Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session LG: Nuclear Astrophysics III |
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Chair: Kate Jones, University of Tennessee Room: Kings 2 |
Saturday, October 17, 2009 2:00PM - 2:15PM |
LG.00001: Unbound states of $^{32}$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, P.D. Parker, K.T. Schmitt Breakout from the SiP cycle [1], which is closed by the $^{31}$S (p,$\alpha$)$^{28}$P reaction, can occur via the $^{31}$S(p,$ \gamma$)$^{32}$Cl proton-capture reaction. The duration of the cycle influences the timescale of explosive hydrogen burning. At novae temperatures 0.1-0.4 GK, the $^{31}$S(p,$\gamma$)$^{32}$Cl reaction rate is dominated by $^{31}$S+p resonances. Discrepancies in the $^{32}$Cl resonance energies have been reported in previous measurements [1,2]. We have used the $^ {32}$S($^{3}$He,t)$^{32}$Cl charge-exchange reaction to produce unbound states in $^{32}$Cl and determined their excitation energies by detecting the tritons at the focal plane of the Enge Spectrograph at the Yale University's Wright Nuclear Structure Laboratory. To determine the proton branching ratios the decay protons coming from the residual $^{32}$Cl nuclei have been detected using a silicon-strip detector array around the target position. Results from the experiment will be presented. \\[4pt] [1]~S.Vouzoukas et al., PRC 50 (1994) 1185.\\[0pt] [2]~C. Jeanperrin et al., NPA 503 (1989) 77. [Preview Abstract] |
Saturday, October 17, 2009 2:15PM - 2:30PM |
LG.00002: The $^{28}$Si(p,t)$^{26}$Si Reaction and Implications for $^{25}$Al(p,$\gamma$)$^{26}$Si K.A. Chipps, D.W. Bardayan, K.Y. Chae, R. Kozub, C. Matei, B.H. Moazen, C.D. Nesaraja, P.D. O'Malley, S.D. Pain, W.A. Peters, S.T. Pittman, K. Schmitt, M.S. Smith We have studied several resonances in $^{25}$Al(p,$\gamma$)$^{26}$Si via the $^{28}$Si(p,t)$^{26}$Si reaction at HRIBF. In addition to measuring angular distributions of the tritons, an additional silicon detector array was used to measure the coincident protons emitted from the decay of states in $^{26}$Si above the proton threshold. We confirm experimentally that the 3$^+$ 5914 keV resonance, the first $\ell$ = 0 state above the proton threshold, does in fact decay essentially 100\% of the time via proton emission, resulting in a proton branching ratio consistent with one. [Preview Abstract] |
Saturday, October 17, 2009 2:30PM - 2:45PM |
LG.00003: Analysis of $^{26}$Al + p elastic and inelastic scattering reactions in inverse kinematics at the HRIBF S.T. Pittman, K.Y. Chae, K.L. Jones, B.H. Moazen, D.W. Bardayan, C.D. Nesaraja, S.D. Pain, M.S. Smith, K.A. Chipps, R.L. Kozub, J.F. Shriner, Jr., C. Matei, M. Matos, P.D. O'Malley, W.A. Peters, P.D. Parker It is unknown to what degree novae contribute to the abundance of $^{26}$Al in the Galaxy. Destruction through the $^{26}$Al(p,$\gamma )^{27}$Si reaction may reduce the nova contribution, but uncertainties in the properties of $^{27}$Si levels above the proton threshold limit reaction rate estimates. Inelastic proton scattering in these environments may also reduce the net production of $^{26}$Al. To constrain estimates of the degree of $^{26}$Al destruction in novae, the $^{26}$Al + p elastic and inelastic reactions were investigated in inverse kinematics (E$_{c.m.}$= 0.5-1.5 MeV) at the HRIBF. The experiment and results of the analysis will be discussed. [Preview Abstract] |
Saturday, October 17, 2009 2:45PM - 3:00PM |
LG.00004: Direct Measurement of $^{21}$Na+$\alpha$ Stellar Reaction Nguyen Binh Dam, H. Yamaguchi, Y. Wakabayashi, S. Hayakawa, T. Hashimoto, D. Kahl, S. Kubono, H.K. Le, T.T. Nguyen, N. Iwasa, N. Kume, S. Kato, T. Teranishi Nucleosynthesis of $^{22}$Na is an interesting subject because of possible $\gamma$-ray observation and isotopic anomalies in presolar grain. $^{22}$Na would have been mainly produced in the NeNa cycle. At high temperature conditions, $^{21}$Na($\alpha$,p)$^{24}$Mg reaction could play a significant role to make flow from the NeNa cycle to the next MgAl cycle and beyond. Clearly, the $^{21}$Na($\alpha$,p)$^{24}$Mg stellar reaction would bypass $^{22}$Na, resulting in reduction of $^{22}$Na production, therefore, it is strongly coupled to the Ne-E problem. It could be also important to understand the early stage of the rp-process. Experiment was performed using a 39~MeV $^{21}$Na radioactive beam obtained by the CNS Radio Isotope Beam separator CRIB of the University of Tokyo. Both protons and alphas were measured from $\alpha$+$^{21}$Na scattering with a thick $^4$He gas target. [Preview Abstract] |
Saturday, October 17, 2009 3:00PM - 3:15PM |
LG.00005: Direct and Indirect Techniques for Determining Reaction Rates Eric Johnson Astrophysically important reactions have been studied through indirect techniques for many years due to their prohibitively small cross sections at Gamow window energies. Indirect techniques, such as $\alpha$-transfer reactions, constrain the reaction cross section of interest in the astrophysically relevant energy range. Recently, we determined the contribution of the 3$^{-}$ state at 6.4 MeV in $^{18}$O to the $^{14}$C($\alpha,\gamma$) reaction rate through the indirect $\alpha$-transfer reaction $^{14}$C($^{7}$Li,t) at the John D. Fox Superconducting Accelerator Laboratory at FSU. Using the same experimental data we were able to determine the asymptotic normalization coefficient (ANC) of the 1$^{-}$ state at 6.2 MeV in $^{18}$O. This state is a mirror of the 6.15 MeV state in $^{18}$Ne, which dominates the $^{14}$O($\alpha$,p) reaction rate at temperatures of Novae and X-ray bursters. An experimental apparatus which will allow for direct measurements of the astrophysically important ($\alpha$,p) reaction rates in the Gamow window, the LSU-FSU Array for Nuclear Astrophysics Studies with Exotic Nucelei (ANASEN), is now under construction. I will discuss our recent results on the $^{14}$C($\alpha$,$\gamma$) and $^{14}$O($\alpha$,p) reaction rates and the current status of the ANASEN project. [Preview Abstract] |
Saturday, October 17, 2009 3:15PM - 3:30PM |
LG.00006: Direct Measurement of the $^{11}$C$(\alpha,p)^{14}$N Reaction S. Hayakawa, S. Kubono, H. Yamaguchi, T. Hashimoto, D.N. Binh, D. Kahl, Y. Wakabayashi, N. Iwasa, N. Kume, Y. Miura, T. Teranishi, J.J. He, Y.K. Kwon, T. Komatsubara, S. Kato, S. Wanajo A recent simulation of the rp-process in neutrino-driven winds in type II supernovae ($\nu p$-process) suggests that the $^{11}$C$(\alpha,p)^{14}$N reaction could be an important breakout pass from the pp-chain region to the CNO region. However, there are only very limited experimental information of the reaction cross section available from the time-reverse reaction studies. In order to determine the reaction rate of $^{11}$C$(\alpha,p)^{14}$N, a direct measurement by means of the thick-target inverse-kinematics method has recently been performed using low-energy $^{11}$C beams from the CNS Radioactive Ion Beam (CRIB) separator, a $^4$He gas target and $\Delta$E-E position-sensitive silicon telescopes at three downstream angles. The experiment covered $E_{\rm CM}$ = 0.5-5 MeV corresponding to the stellar temperature of 1.5-7GK. The obtained reaction cross section including some resonances and transitions to the excited states of $^{14}$N will be reported. [Preview Abstract] |
Saturday, October 17, 2009 3:30PM - 3:45PM |
LG.00007: The resonant structure of $^{18}$Ne and its relevance in the breakout of the Hot CNO cycle S. Almaraz-Calderon, W. Tan, A. Aprahamian, B. Bucher, J. Gorres, A. Roberts, A. Villano, M. Wiescher, C. Brune, Z. Heinen, T. Massey, H. Mach, N. Guray, R.T. Guray In explosive hydrogen burning environments such as Novae and X-ray bursts, temperatures and densities achieved are sufficiently high to bypass the beta decay of the waiting points of the hot CNO cycle by alpha captures, leading to a thermonuclear runaway via the rp-process. One of the two paths to a breakout from the hot CNO cycle is the route starting from $^{14}$O($\alpha$,p)$^{17}$F followed by $^{17}$F(p,$\gamma$)$^{18}$Ne and $^{18}$Ne($\alpha$,p). The $^{14}$O($\alpha$,p) reaction proceeds through resonant states in $^{18}$Ne, making the reaction rate dependent on the excitation energies and spins as well as partial and total widths of these resonances. We used the $^{16}$O($^{3}$He,n) reaction and charged particle-neutron coincidences to measure the structure details of levels in $^{18}$Ne. In particular, the $\alpha$ and proton decay branching ratios via ground state and excited states in $^{17}$F were measured. The analysis of the data will allow us to provide crucial information to be included in the reaction network calculations that could have great impact on the nuclear energy generation and nucleosynthesis that occur in these explosive environments. [Preview Abstract] |
Saturday, October 17, 2009 3:45PM - 4:00PM |
LG.00008: The $^{11}$B(p,$\alpha )\alpha \alpha $ Reaction at Low Energies R.M. Prior, M.C. Spraker, R.H. France III, S. Stave, P.-N. Seo, N. Brown, S.S. Henshaw, M.W. Ahmed, B.A. Perdue, H.R. Weller, A. Teymurzyan, P.P. Martel The $^{11}$B(p,$\alpha )\alpha \alpha $ reaction has been proposed for use in an aneutronic fusion reactor. Detailed knowledge of the angular and energy distribution of the outgoing $\alpha$ particles is needed to model this reactor. The reaction has been previously modeled as a two-step process proceeding through the first excited state of $^{8}$Be. The 2$^{-}$ resonance at 0.675 MeV is critical in the reactor models. We have previously studied the reaction at proton beam energies of 0.40 MeV and above and have developed a three-body reaction model that describes the spectra of the emitted alphas in that energy range. To further the study of the reaction, we have taken data at 5 angles between 50\r{ } and 150\r{ } for several energies between 0.40 MeV and 0.15 MeV which includes the region of the 2$^{+}$ resonance at 0.162 MeV. The measured $\alpha $-particle energy distributions are consistent with the higher energy data and our model except at energies in the vicinity of the 0.162 MeV resonance. We will discuss our results and the deviation from the model. [Preview Abstract] |
Saturday, October 17, 2009 4:00PM - 4:15PM |
LG.00009: Measurement of E1 and E2 cross sections of the $^{12}$C(alpha,gamma)$^{16}$O reaction at E$_{eff}$=1.4 MeV Yasuki Nagai, Hiroyuki Makii, Tatsushi Shima, Mariko Segawa, Kenji Mishima, Hitoshi Ueda, Masayuki Igashira, Toshiro Ohsaki The gamma-ray angular distribution from $^{12}$C(alpha,gamma)$^{16}$O to the ground state of $^{16}$O was measured using a pulsed alpha beam at $E_{eff}$=1.6 and 1.4 MeV. True gamma-ray events of $^{12}$C(alpha,gamma)$^{16}$O were obtained by discriminating backgrounds due to neutrons from $^{13}$C(alpha$,$n)$^{16}$O with a time-of-flight method. A Rutherford backscattering spectrum of alpha particles from enriched $^{12}$C targets was measured during beam irradiation. The astrophysical S factors for E1 and E2 derived from the present cross sections are discussed in comparison with the values derived by the recent R-matrix calculation. [Preview Abstract] |
Saturday, October 17, 2009 4:15PM - 4:30PM |
LG.00010: Performance of the UConn-TUNL O-TPC with the Upgraded Optical Readout System* W.R. Zimmerman, M. Gai, M.W. Ahmed, S.S. Henshaw, C.R. Howell, P.-N. Seo, S.C. Stave, H.R. Weller, P.P. Martel An Optical-Readout Time Projection Chamber (O-TPC) is being used at the High-Intensity $\gamma$amma Source (HI$\gamma$S) at TUNL to study oxygen formation during stellar helium burning by measuring the time-reversed $^{16}O$($\gamma$,$\alpha$)$^{12}$C reaction. The photodissociation of $^{16}$O generates ionization tracks in the 30cm x 30cm x 20.5 cm drift chamber. The electrons drift toward the multiplication region composed of three grids separated by 5 mm. The avalanche electrons induce scintillation light (primarily $\lambda$ = 338 nm) in N$_2$ gas, and a CCD camera records an image of the two-dimensional projection of the tracks; hence the in-plane angle ($\alpha$). Photomultiplier tubes measure the time-projection; hence the out-of-plane angle ($\beta$). The azimuthal ($\phi$) and scattering ($\theta$) angles are reconstructed from $\alpha$ and $\beta$. The total energy deposited in the detector is measured by the charge signal from the last grid, as well as from the photomultiplier tubes. Recent upgrades of the optical-readout system have improved the event identification. The larger design lens (142mm diameter) was installed leading to a factor of 15 increase in the light collection. The operation of the upgraded O-TPC system and measured in-beam events will be discussed. *Work supported by the USDOE grant No. DE-FG02-94ER40870 and DE-FG02-97ER41033. [Preview Abstract] |
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