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 PD: Nuclear Structure VII |
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Room: Patio |
Saturday, October 27, 2012 10:30AM - 10:42AM |
PD.00001: Evolution of Efimov states in 2-neutron halo nuclei -- a general study Indranil Mazumdar, Vidyasagar Bhasin, A.R.P. Rau The discovery of neutron-rich halo nuclei near the drip line has opened up new vistas in contemporary nuclear physics. The structural properties of 2-neutron halo nuclei provide the opportunity to search for the elusive Efimov effect in nuclear physics. We present results of our detailed calculations to search for Efimov states and their evolutions with increasing two-body (neutron-core) interaction in 2-neutron halo nuclei. Working within the framework of a three-body model with realistic finite range two-body interactions we investigate the nuclear three-body system of two halo neutrons very weakly coupled to a heavy core, to investigate necessary conditions for the occurrence of Efimov states. Extending the analysis to the scattering sector, we find that these states evolve into Feshbach type resonances. This behavior is very similar to the 20C nucleus in which the occurrence of Efimov states evolving into resonances in the elastic scattering of n--19C system has been investigated in recent publications. This work, thereby, extends the study of the Efimov effect beyond 20C, showing that 32Ne and 38Mg exhibit a very similar dynamical structure. These nuclei are, therefore, also candidates for probing experimentally the Efimov effect. [Preview Abstract] |
Saturday, October 27, 2012 10:42AM - 10:54AM |
PD.00002: Improving systematic predictions of beta-delayed neutron emission probabilities E.A. McCutchan, A.A. Sonzogni, T.D. Johnson The probability for neutron emission following $\beta$ decay, P$_n$, is a crucial property for a wide range of physics and applications including nuclear structure, astrophysics, the control of nuclear reactors, and the post-processing and handling of nuclear fuel. Despite much experimental effort, knowledge of P$_n$ values is lacking in very neutron-rich nuclei, requiring predictions from either systematics or theoretical models. Traditionally, systematic predictions [1] were made by investigating the P$_n$ value as a function of the $Q$ value of the decay and the neutron separation energy. Here, we will present a new form of systematic studies utilizing the well-known relationship between the P$_n$ value and the half-life of the decay. It will be shown that such systematics provide more robust predictions of P$_n$ values compared with earlier prescriptions, are applicable to all known $\beta$-delayed neutron emitters across the nuclear chart, and are a general feature of not only the data, but also the theoretical models.\\[4pt] [1] B. Pfeiffer {\it et al.,} Prog. Nucl. Energy {\bf 41}, 39 (2002). [Preview Abstract] |
Saturday, October 27, 2012 10:54AM - 11:06AM |
PD.00003: New Nubar Results for Fissionable Materials T.D. Johnson, A.A. Sonzogni, E.A. McCutchan A crucial feature of reactor operation and control is the emission of $\beta$-delayed neutrons from the fuel. For example, uncertainties in the number of delayed neutrons can lead to excessive margins for safety in the operation of fission reactors. The relevant measurable quantity is the beta-delayed neutron emission probability (Pn), which is the probability that the beta-decay proceeds to states above the neutron separation energy and a neutron is emitted following the beta decay. A parameter called ``Delayed Nu-bar'' defines the mean number of delayed neutrons per fission event. Nu-bars have been measured for a number of fuels and provide a benchmark quantity from which databases can be tested. The latest ENDF-B/VII.1 library was benchmarked and sensitivity studies were carried out to understand the contribution of the uncertainties and where improvements could be achieved for Pn values. Nu-bar calculations were then performed for several of the minor actinides. [Preview Abstract] |
Saturday, October 27, 2012 11:06AM - 11:18AM |
PD.00004: Some Aspects of the Giant- Pairing Vibration A.O. Macchiavelli, R.M. Clark, M. Laskin, R.F. Casten Pair correlations in nucleon motion play a key role in our understanding the excitation spectra of even-A nuclei, odd-even mass differences, rotational moments of inertia, and a variety of other phenomena. It has been predicted that there should be a concentration of strength, with L=0 character, in the high-energy region (10-15 MeV) of the pair-transfer spectrum. This is called the Giant Pairing Vibration (GPV) and is understood microscopically as the coherent superposition of 2p (or 2h) states in the next major shell above the Fermi surface. It is analogous to the giant resonances of nuclear shapes which involve the coherent superposition of ph excitations. The GPV should be populated through pair-transfer reactions, but despite many efforts it has never been identified [2]. In this work, we study the possible role of mixing of bound and unbound levels in making the GPV difficult to observe. We illustrate these effects with a set of toy models that capture the essential physics of the GPV. A more realistic (yet still schematic) calculation is used to estimate 2n-transfer cross sections.\\[4pt] [1] R. A. Broglia and D. R. B\`{e}s, Phys. Lett. B 69 129 (1977).\\[0pt] [2] B.Mouginot et al. Phys. Rev. C83 037302 (2011). [Preview Abstract] |
Saturday, October 27, 2012 11:18AM - 11:30AM |
PD.00005: ABSTRACT WITHDRAWN |
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