Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session EE: Mini-Symposium: Beta Decay: Nuclear Astrophysics, Structure, and Applications I |
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Chair: Kay Kolos, LLNL |
Friday, October 30, 2020 10:30AM - 11:06AM |
EE.00001: Half-lives and neutron-branching ratios of the most neutron-rich nuclei Invited Speaker: Iris Dillmann More than 600 out of the 3435 known nuclei have been identified that could emit neutrons after their beta-decay. It is estimated that about 4000 more nuclei are waiting to be discovered, and about 3000 are on the neutron-rich side. Their dominant decay mechanism will be via beta-delayed neutron emission. With the advent of the next generation of RIB facilities, a strong focus will be on the deeper understanding of neutron-rich nuclei towards the neutron-dripline. For the rapid neutron capture process, besides masses and neutron capture cross sections, also the decay half-lives and neutron-emission probabilities play an important role and are needed for a better understanding of the calculated r-process abundances. However, measurements in the next decade(s) will not tackle all nuclei up to the neutron dripline but rather focus on key regions that have been identified by nuclear structure and r-process sensitivity studies, for example around shell and mid-shell closures. Recent experimental campaigns and evaluation of the existing data will improve our present understanding and allow finetuning of theoretical models towards so far unknown nuclei. I will give an overview about recent campaigns and evaluation efforts targeting the most neutron-rich nuclei identified so far. [Preview Abstract] |
Friday, October 30, 2020 11:06AM - 11:18AM |
EE.00002: Measurement of decay properties for r-process models Neerajan Nepal, A. Algora, A. Estrade, S. Nishimura, J. Argamunt, R. Caballero-Folch, F. Calvino, T. Davinson, I. Dillmann, R. Grywacz, G. Kiss, J. Liu, G. Lorusso, V. Phong, B.C. Rasco, K.P. Rykaczewski, J.L. Tain, A. Tarifeno-Saldivia, A. Tolosa-Delgado, P. Woods, R. Yokoyama Understanding the rapid neutron capture nucleosynthesis process (r-process) requires precise data on decay properties, in particular half-lives ($T_{1/2}$) and probability of beta delayed neutron emission ($P_n$). We did an experiment to measure $T_{1/2}$ and $P_n$ values of neutron-rich isotopes around mass A = 100 using the state-of-the-art instrumentation of the beta-delayed neutron detector at RIKEN (BRIKEN) in the Radioactive Ion Beam Factory (RIBF) at RIKEN lab in Japan. The current status of the analysis will be presented. We also performed r-process calculations using the Webnucleo reaction network code using thermodynamic trajectories that parameterize conditions that lead to a r-process. We will present the importance of $T_{1/2}$ and $P_n$ values of neutron-rich isotopes around the mass A = 100 to r-process calculations [Preview Abstract] |
Friday, October 30, 2020 11:18AM - 11:30AM |
EE.00003: Beta-delayed neutron studies performed with trapped ions Barbara Wang, A. Czeszumska, S. Caldwell, N. Scielzo, J. Clark, G. Savard, A. Aprahamian, M. Burkey, C. Chiara, J. Harker, A. Levand, S. Marley, G. Morgan, J. Munson, E. Norman, A. Nystrom, R. Orford, S. Padgett, A. Perez Galvan, K. Sharma, K. Siegl, S. Strauss A detailed study of the beta-delayed neutron ($\beta$n) emission properties of $^{135,136}$Sb, $^{137,138,140}$I, and $^{144,145}$Cs was performed at the CARIBU facility by confining ions in the Beta-decay Paul Trap and measuring the decay particles with an array of radiation detectors. Decay branching ratios and energy spectra of the emitted neutrons were inferred from a measurement of the nuclear-recoil time-of-flight, thereby circumventing the limitations associated with direct neutron detection. The isotopes studied have importance in the areas of nuclear energy and \textit{r}-process nucleosynthesis. The results of this experiment will be presented and compared with direct neutron measurements. In the case of $^{136}$Sb, the $\beta$n energy spectrum has been measured for the first time. [Preview Abstract] |
Friday, October 30, 2020 11:30AM - 11:42AM |
EE.00004: Recoil-ion Time-of-Flight Spectroscopy Studies for Beta-Delayed Neutron Emission Studies Gemma Wilson, S Marley, A Laminack, G Morgan, J Clark, G Savard, N Scielzo, K Kolos, B Wang, J Munson, T Nagel, A Aprahamian, K Siegl Recoil-ion time-of-flight spectroscopy is a novel technique for studying $\beta$-delayed neutron ($\beta n$) emission that uses an array of detectors around a Paul Trap confining a cloud of decaying ions. This technique avoids difficulties inherent in neutron detection and infers all neutron information from the recoiling daughter nucleus. The time difference between detection of the $\beta$ and the recoil ion is used to distinguish $\beta$ and $\beta n$ events, and both the neutron branching ratio and neutron energy can be determined. The energy reconstruction and resolution are impacted by several factors, including the ion cloud size and angular correlations between $\beta$-$\nu$ and $\beta$-$\nu$-$n$, which have been investigated using simulations of the Beta-decay Paul Trap. As some of these factors are physical characteristics of the experimental apparatus, a new dedicated ion trap and detector system called the BEtA Recoil-ion trap (BEARtrap) will exploit this, affording improved efficiency and resolution. Effects of these physical phenomena will be presented, including a preview of BEARtrap. [Preview Abstract] |
Friday, October 30, 2020 11:42AM - 11:54AM |
EE.00005: Beta-delayed neutron emission around doubly magic 78Ni Krzysztof Rykaczewski BRIKEN collaboration operates the world-largest beta-delayed neutron detection array at the BigRIPS fragment separator at RIKEN (Wako, Japan). Multiple experiments including the ones focused on the 78Ni region have been performed profiting from up to 4.3*10$^{\mathrm{11}}$ pps 238U beam at 345 MeV/u. For last experiment focused on 82Cu activity, BRIKEN array was modified to achieve larger gamma efficiency having fragment implantation and beta decay detectors of WASABI array complemented by a position sensitive YSO scintillator developed at the UTK. Isotopes between 61V-69V up to 95Br-97Br were produced and identified. The total rate of identified 78Ni ions during BRIKEN experiments was around 65,000, with about 41,000 ions implanted for decay study. Together with new beta-delayed (multi) neutron branching ratios and half-lives, new data on beta-neutron-gamma correlations help us to analyze the nuclear structure evolution at and beyond N$=$50 shell closure. [Preview Abstract] |
Friday, October 30, 2020 11:54AM - 12:06PM |
EE.00006: Decay study of $^{\mathrm{134}}$In and the beta-delayed neutron emission mechanism with ISOLDE Decay Station Joseph Heideman, Robert Grzywacz, Miguel Madurga, Zhengyu Xu, Rin Yokoyama, Thomas King, Aleksandra Fijalkowska, Razvan Lica, Maninder Singh Beta-delayed neutron emission in very neutron-rich nuclei plays an essential role in nuclear structure and the understanding of the astrophysical r-process. A leading theory poses the intermediate daughter nucleus to behave as a compound nucleus [1]. The beta-delayed neutron emission of $^{\mathrm{134}}$In is not well described by the neutron pandemonium hypothesis [2], therein providing a unique case to study neutron emission [3]. Single-particle states populated in $^{\mathrm{133}}$Sn [4] have dissimilar shell occupancy compared to neutron-hole states in daughter nucleus states populated in Gamow-Teller transitions. A short experiment observing $^{\mathrm{134}}$In decay was conducted with the ISOLDE Decay Station [5]. Multiple neutron-emitting states in $^{\mathrm{134}}$Sn populated in beta decay were identified and will be compared with statistical model predictions to establish if the assumption of the "compound nucleus" behavior can be valid for $^{\mathrm{134}}$In beta-delayed neutron emission. [1] T. Kawano et al., Phys. Rev. C 78, 054601 (2008). [2] J. Hardy et al., Nucl. Phys. A 305, 15 (1978). [3] P. Hoff et al., Phys. Rev. Lett. 77, 1020 (1996). [4] K.L. Jones et al., Nature 465, 454 (2010). [5] Z. Xu et al., this conference. [Preview Abstract] |
Friday, October 30, 2020 12:06PM - 12:18PM |
EE.00007: The ground state mass of $^{73}$Rb from the $\beta$-delayed proton emission of $^{73}$Sr D.E.M. Hoff, A.M. Rogers, P.C. Bender, E.R. Doucet, C.J. Lister, C. Morse, S. Waniganeththi, K. Childers, A.C. Dombos, S. Jin, R. Lewis, S.N. Liddick, H. Schatz, K. Schmidt, S.M. Wang, K. Brandenburg, Z. Meisel, D. Soltesz, S.K. Subedi, J.A. Clark Nuclear structure along the proton dripline has a significant impact on the rapid-proton capture process. In particular, the nuclear flow is heavily influenced by waiting-points, e.g. $^{72}$Kr, where proton captures are limited by the proton-unbound daughter nucleus. To determine the proton separation energy of $^{73}$Rb, and thus the strength of the $^{72}$Kr waiting point, the beta-delayed proton emission of $^{73}$Sr was studied. $^{73}$Sr was produced by the fragmentation of a $^{92}$Mo primary beam on a Be target and subsequent decays measured via ion implantation-decay correlations at the NSCL. Improvements in the analysis have reduced the low-energy charged-particle background and with a Bayesian analysis the proton separation energy of $^{73}$Rb was determined to be $S_p = -640(40)$ keV. With previous $^{73}$Rb non-observation measurements constraining the mass, our measurement provides a firm determination of $S_p$. [Preview Abstract] |
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