Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session JA: Neutron-rich Nuclei, r-Process Nuclei, and Radioisotopes |
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Chair: Barry Davids, TRIUMF Room: Plaza I |
Friday, October 26, 2012 10:30AM - 11:06AM |
JA.00001: Low-energy level structures of neutron-rich Co, Fe, and Mn nuclei near $\emph{N}$ = 40 Invited Speaker: Sean Liddick The region around $\emph{N}$ = 40 below Ni is currently an active area both experimentally and theoretically in an attempt to understand the rapid development of collectivity below $^{68}$Ni as protons are removed from the f$_{7/2}$ single-particle state. The dramatic drop in the energy of the first excited 2$^{+}$ states and increase in the B(E2) values in even-even nuclei along the Fe and Cr isotopic chains has been well documented. The theoretical reproduction of the experimental trends indicates the increasing influence of the neutron g$_{9/2}$ single particle state as $\emph{N}$ = 40 is approached. The increased occupancy of the neutron g$_{9/2}$ single-particle level drives the nuclei below Ni towards deformed structures evidenced by the presence of low-energy isomeric states in nuclei with $\emph{N}$ $<$ 40 and the drop in the energy of the yrast 9/2$^{+}$ states in the neutron-rich Fe nuclei. Recently, investigations have been able to access the rich low-energy level schemes of odd-A and odd-odd nuclei along $\emph{N}$ = 40 and assign tentative spins and parities. The spin and parity assignments of these nuclei can serve as a signature of the underlying neutron and proton configurations and complement information obtained from neighboring even-even nuclei. For example, a low-energy 1/2$^{-}$ isomeric state in $^{67}$Co was taken as evidence of deformed proton states immediately below $^{68}$Ni. To further explore this region, in particular the neutron states, the low-energy level structures of the odd-odd Co, Mn and odd-A Fe isotopes were studied through the beta-decay of the respective Fe, Cr, and Mn isotopes. The inferred level schemes based on both beta-delayed and isomeric gamma ray transitions of the odd-odd Co and Mn nuclei straddling $\emph{N}$ = 40 will be presented. [Preview Abstract] |
Friday, October 26, 2012 11:06AM - 11:42AM |
JA.00002: Beta Decay Half-lives and Delayed Neutron Emission of r-process Neutron-Rich nuclei in the vicinity of 78Ni Invited Speaker: M. Madurga The region of neutron rich isotopes at and beyond the N=50 shell closure in the vicinity of $^{78}$Ni has recently attracted major interest from experimental and theoretical nuclear physics community [1-4]. Moreover, as many nuclei in the region are predicted precursors of r-process nucleosynthesis, their most basic nuclear properties such as mass and beta decay half-life are required parameters in abundance calculations. The availability of hight purity and high quality radioactive beams of nuclei in this region at the Holifield Radioactive Ion Beam Facility has spurred a systematic campaign to study their properties through beta decay. Four new half-lives of $^{82,83}$Zn, $^{85}$Ga and $^{86}$Ge were measured for the first time. The resulting values differ from the predictions of the Finite Range Droplet Model used in r-process abundance calculations. We presented a new model based on Density Functional Theory that correctly reproduced the new half-lives. The revised analysis of the rapid neutron capture process in low entropy environments with our new set of measured and calculated half-lives shows a significant redistribution of predicted isobaric abundances strengthening the yield of A $>$ 140 nuclei. Continuing our effort to systematically understand decay properties in the region of beta-delayed neutron emission, 30 nuclei in the region were studied using the neutron energy Time-of-Flight detector VANDLE. Due to the shell structure in the region, most of the decay strength is expected to concentrate in states above neutron separation energy, in the so-called Pigmy Giant resonance. Precise knowledge of the position and strength of the resonance may help fine tune and develop existing models, with the aim of increasing their reliability beyond what can be experimentally measured. The data resulting from the experimental campaign at Holifield are still being analyzed. In a few species strong shell effects have already been identified and they will be presented. In particular, the decay of $^{84}$Ga shows that more than half of the neutron strength concentrates in a single neutron transition at 2 MeV, suggesting the population of the Pigmy resonance.\\[4pt] [1] P. Hosmer et al., Phys. Rev. Lett. 94, 112501 (2005).\\[0pt] [2] T. Otsuka, T. Suzuki, R. Fujimoto, H. Grawe, and Y. Akaishi, Phys. Rev. Lett. 95, 232502 (2005).\\[0pt] [3] B. Cheal et al., Phys. Rev. Lett. 103, 142501 (2009).\\[0pt] [4] S. Padgett et al., Phys. Rev. C 82, 064314 (2010). [Preview Abstract] |
Friday, October 26, 2012 11:42AM - 12:18PM |
JA.00003: Radioisotope Production for Medical and Physics Applications Invited Speaker: Leonard Mausner Radioisotopes are critical to the science and technology base of the US. Discoveries and applications made as a result of the availability of radioisotopes span widely from medicine, biology, physics, chemistry and homeland security. The clinical use of radioisotopes for medical diagnosis is the largest sector of use, with about 16 million procedures a year in the US. The use of $^{99}$Mo/$^{99m}$Tc generator and $^{18}$F make up the majority, but $^{201}$Tl, $^{123}$I, $^{111}$In, and $^{67}$Ga are also used routinely to perform imaging of organ function. Application of radioisotopes for therapy is dominated by use of $^{131}$I for thyroid malignancies, $^{90}$Y for some solid tumors, and $^{89}$Sr for bone cancer, but production of several more exotic species such as $^{225}$Ac and $^{211}$At are of significant current research interest. In physics $^{225}$Ra is of interest for CP violation studies, and the actinides $^{242}$Am, $^{249}$Bk, and $^{254}$Es are needed as targets for experiments to create superheavy elements. Large amounts of $^{252}$Cf are needed as a fission source for the CARIBU experiment at ANL. The process of radioisotope production is multidisciplinary. Nuclear physics input based on nuclear reaction excitation function data is needed to choose an optimum target/projectile in order to maximize desired isotope production and minimize unwanted byproducts. Mechanical engineering is needed to address issues of target heating, induced mechanical stress and material compatibility of target and claddings. Radiochemists are involved as well since chemical separation to purify the desired final radioisotope product from the bulk target and impurities is also usually necessary. Most neutron rich species are produced at a few government and university reactors. Other radioisotopes are produced in cyclotrons in the commercial sector, university/hospital based facilities, and larger devices at the DOE labs. The landscape of US facilities, the techniques involved, and current supply challenges will be reviewed. [Preview Abstract] |
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