Bulletin of the American Physical Society
17th Annual Meeting of the APS Northwest Section
Volume 61, Number 7
Thursday–Saturday, May 12–14, 2016; Penticton, British Columbia, Canada
Session F4: Nuclear Physics III |
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Chair: Corina Andreoiu, Simon Fraser University Room: PL 107 |
Saturday, May 14, 2016 2:00PM - 2:35PM |
F4.00001: Decay spectroscopy of neutron-rich isotopes for astrophysics Invited Speaker: Iris Dillmann A large fraction of the isotopes for rapid neutron capture-(r) process nucleosynthesis are not yet experimentally accessible and are located in the "Terra Incognita". With the next generation of fragmentation and ISOL facilities presently being built or already in operation, one of the main motivation of all projects is the investigation of very neutron-rich isotopes at and beyond the border of presently known nuclei. However, reaching more neutron-rich isotopes means also that beta-delayed neutron-emission becomes the dominant decay mechanism. Beta-delayed neutron emitters play an important, two-fold role in the stellar nucleosynthesis of heavy elements in the r process. On one hand they lead to a detour of the material beta-decaying back to stability. On the other hand, the released neutrons increase the neutron-to-seed ratio, and are re-captured during the freeze-out phase and thus influence the final solar r-abundance curve. For this reason the neutron branching ratio of very neutron-rich isotopes is a crucial parameter in astrophysical simulations. The investigation of beta-delayed neutron-emitters has recently experienced a renaissance. I will show some results from the measurement of the heaviest beta-delayed neutron emitters identified so far with the BELEN setup at GSI Darmstadt [R. Caballero-Folch et al., subm. to PRL (2015)]. Other high-accuracy measurements of neutron branching ratios of isotopes labelled by the IAEA as "high priority" have been carried out at the IGISOL facility in Jyvaskyla/ Finland. And last but not least I will talk about two neutron detection setups which will start taking data in 2016- the BRIKEN array at RIKEN/ Japan and the GRIFFIN gamma-spectrometer with its neutron detector DESCANT at TRIUMF/ Canada. [Preview Abstract] |
Saturday, May 14, 2016 2:35PM - 2:47PM |
F4.00002: Recent results from the measurement of $\beta $ delayed neutron emitters Roger Caballero-Folch, Iris Dillmann, Jorge Agramunt, Jose Luis Tain The $\beta $-delayed neutron emission probability of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes, and astrophysical processes such as the rapid neutron-capture process (r-process). The production of neutron-rich isotopes at present RIB facilities allowed to measure $\beta $-delayed one-neutron emitters ($\beta $1n) up to regions around mass A\textasciitilde 150, and recently up to masses heavier than A$=$210, beyond the N$=$126 shell closure. It has been a long-standing challenge to measure more exotic species with $\beta $-delayed multiple-neutron emitting branches due to the low production rates, and thus the heaviest $\beta $2n detected so far are $^{\mathrm{98,100}}$Rb. This contribution will present preliminary results of a recent experiment performed at the IGISOL facility of the University of Jyv\"{a}skyl\"{a} (Finland), to produce $^{\mathrm{136}}$Sb, the heaviest multiple-neutron emitter measured so far. $^{\mathrm{136}}$Sb is present in the freeze-out of the r-process and contributes to the second abundance peak around N\textasciitilde 82 in the A$=$130 mass region. [Preview Abstract] |
Saturday, May 14, 2016 2:47PM - 2:59PM |
F4.00003: Calculation of isotope yield rates for radioactive isotope beam production Fatima Garcia, Corina Andreoiu, Peter Kunz, Aurelia Laxdal Access to new and rare radioactive isotopes is key for application in nuclear science. Rare Isotope Beam (RIB) facilities around the world, such as TRIUMF, work towards development of new target materials to generate increasingly exotic species used in nuclear medicine, astrophysics and fundamental physics studies. At Simon Fraser University and TRIUMF, we have built a computer simulation of the RIB targets used at theIsotope Separation and ACceleration (ISAC) facility of TRIUMF, to compliment existing knowledge and to support new target materialdevelopment. The simulation is built in the GEANT4 nuclear transport toolkit, and can simulate the production rate of isotopes from beam and target characteristics specific to TRIUMF. The simulation models the bombardment of a productiontarget by an incident high-energy proton beam and calculates isotopeproduction ratesvia fission, fragmentation and spallation. Results from the simulation will be presented, along with an evaluation of various nuclear reaction physics models as well as experimentally determined RIB yields at ISAC. [Preview Abstract] |
Saturday, May 14, 2016 2:59PM - 3:11PM |
F4.00004: Recent advances in microscopic approaches to neutron-rich matter Francesca Sammarruca Nuclear matter is a convenient theoretical laboratory to test many-body theories. When neutron and proton densities are different, the isospin dependence of the nuclear force gives rise to the symmetry energy term in the equation of state. This quantity plays a fundamental role in a broad spectrum of systems and phenomena, including: the skins of neutron-rich nuclei, the location of the neutron drip lines, and the structure of compact stars. From the theoretical standpoint, microscopic calculations with statistically meaningful uncertainties are essential to guide experiments. In recent years, chiral effective field theory has become popular because of its firm connection with quantum chromodynamics and its systematic approach to the development of nuclear forces. We will report on recent calculations of the nuclear and neutron matter equations of state$^1$ at different orders of the chiral expansion as well as changing resolution scale. We will present applications and discuss the significance of those predictions as a foundation for future studies of convergence of the chiral perturbation series. \\ 1. F. Sammarruca, L. Coraggio, J.W. Holt, N. Itaco, R. Machleidt, and L.E. Marcucci, Phys. Rev. C {\bf 91}, 054311 (2015). [Preview Abstract] |
Saturday, May 14, 2016 3:11PM - 3:23PM |
F4.00005: A High-Statistics Measurement of the Beta Decay of 46K with the GRIFFIN Spectrometer Jennifer Pore, J.K. Smith, C. Andreoiu, P.C. Bender, R. Braid, G.C. Ball, D.S. Cross, R. Dunlop, A.B. Garnsworthy, G. Hackman, K. Kuhn, P. Kunz, A.T. Laffoley, W. Moore, M. Moukaddam, E.E. Peters, C.E. Svensson, S. Williams, S.W. Yates The neutron-rich calcium isotopes are currently a frontier for modern ab-initio calculations based on NN and 3N forces. Detailed experimental data from these nuclei is necessary for a comprehensive understanding of the region. Many excited states in $^{46}$Ca have been identified by various reaction mechanisms, most notably from $(p,p^\prime)$ and $(p,t)$ reactions, but many spins are only tentatively assigned or not measured. A high-statistics data set of the $^{46}$K decay into low-lying levels of $^{46}$Ca was taken with the new GRIFFIN spectrometer located at TRIUMF-ISAC. The level scheme of $^{46}$Ca has been greatly expanded to include 160 new gamma-ray transitions and 12 new excited states. Angular correlations between cascading gamma rays have been investigated to obtain information about the spins of the excited states. An overview of the experiment and a discussion of the results will be presented. [Preview Abstract] |
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