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 FH: Astrophysics: Medium Mass Nuclei |
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Chair: Guy Savard, Argonne National Laboratory Room: Jewett Ballroom F |
Saturday, October 25, 2008 8:30AM - 8:42AM |
FH.00001: Excitation energies of the unbound states in $^{32}$Cl studied via the $^{32}$S($^{3}$He,t)$^{32}$Cl charge exchange reaction M. Mato\v{s}, D.W. Bardayan, J.C. Blackmon, J.A. Clark, C.M. Deibel, L. Linhardt, C.D. Nesaraja, P.D. O'Malley, S.D. Pain, P.D. Parker, K.T. Schmitt Time scales of explosive hydrogen burning processes are influenced by the duration of reaction cycles closed by (p,$\alpha$) reactions, with breakouts occurring due to competing (p,$\gamma$) reactions. In the SiP cycle $^{31}$S(p,$\gamma$)$^{32}$Cl is one such breakout reaction [1]. At novae temperatures 0.1-0.4 GK, the rate for this reaction is dominated by resonances, and thus the properties of these resonances are important in determining the reaction rate. To determine the excitation energies of the proton unbound states in $^{32}$Cl we use the Enge Spectrograph at the Yale University Wright Nuclear Structure Laboratory to measure the $^{32}$S($^{3}$He,t)$^{32}$Cl charge exchange reaction. We are attempting to resolve discrepancies in the resonance energies that have been reported in previous measurements [1,2] and to measure the proton decays from these resonances. [1] S.Vouzoukas, PRC 50 (1994) 1185. [2] C. Jeanperrin, NPA 503 (1989) 77. [Preview Abstract] |
Saturday, October 25, 2008 8:42AM - 8:54AM |
FH.00002: Measurement of the $^{40}$Ca($\alpha $,$\gamma )^{44}$Ti reaction for supernovae nucleosynthesis Steven Sheets, Jason Burke, Darren Bleuel, Tom Brown, Patrick Grant, Rob Hoffman, Eric Norman, Larry Phair, Nick Scielzo, Scott Tumey The $^{40}$Ca($\alpha $,$\gamma )^{44}$Ti reaction is the main production reaction for the radioactive nucleus $^{44}$Ti, which serves as an important diagnostic for understanding explosive nucleosynthesis. A new self-consistent measurement of this reaction was performed to determine the integral cross section below E$_{\alpha }$ = 5.2 MeV. An in-beam measurement using the LLNL CAMS FN Tandem Van de Graaf was performed followed by a low-background counting of the activation product. A report on the progress of this experiment is given. [Preview Abstract] |
Saturday, October 25, 2008 8:54AM - 9:06AM |
FH.00003: Studying Electron-Capture on $^{64}$Zn in Supernovae with the (t,$^{3}$He) Charge-Exchange Reaction G.W. Hitt, Sam M. Austin, D. Bazin, A. Gade, C.J. Guess, D. Galaviz-Redondo, Y. Shimbara, C. Tur, R.G.T. Zegers, M. Horoi, M.E. Howard, E.E. Smith A secondary, 115 MeV/u triton beam has been developed at NSCL for use in (t,$^{3}$He) charge-exchange(CE) reaction studies. This (n,p)-type CE reaction is useful for extracting the full Gamow-Teller (GT) response of the nucleus, overcoming Q-value restrictions present in conventional beta-decay studies. The strength (B(GT)) in $^{64}$Cu has been determined from the absolute cross section measurement of $^{64}$Zn(t,$^{3}$He) near zero-degrees, exploiting an empirical proportionality between cross section and B(GT). The detailed features of the B(GT) distribution in a nucleus has an important impact on electron-capture (EC) rates in Type Ia and Core-Collapse supernovae. The measured B(GT) in $^{64}$Cu is directly compared with the results of modern shell model interactions which are used to calculate the GT contribution to EC on nuclei in supernova simulations. [Preview Abstract] |
Saturday, October 25, 2008 9:06AM - 9:18AM |
FH.00004: Mass Measurements of Proton-Rich Isotopes Between Mo and Pd for $rp$- and $\nu p$-process Models Jennifer Fallis, K.S. Sharma, H. Sharma, J.A. Clark, G. Savard, A.F. Levand, T. Sun, C.M. Deibel, C. Wrede, A. Parikh, D. Lascar, R. Segel, S. Caldwell, J. Van Schelt, F. Buchinger, J.E. Crawford, S. Guilck, J.K.P. Lee, G. Li, N.D. Scielzo, A.A. Hecht The reaction paths of two proposed nucleosynthetic processes on the proton-rich side of stability, the $rp$ and $\nu p$~processes, pass through a series of nuclides between Mo and Pd whose masses have long gone unmeasured. Measurements of these masses would provide the more precise proton-separation energies, $S_p$, needed to properly model the paths and final abundances of these two astrophysical processes. These $S_p$ values are of particular interest to the $\nu p$ process as it is a process which could resolve the long- standing underproduction of light $p$-nuclei such as $^{92}$Mo and $^{94}$Mo. Mass measurements of 14 proton-rich nuclides between Mo and Pd have been performed with the Canadian Penning trap mass spectrometer. These measurements have significantly reduced uncertainties in the associated $S_{p}$ values by up to factors of 60. These results and their astrophysical implications will be discussed. This work supported by: NSERC, Canada and the U.S. DOE, Nuclear Physics Division, Contract Nos. DE-AC02-06CH11357 and DE-FG02- 91ER-40609. [Preview Abstract] |
Saturday, October 25, 2008 9:18AM - 9:30AM |
FH.00005: The rp-process in Type-I X-ray Bursts with REACLIB V1 Richard Cyburt Nuclear astrophysics is a rich and diverse field of research, requiring knowledge of experiments, observations and modeling. Of key importance to modeling is the nuclear physics input, whether it be thermonuclear reaction rates or weak decay rates. The Joint Institute for Nuclear Astrophysics (JINA) has taken a leading role in maintaining an up-to-date database of these rates. The JINA REACLIB Database, based of F. Thielemann's 1995 REACLIB, has been updated to incorporate the latest weak decay data, as well as modern experimental/theoretical reaction rates relevant for various nucleosynthetic processes. I will present several of the rates in the newly released REACLIB library V1, which takes advantage of new experimental data to create a new set of nuclear input for model calculations. I will discuss the impact this V1 library has on explosive hydrogen burning along the rp-process path in Type-I X-ray bursts and where improvements can be made. [Preview Abstract] |
Saturday, October 25, 2008 9:30AM - 9:42AM |
FH.00006: Sensitivity of X-ray Burst Models to Uncertainties in Nuclear Processes Karl Smith, Alan Matthew Amthor, Richard Cyburt, Alexander Heger, Emily Johnson, Hendrik Schatz X-ray burst models simulate thermonuclear explosions on the surface of accreting neutron stars, offering new and exciting research in nuclear astrophysics. The underlying nuclear reaction sequence in the X-ray bursts is the rp-process, a sequence of proton captures and beta decays on proton-rich nuclei. We examine the sensitivity of current X-ray burst models within nuclear reaction rate uncertainties in terms of predicted X-ray light curves and final produced ashes. Many of the relevant reaction rates have significantly large uncertainties, which can greatly impact the results of X-ray burst models. We use an updated nuclear reaction network and run almost 800,000 simulations with a one-zone X-ray burst model to determine the impact of reaction rate variations. We also explore the validity of the one-zone approximation by comparing to a full 1D multi-zone model. Simple one-zone models are shown to be a useful tool for investigating nuclear physics influences on Type I X-ray bursts. [Preview Abstract] |
Saturday, October 25, 2008 9:42AM - 9:54AM |
FH.00007: s-Process Branch Point (n,$\gamma )$ Measurements using NIF$^{\ast }$ Lee Bernstein, D.L. Bleuel, C. Cerjan, U. Greife, R.D. Hoffman, L. Phair, A. McEvoy, K.J. Moody, D.H.G. Schneider, D. Shaughnessy, M.A. Stoyer The National Ignition Facility (NIF) at LLNL is a laser-driven inertial confinement fusion laboratory designed to compress pellets containing small ($<$10$^{20 }$atoms) samples of material to densities in excess of 100 g/cm$^{3}$ and temperatures up to $k_{B}$\textit{T$\approx $10 keV}. Early NIF shots will feature a proton-tritium (HT) fuel mix that creates a neutron spectrum similar to that found in AGB main sequence stars. In this talk I will discuss nuclear physics experiments using NIF and present a plan to measure the $^{171}$Tm(n,$\gamma )$ s-process branch point cross section in a NIF plasma environment which will include the plasma-induced population of the first excited state at $E_{x}$\textit{=5.0 keV}. *This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48 and under Contract DE-AC52-07NA27344. For LBNL this work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. [Preview Abstract] |
Saturday, October 25, 2008 9:54AM - 10:06AM |
FH.00008: Integral Neutron Multiplicity Measurements from Cosmic Ray Interactions in Lead Thomas Ward, Alexander Rimsky-Korsakov, Nikolai Kudryashev, Denis Beller Sixty element $^{3}$He neutron multiplicity detector systems were designed, constructed and tested for use in cosmic ray experiments with a 30-cm cube lead target (306 kg). A series of measurements were performed for the cosmic ray configuration at ground level (3 meters water equivalent, mwe), in the St. Petersburg metro tunnel (185 mwe), and in the Pyh\"{a}salmi mine in Finland (583 and 1185 mwe). Anomalous coincidence events with charged cosmic ray particles at sea level produced events with 100-120 neutrons due possibly to the total disintegration of the Pb nucleus. These events were also detected at 185 mwe, but the particles causing such disintegration are currently unidentified. A two layer 4$\pi $charged particle coincidence/anticoincidence system has been built and integrated into the system to help identify the charge of the originating particle events. Designs for a modular 100-cm cube lead target (11.35 mt) will be presented as well as examples of preliminary data from the various measurements and a discuss of future plans for underground experiments including possible searches for Weakly Interacting Massive Particles (WIMP, dark matter). [Preview Abstract] |
Saturday, October 25, 2008 10:06AM - 10:18AM |
FH.00009: Precision Mass Measurements of Heavy $^{252}$Cf Fission Fragments Near the $r$-Process Path J. Van Schelt, G. Savard, S. Caldwell, M. Sternberg, J.A. Clark, J.P. Greene, A.F. Levand, T. Sun, B.J. Zabransky, J. Fallis, K.S. Sharma, D. Lascar, R.E. Segel, G. Li Precision mass measurements of species near the astrophysical $r$-process path are vital to reduce the uncertainties in the relevant neutron separation energies given by mass models, and the consequent abundance predictions. As part of an ongoing program, the Canadian Penning Trap mass spectrometer at Argonne National Laboratory is measuring the masses of fission products from a 150~$\mu$Ci $^{252}$Cf source placed inside a new large-volume He gas catcher. New precision mass measurements have been made closer to the $r$-process path than have previously been published, with precisions near 15~keV/c$^2$. Presented measurements include Pr, Nd, Pm, Sm, Eu, and Gd to N = 96, 97, 98, 99, and 99 respectively, and our results differ from the AME 2003 by up to 515~keV/c$^2$. Work will continue with the current fission source until 2009, when measurements of many more neutron-rich isotopes will be made at the CARIBU upgrade to the ATLAS accelerator at ANL. [Preview Abstract] |
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