 19F. Comparison of the derived Spectroscopic Factors with shell model calculations within the sd shell, provided a nice confirmation of the single-particle–collective duality observed in the structure of atomic nuclei. In this work we exploit this apparent duality in an analysis of the their experimental results in terms of the rotational model. We consider the structure of 18,19F in terms of Nilsson single-particle orbits originating from the sd spherical levels and calculate the (d,p) spectroscopic strengths to 19F from both the ground and isomeric states following the framework reviewed in [3]. Perhaps not surprisingly, our results show good agreement with the experiment and the shell model. [1] A. Wuosmaa, et al. Nucl. Instrum. Methods, A580, 1290 (2007). [2] D. Santiago-Gonzalez, et al. Phys. Rev. Lett. 120, 122503 (2018). [3] B. Elbek and P. O. Tjøm, in Advances in Nuclear Physics, M. Baranger and E. Vogt eds. (Springer, Boston, MA, 1969). |
Thursday, October 25, 2018 8:45PM - 9:00PM |
EM.00008: New trial wave function for the nuclear cluster structure of nuclei Bo Zhou In the constructed new trial wave function, by removing the spurious center-of-mass |
Thursday, October 25, 2018 9:00PM - 9:15PM |
EM.00009: Search for alpha-cluster state in 20Ne Hidetoshi Akimune, Motoki Murata, Takahiro Kawabata, Tatsuya Furuno, Yuki Fujikawa, Kento Inaba, Miho Tsumura, Makoto Kinoshita, Kazuya Kitamura, Shugo Nagamine, Kyoko Nosaka We searched for a state consisting of many α clusters in 20Ne excited state. Results of an experiment on the emulsion exposure to medium-heavy nuclei of a few GeV have been reported. In this experiment, events that collapse into a number of α particles have been observed. The characteristic of these events is that the relative momentum of released alpha particles relative to the incident nuclei is very small and the momentum transfer to incident particles is small. We considered that this reaction might be excitation of an alpha-cluster state by Coulomb excitation by heavy nuclei in the emulsion. The experiment has been carried out at NewSUBARU electron storage ring facility with an incident laser Compton scattering (LCS) photon beam and the active gas target MAIKo. |
Thursday, October 25, 2018 9:15PM - 9:30PM |
EM.00010: Structure of neutron-rich carbon isotopes: shell evolution and two-neutron-halo at the dripline Toshio Suzuki, Takaharu Otsuka, Naofumi Tsunoda Structure of neutron-rich carbon isotopes are studied by shell-model with new shell-model Hamiltonians, SFO-tls [1] and YSOX [2], as well as microscopic G-matrix including an extended version [3] with contributions from three-nucleon forces. Evolution of effective single-particle energies and ground-state energies is discussed with emphasis on the roles of tensor and three-nucleon forces. Proton shell gap energies of the isotopes support the new magicity at $Z$=6 [4]. Structure and formation of two-neutron halo at the dripline nucleus $^{22}$C are studied by a three-body model with the use of low-energy limit of neutron-neutron interaction [5]. Relation between two-neutron separation energy and halo radius is derived assuming a correlated $^{20}$C-core with appreciable 2s$_{1/2}$-shell admixtures. The three-body model is extended to the case of mixed configurations of 2s$_{1/2}^2$ + 1d$_{5/2}^2$, and applied to $^{17}$B.
[1] T. Suzuki and T. Otsuka, Phys. Rev. C 78, 061302 (2008). [2] C. Yuan et al., Phys. Rev. C 85, 064324 (2012). [3] M. Hjorth-Jensen et al, Phys. Rep. 261, 125 (1995); N. Tsunoda et al., Phys. Rev. C 95, 021304 (R) (2017). [4] D. T. Tran et al., Nature Communications 9, 1594 (2017). [5] T. Suzuki and T. Otsuka, Physics Letters B 753, 199 (2016). |
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