Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session CD: Mini-Symposium: Rare Isotope Science II |
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Chair: Samuel Tabor, Florida State University Room: Jewett Ballroom G-H |
Friday, October 24, 2008 10:30AM - 10:42AM |
CD.00001: Elucidation of complex decay schemes using on-line mass separated sources and a large array of Compton-suppressed germanium detectors N. Brown, J.L. Wood, W.D. Kulp, D. Furse, G.A. Demand, P.E. Garrett, K.L. Green, G.F. Grinyer, K.G. Leach, A.A. Phillips, M.A. Schumaker, C.E. Svensson, J. Wong, G.C. Ball, D.S. Bandyopadhyay, G. Hackman, A.C. Morton, C.J. Pearson, R.A.E. Austin, S. Colosimo, S.W. Yates, D. Cross Complex decay scheme construction using beta decay of isotopes produced by spallation and mass separation on-line at TRIUMF-ISAC and studied with the 8$\pi$ array of 20 Compton-suppressed germanium detectors is described. Results from the analysis of the $^{160}$Yb $\rightarrow$ $^{160}$Tm decay will be presented. Emphasis will be placed on the sensitivity to weak decay branches, assignment of $\gamma$-ray lines to isobars, and the use of conversion electron coincidences to observe low-energy transitions. The goal of this work is to achieve detailed decay scheme spectroscopy far from stability with the same level of detail as obtained with the 8$\pi$ array near stabilty in earlier $N=90$ studies [1] [2]. \newline [1] W.D. Kulp et al., Phys.\ Rev.\ C 69, 064309 (2004). \newline [2] W.D. Kulp et al., Phys.\ Rev.\ C 76, 034319 (2007). [Preview Abstract] |
Friday, October 24, 2008 10:42AM - 10:54AM |
CD.00002: A novel approach for determining level schemes from $\gamma$-ray coincidence data G.A. Demand, P.E. Garrett, K.L. Green, K.G. Leach, A.A. Phillips, M.A. Schumaker, C.E. Svensson, J. Wong, G.C. Ball, D. Bandyopadhyay, G. Hackman, A.C. Morton, C.J. Pearson, R.A.E. Austin, S. Colosimo, J.L. Wood, W.D. Kulp, D. Furse, N. Brown, G.F. Grinyer, S.W. Yates, D. Cross Nuclear structure studies often rely on understanding trends amongst the excited states of large numbers of nuclei. Experiments performed using powerful $\gamma$-ray spectrometers, like GAMMASPHERE or the $8\pi$ array, can often reveal many hundreds of transitions in the nuclei of interest. As a result, the determination of level schemes and the precise calculation of the associated properties, such as transition branching ratios, can become a substantial obstacle to the rapid development and formulation of new ideas. Recent increases in computational power, while insufficient to solve the problem by brute force, make an algorithmic approach possible. We will present results of applying a new algorithm based on evolutionary computation to $\gamma$-ray coincidence data obtained from $\beta$-decay studies of $^{112}$Ag and $^{160}$Tm, using the 8$\pi$ array at TRIUMF-ISAC, to demonstrate the usefulness of this approach for nuclear structure studies. Work supported in part by NSERC. [Preview Abstract] |
Friday, October 24, 2008 10:54AM - 11:06AM |
CD.00003: $\beta -$delayed p-decay of proton-rich nuclei $^{23}$Al and $^{31}$Cl and explosive H-burning in novae L. Trache, A. Banu, J.C. Hardy, M. McCleskey, E. Simmons, G. Tabacaru, R.E. Tribble, J. Aysto, A. Jokinen, A. Saastamoinen, T. Davinson, P.J. Woods, L. Achouri, B. Roeder We developed a technique to measure $\beta $-delayed proton-decay of proton-rich nuclei produced and separated with MARS at TAMU. In particular, we studied the decay of $^{23}$Al and $^{31}$Cl, both important for understanding explosive H-burning in novae. We have pulsed the beam, implanting the source nuclei moving at about 40 MeV/u in a thin Si strip detector, and then measured $\beta -$p and $\beta -\gamma $ coincidences simultaneously. The states populated above the proton threshold in $^{23}$Mg and $^{31}$S, respectively, may proton decay. They are resonances in the reaction $^{22}$Na(p,$\gamma )^{23}$Mg (crucial for the depletion of $^{22}$Na in ONe novae) and in $^{30}$P(p,$\gamma )^{31}$S (critical point in explosive H-burning in novae), but the protons emitted have very low energies, starting at about 200 keV, an experimental challenge. The setup and the results are described. The $\beta $-decay schemes were established for both nuclei, and IAS identified. The technique has shown a remarkable selectivity to $\beta $-delayed charged particle emission and shown to work even at radioactive beam rates of a few pps, for rare isotopes with lifetimes as low as 10s msec. [Preview Abstract] |
Friday, October 24, 2008 11:06AM - 11:18AM |
CD.00004: First Direct Measurement of the $^{17}$F($p,\gamma$)$^{18}$Ne Cross Section K.A. Chipps, U. Greife, D.W. Bardayan, C.D. Nesaraja, S.D. Pain, M.S. Smith, J.C. Blackmon, K.Y. Chae, B.H. Moazen, S.T. Pittman, R. Hatarik, W.A. Peters, R.L. Kozub, J.F. Shriner, C. Matei The rate of the $^{17}$F($p,\gamma$)$^{18}$Ne reaction is of significant importance in astrophysical events like novae and x-ray bursts. A $3^{+}$ state in $^{18}$Ne predicted to dominate the rate was found at 599.8 keV using the $^{17}$F($p,p$)$^{17}$F reaction [1], but the resonance strength was unknown. For the first time, the $^{17}$F($p,\gamma$)$^{18}$Ne reaction has been measured directly with the Daresbury Recoil Separator, using a mixed beam of radioactive $^{17}$F and stable $^{17}$O from the HRIBF at ORNL. Resonant proton capture cross sections, $\gamma$ widths, and resonance strengths for the 599.8 keV and 1178 keV resonances will be reported, as well as an upper limit on the direct capture cross section at an intermediate energy. [1] Bardayan et al., Phys. Rev. C \textbf{62} 055804 (2000) [Preview Abstract] |
Friday, October 24, 2008 11:18AM - 11:30AM |
CD.00005: Beta Decay Half-Life of 84Mo J.B. Stoker, P.F. Mantica, D. Bazin, A. Bickley, A. Becerril, H. Crawford, K. Cruse, A. Estrade, M. Mosby, C.J. Guess, G.W. Hitt, G. Lorusso, M. Matos, R. Meharchand, K. Minamisono, F. Montes, J. Pereira, G. Perdikakis, J.S. Pinter, H. Schatz, J. Vredevoogd, R.G.T. Zegers The $\beta$-decay half-life $^{84}$Mo governs leakage out of the Zr-Nb cycle, a high temperature rp-process endpoint in x-ray binaries [1]. Treatment of the background and the poor statistics accumulated during the previous half-life measurement leave questions about statistical and systematic errors. We have remeasured the half-life of $^{84}$Mo using a concerted setup of the NSCL $\beta$-Counting System [3] and 16 detectors from the Segmented Germanium Array [4]. We will report the half-life for $^{84}$Mo, deduced using 40 times the previous sample size. The application of the NSCL RF Fragment Separator to remove unwanted isotopes, and hence reduce background for the half-life measurement, will also be discussed. [1] H. Schatz et al., Phys. Rep. 294, 167 {\bf 1998} [2] P. Kienle et al., Prog. Part. Nuc. Phys. 46, 73 {\bf 2001} [3] J. Prisciandaro et al., NIM A 505, 140 {\bf 2003} [4] W. Mueller et al., NIM A 466, 492 {\bf 2001} [5] D. Gorelov et al. PAC {\bf 2005}, Knoxville, TN, May 16-20 [Preview Abstract] |
Friday, October 24, 2008 11:30AM - 11:42AM |
CD.00006: $\beta -$Decay Study of the rp-Process Nucleus $^{96}$Cd Ana Becerril, A. Amthor, T. Baumann, D. Bazin, H. Crawford, A. Estrade, A. Gade, T. Ginter, C. Guess, M. Hausmann, G. Hitt, G. Lorusso, P. Mantica, M. Matos, R. Meharchand, K. Minamisono, F. Montes, J. Pereira, G. Perdikakis, J. Pinter, M. Portillo, H. Schatz, K. Smith, J. Stoker, R. Zegers The half-life of $^{96}$Cd, one of the major waiting points along the reaction path of the rp-process [1] has been measured at NSCL. Nuclei of interest were produced by fragmentation of a 120 MeV/u $^{112}$Sn primary beam on a Be target and selected with the A1900 fragment separator in conjunction with the RF Fragment Separator [2]. The experimental setup, which consisted on the NSCL $\beta $-Counting System [3] and the Segmented Germanium Array [4], permitted the correlation of implants and decays as well as the detection of both prompt and $\beta $-delayed $\gamma $-rays from implanted ions. Details of the experiment and results will be presented and their implications discussed. [1] H. Schatz et al., Phys. Rep. 294, 167 1998 [2] D. Gorelov et al. PAC 2005, Knoxville, TN, May 16-20 [3] J. Prisciandaro et al., NIM A 505, 140 2003 [4] W. Mueller et al., NIM A 466, 492 2001 [Preview Abstract] |
Friday, October 24, 2008 11:42AM - 11:54AM |
CD.00007: Astrophysically Interesting Resonances; Another Approach Roby Austin, David Jenkins R.A.E. Austin, R. Kanungo, A. Campbell, S. Colosimo, S. Reeve Saint Mary's University; D.G. Jenkins, C.Aa.Diget, A. Robinson, University of York, UK; P.J. Woods T. Davinson University of Edinburgh; C.-Y. Wu A. Hurst J.A. Becker Lawrence Livermore National Laboratory; G.C. Ball M. Djongolov G. Hackman A.C. Morton, C. Pearson, S.J. Williams TRIUMF; A.A. Phillips, M. Schumaker, University of Guelph H.Boston, A. Grint, D. Oxley, University of Liverpool; D. Cline, A. Hayes, University of Rochester; We describe a prototype experiment to measure resonances of interest in astrophysical reactions. We use the TIGRESS to detect gamma rays in coincidence with charged particles, inelastically scattered in inverse kinematics. The particles are detected with the Bambino detector modified to a $\Delta$E-E silicon telescope spanning 15-40 degrees in the lab. [Preview Abstract] |
Friday, October 24, 2008 11:54AM - 12:06PM |
CD.00008: Reactions and Coulex at TRIUMF, progress and prospects of SHARC Christian Aa. Diget, Fred Sarazin The Silicon Highly-segmented Array for Reactions and Coulex (SHARC) is a multi-purpose array for charged-particle detection. The array is designed to have high spatial resolution, a large solid angle coverage, and particle identification of the measured reaction products. This combination offers unique capabilities when integrated with the TIGRESS gamma-ray detectors and the post-accelerated beams at the ISAC-II facility at TRIUMF, Canada. Two major research programs will gain significantly from the utilization of SHARC: Reaction studies with particular emphasis on transfer reactions used to indirectly probe nuclear reaction rates important for explosive stellar scenarios as well as nuclear structure studies in which Coulomb excitation will play an important role. The project is funded by the UK-STFC and is lead from the University of York with collaborators from the UK Universities of Birmingham, Liverpool, Manchester, and Surrey, and Daresbury Laboratory; Colorado School of Mines and Louisiana State University of the USA; and from Canada: TRIUMF as well as McMaster, Saint Mary's, and Simon Fraser Universities. [Preview Abstract] |
Friday, October 24, 2008 12:06PM - 12:18PM |
CD.00009: Commissioning of the HELIOS Spectrometer at ATLAS J.C. Lighthall The HELIcal Orbit Spectrometer (HELIOS) at the ATLAS facility of Argonne National Laboratory is designed to study inverse-kinematic nucleon transfer reactions using exotic beams. These reactions are of particular interest for nuclear structure away from stability and for nuclear astrophysics. The spectrometer features a 3 Tesla, 90 cm bore superconducting solenoid. Inside the HELIOS solenoid is a hollow detector array aligned with the magnetic field axis, in line with the target. This unique detector geometry has significant advantages over conventional detectors. To demonstrate its principle of operation, HELIOS will be commissioned by studying the well-known $^{2}$H($^{28}$Si,$p)^{29}$Si reaction in inverse kinematics at a bombarding energy of 8 MeV/u. The level density of the residual $^{29}$Si nucleus makes this reaction well suited for demonstrating the resolution and acceptance properties of the spectrometer. Experimental results will be presented. [Preview Abstract] |
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