Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session Q9: Nuclear Structure |
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Sponsoring Units: DNP Chair: Carlos Bertulani, University of Arizona Room: Hyatt Regency Dallas Cumberland B |
Monday, April 24, 2006 1:30PM - 1:42PM |
Q9.00001: The correlation of nucleon masses to nuclear stability is investigated E. Pamfiloff The decay chains and series of unstable isotopes and radioisotopes are studied with particular detailed analysis of nuclei masses and the change in mass experienced by individual nucleons of parent, daughter and product isotopes or other emissions. The data shows a direct correlation between the nucleon mass of a stable product nucleus and that of an unstable parent or daughter nucleon during the transition. This suggests that in addition to proton and neutron quantities, nuclear stability is dependent upon specific mass benchmarks for the nucleons of stable nuclei. It also indicates the probability that 238U is the parent of a series of stable and unstable isotopes situated below the Pb threshold with an unambiguous connection to stable 56Fe nucleons. To confirm these conclusions, the natural and artificial alpha emitter isotopes were also evaluated by the meticulous analysis of nucleon masses relative to the 1H proton. The developed database and system of evaluation allow those decay chain products of uncertain origin to be traced from unstable or stable nuclei back to the immediate source isotope in the series and then to the most probable origin. Often, more than one possible transition source isotope is identified. The system provided good results when tested against the incident and product particles of high and low energy interactions, including events of nuclear transmutation. Every transition from the initial nuclide to the final stable daughter or product demonstrates a strong correlation with a specific mass benchmark per nucleon as a third condition of nuclear stability. [Preview Abstract] |
Monday, April 24, 2006 1:42PM - 1:54PM |
Q9.00002: Moments Method for the Nuclear Density of States Edgar Teran, Calvin Johnson We utilize statistical spectroscopy to model the nuclear level density in the interacting shell model. Low-lying statistical moments of each configuration of the shell model space are computed. Partial (configuration) densities are generated from the moments, and the sum of all the contributions is the total level density. Modified Breit-Wigner (MBW) distributions are used to model the partial densities. The properties of such functions allow for exact reproduction of the moments at large asymmetries, which are needed to accurately reproduce the overall level density. We work in the sd-shell with USD interaction, and the pf-shell with GXPF1, FPD6G an KB3G interactions. Results from level densities generated with method will be shown in the sd-shell and pf-shell, as well as comparisons to exact calculations and experimental data. [Preview Abstract] |
Monday, April 24, 2006 1:54PM - 2:06PM |
Q9.00003: Level density of $^{60}$Ni from $^{59}$Co(d,n) and $^{58}$Fe($^{3}$He,n) reactions. A.V. Voinov, S.M. Grimes, S.I. Al-Quraishi, C.R. Brune, M.H. Hadizadeh, M.J. Hornish, T.N. Massey, J. O'Donnell, A. Salas The level density of $^{60}$Ni in the region below the particle separation energy has been obtained from neutron evaporation spectra measured in the $^{59}$Co(d,n) and $^{58}$Fe($^{3}$He,n) reactions at the Edwards Accelerator Laboratory at Ohio University. The main limitation of such a technique is an unknown distortion of the neutron spectra due to direct and pre-equilibrium reaction mechanisms. The purpose of this experiment was to measure the level density of $^{60}$Ni and estimate the contribution of the direct reaction mechanism, which is expected to be different for different incoming particles. The energy spectra and angular distribution of neutrons have been measured from both reactions. Both angular distributions exhibit a forward peaking shape due to the contribution from direct reaction mechanism The level density function has been extracted from neutron spectra taken from backward angles. The good statistics in the region of known discrete levels of residual $^{60}$Ni allowed one the absolute normalization of the obtained level density function. The level densities of $^{60}$Ni obtained from both reactions agree well, which indicates that the compound reaction is the major contribution to the differential reaction cross sections taken from backward angles. The Fermi-gas level density parameters have been obtained and compared to systematics. [Preview Abstract] |
Monday, April 24, 2006 2:06PM - 2:18PM |
Q9.00004: High-spin states in $^{83}$Se N. Fotiades, A.F. Lisetskiy, J.A. Cizewski, R. Kr\"{u}cken, R.M. Clark, P. Fallon, I.Y. Lee, A.O. Macchiavelli, J.A. Becker, W. Younes High-spin states in $^{83}$Se have been studied following the fission of the $^{226}$Th compound nucleus formed in a fusion-evaporation reaction ($^{18}$O at 91~MeV on $^{208}$Pb). The Gammasphere array was used to detect $\gamma$-ray coincidences. This is the first observation of high-spin states above the 9/2$^{+}$ ground state of this nucleus and extends the level scheme up to spin (17/2$^{+}$). The coupling of the neutron hole in the $g_{9/2}$ orbital, which forms the ground state of $^{83}$Se, to the 2$^{+}$ and 4$^{+}$ yrast states in the $^{84}$Se core can account for the first four high-spin states in $^{83}$Se. There is generally good agreement between the experimentally observed high-spin states and predictions of shell-model calculations. This work has been supported in part by the U.S. Department of Energy under Contracts No. W-7405-ENG-36 (LANL), AC03-76SF00098 (LBNL) and W-7405-ENG-48 (LLNL) and by the National Science Foundation (Rutgers). [Preview Abstract] |
Monday, April 24, 2006 2:18PM - 2:30PM |
Q9.00005: Internal Conversion Coefficient Measurements of Transitions in $\mathrm{^{167}Lu}$ G. G\"urdal, C.W. Beausang, D.S. Brenner, H. Ai, R.F. Casten, A. Heinz, E. Williams, B. Crider, R. Raabe, D.J. Hartley, M. Carpenter, R.V.F. Janssens, T. Lauritsen, C.J. Lister, D. Seweryniak, S. Zhu, A.A. Hecht, J.X. Saladin Experimental internal conversion coefficients can be used to determine the multipolarities of electromagnetic transitions between nuclear energy levels and thus are valuable for assigning or confirming spins and parities of excited states. The normal and highly deformed bands of $\mathrm{^{167}Lu}$ were populated by the $\mathrm{^{123}Sb}(\mathrm{^{48}Ca}$,4n) reaction. Five fold $\gamma$ or $\gamma$-$\gamma$-e coincidence measurements were performed using Gammasphere and ICE Ball arrays at ANL. Internal conversion coefficients were determined for transitions in $\mathrm{^{167}Lu}$ and multipolarities were deduced. The preliminary results of the analysis will be presented. This work was supported by the U.S.D.O.E grants DE-FG02-88ER40417, DE-FG02-91ER-40609, DE-FG-05NA25929, DE-FG02-05ER41379, by the NSF grant number PHY-0300673 and in part by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. W-31-109-ENG-38. [Preview Abstract] |
Monday, April 24, 2006 2:30PM - 2:42PM |
Q9.00006: Further tests of internal-conversion theory with precise $\gamma $- and x-ray spectroscopy. N. Nica, W.E. Rockwell, J.C. Hardy, V.E. Iacob, H.I. Park, J. Goodwin, M.B. Trzhaskovskaya Recently we reported [1] a measurement of the $K$-shell internal conversion coefficient (ICC) of the 80.2-keV $M4$ transition in $^{193}$Ir$^{m}$. Our result, $\alpha _{K}$=103.0(8), agreed well with the value 103.5(1) calculated with the $K$-shell hole accounted for in the ``frozen orbital'' approximation, and disagreed strongly with the value 92.2(1) calculated when the hole is ignored, a common approach taken in the past. Of the 100 transitions listed and compared with theory in the review by Raman \textit{et al.} [2], this is the most sensitive to the treatment of the hole. However, there are some other cases listed where experiment disagrees significantly with both types of calculation, making it difficult for one to whole-heartedly endorse the ``frozen orbital'' calculation. As a further step in settling this issue, we report here a measurement of the ratio of $\alpha _{K}$ values for the 127.5-keV $E3$ transition in $^{134}$Cs$^{m}$ and the 662-keV $M4$ transition in $^{137}$Ba. Our preliminary result, $\alpha _{K}$(Cs)/$\alpha _{K}$(Ba)=30.4(3), should be compared with the experimental ratio quoted in [2], 28.8(5), and with calculated ratios, 30.0 (hole) and 29.5 (no hole). The disagreement between experiment and theory is now removed and, furthermore, our result again points to the calculation that includes the hole. [1] N. Nica et al., Phys. Rev. C 70 (2004) 054305, [2] S. Raman et al., Phys. Rev. C 66 (2003) 044312. [Preview Abstract] |
Monday, April 24, 2006 2:42PM - 2:54PM |
Q9.00007: Search for the Wobbling Mode in $^{171}$Ta D.J. Hartley, W.H. Mohr, J.R. Vanhoy, M.A. Riley, A. Aguilar, C. Teal, R.V.F. Janssens, M.P. Carpenter, F.G. Kondev, A.A. Hecht, T. Lauritsen, E.F. Moore, S. Zhu, M.K. Djongolov, M. Danchev, L.L. Riedinger, G.B. Hagemann, G. Sletten, P. Chowdhury, S.K. Tandel, W.C. Ma, S.W. Odegard Perhaps the strongest evidence for a nucleus possessing {\it stable} triaxial deformation is the observation of a wobbling excitation. Such exotic sequences have been confirmed in $\pi i_{13/2}$ bands of $N\approx 94$ Lu nuclei [1], and the region may extend to $N\approx 100$ in Hf nuclei. However, it has not been possible to confirm the presence of wobbling structures in the heavier isotopes [2]. In order to determine whether stable triaxiality plays a role in $N\approx 100$ nuclei, an experiment was conducted to search for the wobbling mode in $^{171}$Ta. High-spin states in $^{171}$Ta were produced in the $^{124}$Sn($^{51}$V,$4n$) reaction and the $\gamma$ rays were detected with Gammasphere. Although the $i_{13/2}$ band was extended to (101/2), no wobbling structure was identified. The implications of this result on the region of triaxiality will be discussed. [1] S.W. Odegard {\it et al.}, Phys. Rev. Lett. {\bf 86}, 5866 (2001). [2] D.J. Hartley {\it et al.}, Phys. Lett. B {\bf 608}, 31 (2005). [Preview Abstract] |
Monday, April 24, 2006 2:54PM - 3:06PM |
Q9.00008: Full major-shell calculation for states that are degenerate in a single-$j$-shell calculation Alberto Escuderos, Larry Zamick, Shadow Robinson In a previous work~\footnote{A.~Escuderos, B.F.~Bayman, L.~Zamick, and S.J.Q.~Robinson, Phys. Rev. C {\bf 72}, 054301 (2005)}, we explained why certain states were degenerate in the single $j$ shell for an interaction in which the isospin $T=0$ two-body matrix elements were set to zero. The degeneracy splitting was recovered by reintroducing the full interaction. In this work, we perform a full $fp$-shell calculation with the FPD6 interaction to obtain these energy splittings; the interaction obtained by setting the $T=0$ matrix elements to zero but keeping the $T=1$ ones unchanged will be called T0FPD6. Comparing the results with FPD6 and T0FPD6, we can see that most of the splitting in a complete shell calculation (but not all) comes from the $T=0$ part of the interaction. For example, the $(9^+_1-10^+_1)$ splitting in $^{44}$Ti is 1.214~MeV for FPD6, but it is only 0.094~MeV for T0FPD6. In $^{47}$V, the $(29/2^-_1-31/2^-_1)$ splitting is 0.780~MeV with FPD6, in agreement with the experimental value of 0.765~MeV, but T0FPD6 yields only 0.072~MeV. In general, we observe a continuity in the splittings between the single-$j$ and the full-$fp$ calculations; only in two cases we see an inversion of the states. These two cases involve low angular momentum states ($1/2^-$ in $^{43}$Sc and $3^+$ in $^{44}$Ti), for which there tends to be much more configuration mixing. [Preview Abstract] |
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