Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session DC: Nuclear Structure 110-150 |
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Chair: Shea Mosby, Los Alamos National Laboratory Room: Sweeney Ballroom B |
Thursday, October 29, 2015 10:30AM - 10:42AM |
DC.00001: Beta-Decay Spectroscopy of Neutron-Rich Isotopes Utilizing a Planar Ge Double-Sided Strip Detector N. Larson, S.N. Liddick, C.J. Prokop, F.G. Kondev, S. Kumar, B.P. Crider, S.V. Paulauskas, S. Suchyta In nuclear science, rapid changes in the structure of the atomic nucleus have been inferred with small changes in the neutron and proton numbers. These changes are manifested in variations of the low-energy level schemes of exotic isotopes. One region of the nuclear chart where rapid changes in deformation have been suggested based on the behavior of the first excited 2$+$ states is in neutron-rich nuclei near A$=$110. Beta-decay spectroscopy is a sensitive and selective technique that can be used to investigate the low-energy level schemes exotic nuclei at low production rates. At the National Superconducting Cyclotron Laboratory (NSCL), a recently commissioned planar Ge double-sided strip detector (GeDSSD) is used in a novel application for these studies. Preliminary results from the decay of Tc isotopes in an experiment aimed at nuclei near A$=$110 will be presented. This work was supported by the DOE NNSA DE-NA0000979 and the NSF Grant PHY1102511. [Preview Abstract] |
Thursday, October 29, 2015 10:42AM - 10:54AM |
DC.00002: Revealing the structural nature of the Cd isotopes P.E. Garrett, A. Diaz Varela, K.L. Green, D.S. Jamieson, B. Jigmeddorj, J.L. Wood, S.W. Yates The even-even Cd isotopes have provided fertile ground for the investigation of collectivity in nuclei. Soon after the development of the Bohr model, the stable Cd isotopes were identified as nearly harmonic vibrators based on their excitation energy patterns. The measurements of enhanced $B(E2)$ values appeared to support this interpretation. Shape co-existing rotational-like intruder bands were discovered, and mixing between the configurations was invoked to explain the deviation of the decay pattern of multiphonon vibrational states. Very recently, a detailed analysis of the low-lying levels of $^{110}$Cd combining results of the $(n,n^{\prime}\gamma)$ reaction and high-statistics $\beta$ decay, provided strong evidence that the mixing between configurations is weak, except for the ground-state band and ``$K^{\pi}=0^+$'' intruder band. The analysis of the levels in $^{110}$Cd has now been extended to 3 MeV, and combined with data for $^{112}$Cd and previous Coulomb excitation data for $^{114}$Cd, enables a detailed map of the $E2$ collectivity in these nuclei, demanding a complete re-interpretation of the structure of the stable Cd isotopes. [Preview Abstract] |
Thursday, October 29, 2015 10:54AM - 11:06AM |
DC.00003: Oblate deformation in $^{118,119}$Ag E.H. Wang, J.H. Hamilton, A.V. Ramayya, J.K. Hwang, H.J. Li, Y.X. Liu, Y.X. Luo, J.O. Rasmussen, Y. Sun, S.J. Zhu, G.M. Ter-Akopian, Yu.Ts. Oganessian High spin level schemes of $^{118,119}$Ag are established for the first time by analyzing the high statistics $\gamma$-$\gamma$-$\gamma$ and $\gamma$-$\gamma$-$\gamma$-$\gamma$ coincidence data from the spontaneous fission of $^{252}$Cf at Gammasphere. Two bands with 12 new levels in $^{118}$Ag and two bands with 13 new levels in $^{119}$Ag have been identified. Spins and parities are tentatively assigned according to the systematics. A total Routhian surface calculation and projected shell model calculation have been performed to understand the behavior of these two nuclei. The calculations indicate oblate shape in $^{118,119}$Ag. The dramatic change of signature inversion point in $^{118}$Ag among odd-odd Ag nuclei needs further theoretical consideration. [Preview Abstract] |
Thursday, October 29, 2015 11:06AM - 11:18AM |
DC.00004: High-statistics beta-plus/EC decay study of Xe-122 B. Jigmeddorj, P.E. Garrett, B. Hadinia, A.J. Radich, E.T. Rand, C.E. Svensson, C.A. Andreoiu, D.S. Cross, J. Pore, U. Rizman, P. Voss, G.C. Ball, T. Bruhn, A.B. Garnsworthy, G. Hackman, M. Moukaddam, J. Park, M.M. Rajabali, Z. Wang, J.L. Wood, S.W. Yates The isotopes of Xe are centrally located with respect to the evolution of collectivity in the $Z>50$, $N<82$ region, which exhibits an extraordinarily smooth evolution of simple collective signatures. Excited $0^+$ states in $^{124-132}$Xe are very strongly populated, suggesting that there are important proton subshell gaps influencing the low-lying structure of these isotopes and possibly shape-coexistence that would lead to strong $E0$ transitions. However, collectivity in this region is very poorly characterized because of a lack of spectroscopic data for low-spin states. A high-statistics $^{122}$Cs $\beta^+/EC$ decay experiment to obtain detailed spectroscopic data for low spin states was performed at the TRIUMF-ISAC facility using the 8$\pi$ $\gamma$-ray spectrometer and PACES array of five Si(Li) detectors, for conversion electrons spectroscopy. Preliminary results will be presented. [Preview Abstract] |
Thursday, October 29, 2015 11:18AM - 11:30AM |
DC.00005: Impact of comprehensive simulations on trapped ion beta-delayed neutron spectroscopy Kevin Siegl, A. Aprahamian, N.D. Scielzo, G. Savard, J.A. Clark, A.F. Levand, M. Burkey, S. Caldwell, A. Czeszumska, T.Y. Hirsh, S.T. Marley, G.E. Morgan, E.B. Norman, A. Nystrom, R. Orford, S. Padgett, A. P\'erez Galv\'an, K.S. Sharma, S. Strauss, B.S. Wang The decay of radioactive ions confined in an RF ion trap allows indirect measurements of beta-delayed neutron emission. This is accomplished by measuring the energy of the recoiling ion which can be much larger after neutron emission than from just beta decay. This method removes most systematic errors from neutron detection but introduces dependencies on specifics of the decay and interactions of the ion with the RF fields. Measurements were made of the \textsuperscript{134-136}Sb beta decays with this technique at Argonne National Laboratory using the Californium Rare Isotope Breeder Upgrade (CARIBU). A suite of simulations were developed to model the interaction of the decays and the influence of the trap fields on the recoiling ions. Measurements of these data can impact many fields, such as nuclear energy, nuclear astrophysics, and stockpile stewardship. Results of the simulations and analyses will be reported. [Preview Abstract] |
Thursday, October 29, 2015 11:30AM - 11:42AM |
DC.00006: Precision Mass Measurements at the Canadian Penning Trap using a Phase-Imaging Technique Andrew Nystrom, A. Aprahamian, S.T. Marley, M. Mumpower, N. Paul, K. Siegl, S. Strauss, R. Surman, T. Kuta, G. Savard, J.A. Clark, A.F. Levand, A. Perez Galvan, T. Hirsh, J. Rohrer, S. Caldwell, J. Van Schelt, R. Orford, F. Buchinger, G. Morgan, K. Sharma Precision mass measurements at Penning Trap facilities have traditionally used a time-of-flight (TOF) technique to measure the cyclotron frequency of ions and therefore determine their masses. At the Canadian Penning Trap (CPT), this technique is able to provide mass measurements to a precision of about $\delta $m/m $=$ 10$^{-8}$ with measurement times as low as 200ms. However, a new phase-imaging technique, which instead determines the cyclotron frequency by projecting the radial ion motion on a position-sensitive detector, is being implemented at the CPT. It provides at least a tenfold gain in resolving power while allowing for measurement times of less than 100ms, allowing measurements of more exotic neutron-rich nuclei from CARIBU with respect to the TOF technique. Details of its commissioning at the CPT will be discussed alongside new neutron-rich mass measurements. [Preview Abstract] |
Thursday, October 29, 2015 11:42AM - 11:54AM |
DC.00007: Coincident measurements of prompt fission $\gamma$ rays and fission fragments at DANCE C.L. Walker, B. Baramsai, M. Jandel, G. Rusev, A. Couture, S. Mosby, J. Ullmann, T. Kawano, I. Stetcu, P. Talou Modern statistical approaches to modeling fission involve the calculation of not only average quantities but also fully correlated distributions of all fission products. Applications such as those involving the detection of special nuclear materials also rely on fully correlated data of fission products. Experimental measurements of correlated data are thus critical to the validation of theory and the development of important applications. The goal of this experiment was to measure properties of prompt fission gamma-ray emission as a function of fission fragments' total kinetic energy in the spontaneous fission of $^{252}$Cf. The measurement was carried out at the Detector for Advanced Neutron Capture Experiments (DANCE), a 4$\pi$ $\gamma$-ray calorimeter. A prototype design consisting of two silicon detectors was installed in the center of DANCE, allowing simultaneous measurement of fission fragments and $\gamma$ rays. Effort has been taken to simulate fragment kinetic energy losses as well as $\gamma$-ray attenuation in DANCE using such tools as GEANT4 and SRIM. Theoretical predictions generated by the code CGMF were also incorporated as input for these simulations. Results from the experiment and simulations will be presented, along with plans for future measurements. [Preview Abstract] |
Thursday, October 29, 2015 11:54AM - 12:06PM |
DC.00008: The search for an E(5) critical-point nucleus among the stable xenon isotopes E.E. Peters, T.J. Ross, A. Chakraborty, B.P. Crider, A. Kumar, F.M. Prados-Est\'{e}vez, S.F. Ashley, M.T. McEllistrem, S.W. Yates A critical-point has been proposed to exist within the shape/phase transition of the U(5), spherical, and O(6), $\gamma$-soft rotor, limits of the IBM. The xenon isotopes exhibit such a transition and have, therefore, been proposed as a chain in which to search for the E(5) critical-point symmetry. The candidacy for an E(5) nucleus has been largely based on the decays of the excited 0$^+$ states, which for some of the xenon isotopes were not yet known. Inelastic neutron scattering measurements at the University of Kentucky Accelerator Laboratory have been performed using highly enriched ($>$99.9\%) $^{130}$Xe, $^{132}$Xe, $^{134}$Xe and $^{136}$Xe gases converted to solid xenon difluorides. From these measurements, new excited 0$^+$ states and their decays were identified, level lifetimes were measured, and transition probabilities were determined. This new information allows definitive conclusions to be drawn about the occurrence of the E(5) symmetry within the stable xenon isotopes. [Preview Abstract] |
Thursday, October 29, 2015 12:06PM - 12:18PM |
DC.00009: Octupole deformation in $^{144,146}$Ba measured by Coulomb excitation of radioactive beams Brian Bucher, Shaofei Zhu The exotic, neutron-rich $^{144}$Ba ($t_{1/2}$=11.5 s) and $^{146}$Ba ($t_{1/2}$=2.2 s) nuclei are expected to exhibit some of the strongest octupole correlations in A$<$200 systems. Up to now, evidence for such strong octupole correlations has been inferred from observations of low-lying negative-parity states and from the interleaving of positive- and negative-parity levels in the ground-state band. However, the E1 transition strengths are very different in these two nuclei, with two orders of magnitude reduction in $^{146}$Ba. In this experiment, we measure the octupole strength directly by Coulomb excitation of post-accelerated $^{144,146}$Ba beams produced at CARIBU using CHICO2 and GRETINA. In $^{144}$Ba, we found B(E3;3$\rightarrow$0)=48($^{+25}_{-34}$) W.u., a value considerably larger than theoretical predictions, while preliminary results for $^{146}$Ba are also indicative of strong octupole collectivity. The experimental conditions, the analysis, and the results from these challenging new measurements will be presented. [Preview Abstract] |
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