Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session G11: Nuclear Structure and Reactions II |
Hide Abstracts |
Sponsoring Units: DNP Chair: Christopher Chiara, University of Maryland Room: Embassy F |
Sunday, April 1, 2012 8:30AM - 8:42AM |
G11.00001: New high-spin level scheme of $^{112}$Rh: signature inversion and possible chirality Shaohua Liu, J.H. Hamilton, A.V. Ramayya, S.J. Zhu, Y. Shi, F.R. Xu, J.C. Batchelder, N.T. Brewer, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, W.C. Ma Neutron-rich Rh ($Z=45$) isotopes are located in the $A\approx110$ region where the nuclear structures are characterized by shape coexistence and shape transitions. The appearance of triaxial deformations have been found for nuclei $Z\ge41$ in this mass region. $^{112}$Rh has been re-investigated by examining the prompt $\gamma$-rays emitted in the spontaneous fission of $^{252}$Cf with the Gammasphere detector array. A new side band was built in $^{112}$Rh which can be called a yrare band that has been found in $^{104}$Rh, $^{106}$Rh, and $^{114}$Rh. The phenomena of signature inversion in the yrast band of $^{112}$ and possible chirality were discussed. [Preview Abstract] |
Sunday, April 1, 2012 8:42AM - 8:54AM |
G11.00002: High-spin states in $^{122,124}$Sn above the 10$^{+}$ isomers. N. Fotiades, M. Devlin, R.O. Nelson, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, W. Younes High-spin states above the previously known 10$^{+}$ isomers of $^{122}$Sn and $^{124}$Sn were studied via prompt $\gamma$-ray spectroscopy. $^{122}$Sn and $^{124}$Sn were populated as fission fragments in the fission of the $^{226}$Th compound nucleus formed in a fusion-fission reaction in a Gammasphere experiment at LBNL. $^{122}$Sn was also populated and studied as evaporation residue in the $^{124}$Sn$(n,3n)$ reaction using the GEANIE array coupled to the spallation neutron source of the Los Alamos Neutron Science Center's WNR facility. The $^{124}$Sn$(n,n^{\prime})$ reaction in this experiment did not bring in enough angular momentum to adequately populate states above the 10$^{+}$ isomer in $^{124}$Sn. Sequences of transitions were observed for the first time feeding the previously known 10$^{+}$ isomers, at 2766-, and 2657-keV excitation energy, and with 62$\mu$s and 45$\mu$s half-life, for $^{122}$Sn and $^{124}$Sn, respectively. The level schemes above the isomers were established up to 5386-, and 5952-keV excitation energy, for $^{122}$Sn and $^{124}$Sn, respectively. The experimental results are compared with predictions from shell-model calculations. [Preview Abstract] |
Sunday, April 1, 2012 8:54AM - 9:06AM |
G11.00003: Collective structures up to spin $\sim$ $65\hbar$ in the $N = 90$ isotones $^{158}$Er and $^{157}$Ho X. Wang, M.A. Riley, S.L. Miller, J. Simpson, E.S. Paul, H.C. Boston, P. Hampson, D.S. Judson, P.J. Nolan, J.M. Rees, J.P. Revill, R.V.F. Janssens, M.P. Carpenter, C.R. Hoffman, F.G. Kondev, T. Lauritsen, S. Zhu, C.J. Chiara, U. Garg, A.D. Ayangeakaa, J. Matta, D.J. Hartley, D.C. Radford, L.L. Riedinger, I. Ragnarsson Stable asymmetric or triaxial shapes are a longstanding prediction of theory [1]. In the present work, a third collective band in $^{158}$Er at spins beyond band termination was found in addition to the two previously reported ones [2]. The measured transition quadrupole moments ($Q_{\rm t}$ $\sim$ 10$-$11eb) have suggested that these bands possess a triaxial strongly deformed shape, based on comparisons with CNS calculations and with TAC calculations using the SHF model [3]. Three new collective bands with similar characters, tentatively assigned to $^{157}$Ho, will also be presented. [1] A. Bohr and B. R. Mottelson, Nuclear Structure, vol. II (1975); [2] E. S. Paul $\it{et~al.}$, Phys. Rev. Lett. 98, 012501 (2007); [3] Y. Shi $\it{et~al.}$, in preparation. [Preview Abstract] |
Sunday, April 1, 2012 9:06AM - 9:18AM |
G11.00004: Search for the Wobbling Mode in $^{169}$Re D.J. Hartley, E.E. Pedicini, J.R. Vanhoy, M.A. Riley, X. Wang, L.L. Riedinger, P.F. Bertone, M.P. Carpenter, C.J. Chiara, G. Gurdal, R.V.F. Janssens, F.G. Kondev, T. Lauritsen, E.A. McCutchan, S. Zhu, A.D. Ayangeakaa, U. Garg, J. Matta, W.C. Ma, S. Mukhopadhyay, P. Chowdhury, S. Hota The appearance of ``wobbling" sequences can only occur with the rotation of an asymmetrically shaped nucleus. Although once thought to be a general feature of the $Z$=72, $N$=94 region [1], the lack of such sequences observed in isotopes other than lutetium led to a suggestion that the $Z$=71 nuclei may be unique in displaying this exotic mode [2]. However, the recent identification of a wobbling band in $^{167}$Ta [3] has reopened questions about the influence the proton Fermi surface has on the observation of wobbling. An experiment using Gammasphere was performed to search for evidence of an asymmetric shape in the $N$=94 nucleus $^{169}$Re. The $\pi $i$_{13/2 }$sequence (the configuration on which all known wobbling structures are based) was identified for the first time in $^{169}$Re, and will be discussed in relation to the wobbling phenomenon.\\[4pt] [1] G. Sch\"{o}nwasser \textit{et al}, Phys. Lett. B \textbf{552}, 9 (2003);\\[0pt] [2] N. S. Pattabiraman \textit{et al}., Phys. Lett. B \textbf{647}, 243 (2007);\\[0pt] [3] D. J. Hartley \textit{et al}., Phys. Rev. C \textbf{80}, 041304(R) (2009). [Preview Abstract] |
Sunday, April 1, 2012 9:18AM - 9:30AM |
G11.00005: Unusual Quasiparticle Alignments in $^{168, 169}$W S.L. Miller, X. Wang, M.A. Riley, D.J. Hartley, E. Pedicini, J.R. Vanhoy, L.L. Riedinger, R.V.F. Janssens, P. Bertone, M.P. Carpenter, C.J. Chiara, G. Gurdal, F.G. Kondev, T. Lauritsen, E.A. McCutchan, S. Zhu, A.D. Ayangeakka, U. Garg, J. Matta, W.C. Ma, S. Mukhopadhyay, P. Chowdhury, S. Hota While the basic concepts of normal deformed low-spin quasiparticle excitations are thought to be well understood, unusual behavior may still be encountered. A recent data set obtained using the Gammasphere spectrometer on $^{168}$W and $^{169}$W is a case in point. Anomalies were observed between the expected [1] and observed alignment gains and crossing frequencies in the positive parity bands for both nuclei. Analysis of these structures will be discussed along with comparisons to neighboring nuclei [2, 3].\\[4pt] [1] D. R. Jensen \textit{et al.}, Phys. J. A \textbf{8}, 165 (2000);\\[0pt] [2] R. B. Yadav \textit{et al.}, Phys. Rev. C \textbf{78}, 044316 (2008);\\[0pt] [3] G. D. Dracoulis \textit{et al.}, Nuc. Phys. A. \textbf{486}, 414 (1988). [Preview Abstract] |
Sunday, April 1, 2012 9:30AM - 9:42AM |
G11.00006: Isotopic Trends in Dynamical Breakup Sylvie Hudan, Romualdo de Souza The simultaneous measurement of neutrons and charged particles produced in peripheral and mid-peripheral collisions in a heavy-ion cross-bombardment reaction $^{124,136}$Xe + $^{112,124}$Sn at E/A = 50 MeV is described. Dynamical decay in which the excited projectile-like fragment (PLF) decays on the timescale of its rotation is observed. The correlation between the composition of the lighter fragment, the size of the lighter fragment, the velocity damping and the decay orientation is examined. The influence of the target N/Z on the fragment composition is also studied. [Preview Abstract] |
Sunday, April 1, 2012 9:42AM - 9:54AM |
G11.00007: Asymmetry Dependence of Nuclear Caloric Curves A.B. McIntosh, A. Bonasera, S. Galanopoulos, K. Hagel, Z. Kohley, L. May, D.V. Shetty, W.B. Smith, S.N. Soisson, G.A. Souliotis, B.C. Stein, R. Tripathi, S. Wuenschel, S.J. Yennello Quasi-projectile sources produced in collisions of 70Zn+70Zn, 64Zn+64Zn and 64Ni+64Ni at E/A=35MeV have been reconstructed using the charged particles and free neutrons measured in the NIMROD-ISiS 4-pi detector. Equilibrated sources were selected which have a mass A=48-52 and which are on average spherical. Caloric curves for these quasi-projectiles have been extracted with the quadrupole momentum fluctuation thermometer. The caloric curves for the different light charged particle probes show a clear ordering which is consistent with a scenario in which the ``expensive'' particles are emitted preferentially at early times, when the source is hottest. For all light charged particle probes, the caloric curves show a clear dependence on the composition, (N-Z)/A, of the source. For a given excitation (E*/A), the neutron-poor sources exhibit higher temperatures. A consistent but smaller dependence is observed by selecting on the composition of the initial system rather than the composition of the source. The dependence on source composition is also observed in caloric curves extracted with the Albergo yield-ratio thermometer. [Preview Abstract] |
Sunday, April 1, 2012 9:54AM - 10:06AM |
G11.00008: Production of radon and thorium isotopes near N=126 shell closure in 48Ca and 54Cr induced fusion reactions on 162Dy Dmitriy Mayorov, Tyler Werke, Marisa Alfonso, Charles Folden Production of spherical evaporation residues (EVRs) near N=126 shell in 48Ca and 54Cr induced reactions on a 162Dy target was investigated at the Texas A{\&}M University Cyclotron Institute using the vacuum separator MARS. For the 54Cr+162Dy reaction, only upper limits for the 4n exit-channel cross section were measured; this can be attributed to a sizably increased fissility of the 216Th compound nucleus relative to 210Rn formed in the 48Ca bombardment. A factor of $>$ 7300 separates the production cross sections of the 4n EVRs from each reaction. A semi-empirical estimate of the lower limit on the fusion probability, PCN, ratio between the two heavy ion projectiles is PCN(48Ca+162Dy)/PCN(54Cr+162Dy) $>$ 1.2. Investigation of spherical nuclei produced by heavy ion fusion reactions is of current interest due to efforts to synthesize superheavy nuclei near Z=120, N=184 nucleon shells. EVRs produced near the N=126 shell closure have previously revealed surprisingly low survival probabilities despite stabilization from shell effects. Similarly, enhancement of the fission channel in the de-excitation cascade of 210Rn and 216Th is observed in this work and this result can be well modeled by the inclusion of collective effects into the statistical decay of excited nuclei calculations. These results suggest that cross sections for production of superheavy nuclei near predicted Z=120, N=184 closed shells may be small regardless of the anticipated strong shell effects. [Preview Abstract] |
Sunday, April 1, 2012 10:06AM - 10:18AM |
G11.00009: Event-by-Event Fission Modeling with FREYA Ramona Vogt, Jorgen Randrup The recently developed code $\mathtt{FREYA}$ (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. Concentrating on $^{239}$Pu$(n,f)$ and $^{252}$Cf(sf), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also suggest novel fission observables that could be measured with modern detectors. [Preview Abstract] |
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