Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session CH: Nuclear Structure: 60<A<110 |
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Chair: William Walters, University of Maryland Room: Lamy |
Thursday, November 4, 2010 8:30AM - 8:42AM |
CH.00001: $E2$ decay rates from ($n,n'\gamma$) measurements of $^{62}$Ni A. Chakraborty, S.F. Ashley, B. Crider, E. Elhami, M.T. McEllistrem, S. Mukhopadhyay, J.N. Orce, E. Peters, S.W. Yates The low-lying levels of $^{62}$Ni have been explored via the ($n,n'\gamma$) reaction, and the lifetimes of many excited levels have been measured using the Doppler-shift attenuation method. Results from earlier inelastic neutron scattering measurements deviate from what has been accepted in the latest version of the NNDC database. For the present measurements, incident neutron energies were chosen as close to threshold for exciting the levels as was consistent with obtaining yields with good statistics. In this way, feeding to the level of interest from higher levels was avoided, guaranteeing results specific to that level. Enhanced $B(E2)$ values extracted from our measurements and spectral regularities seem to support the onset of vibrational collectivity in this nucleus, although deviations from a purely harmonic picture are present as well. Detailed results from the analysis will be presented. [Preview Abstract] |
Thursday, November 4, 2010 8:42AM - 8:54AM |
CH.00002: Studies of A=76 Nuclei with Inelastic Neutron Scattering B.P. Crider, S.F. Ashley, A. Chakraborty, M.T. McEllistrem, E.E. Peters, S.W. Yates Following the observation of neutrinoless double-beta decay, an accurate calculation of the nuclear matrix elements (NMEs) is vital to reach quantitative conclusions about the absolute neutrino mass scale as well as the mass hierarchies. Understanding the nature of the wave functions of the participating states for double-beta decay is of fundamental importance in determining the NMEs. One of the prominent candidates for neutrinoless double-beta decay is $^{76}$Ge, which decays to $^{76}$Se. In order to further investigate these nuclei and provide information for the calculation of the NMEs, excitation function and gamma-ray angular distribution measurements utilizing the $^{76}$Ge$(n, n'\gamma)$ and $^{76}$Se$(n, n'\gamma)$ reactions were performed at the University of Kentucky. Lifetimes will be determined using the Doppler-shift attenuation method. [Preview Abstract] |
Thursday, November 4, 2010 8:54AM - 9:06AM |
CH.00003: Fine Structure of the Giant \textit{M}1 Resonance in $^{90}$Zr G. Rusev, E. Kwan, A.P. Tonchev, W. Tornow, A.S. Adekola, S.L. Hammond, C. Huibregtse, J.H. Kelley, S. Frauendorf, F. D\"onau, R. Schwengner, A. Wagner The High-Intensity $\vec{\gamma}$-ray Source of the Triangle Universities Nuclear Laboratory, in connection with high-resolution Ge detectors, opens up the possibility to deduce precisely the strengths and locations of individual $M1$ transitions, comprising the giant $M1$ resonance, and to distinguish them unambiguously from $E1$ and $E2$ deexcitations. We will present the results of an investigation of the fine structure of the giant $M1$ resonance in $^{90}$Zr performed with polarized and mono-energetic photon beams from 7 to 11 MeV. The strength of numerous $M1$ transitions will be compared to calculations using the quasiparticle-random-phase approximation in a Wood-Saxon potential and with the Instantaneous Shape Sampling model in order to study the observed fragmentation. [Preview Abstract] |
Thursday, November 4, 2010 9:06AM - 9:18AM |
CH.00004: Mysteries of GMR strengths in A $\sim$ 90 region Krishichayan, Dave Youngblood, Y.-W. Lui, J. Button The giant monopole resonance (GMR) in $^{90}$Zr [1] is an almost symmetric peak with a second component at higher energy that significantly affects the energy of the GMR and hence the nuclear compressibility extracted from its position. We have studied several Zr and Mo nuclei to investigate this second component. For $^{90}$Zr and $^{96,100}$Mo the lower narrow peak at E$_{x} \quad \sim $15-17 MeV contains the bulk of the E0 strength whereas the upper peak at E$_{x}\sim $24 MeV in these nuclei contains less than 25{\%} of the E0 EWSR. However the addition of two nucleons to $^{90}$Zr results in a very different picture. In $^{92}$Zr, the higher peak at E$_{x}\sim $25.5 MeV contain 38{\%} of the E0 EWSR and in $^{92}$Mo the higher peak at E$_{x}\sim $24 MeV contains 65{\%} of the E0 EWSR while only 42{\%} is located in the narrow lower peak. Due to this pronounced high energy component, the centroid energy in $^{92}$Mo is more than 2 MeV higher than in $^{90}$Zr. The energies of the lower peaks in these nuclei changes as expected ($\sim $A$^{-1/3})$ while the energies of the higher peaks are close to the same. In order to explore the feature in detail, data from $^{90,92,94}$Zr and $^{92,94,96,98,100}$Mo are being analyzed and the results will be presented. [1] D.H.Youngblood. et al., PRC 69, 054312 (2004) [Preview Abstract] |
Thursday, November 4, 2010 9:18AM - 9:30AM |
CH.00005: Multipole mixing ratios of $\gamma$-band to ground band transitions in neutron-rich Mo and Ru isotopes B.B. Fenker, C. Goodin, J.H. Hamilton, A.V. Ramayya, S.H. Lui, J.K. Hwang, N.T. Brewer, Y.X. Luo, A. Daniel, G. Ter-Akopian, Y. Oganessian, J.O. Rasmussen, S.J. Zhu Multipole mixing ratios, $\delta $(E2/M1) for the $\Delta $I=0,1 transitions from the $\gamma $ vibrational bands to the ground bands in neutron-rich nuclei $^{104-108}$Mo and $^{106-112}$Ru were determined from $\gamma -\gamma (\theta )$ correlations. The prompt $\gamma -\gamma -\gamma $ coincidences in the spontaneous fission of $^{252}$Cf were measured with Gammasphere. The data were sorted first into 64 angle bins and then compressed into 17 angle bins. The $\gamma -\gamma (\theta)$ data between two transitions were analyzed directly or by gating the data by transitions that feed or follow the two transitions of interest. Special interest was given to eliminate unwanted transitions of similar energy by selecting different gate transitions. The E2/M1 mixing ratios were measured for 2$_{\gamma }$-2$_{g}$, 3$_{\gamma}$-2$_{g}$, up to 9$_{\gamma}$-8$_{g}$ in some nuclei. All the accurate $\delta $ values yielded E2 $>$ 95{\%}. [Preview Abstract] |
Thursday, November 4, 2010 9:30AM - 9:42AM |
CH.00006: Half-lives of $^{101}$Rh, $^{102}$Rh and $^{102m}$Rh Howard A. Shugart, Eric B. Norman, Edgardo Browne Although $^{102, 102m}$Rh half-lives are known,\footnote{Shibata M., et al., Appl. Radio. Isot. 49, No.12, 1481 (1998)} the $^{101}$Rh half-life was previously determined only to within 9{\%}. A .5 x .5 x .050 in. rhodium piece was irradiated with 40 MeV protons at the LBNL 88-in. cyclotron producing the reactions $^{103}$Rh(p,3n)$^{101}$Pd, which decays to $^{101}$Rh, as well as $^{103}$Rh(p,t)$^{101}$Rh, $^{103}$Rh(p,pn) and (p,d)$^{102, 102m}$Rh. Two- or three-day spectra of the foil were taken using a HPGe detector weekly or every two weeks. 66 days after bombardment the shorter-lived activities had mostly decayed leaving only $^{101,102,102m}$Rhodium. The gamma spectra of three rhodium isotopes have, thus far, been followed for 475 days. Using the decay of the 127-, 198-, and 325-keV gammas for $^{101}$Rh, 556-keV for $^{102}$Rh, and 698- and 767-keV for $^{102}$Rh, our preliminary, self-consistent, half-life results shown in \textbf{{\{} {\}}} are compared with previous values shown in [ ]: [$^{101}$Rh $\sim $2.9y, 3.0(4)y, 3.3(3)y] \textbf{{\{}}3.9(2)y\textbf{{\}}} [$^{102m}$Rh 2.1(9)y, 3.742(10)y$^{a}$] \textbf{{\{}}3.6(1)y\textbf{{\}}} [$^{102}$Rh 210(6)d, 205(10)d, 207.3(17)d$^{a}$]$^{ }$\textbf{{\{}}206.3(8)d\textbf{{\}}} [Preview Abstract] |
Thursday, November 4, 2010 9:42AM - 9:54AM |
CH.00007: Isotopic Dependence of Giant Monopole Resonance (GMR) in the $^{106-116}$Cd isotopes and the asymmetry term in nuclear incompressibility D. Patel, U. Garg, M. Fujiwara, H. Akimune, G.P.A. Berg, M.N. Harakeh, M. Itoh, M. Ichikawa, T. Kawabata, K. Kawase, R. Matsau, B.K. Nayak, S. Okumura, T. Terazono, M. Uchida, H.P. Yoshida, M. Yosoi The asymmetry term associated with the neutron excess, K$_{\tau}$, plays a very important role in the Equation of State (EOS) for neutron matter. The GMR studied over a series of isotopes provides a direct way to measure this term. We have measured GMR strength distributions in even A, $^{106-116}$Cd isotopes in an experiment performed at RCNP, Osaka University, Japan. Measurements were taken at forward angles, including 0\r{ }, using a 400 MeV $\alpha $ beam. The results affirm the conclusions of a recent experiment with the Sn isotopes. The constraints put by values of K$_{\tau}$ and K$_{\infty}$, obtained from this experiment on the effective interaction currently in use in nuclear structure and EOS calculations, will be discussed. [Preview Abstract] |
Thursday, November 4, 2010 9:54AM - 10:06AM |
CH.00008: Precise Lifetime Measurements in $^{98}$Ru using Inverse Coulomb Excitation D. Radeck, V. Werner, G. Ilie, T. Ahn, R. Casperson, A. Heinz, E. Wiliiams, M. Smith, L. Bettermann, R. Chevrier, D. McCarthy, V. Anagnostatou The mass region A$\approx$90-100 is of great interest in the study of the evolution of proton-neutron collectivity from spherical to deformed nuclei. Controversial publications concerning the vibrational character of ${98}$Ru can be found in literature [1.2]. To get a comprehensive understanding of the structure, absolute transition strengths are important. With large uncertainties in essential quantities like the $B_{4/2}$ value, theoretical interpretations remain difficult. In order to reduce uncertainties, the RDDS method using inverse Coulomb excitation was used to measure lifetimes. This technique, combined with the selective reaction, yields high precision lifetimes but several corrections are required due to relativistic and deorientation effects. Analysis techniques and results will be presented. New results on the absolute transition strengths are compared to known data on other nuclei in the mass region. [1] B. Cakirli et al., PRC 70, 044312 (2004). [2] E. Williams et al., PRC 74, 024302 (2006). This work was supported by the US DOE grant no. DE-FG02-91ER-40609 and D.R. thanks for financial support by the German Academic Exchange Service (DAAD). [Preview Abstract] |
Thursday, November 4, 2010 10:06AM - 10:18AM |
CH.00009: Relative magnetic moments in $^{106,108}$Pd from the new g-plunger technique G. Ilie, V. Werner, J.R. Terry, D. Radeck, T. Ahn, L. Bettermann, R.J. Casperson, R. Chevrier, N. Cooper, A. Heinz, E. Holland, D. McCarthy, M.K. Smith, E. Williams, C. Beausang, T.C. Bonniwell, B. Pauerstein The aim of the present work was the proof-of-principle for the new g-plunger technique to measure the deorientation and the lifetime of a state after an inverse kinematics reaction. The deorientation effect, observed in nuclei recoiling from thin targets into vacuum, is due to the hyperfine interactions between the nuclear spin and the surrounding electron configurations. The attenuation of $\gamma$-ray angular distributions has been measured for the $2^+_1$ states in $^{106}$Pd and $^{108}$Pd. $^{106,108}$Pd beams with energies of 330~MeV and 336~MeV, respectively, were Coulomb excited into their $2^+_1$ state on a $^{24}$Mg target. Forward scattered Mg was detected, passing a Cu foil which served as a stopper for the beam. We measured the time-dependence of the attenuation as a function of distance, in parallel to measuring the lifetimes of the $2^+_1$ states via RDDS method. This the attenuation is used to measure the g factor of the decaying states relative to each other. The results of this work will be presented. [Preview Abstract] |
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