Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session BH: Nuclei far from Stability |
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Sponsoring Units: DNP JPS Chair: Michael Thoennessen, Michigan State University Room: Ritz-Carlton Hotel Plantation 1 |
Monday, September 19, 2005 7:00PM - 7:15PM |
BH.00001: First Penning Trap Mass Measurements of Rare Isotopes produced by Fast Beam Fragmentation G. Bollen, D. Davies, M. Facina, J. Huikari, E. Kwan, A. Prinke, D.J. Morrissey, R. Ringle, J. Savory, P. Schury, S. Schwarz, C. Sumithrarachchi, T. Sun LEBIT is a facility designed for Penning trap mass measurements on rare isotope produced by fast beam fragmentation. LEBIT has now been used to perform a precision mass measurement of the super-allowed $\beta $-emitter $^{38}$Ca. For this purpose $^{38}$Ca was produced via fragmentation of a $^{93}$MeV $^{40}$Ca beam. After appropriate degrading of its energy the $^{38}$Ca beam was stopped in the NSCL gas cell. A low energy beam was extracted in the form of doubly-charged $^{38}$Ca(H$_{2}$0)$_{n}$ molecules. A RFQ mass filter was used to select ($^{38}$Ca-H$_{2}$0)$^{2+}$ ions, which were transported into the gas-filled RFQ beam accumulator and buncher of LEBIT. Here the water was stripped off in collisions with Ne buffer gas. The resulting $^{38}$Ca$^{2+}$ ions were then transferred into LEBIT's 9.4T Penning trap mass spectrometer, where their mass was measured. This first direct measurement of the mass of $^{38}$Ca provides an improved mass value, making this isotope more suitable for contributing to the test of the conserved vector current hypothesis. The experiment is also the first successful demonstration that rare isotopes produced by beam fragmentation at energies of 100MeV/u can be slowed down and prepared such that precision experiments with low-energy beams are possible. [Preview Abstract] |
Monday, September 19, 2005 7:15PM - 7:30PM |
BH.00002: Mass determination of the lowest $T = 2$ state in $^{32}{\rm S}$ Smarajit Triambak, Alejandro Garcia, Gregory Hodges, Eric Adelberger, Erik Swanson, Seth Hoedl, Skykilo Sjue, Anne Sallaska We present data of a recent mass determination of the lowest $T = 2$ state in $^{32}$S ($E_x$ $\approx$ 12 MeV) with an uncertainty of $\approx$ 0.3 keV using the $^{31}$P$(p,\gamma)$ reaction. The state of interest was populated using the resonance at $E_p$ = 3285 keV and the decaying gammas of energies $\approx$ 8124 keV and 3923 keV were detected using HPGe detectors at $\pm90^\circ$ and $0^\circ$ to the incident beam. Systematic effects and implications to the Isobaric Multiplet Mass Equation for the A = 32 multiplet will be discussed. [Preview Abstract] |
Monday, September 19, 2005 7:30PM - 7:45PM |
BH.00003: Decay of $^{47-50}$Ar isotopes. Uffe Bergman, Joakim Cederkall, Luis Fraile, Serge Franchoo, Tomas Fritioff, Ulli Koester, Thomas Nilsson, Oliver Arndt, Iris Dillmann, Oliver Hallman, Karl-Ludwig Kratz, Bernd Pfeiffer, Laurant Gaudefroy, Oliver Sorlin, Alexandre Lisetsky Information on beta-decay properties of neutron-rich $^{47-50}$Ar was obtained at the ISOLDE mass-separator facility at CERN using isobaric selectivity. This was achieved by a combination of a plasma-ion source with a cooled transfer line and subsequent mass-separation. Most of these beams suffer from intense multi-charged symmetric fission contaminants that cannot be mass-separated from asymmetric fission argon products. The identification of the gamma-ray transitions from $^{47-50}$Ar decay was performed by comparing the spectra obtained from direct proton bombardment of the ISOLDE target and those obtained with the neutron converter. In addition, an Electron Cyclotron Resonance Ion Source (ECRIS) installed at ISOLDE was used for purification of the singly-charged $^{48}$Ar beam. The obtained data are compared to the result of large-scale shell model calculations and QRPA predictions. Implication of the obtained information for a better understanding of the origin of the $^{48}$Ca/$^{46}$Ca isotopic anomaly discovered in inclusions from the Allende meteorite is discussed. [Preview Abstract] |
Monday, September 19, 2005 7:45PM - 8:00PM |
BH.00004: Laser Spectroscopic Determination of the Nuclear Charge Radius of $^6$He and $^8$He P. Mueller, L.-B. Wang, K. Bailey, J.P. Greene, D. Henderson, R.J. Holt, R.V.F. Janssens, C.L. Jiang, Z.-T. Lu, T.P. O'Connor, R.C. Pardo, K.E. Rehm, J.P. Schiffer, X.D. Tang, G.W.F. Drake Laser spectroscopic measurements of atomic isotope shifts provide unique access to the nuclear charge distribution of short-lived isotopes. The isotopes of interest for this study are $^6$He (t$_{1/2}$ = 807 ms) and $^8$He (t$_{1/2}$ = 119 ms), which exhibit a loosely bound neutron halo around an $\alpha $-like core. Charge radii measurements of both isotopes provide corroboration for their halo structure and test nuclear structure theories of light nuclei. We have performed high-resolution laser spectroscopy on individual radioactive helium atoms captured in a magneto-optical trap. This technique enabled us to accurately measure the isotope shift between $^6$He and $^4$He in a selected atomic transition. Based on this result and precision atomic theory calculation of helium, the root-mean-square charge radius of the $^6$He nucleus could be determined to be 2.054(14) fm [1]. Currently, we are working to expand this technique to also measure the nuclear charge radius of $^8$He, and we will report on first results from this experiment. [1] L.-B. Wang {\it et al.}, PRL 93, 142501 (2004) [Preview Abstract] |
Monday, September 19, 2005 8:00PM - 8:15PM |
BH.00005: Beta-delay Neutron Emission from Heavy Nitrogen Isotopes David Morrissey, Chandana Sumithrarachchi, Don Anthony, Patrick Lofy Beta-delayed neutrons from the decay of $^{19,20}$N and most recently $^{22}$N have been measured for the first time using neutron time-of-flight spectroscopy. The nuclei were produced by projectile fragmentation reactions and the decays observed in a batch-mode experiment using plastic scintillators and germanium detectors. The half-lives, total neutron emission probability, and the branching to bound and neutron-unbound states were determined in the present work. The $\beta-\gamma$, $\beta-n$, and $\beta-n-\gamma$ coincidence data were used to construct level schemes for the oxygen daughters and the two lighter isotopes compare well to the results of other determinations. The results do not compare well to USD shell model calculations. [Preview Abstract] |
Monday, September 19, 2005 8:15PM - 8:30PM |
BH.00006: Level assignments of $^{11}$Be$^{\ast }$ through $\beta $-delayed low energy neutron emissions Yosuke Akasaka, T. Shimoda, K. Kawai, H. Izumi, I. Wakabayashi, Y. Hirayama, H. Miyatake, K.P. Jackson, C.D.P. Levy The low energy neutron emissions from $^{11}$Be$^{\ast }$ were studied in the $\beta $-n and $\beta $-n-$\gamma $ coincidence measurements from a \textit{spin-polarized} $^{11}$Li$_{gs}$. The spin-parity assignments for the $^{11}$Be$^{\ast }$ states were made based on the fact that the allowed $\beta $-transition from the polarized $^{11}$Li shows $\beta $-decay asymmetry depending on the spin value of the daughter state in $^{11}$Be. The experiment was performed at TRIUMF ISAC, where approximately 55{\%} nuclear-polarized $^{11}$Li beam was available. The $\beta $-decay asymmetries were measured in coincidence with the delayed neutrons from $^{11}$Be$^{\ast }$ and/or the subsequent $\gamma $-rays from $^{10}$Be$^{\ast }$. In the $\beta $-n coincidence, very low energy neutrons with E$_{n}$ = 73 (5) keV and 17 (1) keV were observed. From the $\beta $-decay asymmetries in coincidence with the respective neutron, the spins and parities of the neutron emitting states in $^{11}$Be were unambiguously determined to be 3/2- and 5/2-, respectively. From the $\beta $-n-$\gamma $ coincidence the level energies of the $^{11}$Be states were determined to be E$_{x}$ = 3.951(6) and 3.890(1) keV, respectively. The I$^{\pi }$ assignment for the former is consistent with that in the literature, whereas the latter is in contradiction to the previous assignment (3/2+) based on the $^{9}$Be(t,p)$^{11}$Be$^{\ast }$ reaction data. [Preview Abstract] |
Monday, September 19, 2005 8:30PM - 8:45PM |
BH.00007: Study of the $\beta$-decay of $^{32}$Na at ISAC/TRIUMF Caleb M. Mattoon, Fred Sarazin, Greg Hackman The $\beta$-decay of $^{32}Na$ is investigated at TRIUMF/ISAC. A beam of 2-3 atoms per second, produced by impinging a proton beam on a Tantalum target, was implanted on a tape at the center of the $8\pi$ + Sceptar array, a combination of 20 Compton-suppressed HPGe detectors and 20 plastic scintillators. The tape transport system removed long-lived daughter products from the array. Additionally, $(\beta\gamma)$-coincidences provided clean-up of the spectrum by removing events unrelated to the $\beta$-decay. Work is in progress in determining $\gamma$-emission schemes, relative intensities, and possible placements of unknown lines. [Preview Abstract] |
Monday, September 19, 2005 8:45PM - 9:00PM |
BH.00008: Measurement of the absolute B(E2;0$^+ _1 \rightarrow$2$^+ _1$) strength in the $^{106-110}$Sn isotopes via intermediate-energy Coulomb excitation. C. Vaman, D. Bazin, A. Becerril, A. Chester, J. Cook, A. Gade, D. Galaviz, T. Glasmacher, V. Moeller, W. Mueller, T. Russ, A. Schiller, K. Starosta, C. Andreoiu Sn isotopes at Z=50 provide the longest shell-to-shell chain of semi-magic nuclei investigated to date in nuclear spectroscopy. The nearly constant energy of the first excited 2$^+ _1$ states for isotopes between N=50 and N=82 is attributed to the fact that the valence nucleons of one kind outside the doubly magic core do not affect the near-spherical nuclear shape. Except for the stable Sn isotopes, the B(E2, 0$^+ _1\rightarrow$ 2$^+ _1$) values are sparsely known. An intermediate energy Coulomb excitation experiment was performed at the NSCL to study the first excited 2$^+ _1$ states in the $^{106-110}$Sn isotopes. The Sn isotopes beams obtained following the fragmentation of $^{124}$Xe and selection with the A1900 fragment analyzer, impinged on a 212 mg/cm2 thick Au target at an energy of 140 MeV/nucleon. Gamma rays were observed using the highly segmented high purity SeGA Ge array. The particle identification and the determination of the scattering angles were performed with the detector system of the high-resolution S800 spectrograph. This talk presents the results of the B(E2, 0$^+ _1 \rightarrow$ 2$^+ _1$) excitation strength measurements and a comparison with the shell model predictions for $^{106-110}$Sn isotopes. [Preview Abstract] |
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