Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session Q7: Nuclear Astrophysics I |
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Sponsoring Units: DNP Chair: Richard Cyburt, Michigan State University Room: Grand E |
Monday, May 2, 2011 10:45AM - 10:57AM |
Q7.00001: Radiative Neutron Capture on Lithium-7 Gautam Rupak, Renato Higa The radiative neutron capture on lithium-7 is calculated model independently using a low energy halo effective field theory. The cross section is expressed in terms of scattering parameters directly related to the $S$-matrix element. The cross section depends on the poorly known $p$-wave effective range parameter $r_1$. This constitutes the leading order uncertainty in traditional model calculations. It is explicitly demonstrated by comparing with potential model calculations. A single parameter fit describes the low energy data extremely well and yields $r_1\approx -1.47$ fm$^{-1}$. [Preview Abstract] |
Monday, May 2, 2011 10:57AM - 11:09AM |
Q7.00002: {\it Ab initio} calculations of $p$-$^7$Be scattering and $^7$Be($p$,$\gamma$)$^8$B capture Petr Navratil, Sofia Quaglioni, Robert Roth We build a new {\it ab initio} many-body approach [1] capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method [2] with the {\it ab initio} no-core shell model [3]. In this way, we complement a microscopic-cluster technique with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. We will present results for the proton scattering on $^7$Be and for the S-factor of the $^7$Be($p$,$\gamma$)$^8$B capture reaction important for astrophysics. Our calculations predict low-lying resonances in $^8$B that have not been clearly identified experimentally so far. Finally, we will also highlight the first results of the $d$-$^3$H and $d$-$^3$He fusion calculation obtained within our {\it ab initio} approach. \\[4pt] [1] S. Quaglioni and P. Navratil, Phys. Rev. Lett. 101, 092501 (2008); Phys. Rev. C 79, 044606 (2009).\\[0pt] [2] K. Wildermuth and Y. C. Tang, A unified theory of the nucleus, (Vieweg, Braunschweig, 1977).\\[0pt] [3] P. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. Lett. 84, 5728 (2000). [Preview Abstract] |
Monday, May 2, 2011 11:09AM - 11:21AM |
Q7.00003: Angular Distribution Anisotropy of the $E_{c.m.}$=2.68-MeV Resonance in the $^{12}$C($\alpha$,$\gamma$)$^{16}$O Reaction Daniel Sayre, Carl Brune, Donald Carter, Thomas Massey, John O'Donnell The ${}^{12}{\rm C}(\alpha,\gamma){}^{16}{\rm O}$ reaction, in combination with the triple-alpha process, determines the $^{12}{\rm C}/{}^{16}{\rm O}$ fraction at the end of stellar helium-burning. This fraction has been shown to strongly influence any subsequent stellar evolution and, due to imprecise knowledge of ${}^{12}{\rm C}(\alpha,\gamma){}^{16}{\rm O}$ reaction rate, severely complicate precision tests of stellar models. A large uncertainty in the reaction belongs to the cross section for electric-quadrupole ($E2$) capture into the ground state of ${}^{16}{\rm O}$. A prominent feature in the measured $E2$ cross section is the narrow resonance at $E$=2.68~MeV. The resonance affects the $E2$ cross section over a region of experimental significance. How the resonance affects the cross section depends on the relative sign of its amplitude to other $E2$ amplitudes. The sign is not well determined by existing capture data and has a non-negligible effect on extrapolating the $E2$ cross section to helium-burning energies ($E_0$). Details about the recent measurement of the sign at the Ohio University Accelerator Laboratory and its importance for a new $E2$ cross section at $E_0$ will be discussed. [Preview Abstract] |
Monday, May 2, 2011 11:21AM - 11:33AM |
Q7.00004: Reducing the Uncertainty of the $^{23}{\rm Na}(\rm p,\gamma)^{24}{\rm Mg}$ Reaction Rate John Cesaratto, Art Champagne, Matthew Buckner, Thomas Clegg, Stephen Daigle, Christian Iliadis, Babatunde Oginni The $^{23}{\rm Na}(\rm p,\gamma)^{24}{\rm Mg}$ reaction is the link between the NeNa and MgAl cycles for hydrogen burning in Red Giant Branch (RGB) stars, Asymptotic Giant Branch (AGB) stars, and classical novae. The present uncertainty in the $^{23}{\rm Na}(\rm p,\gamma)^{24}{\rm Mg}$ reaction rate at temperatures relevant to these environments is due to the expected, but unobserved resonance at E$^{lab}_{p}$ = 144 keV. An experiment to measurement this reaction was performed at Triangle Universities Nuclear Laboratory's (TUNL) Laboratory for Experimental Nuclear Astrophysics (LENA) using its new, high-intensity ECR ion source and accelerator system. Proton beam currents up to 1.2 mA were incident on target. At E$_{p}$ = 148 keV, with 55 C proton charge accumulated on target, a signal from this resonance was not observed. However, an upper limit of the resonance strength at E$^{lab}_{p}$ = 144 keV was determined and corresponds to a factor of 7 reduction from the present value. The new upper limit of resonance strength has reduced the uncertainty of the $^{23}{\rm Na}(\rm p,\gamma)^{24}{\rm Mg}$ reaction rate for temperatures of interest. Future experiments with higher sensitivity will be performed. Details of the experiment, observations, and results to date will be presented. [Preview Abstract] |
Monday, May 2, 2011 11:33AM - 11:45AM |
Q7.00005: ABSTRACT WITHDRAWN |
Monday, May 2, 2011 11:45AM - 11:57AM |
Q7.00006: Threshold Photoneutron Cross Sections for 26Mg Richard deBoer, Andreas Best, Joachim Goerres, Wanpeng Tan, Michael Wiescher, Richard Longland, Christian Iliadis, Rajarshi Raut, Gencho Rusev, Anton Tonchev The $^{22}$Ne$(\alpha,n)^{25}$Mg reaction rate is of critical importance for the calculation of the available neutron flux in s-process nucleosynthesis scenarios. The precision of the reaction rate is mainly hampered by the limited knowledge of the resonances near the neutron separation energy of $^{26}$Mg ($S_n$=11.093 MeV). The HI$\gamma$S facility offers a unique possibility for studying these resonances via the $^{26}$Mg$(\gamma,n)^{25}$Mg reaction. Preliminary results are presented for neutron measurements using both a high efficiency, nearly 4$\pi$, $^3$He neutron detector setup and a time of flight setup using nine liquid scintillator detectors. [Preview Abstract] |
Monday, May 2, 2011 11:57AM - 12:09PM |
Q7.00007: Shell-model studies of the $^{29}$P(p,$\gamma$)$^{30}$S reaction rate W.A. Richter, B. Alex Brown In $^{30}$S the properties of only the few lowest levels are well established. As the structure of proton unbound $^{30}$S states is important for determining the $^{29}$P(p,$\gamma$)$^{30}$S reaction rate, which influences explosive hydrogen burning in classical novae and type I X-ray bursters, we make use of a method based on the IMME (Isobaric Mass Multiplet Equation) to predict the properties of such states. We present results for levels in $^{30}$S (the mirror of nucleus $^{30}$Si). The calculated gamma-decay lifetimes and $^{29}$P to $^{30}$S spectroscopic factors together with experimental information on the levels of excited states are used to determine the $^{29}$P(p,$\gamma$)$^{30}$S reaction rates based on the use of the USDA and USDB interactions. Some theoretical error estimates based on the use of different interactions are given. Our predictions also agree well with observations of two dominant states [1], $J^\pi =$ 3$^+$ and 2$^+$ around 4.7 and 4.8 MeV respectively. \\[4pt] [1] K. Setoodehnia et al., Phys. Rev C 82, 022801(R) (2010) [Preview Abstract] |
Monday, May 2, 2011 12:09PM - 12:21PM |
Q7.00008: Se-68 rp-process waiting point and X-ray bursts M. Del Santo, H. Schatz, G. Lorusso, H. Crawford, G.F. Grinyer, Z. Meisel, A. Becerril, F. Montes, J. Pereira, K. Smith, S. George, D. Bazin, P. Mantica The x-ray light curve of astrophysical X-ray bursts and the composition of their nuclear ashes are shaped by the effective half-life of Se-68, a rare neutron deficient isotope near the proton drip line and a waiting point in the rapid proton capture process (rp-process). We addressed the nuclear physics uncertainty in the Se-68 half-life by studying the beta-delayed particle emission of Kr-69. The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL). The rare isotope beam was produced by fragmentation of a Kr-78 primary beam, separated using the A1900 and Radio Frequency Fragment Separator, and sent to the Beta Counting Station (BCS). The remaining fragments were implanted into a 500 micron double-sided-Si-strip-detector (DSSD) to detect charged particles (fast electrons and protons) following beta decay. The measured decay curve and delayed proton spectrum will be presented and the possible implications on the energy production in X-ray bursts and mass flow along the rp-process path in the A$\sim $70 region will be discussed. This work was supported in part by the National Science Foundation. [Preview Abstract] |
Monday, May 2, 2011 12:21PM - 12:33PM |
Q7.00009: Commissioning and first radioactive beam experiments at the CARIBU facility Guy Savard, Sam Baker, Shane Caldwell, Jason Clark, Cary Davids, Daniel Lascar, Anthony Levand, Richard Pardo, Donald Peterson, Don Phillips, Matthew Sternberg, Tao Sun, Jon Van Schelt, Rick Vondrasek, Bruce Zabransky The Californium Rare Ion Breeder Upgrade (CARIBU) of the ATLAS superconducting linac facility aims at providing low energy and reaccelerated neutron-rich radioactive beams to address key nuclear physics and astrophysics questions. These beams are obtained from fission fragments of a 1 Ci 252Cf source, thermalized and collected into a low-energy particle beam by a helium gas catcher, mass analyzed by an isobar separator, and charge breed to higher charge states for acceleration in ATLAS. The facility has ramped up with first operation with a weaker 2.5 mCi source and now a 100 mCi source. Low-energy mass separated radioactive beams have been extracted, charge bred with an efficiency of about 8\%, and reaccelerated to 6 MeV/u. Commissioning results, together with the results from first astrophysics experiments at CARIBU using the beams from the 100 mCi source will be presented. The final 1 Ci source is expected to be available in the spring. [Preview Abstract] |
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