### Session M15: Nuclear Astrophysics II

 Sunday, April 15, 2007 3:15PM - 3:27PM M15.00001: ABSTRACT WITHDRAWN Sunday, April 15, 2007 3:27PM - 3:39PM M15.00002: Determination of the Reaction Rate for $^{17}$F(p,$\gamma )^{18}$Ne using the Neutron Transfer Reaction($^{17}$O,$^{18}$O) in Mirror Nuclei. Tariq Al-Abdullah , X. Chen , C.A. Gagliardi , Y.-W. Lui , G. Tabacaru , Y. Tokimoto , L. Trache , R.E. Tribble , Y. Zhai , F. Carstoiu Studying the reaction rate for $^{17}$F(p,$\gamma )^{18}$Ne in ONe novae is important to understand the production of the elements in the HCNO cycle, and investigate the missing $\gamma$-ray from the synthesis of $^{18}$F. The Gamow windows of the reaction in ONe novae imply that the reaction occurs at energies of the order of few hundreds keV. The reaction rate at low temperature is dominated by the direct capture to the lowest 2$^{+}$ states in $^{18}$Ne. The ANCs for the 2$^{+}$ excited states at 1.98 MeV and 3.92 MeV in $^{18}$O are sought through measuring the peripheral reaction $^{13}$C($^{17}$O,$^{18}$O$^{\ast})^{12}$C, and then transposed to the mirror states in $^{18}$Ne. The experiment was conducted with $^{17}$O and $^{18}$O beams at 12 MeV/A using the MDM spectrometer of Texas A{\&}M University. The elastic scatterings for the incoming and outgoing channels were measured separately to obtain the OMPs that are needed for the DWBA calculation to predict the angular distribution for the transfer reaction. Results will be presented and discussed. Sunday, April 15, 2007 3:39PM - 3:51PM M15.00003: The structure of $^{23}$Al and consequences on the depletion of $^{22}$Na from ONe novae Y. Zhai , L. Trache , V.E. Iacob , J.C. Hardy , C. Fu , T. Al-Abdullah , N. Nica , M. McCleskey , V.V. Golovko , H.I. Park , G. Tabacaru , A. Banu , R.E. Tribble There is interest in the structure of $^{23}$Al due to the contribution of the $^{22}$Mg(p, $\gamma )^{23}$Al and $^{22}$Na(p, $\gamma )^{23}$Mg reactions in the depletion of $^{22}$Na from ONe novae. Using MARS we produced and separated pure $^{23}$Al samples with a 48 MeV/u $^{24}$Mg beam from the K500 cyclotron at Texas A{\&}M University. New $\beta$ and $\beta -\gamma$ coincidence measurements were made with a thin scintillator, an HPGe detector and a fast tape transport system. Addition of a BGO Compton shield improved very much the quality of the $\gamma$ spectra around the transitions from the IAS state at 7803 keV. From the measured $\beta$ singles and $\beta -\gamma$ coincidence decay spectra we obtained the $^{23}$Al $\beta$-decay scheme, branching ratios and absolute log\textit{ft} values for several transitions. We clearly determined that the $^{23}$Al ground state spin and parity is J$^{\pi }$=5/2$^{+}$ , not 1/2$^{+}$, and also found spectroscopic information for the states that are resonances in the $^{22}$Na(p, $\gamma )^{23}$Mg reaction. It follows that the larger capture rate implied by the now-rejected lower spin value for $^{23}$Al can not explain the missing 1275 keV cosmic $\gamma$ -ray from the decay of long-lived $^{22}$Na, the last step in the hot NeNa cycle. Sunday, April 15, 2007 3:51PM - 4:03PM M15.00004: Studying the $^{30}$P(p,$\gamma$)$^{31}$S reaction using the $^{31}$P($^{3}$He,t)$^{31}$S$^{*}$(p)$^{30}$P reaction C. Wrede , J.A. Caggiano , J.A. Clark , C. Deibel , R. Lewis , A. Parikh , P.D. Parker , C. Westerfeldt Enriched isotopic abundance ratios of $^{30}$Si/$^{28}$Si in several presolar SiC and graphite grains qualitatively indicate oxygen-neon (ONe) nova origins but fall short of ONe nova model predictions by factors of 20-90. The $^{30}$P(p,$\gamma$)$^{31}$S reaction rate uncertainty in ONe novae spans four orders of magnitude through which the predicted amount of ejected $^{30}$Si can vary by a factor of 100. By measuring the $^{31}$P($^{3}$He,t)$^{31}$S$^{*}$(p)$^{30}$P reaction we have determined the energies of astrophysically relevant $^{31}$S excited states to $\pm$ 3 keV, and have found one new resonance. Proton branching ratios have been constrained by detecting decay protons in coincidence with tritons. Implications for the $^{30}$P(p,$\gamma$)$^{31}$S reaction rate, $^{30}$Si production, and S-Ca production in ONe novae will be presented. Sunday, April 15, 2007 4:03PM - 4:15PM M15.00005: Particle decay from the states of $^{18}Ne^*$ in the $^{14}O+\alpha$ interaction Changbo Fu , V.Z. Goldberg , A.M. Mukhamedzhanov , G.G. Chubarian , Y. Zhai , T. Al-Abdullah , M. McCleskey , L. Trache , R.E. Tribble , G.V. Rogachev , B. Skorodumov By using a 32.7 MeV $^{14}{\rm O}$ beam provided by the MARS at the TAMU and the modified thick target inverse kinematics technique, we have measured the excitation functions for the $(\alpha, p)$, $(\alpha, 2p)$, and $(\alpha, \alpha)$. Excitation functions for the elastic alpha scattering manifest many strong resonances in the excitation region 0-11 MeV. By measuring coincident protons, we have found that sequential decay dominates the two proton emission process of the $^{18}{\rm Ne}$ compound nuclei. We also found that two proton decay of a state at 8.45 MeV in $^{18}{\rm Ne}$ demonstrates the properties of the decay by a correlated proton pair. With an assumption of $^2{\rm He}$ decay, we calculated the relative energy between the 2 protons from this level using the Faddeev approach with first rank Yamaguchi separable potential.There is a good agreement between the experiment and calculations. We also demonstrated that measurements of the TOF for protons in the TTIK method can be used to identify reactions occurring at different places in the gas target, thus making it possible to identify the $(\alpha,p)$ reaction for astrophysical interesting. Sunday, April 15, 2007 4:15PM - 4:27PM M15.00006: First Measurement of the Cascade Transition via the 6.049-MeV State of $^{16}$O in the $^{12}$C($\alpha,\gamma$)$^{16}$O Reaction Catalin Matei , C.R. Brune , L. Buchmann , D.A. Hutcheon , C. Ruiz , J. Caggiano , A. Laird , Z.H. Li , A. Olin , D. Ottewell , G. Ruprecht , M. Trinczek , C. Vockenhuber , J. D'Auria , M. Lamey , C. Wrede , A.A. Chen , J. Pearson , W.R. Hannes The cascade through the 6.049-MeV state of $^{16}$O has rarely been discussed as contributing to the $^{12}$C ($\alpha$,$\gamma$)$^{16}$O cross section at low energies largely due to experimental difficulties in observing this transition. We report here first measurements of this transition in $^{12}$C($\alpha$,$\gamma$)$^{16}$O using the DRAGON separator facility at TRIUMF. The experiment was performed in inverse kinematics with an incident $^{12}$C beam on a windowless $^{4}$He gas target. The coincidence setup included a BGO array around the gas target and a DSSSD detector for the detection of $^{16}$O recoils. The acceptance of DRAGON including the BGO array has been simulated in GEANT as well as measured directly. The transition strength has been derived and analyzed in the R- matrix formalism. We find an extrapolated value of $S_{6.05} (300)=25\pm16$ keVb showing that this transition is likely the most important cascade contribution for $^{12}$C ($\alpha$,$\gamma$)$^{16}$O. Sunday, April 15, 2007 4:27PM - 4:39PM M15.00007: Reaction rates of the fusion reaction $^{12}$C+$^{12}$C at E$_{CM}$ = 2.10 to 4.75 MeV for the $^{20}$Ne and $^{23}$Na exit channels Timothy Spillane , Francesco Raiola , Sheng Zeng , Hans-Werner Becker , Cristina Bordeanu , Claus Rolfs , Jeffrey Schweitzer , Frank Strieder , Daniel Sch\"urmann , Lucio Gialanella The fusion reaction $^{12}$C + $^{12}$C has been studied at E$_{CM}$ = 2.10 to 4.75 MeV by $\gamma$-ray spectroscopy using a C target of ultra-low hydrogen contamination. The deduced astrophysical \~{S}(E) factor exhibits previously unknown resonances at E $\leq$ 3.0 MeV, in particular a strong narrow resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present non-resonant reaction rate of the $\alpha$ channel significantly near T = 8 x 10$^{8}$ K. Due to the resonance structure, extrapolation to the Gamow energy E$_{G}$ = 1.5 MeV is quite uncertain.