Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session KB: Mini-Symposium on Using Particle-gamma Coincidences to Study Nuclear Reactions and Structure II |
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Chair: Con Beausang, University of Richmond Room: Kohala 2 |
Saturday, October 11, 2014 9:00AM - 9:30AM |
KB.00001: Particle-gamma measurements around the Coulomb barrier Invited Speaker: Steven Pain Reactions performed around Coulomb barrier energies have contributed significantly to our foundation of nuclear structure knowledge over the decades, being highly selective probes of specific components of the nuclear wave function. In particular, such reactions can be used as probes of single-particle structure, pairing and collective structure, etc. Many of these reactions are more recently being revisited, but employed in inverse kinematics to study reactions using radioactive beams. In this effort, the addition of gamma-ray detection is becoming increasingly recognized as crucial to fully exploiting such measurements, and in some cases is critical to the experimental approach. An brief overview of techniques and some state of the art measurements will be presented. Work supported in part by the US Department of Energy. [Preview Abstract] |
Saturday, October 11, 2014 9:30AM - 9:45AM |
KB.00002: The Study of Halo States in $^{10}$Be and $^{11}$Be K. Kuhn, F. Sarazin One-neutron transfer reactions are being used to study single-particle neutron states in nuclei. For one-neutron halo nuclei, such as $^{11}$Be, the (p,d) reaction enables the removal of the halo neutron or of one of the core neutrons. This way, it is possible to simultaneously study the halo wavefunction of the $^{11}$Be ground-state but also a possible excited halo state in $^{10}$Be. The $^{11}$Be(p, d)$^{10}$Be transfer reaction at 10 MeV/nucleon is being investigated at the TRIUMF-ISAC II facility with the Printed Circuit Board Based Charged Particle ((PCB)$^2$) array inside the TRIUMF ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). The ground state and first excited state of $^{10}$Be can be directly identified using deuteron identification and kinematics from the charged particle array. To differentiate between the four excited states in$^{10}$Be around 6 MeV, including the suspected halo state (2$^-$ state), the gamma rays from TIGRESS are used in coincidence with the identified deuterons. Analysis is still in progress and the preliminary angular distributions for the $^{10}$Be ground state and first excited will be shown along with gamma ray data used in coincidence with the deuterons. [Preview Abstract] |
Saturday, October 11, 2014 9:45AM - 10:00AM |
KB.00003: Single particle structure in neutron-rich Sr isotopes approaching N=60 Reiner Kr\"ucken The shape coexistence and shape transition at N=60 in the Sr, Zr region is of subject of substantial current experimental and theoretical effort. An important aspect in this context is the evolution of single particle structure for N$<$60 leading up to the shape transition region, which can be calculated with modern large scale shell model calculations using a 78Ni core or Beyond Mean Filed Models. One-neutron transfer reactions are an ideal tool to study single-particle energies as well as occupation numbers. Here we report on the study of the single-particle structure in 95-97Sr via (d,p) one-neutron transfer reactions in inverse kinematics. The experiments were performed at TRIUMF's ISAC facility using the TIGRESS gamma-ray spectrometer in conjunction with the SHARC charge particle detector. Highly charged beams of 94,95,96Sr, produced in the ISAC UC$_x$ target, were accelerated to 5.5 AMeV in the superconducting ISAC-II linac. Initial results of these experiment will be discussed in the context of the evolution of single-particle structure in this region. Results of both angular distributions and spectroscopic factors extracted from the collected observables will be presented and discussed in the context of theoretical shell model calculations. [Preview Abstract] |
Saturday, October 11, 2014 10:00AM - 10:15AM |
KB.00004: ABSTRACT WITHDRAWN |
Saturday, October 11, 2014 10:15AM - 10:30AM |
KB.00005: The Particle-Gamma Detector GODDESS A. Ratkiewicz, J.A. Cizewski, T. Baugher, S. Burcher, S. Hardy, S. Lonsdale, C. Shand, S.D. Pain, I. Marsh, K.L. Jones, W.A. Peters, M.P. Carpenter, D. Seweryniak, S. Zhu, R.L. Kozub, L. Afanasieva, J.C. Blackmon Transfer reactions in inverse kinematics provide a powerful probe of the single-particle structure of nuclei far from stability. The Californium Rare Isotope Breeder (CARIBU) at ATLAS produces exotic nuclei near possible \textit{r}-process paths and makes them available for study. Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies (GODDESS) employs the large internal geometry of the high-resolution $\gamma$-ray detector Gammasphere to instrument the large-area position-sensitive particle detector ORRUBA. This coupling of Gammasphere and ORRUBA allows high-efficiency, high-resolution measurements of surrogate reactions for neutron capture, collective excitations via inelastic scattering, pickup reactions (such as (d,t)), and stripping reactions (e.g. (d,p)). Results from commissioning measurements and plans for future experiments will be presented. This work is supported in part by the U.S. Department of Energy and the National Science Foundation. [Preview Abstract] |
Saturday, October 11, 2014 10:30AM - 10:45AM |
KB.00006: Digital Shaping Algorithms for GODDESS Sarah-Jane Lonsdale, Jolie Cizewski, Andrew Ratkiewicz, Steven Pain Gammasphere-ORRUBA: Dual Detectors for Experimental Structure Studies (GODDESS) combines the highly segmented position-sensitive silicon strip detectors of ORRUBA with up to 110 Compton-suppressed HPGe detectors from Gammasphere, for high resolution for particle-gamma coincidence measurements. The signals from the silicon strip detectors have position-dependent rise times, and require different forms of pulse shaping for optimal position and energy resolutions. Traditionally, a compromise was achieved with a single shaping of the signals performed by conventional analog electronics. However, there are benefits to using digital acquisition of the detector signals, including the ability to apply multiple custom shaping algorithms to the same signal, each optimized for position and energy, in addition to providing a flexible triggering system, and a reduction in rate-limitation due to pile-up. Recent developments toward creating digital signal processing algorithms for GODDESS will be discussed. This work is supported in part by the U.S. D.O.E. and N.S.F. [Preview Abstract] |
Saturday, October 11, 2014 10:45AM - 11:00AM |
KB.00007: Development of a high-rate ion counter for particle identification with GODDESS Travis Baugher, Jolie Cizewski, Andrew Ratkiewicz, Steven Pain Gammasphere-ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS) consists of the Oak Ridge-Rutgers University Barrel Array (ORRUBA) of position-sensitive silicon detectors placed inside the Gammasphere target chamber to measure particle-gamma coincidences. Experiments performed in inverse kinematics result in heavy-ion recoils at very forward angles. Detecting and identifying these recoils with high efficiency and low dead time is crucial for experiments, in particular experiments with contaminated beams. An ionization chamber has been designed, built and tested to be incorporated into the GODDESS setup to count and identify recoiling heavy ions. The design of the gas-filled, gridded ionization chamber utilizes 22 anode grids to measure energy loss of the heavy ion recoils and a plastic scintillator for timing measurements. The anode grids are tilted at 30 degrees to handle high incident-particle rate. The detector was developed, built and tested at Oak Ridge National Laboratory and will be used in GODDESS measurements with stable and rare isotope beams. [Preview Abstract] |
Saturday, October 11, 2014 11:00AM - 11:15AM |
KB.00008: Validating a surrogate for neutron capture on short-lived nuclei: intensities of discrete transitions as a function of neutron energy J.A. Cizewski, A. Adekola, S. Burcher, M.E. Howard, B. Manning, A. Ratkiewicz, C. Shand, A.J. Couture, M. Devlin, N. Fotiades, M. Jandel, R.O. Nelson, J.M. O'Donnell, D.J. Vieira, J.T. Burke, J.E. Escher, R. Hatarik, N.D. Scielzo, S.A. Sheets, W.A. Peters, S. Ilyushkin, P.D. O'Malley, K. Koehler Neutron capture is responsible for the synthesis of most of the elements heavier than iron, with about half produced in the rapid neutron capture process that takes place far from stability. Understanding neutron capture rates on short-lived nuclei requires a valid surrogate measurement that uses radioactive ion beams on light targets with gamma rays and light reaction products measured in coincidence. Much of the surrogate reaction efforts [1] have used the high-intensity discrete gamma rays at the bottom of the cascade to deduce the neutron-induced cross sections. However, there is little information on how the intensities of discrete gamma rays vary as a function of neutron energy in neutron capture. We have recently measured the 95Mo(n,$\gamma$) reaction at LANSCE to obtain the pattern of discrete transition intensities as a function of neutron energy. This is part of the larger effort to validate the (d,p$\gamma$) reaction as a surrogate for neutron capture. Preliminary results will be presented.\\[4pt] [1] J.E. Escher et al., Rev. Mod. Phys. 84, 353 (2012). [Preview Abstract] |
Saturday, October 11, 2014 11:15AM - 11:30AM |
KB.00009: Surrogate measurements of (n,2n) cross sections using NeutronSTARS R.J. Casperson, J.T. Burke, J.E. Escher, R.O. Hughes, N.D. Scielzo, M. Barbui, K. Hagel, E. McCleskey, J.B. Natowitz, S. Wuenschel, H. Zheng, Y.G. Ma Accurate (n,2n) cross sections on actinides are important for reactor modeling, but experimental challenges make direct measurements of these cross sections difficult. The surrogate ratio technique can overcome many of these challenges by allowing the determination of an unknown reaction cross section using a direct reaction on a more-convenient target nucleus. In the case of an (n,2n) reaction, the outgoing particle from the direct reaction provides a time tag and an effective neutron energy, and the charged particle beam generates a relatively low neutron background. We plan to use NeutronSTARS, which is a combination of the Silicon Telescope Array for Reaction Studies (STARS) and the TAMU Neutron Ball, to field (n,2n) measurements on actinide targets using ratios to known (n,f) cross sections. Preparation for this experimental campaign is underway, and progress will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and was supported by the U. S. Department of Energy under Grant DE-FG03-93ER40773 and by The Robert A. Welch Foundation under Grant A0330. [Preview Abstract] |
Saturday, October 11, 2014 11:30AM - 11:45AM |
KB.00010: Investigation of $^{88}$Y via (p,d$\gamma$) reactions R.O. Hughes, J.T. Burke, R.J. Casperson, J.E. Escher, S. Ota, J.J. Ressler, N.D. Scielzo, E. McCleskey, M. McCleskey, A. Saastimoinen, R.A.E. Austin, T.J. Ross The odd-odd nucleus $^{88}$Y is of importance in radchem applications due to its proximity to monoisotopic $^{89}$Y. It has 49 neutrons and 39 protons, and sits adjacent to the N=50 neutron shell closure and Z=40 proton subshell closure. The structure is complex due to a high density of states, while analysis of the decay scheme is compounded by the presence of several isomers at low energy. As a result, while numerous states have been identified, many inconsistencies remain and most states lack firm spin and parity assignments. In the present work, 28.5 MeV protons from the K150 cyclotron at Texas A\&M University were used to bombard $^{89}$Y, and the resulting light ions and gamma rays were detected with STARLiTeR. $^{88}$Y was populated via the (p,d$\gamma$) reaction and substantial statistics were collected. Results from the ongoing analysis will be discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 [Preview Abstract] |
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