Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session J13: Nuclear Astrophysics |
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Sponsoring Units: DNP Chair: C. Brune, Ohio University Room: Marriott Tampa Waterside Room 12 |
Sunday, April 17, 2005 10:45AM - 10:57AM |
J13.00001: $^7$Be($p,\gamma$)$^8$B S-factor from {\it ab initio} wave functions: I. Overlap integral calculation Petr Navratil, Carlos Bertulani, Etienne Caurier Nuclear structure of $^7$Be and $^8$B is studied within the {\it ab initio} no-core shell model (NCSM). Starting from realistic inter-nucleon interactions, $^7$Be and $^8$B wave functions are obtained in basis spaces up to $10\hbar\Omega$ with the matrix dimensions exceeding $7\times 10^7$. These wave functions are then used to calculate cluster form factors or overlap integrals of the $^8$B ground state with the $^7$Be$+p$ as a dependence on the separation between the proton and the center-of-mass of $^7$Be. Due to the use of the harmonic oscillator basis, the overlap integrals have incorrect asymptotics. To fix this problem, we perform a least-square fit of Woods-Saxon potential solutions to the NCSM overlap integrals in the 0-4 fm range under the constraint that the experimental $^8$B binding energy with respect to the $^7$Be$+p$ is reproduced. The corrected overlap integrals can then be used for the $^7$Be($p,\gamma$)$^8$B S-factor calculation. Support from the LDRD contract No. 04-ERD-058 as well as partial support from the DOE grants SCW0498 and DE-FG02-04ER41338 is acknowledged. [Preview Abstract] |
Sunday, April 17, 2005 10:57AM - 11:09AM |
J13.00002: $^7$Be($p,\gamma$)$^8$B S-factor from {\it ab initio} wave functions: II. S-factor calculation Carlos Bertulani, Petr Navratil, Etienne Caurier The S-factors ($S_{17}$ for the radiative capture reaction p+$^7 $Be$\rightarrow ^8$B+$\gamma$ are calculated using {\it ab initio} no-core shell model (NCSM) overlap integrals with corrected asymptotics. Momentum distributions for the reactions $^8$B (41 MeV/nucleon) + $^9$Be$\rightarrow ^7$Be+X and $^8$B (936 MeV/nucleon) + $^{12}$C$\rightarrow ^7$Be+X have also been studied. A good description of both the experimental data of both the astrophysical S-factor and of the momentum distributions over a wide energy/momentum spectrum is obtained. The spectroscopic factors obtained with the NCSM wavefunctions are also shown to be in good agreement with the experimental data. Our studies support a value of $S_{17}$ in agreement with recent Coulomb dissociation experiments, but which are slightly below the averaged values from direct capture experiments [1]. [1] W.C. Haxton, P.D. Parker, C.E. Rolfs, archive preprint nucl- th/0501020. [Preview Abstract] |
Sunday, April 17, 2005 11:09AM - 11:21AM |
J13.00003: $^{19}$F(p,$\gamma$): Putting a Lid on the CNO Cycle Aaron Couture, Mano\"el Couder, Joachim G\"orres, Hye-Young Lee, Edward Stech, Elizabeth Strandberg, Ethan Uberseder, Claudio Ugalde, Wanpeng Tan, Michael Wiescher The cold CNO cycle in massive stars (M$>$3M$_{\sun}$) has long been considered a closed cycle. The $^{19}$F(p,$\gamma$)$^{20}$Ne reaction represents the only possible path for breakout and depletion of catalytic material. In addition, the corresponding production of Ne would be important for later stellar burning cycles. The strong background from $^{19}$F(p,$\alpha_2\gamma$)$^{16}$O has prevented detailed measurements of the $^{19}$F(p,$\gamma$)$^{20}$Ne reaction from being made in the past. A new series of measurements investigating low energy resonances and interference terms have been made at Notre Dame. The results and predictions of the new resonance parameters and their effects on the CNO cycle will be discussed. [Preview Abstract] |
Sunday, April 17, 2005 11:21AM - 11:33AM |
J13.00004: Nova Nucleosynthesis with a New 18F(p,alpha) Reaction Rate Michael Smith, Jason Scott, W. Raphael Hix, Daniel Bardayan, Eric Lingerfelt, Raymond Kozub, Carl Brune, Sumner Starrfield The long-lived radionuclide $^{18}$F is synthesized in nova outbursts and its decay may serve as an observational tracer of the explosion mechanism. Because the $^{18}$F(p,$\alpha$)$^{15}$O reaction is the dominant destruction mechanism for $^{18}$F, the flux of gamma rays from $^{18}$F decay is very sensitive to the rate of this reaction. A revised $^{18}$F(p,$\alpha$)$^{15}$O rate was determined from recent ORNL measurements of $^1$H($^{18}$F,p)$^{18}$F and $^2$H($^{18}$F,p)$^{19}$F, combined with a reanalysis of archival $^{15}$N($\alpha$,$\alpha$)$^{15}$N data. We used this new rate in nova element synthesis calculations and compared new predictions of the synthesized abundance $^{18}$F (and other nuclides) to that obtained using the two most recent (p,$\alpha$) rates. We used a post- processing approach with temperature and density histories of 28 zones of ejected material determined from separate hydrodynamics calculations. The implications for satellite observations of novae will be discussed. These calculations were performed and visualized with the {\bf Computational Infrastructure for Nuclear Astrophysics}, an online suite of codes available at {\bf nucastrodata.org}. [Preview Abstract] |
Sunday, April 17, 2005 11:33AM - 11:45AM |
J13.00005: $^{19}$F alpha widths from $^{15}$N($\alpha,\alpha$)$^{15}$N data and the $^{18}$F$+p$ reaction rates Dan Bardayan, Ray Kozub, Michael Smith The rates of the $^{18}$F($p,\alpha$)$^{15}$O and $^{18}$F ($p,\gamma$)$^{19}$Ne reactions are important for understanding production of the long-lived radioisotope $^{18}$F in novae and the transition to heavy- element production in X-ray bursts. A knowledge of the alpha widths of numerous $^ {19}$Ne levels is critical for calculating these rates. These widths are generally not known and must be extrapolated from information on the isospin mirror nucleus $^{19}$F. Much of this information comes from a measurement of the $^{15}$N($\alpha,\alpha$)$^{15}$N reaction [1], and we have reanalyzed this data using a multilevel $R$-matrix approach to determine properties of resonances in the astrophysically- important range $E_x = 6.4 - 7.5$ MeV. We find the energies and widths of broad levels to be different than previously reported. We have also set upper limits on the widths of postulated 3/2$^{+}$ resonances, analogs of which are important for the $^{18}$F$+p$ reaction rates. The method and results will be presented. \bibitem{smotrich} [1] H. Smotrich {\it et al.}, Phys. Rev. {\bf 122}, 232 (1961). [Preview Abstract] |
Sunday, April 17, 2005 11:45AM - 11:57AM |
J13.00006: \textbf{Study of Excited Levels of }$^{19}$\textbf{Ne with the }$^{17}$\textbf{O(}$^{3}$\textbf{He,}\textbf{\textit{n}}\textbf{)}$^{19}$\textbf{Ne Reaction} Michael Hornish, Carl Brune, Thomas Massey, Hadi Hadizadeh, Alexander Voinov, Steven Grimes, Americo Salas, Catalin Matei In novae, the survival of the long-lived radioisotope $^{18}$F, which is important in nova gamma-ray astronomy, depends on the parameters of excited states of $^{19}$Ne, which dictate the rates of the $^{18}$F($p$,\textit{$\alpha $})$^{15}$O and $^{18}$F($p$,\textit{$\gamma $})$^{19}$Ne reactions. Of particular importance is the level structure of $^{19}$Ne above the proton threshold ($E_{x}$ = 6.411 MeV), where analogs for several states in the mirror nucleus $^{19}$F have not yet been identified in $^{19}$Ne. The present experiment involves a study of the $^{17}$O($^{3}$He,$n)^{19}$Ne reaction and was performed at the Edwards Accelerator Laboratory at Ohio University. Neutron time-of-flight techniques were employed to study $^{19}$Ne excited levels, particularly those between 6 and 7 MeV. In addition to measuring the energy of observed levels and their widths provided they are large enough, the cross section of the reaction to these levels can be compared to Hauser-Feshbach calculations in order to identify the spin of the states. The significance of these levels in relation to proton-induced reactions on $^{18}$F will be discussed. [Preview Abstract] |
Sunday, April 17, 2005 11:57AM - 12:09PM |
J13.00007: Mass Measurements of $^{22}$Mg and $^{26}$Si A. Parikh, J. A. Caggiano, C. Deibel, R. Lewis, P. D. Parker, C. Wrede, J. P. Greene The detection of characteristic $\gamma $-ray lines of astrophysical origin allows important nuclear physics constraints to be set on nucleosynthesis models of astrophysical phenomena. The 1.809 MeV and 1.275 MeV $\beta $-delayed $\gamma $-rays from $^{26}$Al$_{(g.s.)}$ ($t_{1/2} =7.2\times 10^5$y) and $^{22}$Na ($t_{1/2} =2.6$y) respectively, constitute two of these production signatures. Much recent experimental work$^{1,2,3 }$has been concentrated on determining the rates of the reactions $^{21}$Na(p,$\gamma )^{22}$Mg and $^{25}$Al(p,$\gamma )^{26}$Si to better establish the contribution of novae to the overall abundances of these two species. For indirect determinations of these reaction rates, it is important to have precise mass values of the nuclei involved$^{4,5}$. Using a 33 MeV proton beam in conjunction with our Enge Split-Pole spectrograph, we measured the $Q_0 $ values of the $^{24}$Mg(p,t)$^{22}$Mg and $^{28}$Si(p,t)$^{26}$Si reactions relative to that of the $^{16}$O(p,t)$^{14}$O reaction. We find the mass excesses $\Delta (^{22}$Mg) = -400.5(1.0) keV and $\Delta (^{26}$Si) = -7139.5(1.0) keV. This work was supported by the US DOE, Grant No. DE-FG02-91ER-40609 and Contract No. W-31-109-ENG-38. $^{1}$ S. Bishop et al., Phys. Rev. Lett. \textbf{90}, 162501 (2003). $^{2}$ J. A. Caggiano et al., Phys. Rev. C \textbf{65}, 055801 (2002). $^{3}$ D. W. Bardayan et al., Phys. Rev. C \textbf{65}, 032801(R) (2002). $^{4}$ G. Savard et al., Phys. Rev. C \textbf{70}, 042501 (2004). $^{5}$ M. Mukherjee et al., Phys. Rev. Lett. \textbf{93}, 150801 (2004). [Preview Abstract] |
Sunday, April 17, 2005 12:09PM - 12:21PM |
J13.00008: \textbf{Extracting the ANCs for }$^{23}$\textbf{Al$\to $}$^{22}$\textbf{Mg + p from the mirror system} $^{23}$\textbf{Ne$\to $}$^{22}$\textbf{Ne + n } Tariq Al-Abdullah, X. Chen, H.L. Clark, C. Fu, C.A. Gagliardi, Y.-W. Lui, G. Tabacaru, Y. Tokimoto, L. Trache, R.E. Tribble, F. Carstoiu, S. Piskor Data from $\gamma $-ray space telescopes suggest that $^{22}$Na is under produced in ONe novae compared to model calculations. This could be explained if the parent $^{22}$Mg is depleted by the $^{22}$Mg(p,$\gamma )^{23}$Al reaction. We are determining the asymptotic normalization coefficients (ANCs) for $^{23}$Al$\to ^{22}$Mg+p to estimate this reaction rate. The neutron transfer reaction $^{13}$C($^{22}$Ne,$^{23}$Ne)$^{12}$C, $\theta _{C.M}$ =3$^{o}$-34$^{o}$, was measured using a 264 MeV $^{22}$Ne beam from the Texas A{\&}M K500 cyclotron to extract the ANCs for the ground and first excited states in $^{23}$Ne, and then transpose to the corresponding states of the mirror nucleus $^{23}$Al. Another experiment was carried out to obtain the ANC for $^{13}$C$\to ^{12}$C+n, $\theta _{C.M}$ =3$^{o}$-38$^{o}$, which is the other vertex in the above reaction. Elastic scattering angular distributions for both reactions were also measured to obtain reliable optical potential parameters that will be used in DWBA calculations. New results will be presented and discussed. [Preview Abstract] |
Sunday, April 17, 2005 12:21PM - 12:33PM |
J13.00009: Gamow-Teller Strengths from (t,3He) Charge Exchange Experiments M.E. Howard, S.D. Reitzner, E.E. Smith, S. Austin, D. Bazin, A.L. Cole, M. Famiano, A. Gade, D. Galaviz Redondo, G.W. Hitt, W. Martinez, M. Matos, H. Schatz, B. Sherrill, C. Simenel, A. Stolz, R.G.T. Zegers, B. Davids, Y. Shimbara, C. Samanta In pre-collapse and post-bounce evolutionary stages of massive stars, electrons have energies high enough to excite Gamow-Teller (GT) resonances. GT-Strengths are important inputs for codes modeling the dynamics of supernovae. To validate theoretical estimates for GT-Strength distribution, detailed comparisons with experimental results are important. Charge exchange experiments fill this demand. Preliminary results of a recent (t,3He) experiment run at the National Superconducting Cyclotron Laboratory on CD2, 24Mg, 63Cu, 94Mo targets are presented, including a brief discussion of models used to calculate GT strengths. [Preview Abstract] |
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