Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session MF: Nuclear Structure VII |
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Chair: Noemie Koller, Rutgers University Room: 104AB |
Saturday, October 29, 2011 8:30AM - 8:42AM |
MF.00001: The $g$ factor of the 2$^+_1$ state in $^{126}$Sn G.J. Kumbartzki, N. Benczer-Koller, D.A. Torres, G. G\"urdal, C.J. Gross, A. Galindo-Uribarri, C. Bingham, N. Stone, A.E. Stuchberry, K.-H. Speidel In the quest to develop the necessary tools and gather experience in using the transient field technique to measure $g$ factors of low-lying short-lived nuclear states in radioactive beam experiments, the $^{126}$Sn (t$_{1/2} = 2.3\cdot10^5$ years) will be measured at the HRIBF, ORNL. Each radioactive beam experiment presents its own set of problems and challenges due to the radioactive background from the beam and beam contaminants and their life times, and the low beam intensity. This experiment is a test with a very long lived, nearly stable beam. The target is designed to stop the reaction products in the backing of the target but to allow the bulk of the beam to pass through and stop in a foil placed between the target and the particle detector. This foil can be changed in the course of the experiment, should it become too radioactive. The experiment is scheduled to run in July 2011. Success or failure will provide a wealth of information on working in different radioactive environments and will extend the spectroscopic information on g factors of 2$^+_1$ states in Sn isotopes. The transient field measurement will provide the sign of the $g$ factor. [Preview Abstract] |
Saturday, October 29, 2011 8:42AM - 8:54AM |
MF.00002: Measuring $g$ factors of $4_1^+$ and $6_1^+$ states in even-even nuclei with 80$<$A$<$100 Diego Torres, N. Benczer-Koller, G. Kumbartzki, G. G\"urdal, Y.Y. Sharon, L. Zamick, K.-H. Speidel, G. Ilie, A. Heinz, T. Ahn, V. Werner, S.J.Q. Robinson The measurement of $g$ factors of the low lying excited states in even-even nuclei with lifetimes of the order of 1 to 50 picoseconds presents challenging questions for both theory and experiment. The experimental determination of accurate $g$ factor values uses the transient field technique in inverse kinematics and requires an understanding of the reaction mechanism used to populate the final states. So far, the main method of excitation has been Coulomb excitation. More recently, alpha transfer from a $^{12}$C target to selected beams made it possible to populate states in nuclei not available as stable beams. This method has been successful for lighter nuclei up to A$\sim$70~[1]. A comparison between Coulomb excitation and alpha transfer reactions will be presented. The experiments used the Tandem at the Wright Nuclear Structure Laboratory at Yale University. Preliminary results for the $^{100}$Pd, $^{96}$Ru and $^{86}$Sr nuclei will be presented. Experimental challenges for future experiments will be discussed. \\[4pt] [1]~J. Leske, {\it et al}., Phys. Rev. C{\bf71}, 044316, (2005). [Preview Abstract] |
Saturday, October 29, 2011 8:54AM - 9:06AM |
MF.00003: Lifetime and relative g factor measurements in $^{104,106,108}$Pd isotopes G. Ilie, V. Werner, D. Radeck, T. Ahn, C.W. Beausang, L. Bettermann, R.J. Casperson, R. Chevrier, N. Cooper, T.C. Bonniwell, A. Heinz, E. Holland, D. McCarthy, B. Pauerstein, M.K. Smith, J.R. Terry, E. Williams The purpose of this research 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 is due to the hyperfine interaction between the nuclear spin and the surrounding electron configurations. The attenuation of $\gamma$-ray angular distributions has been measured for the $2^+_1$ and $4^+_1$ states of $^{104}$Pd, $^{106}$Pd and $^{108}$Pd. The beams with energies of 324~MeV, 330~MeV and 336~MeV, respectively, were Coulomb excited into their $2^+_1$ state on a $^{24}$Mg target. Forward scattered Mg was detected after 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 $2^+_1$ and $4^+_1$ states. This attenuation is used to measure the g factor of the decaying states relative to each other. In this work, hyperfine parameters have been calibrated for the Pd isotopes. The results of this work and a discussion of the parameterization used to fit the data in this work will be presented. Research was supported by the U.S. Department of Energy under Grant No. DE-FG02-91ER-40609. [Preview Abstract] |
Saturday, October 29, 2011 9:06AM - 9:18AM |
MF.00004: Connecting the Super-Heavy Island to the Nuclear Mainland K. Rykaczewski, K. Miernik, R. Grzywacz, D. Miller The reactions between radioactive actinide targets and doubly-magic $^{48}$Ca beam led the identification of 6 new super-heavy elements (SHE) and 48 nuclei. Since the observed decay chains are ended by a fission process, these super-heavy nuclei are forming an isolated island in the nuclear chart. The HRIBF development of new detector system and digital data acquisition sensitive to very short-lived $\alpha$-emitters made possible to attempt the studies extending the SHE island. The experiments aiming in new nuclei produced in the reactions with $^{248}$Cm and $^{239,242}$Pu targets and $^{40,44,48}$Ca projectiles and connecting the SHE island to the known nuclear mainland will be discussed. [Preview Abstract] |
Saturday, October 29, 2011 9:18AM - 9:30AM |
MF.00005: Internal conversion electron study of excited states in $^{76}$As F.M. Prados-Est\'{e}vez, S.W. Yates, B.P. Crider, E.E. Peters, T. Kib\`{e}di, G.D. Dracoulis, R.F. Leslie, A.E. Stuchbery, N.M. Cooper, V. Werner, T. Williams, A.P. Tonchev Experiments on $^{76}$Ge and $^{76}$Se are revealing new information about double beta decay and giving better insight into whether or not the neutrino is Majorana particle. New data on intermediate nucleus $^{76}$As, which is virtually populated by double beta decay modes (2$\nu\beta\beta$, 0$\nu\beta\beta$), should lead to important constraints on the theoretical models that allow the determination of the neutrino mass. We carried out the $^{76}$Ge(p,n$\gamma$e$^{-}$)$^{76}$As reaction at 6.0 MeV at the ANU. Internal conversion coefficients have been obtained, giving better insight into the level structure of $^{76}$As. First results of the ongoing data analysis will be presented. [Preview Abstract] |
Saturday, October 29, 2011 9:30AM - 9:42AM |
MF.00006: Proof-of-principle measurement of beta-delayed neutron precursor 89Br using VANDLE Stanley Paulauskas, R. Grzywacz, M. Madurga, S. Padgett The Versatile Array of Neutron Detectors at Low Energy (VANDLE) uses the time of flight technique to measure the energy of neutrons from various nuclear processes. Beta delayed neutrons from fission fragments typically have an energy below 1 MeV, making measurements of their energy challenging. This has led to the use of a reliable off-the-shelf digital electronics system to instrument VANDLE. However, the timing resolution and neutron-energy threshold of the system required investigation. Timing resolutions better than 1 ns have been obtained. The digital system can be operated with low thresholds to obtain high detection efficiency for low energy neutrons (E$>$150 keV). A proof-of-principle experiment using $^{89}$Br was conducted at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). $^{89}$Br is produced in proton induced fission of $^{238}$U and was chosen because its neutron energy spectrum has been measured by G. Ewan et. al.(Z. Phys. A. 318, 309-314, (1984)). [Preview Abstract] |
Saturday, October 29, 2011 9:42AM - 9:54AM |
MF.00007: Partitioning the double $\beta$ decay of $^{116}$Cd: Electron-capture on $^{116}$In C. Wrede, I. Ahmad, A. Algora, V.-V. Elomaa, T. Eronen, A. Garc{\'I}a, J. Hakala, V.S. Kolhinen, I.D. Moore, H. Penttil{\"a}, M. Reponen, J. Rissanen, A. Saastamoinen, S. Sjue, H.E. Swanson, J. {\"A}yst{\"o} $^{116}$Cd undergoes double $\beta$ decay to $^{116}$Sn. This rare process may be described by virtual transitions through states in the intermediate nucleus $^{116}$In and there could be a major contribution from the $^{116}$In ground state. It is, therefore, valuable to determine the matrix elements for the decays of $^{116}$In to $^{116}$Cd and $^{116}$Sn in order to provide benchmarks for nuclear models that are used to calculate double $\beta$ decay matrix elements. We have experimentally constrained the small decay branch for electron capture on the ground state of $^{116}$In. Samples of $^{116}$In were produced using the IGISOL facility at the University of Jyv{\"a}skyl{\"a}, isobarically purified using the JYFLTRAP double-Penning trap, and delivered to a counting station consisting of a high-purity Ge x-ray detector and a 4$\pi$ scintillator to discriminate $\beta$-decay events. Our result sheds light on discrepancies between past values for the Gamow-Teller strength obtained via electron capture and charge-exchange, providing a more consistent benchmark in the $A=116$ system for nuclear models of double $\beta$ decay. [Preview Abstract] |
Saturday, October 29, 2011 9:54AM - 10:06AM |
MF.00008: ${}^{69}$Kr $\beta$-delayed proton emission A.M. Rogers, C.J. Lister, J.A. Clark, S.M. Fischer, S. Gros, E.A. McCutchan, G. Savard, D. Seweryniak, J. Giovinazzo, B. Blank, G. Canchel, G. de France, S. Grevy, F. de Oliveira Santos, I. Stefan, J.-C. Thomas Proton-rich nuclei beyond the $N=Z$ line play a key role in our understanding of astrophysics, weak-interaction physics, and nuclear structure tests. In particular, the decay of ${}^{69}$Kr populates states in the proton-unbound nucleus ${}^{69}$Br. While recent measurements of ${}^{65}$As and ${}^{69}$Br have constrained key $rp$- process waiting points, spectroscopic and structural information remains elusive. An experiment was conducted at GANIL which utilized implant-$\beta$-$p$ and $\beta$-$\gamma$ correlations to study physics related to the $\beta$ decays of ${}^{69,70,71}$Kr. Isotopes were implanted into a Si-DSSD, also used to detect decay protons, located at the end of the LISE spectrometer. Coincident $\gamma$-rays were measured in surrounding HpGe EXOGAM clovers. We identified $212$ ${}^{69}$Kr implantation-decay events and observed a dominant superallowed $\beta$-decay branch ($T_{1/2}=27(3)$~ms) to the isobaric analog state which decays via $2.97(5)$~MeV protons to the first excited state in ${}^{68}$Se. This decay path strongly constrains the spin and mass of ${}^{69}$Kr. [Preview Abstract] |
Saturday, October 29, 2011 10:06AM - 10:18AM |
MF.00009: Beta-decay of $^{122}$Ag and structure of $^{122}$Cd A.V. Ramayya, Y.X. Luo , N.T. Brewer , J.C. Batchelder , J.H. Hamilton , C.J. Gross, K.P. Rykaczewski, R. Grzywacz, M. Madurga, D. Miller, D. Stracener, C. Jost, E. Zganjar, J.A. Winger, M. Karny, S.V. Paulauskas, S.H. Liu, M. Wolinska-Cichocka, S. Padgett, T. Mendez, K. Miernik, A. Kuzniak The structures of even-even Cd nuclei are considered to be an important testing ground for vibrational states coupled to intruder states with rotational degrees of freedom. In addition, there may be up to 3 isomeric states in $^{122}$Ag. Two of them are very similar in their adopted values for lifetime. We produced a $^{122}$Ag nucleus via proton induced fission of $^{238}$U. Subsequent decay of $^{122}$Ag to $^{122}$Cd is investigated at the Low-energy RIB Spectroscopy Station (LeRIBSS) at the HRIBF. Many new levels and new gamma transitions in $^{122}$Cd were observed. The parent half-life was also observed. The structure of this isotope will be discussed. [Preview Abstract] |
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