Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session FJ: Nuclear Astrophysics |
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Chair: Michael Wiescher, University of Notre Dame Room: Blue Point I |
Thursday, October 24, 2013 4:00PM - 4:12PM |
FJ.00001: Experimental Investigation of (p,n) reactions relevant to the astrophysical $\nu p$~process G. Perdikakis, R.M. Almus, R. Avetisyan, A.A. Bataglia, B.M. Bucher, C.R. Casarella, C. Fr\"{o}hlich, S. Lipschutz, A.M. Long, S. Lyons, S.T. Marley, K.M. Ostdiek, T.H. Redpath, K.I. Smith, M.K. Smith, A. Spyrou, E.J. Stech, W. Tan, R. Talwar, M. Wiescher, R.G.T. Zegers A recently discovered nucleosynthesis process, the $\nu$p process is thought to take place in core-collapse supernovae and could explain some of the observed abundance trends. The underlying nuclear physics and its role is not yet known due to a lack of experimental information. Aiming to study relevant reaction rates, the (n,p) reactions on $^{61}$Cu and $^{59}$Ni have been studied through their time-inverse reactions $^{61}$Ni(p,n) and $^{59}$Co(p,n). Protons with energies between 2.2 and 4~MeV from the FN Tandem of the University of Notre Dame were used to extract excitation functions in 100~keV steps covering the energy range of relevance. Neutrons from the (p,n) reactions with energies between 130~keV and 1~MeV where detected using a subset of the LENDA neutron array. Preliminary results from this investigation will be presented and the impact to nucleosynthesis will be discussed. [Preview Abstract] |
Thursday, October 24, 2013 4:12PM - 4:24PM |
FJ.00002: Capture reaction measurements for the astrophysical p-process S.J. Quinn, A. Simon, A. Spyrou, A.C. Dombos An accurate description of the nucleosynthesis of the group of stable, neutron deficient isotopes heavier than iron remains one of the main open questions in the field of nuclear astrophysics. These isotopes, known as the p-nuclei, are shielded from production by the s- and r- neutron capture processes by the valley of $\beta $-stability and therefore must originate from some other astrophysical scenario or scenarios. The most heavily studied scenario to date, the p-process or $\gamma $-process, involves photodisintegration reactions, their inverse capture reactions, and $\beta ^{\mathrm{+}}$ decays on existing seed nuclei in the shock front of Type II SNe. The complete description of the p-process involves reaction networks of over ten-thousand reactions, including many reactions on unstable isotopes. Since only limited experimental data exists, nearly all p-process reaction rates are calculated by the statistical Hauser-Feshbach model, which rely on accurate optical model potentials, level densities, and $\gamma $-widths. In an effort to improve the input parameters to the statistical model, particularly the troublesome $\alpha $- optical model potential, a series of ($\alpha $,$\gamma )$ reactions were carried out at the FN Tandem Accelerator at the University of Notre Dame in combination with the NSCL SuN detector. Cross section results and their comparison to theoretical calculations will be presented. Also discussed will be the results of the first ever (p,$\gamma )$ measurements using the summing technique in inverse kinematics, a significant experimental development towards measuring p-process reaction cross sections with unstable isotopes. [Preview Abstract] |
Thursday, October 24, 2013 4:24PM - 4:36PM |
FJ.00003: ABSTRACT WITHDRAWN |
Thursday, October 24, 2013 4:36PM - 4:48PM |
FJ.00004: Recent research on the structure of $^{31}$Si Pei-Luan Tai, Leanne Hamilton, Peter Bender, Samuel Tabor, Vandana Tripathi, Calem Hoffman, Roderick Clark, Paul Fallon, Augusto Macchiavelli, S. Paschalis, M. Petri, Michael Carpenter, Robert Janssens, T. Lauritsen, E.A. McCutchan, D. Seweryniak, S. Zhu, C. Chiara, X. Chen, W. Reviol, D. Sarantites $^{31}$Si was produced through the $^{18}$O ($^{18}$O, $\alpha$n) reaction at the beam energy of 25 MeV, which preferentially populates the high spin states. The $\alpha$ particles were detected in Microball and the multiple $\gamma$-ray coincidences were detected by Gammashpere. Event by event kinematic correction of the $^{31}$Si recoil energies and angles using information from Microball on the energies and angles of the $\alpha$ evaporations led to a better Doppler correction, which allowed us to discover 5 more new states and 15 new transitions in addition to the 11 more states and 22 $\gamma$ transitions found before kinematic correction compared to earlier works. A strong competition is seen between negative-parity ``intruder'' states and positive-parity pure s-d states. Shell model calculations agree relatively well with both groups of states. [Preview Abstract] |
Thursday, October 24, 2013 4:48PM - 5:00PM |
FJ.00005: The Beta-Delayed Proton and Gamma Decay of 27P for Nuclear Astrophysics E. McCleskey, A. Banu, M. McCleskey, B. Roeder, A. Saastamoinen, A. Spiridon, L. Trache, R.E. Tribble, T. Davinson, D. Doherty, G.J. Lotay, J. Wallace, P.J. Woods The main creation site of $^{26}$Al is currently under debate. The reactions for its creation or destruction are also not completely known. When $^{26}$Al is created in novae, the reaction chain is: $^{24}$Mg(p,$\gamma)^{25}$Al($\beta +$v)$^{25}$Mg(p,$\gamma)^{26}$Al, but this chain can be by-passed by another chain: $^{25}$Al(p,$\gamma)^{26}$Si(p,$\gamma)^{27}$P and it can also be destroyed directly. Another way to by-pass it is through $^{26m}$Al(p,$\gamma)^{27}$Si* which is dominated by resonant capture. Using the Momentum Achromat Recoil Spectrometer (MARS) at the Texas A\&M Cyclotron Institute and inverse kinematics, this destruction reaction was studied by the beta-delayed proton and gamma decay of $^{27}$P. Due to selection rules, states populated above the proton threshold in the compound system ($^{27}$Si*) can decay to $^{26m}$Al, which are the states of interest for the capture reaction. [Preview Abstract] |
Thursday, October 24, 2013 5:00PM - 5:12PM |
FJ.00006: Recent Activities at the Low-Energy Beam and Ion Trap Facility at NSCL Scott Bustabad, Georg Bollen, Maxime Brodeur, David Lincoln, Samuel Novario, Matthew Redshaw, Ryan Ringle, Stefan Schwarz, Adrian Valverde The Low-Energy Beam and Ion Trap (LEBIT) facility, for high precision Penning trap mass measurements, has been relocated and upgraded for the expansion of the thermalized beam program at NSCL. I will summarize the changes to the facility and will focus on recent atomic mass measurements of candidates for neutrinoless double-$\beta$ decay experiments including $^{82}$Se and $^{48}$Ca. I will also present the first results from the recent successful LEBIT commissioning experiment and will conclude by discussing the exciting future opportunities with the upgraded facility. [Preview Abstract] |
Thursday, October 24, 2013 5:12PM - 5:24PM |
FJ.00007: Measuring the Half Life of $^{60}$Fe for Stellar and Early Solar System Models K. Ostdiek, P. Collon, W. Bauder, M. Bowers, W. Lu, D. Robertson, S. Austin, J. Green, W. Kutschera, M. Paul, A. Wallner Radioisotopes, produced in stars and ejected through core collapse supernovae (SNe), are important for constraining stellar and early Solar System (ESS) models. The presence of these isotopes, specifically $^{60}$Fe, can identify progenitors of SN types, give evidence for nearby SNe, and can be a chronometer for ESS events. The $^{60}$Fe half-life, which has been in dispute in recent years, can have an impact on calculations for the timing for ESS events, the distance to nearby SN, and the brightness of individual, non-steady state $^{60}$Fe $\gamma$ ray sources in the Galaxy. To measure such a long half life, one needs to simultaneously determine the number of atoms in and the activity of an $^{60}$Fe sample. We have undertaken a half-life measurement at Notre Dame and have successfully measured the $^{60}$Fe concentration of our samples using Accelerator Mass Spectrometry (AMS). We will couple this result with an ongoing activity measurement using isomeric decay in $^{60}$Co rather than the traditional $^{60}$Co grow-in decay. I will present our AMS data and the most recent results of the activity measurement. [Preview Abstract] |
Thursday, October 24, 2013 5:24PM - 5:36PM |
FJ.00008: The current status of Zr-Nb isobar separation experiments for future $^{93}$Zr AMS measurement Wenting Lu, Philippe Collon, Yoav Kashiv, Daniel Robertson, Christopher Schmitt, Matthew Bowers, Karen Ostdiek, William Bauder The rare isotope $^{93}$Zr (t$_{1/2}=$ 1.6 Ma) can be produced (1) in the $s$-process, (2) by the spontaneous fission of Uranium and Plutonium, and (3) by the activation of cladding Zr in nuclear reactors. The production method (1) makes it relevant in astrophysical modeling of nucleosynthesis processes, while (2) and (3) makes it of interest to people dealing with nuclear waste management and transmutation study. The main challenge in AMS detection of $^{93}$Zr is the adequate separation from its stable isobar $^{93}$Nb which is only one atomic number away. The nuclear Science Laboratory at the University of Notre Dame is developing the capability to measure $^{93}$Zr by AMS, featuring the combination of gas-filled magnet with the position-sensitive parallel grid avalanche counter and gas chamber (ionization chamber and Bragg curve detector). The chemical reduction and the suppression in the ion source of $^{93}$Nb have been deemed as necessary. [Preview Abstract] |
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