Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session J11: Nuclear Structure II: A>70 |
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Sponsoring Units: DNP Chair: Jolie Cizewski, Rutgers University Room: Garden 2 |
Sunday, May 1, 2011 1:30PM - 1:42PM |
J11.00001: High-spin states in neutron-rich Nb isotopes near the line of stability N. Fotiades, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, W. Younes The study of nuclei with a few valence particles outside the subshell closure nucleus of $^{96}$Zr$_{56}$ is interesting due to the rapid changes observed in their level structures. The addition of only four neutrons introduces considerable deformation and the addition of an extra proton in the neighboring Nb isotopes located close to the line of stability is likely to enhance this rapid change. We have recently established high-spin states in $^{97}$Nb~[1] by studying this nucleus as a fission fragment produced in heavy-ion induced reactions. The level pattern observed in $^{97}$Nb follows closely that of $^{96}$Zr. Next in the sequence of the odd-mass Nb isotopes is $^{99}$Nb for which only low-spin states ($<$~9/2 ground state) are known. High-spin states in heavier odd-mass Nb isotopes have been studied~[2] as actinide fission fragments, so $^{99}$Nb is the missing link in the systematics of high-spin states between the neutron-deficient and neutron-rich odd-mass Nb isotopes. Preliminary results on high-spin states in $^{99}$Nb studied as a fission fragment will be presented together with results in $^{97}$Nb. A comparison with excited states in neighboring N=56 and N=58 isotones will be discussed. This work was supported by the U.S. Department of Energy and the National Science Foundation. [1] N. Fotiades, {\it et al.}, Phys. Rev. C {\bf 82}, 044306 (2010). [2] Y. X. Luo, {\it et al.}, J. Phys. G {\bf 31}, 1303 (2005). [Preview Abstract] |
Sunday, May 1, 2011 1:42PM - 1:54PM |
J11.00002: ABSTRACT WITHDRAWN |
Sunday, May 1, 2011 1:54PM - 2:06PM |
J11.00003: Experimental Investigation of Nuclear Tidal Waves in ${}^{102}Pd$ A.D. Ayangeakaa, U. Garg, S. Frauendorf, J.T. Matta, D. Patel, R. Chakrabarti, S.S. Ghugre, S. Mukhopadhyay, M.P. Carpenter, F. Kondev, D. Seweryniak, S. Zhu The region of the transitional nuclei has been shown to exhibit yrast state properties that are intermediate between those of a rotor and a vibrator and have been described in the Tidal Wave theory as quadrupole running waves on the surface of the nucleus. The concept of nuclear tidal waves allows for the microscopic calculation of the energies and transition probabilities of yrast states by means of the cranked mean field theory. In the present study, we investigated this concept by measuring lifetimes of the yrast band in the ${}^ {102}Pd$ nucleus using the ${}^{76}Ge({}^{30}Si,4n){}^{102}Pd$ reaction with GAMMASPHERE. Tidal wave calculations have shown that ${}^{102}Pd$ is a candidate nucleus for affirming this phenomenon in the transitional region. The extracted B(E2)'s for the yrast band appear to follow the increase with spin predicted by theory. [Preview Abstract] |
Sunday, May 1, 2011 2:06PM - 2:18PM |
J11.00004: Continuum studies in Gd nuclei by particle-$\gamma $ coincidences T.J. Ross, R.O. Hughes, C.W. Beausang, J.M. Allmond, J.T. Burke, L.W. Phair, N. Scielzo, C.T. Angell, M.S. Basunia, D.L. Bleuel, R.J. Casperson, P. Fallon, R. Hatarik, J. Munson, S. Paschalis, M. Petri, J.J. Ressler An experiment was carried out at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory to study Gd isotopes in the vicinity of the N=90 transitional region. A 25 MeV proton beam was incident on $^{158/155/154}$Gd targets and used to populate states in $^{152-158}$Gd by (p,p'), (p,d) and (p,t) reactions. The exit channel is selected by gating on charged particles using the STARS Si-Telescope array, which also gives the excitation energy of the residual nucleus. Coincident $\gamma $ information is obtained using the LIBERACE Clover array. Particle-$\gamma $ coincidences provide a powerful tool for probing the residual nucleus [1]. For example, particles in coincidence with a specific $\gamma $ ray produce a spectrum representing all levels populated in the nucleus that subsequently decay into the state from which the $\gamma $ ray originates. Results will be presented that give an insight into the population distribution of the high level density region above the pair gap in the even-even Gd nuclei via light ion reactions. [1] J. M. Allmond et al. Phys.Rev.C 81, 064316 (2010) Work supported in part via DOE grant numbers DE-FG02-05 ER41379 {\&} DE-FG52-06 NA26206(University of Richmond), DE-AC52 07NA27344(LLNL) and DE-AC02 05CH11231(LBNL). [Preview Abstract] |
Sunday, May 1, 2011 2:18PM - 2:30PM |
J11.00005: Ultrahigh-spin spectroscopy of $^{168,171,172}$Hf W.C. Ma, S. Mukhopadhyay, R.B. Yadav, Y.C. Zhang, Q.A. Ijaz, J. Marsh, G.B. Hagemann, D.M. Cullen, L.L. Riedinger, D.J. Hartley, S. Lakshmi, S.S. Hota, P. Chowdhury, C.J. Chiara, M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, F.G. Kondev, T. Lauritsen, S. Zhu Strongly deformed bands have been observed up to spins 50 - 60 in $^{168,171,172}$Hf from Gammasphere experiments. We identified triaxial and prolate strongly deformed (TSD and SD) structures, as well as shapes with slightly enhanced deformation with respect to normal defomed states, associated with different bands. Cranking caulations agree in general with observations in mass 160 region, but failed to reproduce the SD bands in $^{172}$Hf and heavier Hf isotopes. Wobbling excitations, an experimental finger print of triaxial nuclei, have been established in neighboring Lu and Ta (odd-Z) isotopes, but not in any Hf (even-Z) isotopes which are located in the center of the prerdicted island of TSD structures. Possible reasons will be discussed. [Preview Abstract] |
Sunday, May 1, 2011 2:30PM - 2:42PM |
J11.00006: Search for the Exotic Wobbling Mode in $^{171}$Re E.E. Pedicini, D.J. Hartley, J.R. Vanhoy, M.A. Riley, X. Wang, R.V.F. Janssens, P.F. Bertone, M.P. Carpenter, C.J. Chiara, G. G\"{u}rdal, F.G. Kondev, T. Lauritsen, E.A. McCutchan, S. Zhu, L.L. Riedinger, A.D. Ayangeakaa, U. Garg, J.T. Matta, W. Ma, S. Mukhopadhyay, P. Chowdhury, S. Hota The observation of a wobbling band is a strong indication that a nucleus possesses triaxial deformation. The wobbling mode has been found in the $Z\approx 72$, $N\approx 94$ region in five Lu isotopes and in $^{167}$Ta and is associated with the $i_{13/2}$ band. In order to determine the role of the proton Fermi surface, an experiment was conducted to search for the wobbling mode in $^{171}$Re. High-spin states in $^{171}$Re were produced in the $^{120}$Sn($^{55}$Mn, $4n$) reaction and the gamma rays were detected with Gammasphere. Several bands have been found to feed into the $i_{13/2}$ structure, and their characteristics will be assessed to determine if these sequences are associated with wobbling. The implications of this result on the region of triaxiality will be discussed. [Preview Abstract] |
Sunday, May 1, 2011 2:42PM - 2:54PM |
J11.00007: Particle$\gamma $/fission studies of Uranium nuclei via (p,x) reactions R.O. Hughes, T.J. Ross, C.W. Beausang, J.T. Burke, N.D. Scielzo, J.M. Allmond, M.S. Basunia, C.M. Campbell, R.J. Casperson, H.L. Crawford, J. Munson, L. Phair, J.J. Ressler An experiment was conducted at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory to study the structure and measure (n,$\gamma )$/(n,fission) cross-sections (via surrogate reactions) of Uranium isotopes. A 28 MeV proton beam incident on$^{\mbox{ 2}\mbox{36}}$U and $^{\mbox{23}}$8U targets populated states in Uranium isotopes via (p,p'), (p,d) and (p,t) reactions. The STARS array was used for detection of the outgoing light ions for exit channel nucleus tagging (as well as nuclear excitation energy information), and included a detector at backward angles for fission events. Coincident$\gamma $ rays were detected using the 6 Clover detectors of the LIBERACE array and both p-$\gamma $ and p-fission events were collected. The data provide a number of results including internal surrogate ratio measurements of (n$\gamma )$/(n,fission) cross-sections, and detailed structure information for nuclear levels from the ground state to well above the neutron evaporation thresholds across a range of Uranium isotopes. Preliminary results will be presented. This work is supported in part by the U.S. Department of energy via grant numbers DE-FG02-05 ER41379 \& DE-FG52-06 NA26206(University of Richmond), DE-AC52 07NA27344(LLNL) and DE-AC02 05CH11231(LBNL). [Preview Abstract] |
Sunday, May 1, 2011 2:54PM - 3:06PM |
J11.00008: Experimental details for determining neutron-induced fission cross sections of picosecond states R.J. Casperson, J.T. Burke, I.J. Thompson, F.S. Dietrich, J.E. Escher, J.J. Ressler, N.D. Scielzo, E. Swanberg, W. Younes The first excited state neutron-induced fission cross section of $^{239}$Pu is not directly measurable, due to the short lifetime of the 8 keV 3/2+ excited state. We will use recent developments in transfer reaction theory to identify the angular momentum distribution of excited states in the pre-fission nucleus $^{240}$Pu$^*$. This nucleus will be produced in a (d,p) reaction on $^{239}$Pu, and the fission probability as a function of outgoing proton angle and energy will be measured. By combining this measurement with (d,p) reaction theory, the fission probability of individual angular momenta can be determined, and recombined into the excited state fission probability. The experimental details for measuring the proton distributions and fission probabilities will be described in detail. Recent progress in the development of the VME based data acquisition system will be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Sunday, May 1, 2011 3:06PM - 3:18PM |
J11.00009: Occupation-number-based energy functional for nuclear masses Michael Bertolli We consider an occupation-number based nuclear energy functional. It is based on the theorems by Hohenberg and Kohn, and the practical implementation follows the ideas of the mass formula by Duflo and Zuker. The global fit of a 15-parameter functional to known masses yields a RMS error of 0.95MeV with good extrapolation properties. This approach to nuclear masses is computationally much less expensive than nuclear density functionals. A simple model for nuclear radii also yields a satisfactory description of charge radii. [Preview Abstract] |
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