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 CB: Nuclear Structure A=6-20 Part I |
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Chair: Ritu Kanungo, St. Mary's University Room: Hilton Kohala 1 |
Wednesday, October 24, 2018 7:00PM - 7:15PM |
CB.00001: Role of α-cluster structure in electric-dipole excitations of 6Li Shuji Satsuka, Wataru Horiuchi 4He (α)-cluster structure often appears in light nuclei, for example, 6Li is well approximated by a three-body model of α + p + n [1]. Recently, the photoabsorption cross sections of 6Li was measured showing two-peak structure [2]. Since the reaction occurs mainly through the electric-dipole (E1) transition, the lower and higher peaks were conjectured as the giant dipole resonance (GDR) of 6Li and the GDR of α cluster in 6Li, respectively. If this conjecture is true, making its excitation mechanism clear is important because it can appear in the nuclei in which an α cluster is well developed. In this work, we perform a fully microscopic six-body calculation that can take the excitation of α cluster into account. We calculate the E1 transition strengths, E1 transition densities and α-spectroscopic factors in order to discuss the E1 excitation mechanism and the role of α cluster in 6Li.
References
[1] W. Horiuchi and Y. Suzuki, Phys. Rev. C 76, 024311 (2007) [2] T. Yamagata et al., Phys. Rev. C 95, 044307 (2017) |
Wednesday, October 24, 2018 7:15PM - 7:30PM |
CB.00002: 1st Measurement of the B(E2) of the 1/2- ->3/2- transition in Be-7 Samuel L Henderson, Tan Ahn, Anna Simon, Wanpeng Tan, Patrick D O'Malley, James J Kolata, Daniel W Bardayan, Matthew Hall, Jacob Allen, Xuyang Li, Ramon O Torres-Isea, Jay Riggins Several ab-initio methods have made predictions on the E2 transition strengths for the first excited state transition in Be-7 This Be-7 B(E2) has never been measured and the ab-initio results vary depending on nuclear structure assumptions made. This measurement will help provide guidance on the structures of importance in this nucleus, especially considering the role clustering plays. To measure this E2 transition strength, a Coulomb Excitation experiment was performed at the University of Notre Dame. Be-7 was produced and separated using TwinSol, two solenoid magnets designed to separate out ions of interest. A beam of Be-7 ions were scattered off a gold target and the gamma rays from the inelastically scattered ions were detected using six clover Ge detectors. The results for the E2 transition strength and its comparison to multiple Ab-Initio approaches will be shown. In addition, Geant4 simulations for a future experiment with Li-8 will be shown, with the goal of both measuring the B(E2) value and of determining the effect virtual E1 excitations have on the overall Coulomb Excitation cross-section. |
Wednesday, October 24, 2018 7:30PM - 7:45PM |
CB.00003: Re-measurement of the 4He(8He,8Be) reaction Shoichiro Masuoka, Susumu Shimoura, Motonobu Takaki, Shin'ichiro Michimasa, Shinsuke Ota, Masanori Dozono, Chihiro Iwamoto, Keita Kawata, Noritaka Kitamura, Motoki Kobayashi, Ryo Nakajima, Hiroshi Tokieda, Rin Yokoyama, for the SHARAQ10 collaboration The 4He(8He,8Be)4n reaction has been measured again at 186 AMeV for studying the 4n system (tetra-neutron). interest on the tetra-neutron system was attracted by a candidate resonance in ref. [1]. A new measurement with higher statistics and better accuracy are anticipated for more detailed study of the tetra-neutron system. The intensity of the 8He beam was approximately twice that in the previous experiment (3.5 × 106 cps at the target). For the absolute calibration of the missing-mass, we measure the 1H(3H,3He) reaction at 310 AMeV without changing the settings of the beamline magnets and the SHARAQ spectrometer, since the magnetic regidities of the 186 AMeV 8He and the 310 AMeV 3H are the same. In the preliminary result, the accuracy of the excitation energy of 4n is evaluated to be approximately 100 keV. In this contribution, we will report the current status of the data analysis of the present experiment for understandings of the tetra-neutron system. [1]: K. Kisamori et al., Phys Rev. Lett. 116, 052501 (2016). |
Wednesday, October 24, 2018 7:45PM - 8:00PM |
CB.00004: Measurement of 9He ground and excited states Daniel Votaw, Paul A Deyoung, Thomas Baumann, Anthony N Kuchera, Cole F Persch, Tan Phan, Michael R Thoennessen, The MoNA Collaboration The low-lying structure of exotic nuclide 9He is still a subject of experimental and theoretical debate. Experiments have not yet been able to provide a consistent picture of the existence of resonances, nor their spin and parity assignments. An extreme independent particle shell model approach suggests that the ground state of 9He resembles a 8He core coupled to a valence neutron in the 0p1/2 shell model orbital, leaning to a total spin and parity of (1/2)-. However systematics along the N = 7 isotone, and certain theoretical calculations suggest that there may be parity inversion in the ground state of 9He, implying that the total spin and parity would be (1/2)+. A recent experiment at the NSCL populated low-lying 9He resonant states using two different beams and knockout reactions (11Be(-2p) and 12B(-3p)) in order to simultaneously constrain both the 0p1/2 and 1s1/2 valence neutron orbitals. Preliminary results of the analysis will be presented. |
Wednesday, October 24, 2018 8:00PM - 8:15PM |
CB.00005: low-energy dipole excitation modes in 10Be Yuki Shikata, Yoshiko Kanada-En'yo, Hiroyuki Morita In the past a few decades, research on neutron excess nuclei has been progressing, and a variety of novel phenomena which can not be seen in N = Z nuclei are found. One of them is low energy dipole (LED) excitation that appears in the energy region lower than the giant dipole resonance. It has not been yet clarified what type of excitation modes contributes to the LED. As a candidate for the excitation mode of LEDs, the so-called “pigmy mode”, the excess neutron mode oscillating in opposite phases with respect to the core has been proposed. However, in recent years, a new-type of excitation mode, “toroidal dipole (TD) mode”, which has hydrodynamic vortical character has been attracting an interest. In addition, it is expected that cluster excitation mode contributes isoscalar LED excitations. We investigated the LED excitation mode in terms of cluster structure in 10Be with 6He + α and 2α + nn GCM. As a result, we obtain some LED strengths. We reveal TD mode occurred by rotation of deformed 6He cluster. Also, cluster excitation contributes isoscalar dipole excitation. In addition, we discuss contribution of cluster excitation to toroidal excitation mode. |
Wednesday, October 24, 2018 8:15PM - 8:30PM |
CB.00006: Study of 10be excited states using single-neutron pickup reactions on 11be. Frederic Sarazin, Keri Kuhn, Ryan Braid On behalf of the (PCB)2 and TIGRESS collaborations. One-neutron transfer reactions are used to study single-particle neutron states in nuclei. In this work, we use two pickup reactions on one-neutron halo nucleus 11Be to study 10Be excited states, including the 2- state at 6.26 MeV, which has been suggested to be an excited halo state. Both experiments were performed at the TRIUMF-ISAC II facility using the Printed Circuit Board Based Charged Particle ((PCB)2) array inside the TRIUMF ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). The first experiment used the (p,d) reaction in inverse kinematics at 10MeV per nucleon and the identification of the 10Be states was obtained by detecting the deuteron and, as needed, gamma-rays in coincidence. The second experiment used a 9Be target to produce two 10Be outgoing nuclei (quasi-projectile / quasi-target) allowing for multiple methods to identify the 10Be states. We will show results from the two experiments. |
Wednesday, October 24, 2018 8:30PM - 8:45PM |
CB.00007: Beta-NMR of short lived nuclei in liquid media for g-factor measurement Mototsugu Mihara, Takanobu Sugihara, Kensaku Matsuta, Mitsunori Fukuda, Masaomi Tanaka, Ryo Wakabayashi, Kosuke Onishi, Shoichi Yagi, Takuji Izumikawa, Sadao Momota, Tadanori Minamisono, Akira Honma, Takashi Ohtsubo, Daiki Nishimura, A. Ozawa, Takashi Nagatomo, Atsushi Kitagawa, Shinji Sato For the study of nuclear electromagnetic moments of unstable nuclei, the technique of the beta-ray detected nuclear magnetic resonance (beta-NMR) has been applied for many years. So far, in the beta-NMR measurement, solid materials have been used as a catcher in which objective unstable nuclei are stopped for NMR detection. One of the most important characteristics required for the catcher materials is that they maintain spin polarization for longer than the nuclear lifetime, which however depends on the combination of the material and the species of atomic nucleus. This sometimes makes it difficult to measure the nuclear moments even though the nuclear spin polarization is generated. We expect that the NMR detection in liquid samples is easier than in solid ones even with the beta-NMR as in the case of the conventional NMR, since the fast motion of molecules in solution averages the internal field distribution and reduces nuclear spin relaxation. Here, we demonstrate that the beta-NMR in liquid media is quite useful for the precise g-factor measurement from our recent results on 12B, 12N and 17N. |
Wednesday, October 24, 2018 8:45PM - 9:00PM |
CB.00008: The Puzzle of the 13Be Marija Vostinar, Katherine Jones, Rituparna Kanungo, Matthias Holl, Steven D. Pain, Orry Workman, IRIS S1506 Collaboration The structure of 13Be is of significant scientific importance since it offers insights on the evolution of the N=8 shell gap, the influence of the continuum, the nature of the neutron-drip line nuclei and the Borromean 14Be nucleus. Despite the considerable experimental work performed in the past, the position and ordering of the low-lying states remains uncertain. Consequently, we performed a transfer reaction experiment at ISAC II, TRIUMF using the 12Be(d,p)13Be reaction. The beam at 9.5 AMeV interacted with the IRIS solid D2 target. The data are currently being analyzed and the preliminary results on the 13Be low-lying states will be presented here. |
Wednesday, October 24, 2018 9:00PM - 9:15PM |
CB.00009: Coulomb shift in 14O as the signature of the linear-chain structure Tomoyuki Baba, Masaaki Kimura Recent years have seen many important experimental studies for the linear-chain states (linearly aligned 3α articles) in 14C and 16C. These new data motivated us to perform ananalysis and to summarize the calculated and observed properties of the linear-chain bands in carbon isotopes. In addition, it can be expected that the reduction of the Coulomb shift for the mirror system, known as the Thomas-Ehrman shift, is induced by the developed α cluster such as the linear-chain structure. In this presentation, the linear-chain states of 14C and 14O are theoretically investigated by using the antisymmetrized molecular dynamics (AMD). Especially, we focus on the suppressed energy shift of 14O(0+) which is considered as the new signature of the linear-chain configuration. Moreover, we also estimate the α decay width of the linear-chain states. As the result, it is found that the positive-parity linear-chain states of 14C have the molecular orbit configuration and primary decay to the 1st excited state of 10Be as well as to the 10Be(g.s.) by the particle emission. |
Wednesday, October 24, 2018 9:15PM - 9:30PM |
CB.00010: Low-Energy Gamow-Teller Transitions in deformed N=Z odd-odd Nuclei Hiroyuki Morita, Yoshiko Kanada-En'yo We have investigated the Gamow-Teller(GT) transitions for 10Be->10B and 22Ne->22Na by applying the isospin-projected AMD+GCM. |
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