Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session EH: Mini-symposium on Nuclear Physics in Extreme Astrophysical Conditions I |
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Sponsoring Units: DNP JPS Chair: Shigeru Kubono, University of Tokyo Room: Ritz-Carlton Hotel Plantation 1 |
Wednesday, September 21, 2005 9:00AM - 9:30AM |
EH.00001: Measurement of the astrophysical $^{8}$Li($\alpha $, n) reaction cross section Invited Speaker: It has been discussed that ($\alpha $, n) reactions of light neutron-rich radioactive nuclei play important roles in the r-process at a `hot bubble' formed in a supernova explosion[1]. A systematic study of these astrophysical reaction rates has been started at the Tandem facility in Japan Atomic Energy Research Institute (JAERI). Direct measurements of $^{8}$Li($\alpha $, n)$^{11}$B, $^{12}$B($\alpha $, n)$^{15}$N, $^{16}$N($\alpha $, n) $^{19}$F reaction cross sections have been performed, so far. In particular, the $^{8}$Li($\alpha $, n) is one of critical reactions in going to heavier elements across the stability gap of A = 8 not only in the r-process but also in the possible nucleosynthesis at the Big Bang. We will report a result of the exclusive measurement in the energy region of E$_{cm}$ = 0.7 - 2.6 MeV together with a preliminary one in the lower energy region of E$_{cm}$ = 0.14 - 1.7 MeV covering the Gamow window at T$_{9}$=1. The $^{8}$Li-RNB was produced via the $^{9}$Be ($^{7}$Li, $^{8}$Li) $^{8}$Be transfer reaction and was separated using the recoil mass separator. The typical intensity and purity were 5.0 kpps and 99{\%}, respectively. Then, $^{8}$Li enters directly to a gas counter named as Multiple-Sampling and Tracking Proportional Chamber (MSTPC) filled with He (90{\%}) + CO$_{2 }$(10{\%}). The He-gas works not only as a counter gas but also as a gas target. Three-dimensional trajectories and energy losses of all the charged particles were measured to identify the reaction point and its energy. Neutrons emitted simultaneously were also measured by a plastic-scintillator array. The excitation function of the reaction cross section was thus measured in the broad energy range. The obtained result has ten times better statistics compared to the previous exclusive measurement[2]. An improved astrophysical S-factor will be discussed together with some information of excited states in the compound nucleus, $^{12}$B. I will also mention about relevant experimental plan, which will be performed using light neutron-rich RNBs supplied from JAERI-RMS or Tokai Radioactive Ion Accelerator Complex (TRIAC)[3]. [1] M. Terasawa et al., Astrophy. J. 562 (2001) 470. [2] Y. Mizoi et al., Phys. Rev. C62 (2000) 065801. [3] H. Miyatake et al., Nucl. Instrum. Meth. B204 (2003) 746. [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
EH.00002: Measurements with $^7$Be beams at the HRIBF D.W. Bardayan, J.C. Blackmon, J.J. Das, C.D. Nesaraja, M.S. Smith, D.W. Stracener, K.Y. Chae, Z. Ma, A.E. Champagne, R. Fitzgerald, D.W. Visser, U. Greife, R.J. Livesay, V. Guimaraes, J. Howard, R.L. Kozub, M.S. Johnson, K.L. Jones, S.D. Pain, J.S. Thomas, P.D. Parker A $^7$Be beam has been used at the HRIBF to study important reactions in stellar burning. Precise knowledge of the $^7$Be($p,\gamma$)$^8$B rate is important for interpreting solar neutrino flux observations. A direct measurement of the $^7$Be($p,\gamma$)$^8$B cross section is being made by bombarding a H$_2$ gas target with a $^7$Be beam and counting $^8$B recoils at the focal plane of the DRS mass spectrometer. The $^3$He($^3$He,2$p$)$^4$He reaction also occurs in stellar burning, but interpretation of low energy measurements have been hindered by a surprisingly strong low-energy rise in the cross section. This rise could, in part, be due to broad $^6$Be resonances. We have studied $^2$H($^7$Be,$t$)$^6$Be to search for any such broad $^6$Be levels. Initial results from these measurements will be presented. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
EH.00003: Is There a Significant Difference Between The Slope of CD and DC Data on $^7Be(p,\gamma)^8B$ Reaction. Moshe Gai The RIKEN data on the Coulomb Dissociation (CD) of $^8B$ were shown to be in good agreement with the Direct Capture (DC) data on the $^7Be(p,\gamma)^8B$ reaction (that were known at that time) of Filippone {\em et al.} Yet recently it was claimed [1] that the RIKEN2 CD data must be corrected in order to be reconciled with the slope of DC data. Considering the (correct) so called scale independent b-slope parameter of the RIKEN2 CD data, the resultant corrected b- slope parameter suggested by Esbensen, Bertsch and Snover is shown to be considerably smaller than the so called average b-slope parameter of DC data. The suggested corrections of the b-slope parameter lead to a large disagreement with DC data, in sharp contrast to the claim. The slope corrections are only significant for the RIKEN2 CD data. For the GSI kinematics, where in fact one may observe slope different than for DC (at least for the GSI1 data), they find a fortuitous cancellation that leads to a vanishingly small slope correction. Hence the validity of these correction based on the observed slopes can not be substantiated. \newline \newline [1] H. Esbensen, G. F. Bertsch, and K. A. Snover; Phy. Rev. Lett. {\bf94}(205)042502. [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
EH.00004: Low energy nuclear reaction measurements using monolithic silicon telescope Shunji Nishimura, Mizuki Kurata-Nishimura, Hisashi Fujikawa, Amadio Guilherume, Jan-jun He, Shigeru Kubono, Hidetoshi Yamaguchi, Takashi Teranishi, Yasuo Wakabayashi, Shawn Bishop, Meiko Kurokawa, Takashi Kishida, Toru Motobayashi $^8$Li($\alpha$,n)$^{11}$B is recognized as an important reaction for passing through the valley of A=8 in nucleosynthesis. While, there are some difficulties of measuring the most interesting energy region of data below 1 MeV due to the background particles consists of elastically scattered $^8$Li ions, and $\alpha$ particles as well as the decay products of $^8$Li. A new experimental apporach for exploring these low-energy nuclear reactions using a monolithic silicon telescope have been performed at the CNS-CRIB spectrometer. Our preliminary results will be presented. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
EH.00005: New Measurement of the E1 Component of the $^{12}$C($\alpha $,$\gamma )^{16}$O Reaction X.D. Tang, M. Notani, K.E. Rehm, I. Ahmad, J. Greene, A.A. Hecht, D. Henderson, R.V.F. Janssens, C.L. Jiang, E.F. Moore, R.C. Pardo, G. Savard, J.P. Schiffer, S. Sinha, M. Paul, L. Jisonna, R.E. Segel, C. Brune, A. Champagne, A. Wuosmaa The radiative capture reaction $^{12}$C($\alpha $,$\gamma )^{16}$O is an important process in nuclear astrophysics. Since the cross sections at red-giant temperatures are extremely small ($\sim $10$^{-17}$ b) indirect techniques have to be used to determine its astrophysical reaction rate. The E1 component of this rate is best determined through a measurement of the beta-delayed alpha decay of $^{16}$N. For a measurement of this decay we have built a system of high-acceptance gas-ionization detectors, which are insensitive to beta particles that limited earlier measurements. Beam impurities that affected one of the earlier experiments were eliminated through the choice of the $^{16}$N production technique. New results from this experiment and comparisons with earlier data will be presented. This work was supported by the US Department of Energy, Nuclear Physics Division, under contract No. W-31-109-ENG and by the NSF Grant No. PHY-02-16783 (Joint Institute for Nuclear Astrophysics). [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
EH.00006: Investigation of proton resonant states in $^{23}$Al and $^{22}$Mg using radioactive beams at CNS Jianjun He, Shigeru Kubono, Takashi Teranishi, Masahiro Notani, Hidetada Baba, Shin'ichiro Michimasa, Shunji Nishimura, Mizuki Nishimura, Yoshiyuki Yanagisawa, Hironori Iwasaki, Naho Hokoiwa, Michiya Kibe, Yasuyuk Gono, Jun-Yung Moon, Ju-Hahn Lee, Chun-Sik Lee, Seigo Kato We have studied the proton resonances in $^{23}$Al and $^{22}$Mg via the resonant scattering of radioactive beams on a thick CH$_{2}$ target. The $^{22}$Mg and $^{21}$Na beams were separated by the {\textbf C}NS {\textbf R}adioactive {\textbf I}on {\textbf B}eam separator (CRIB) with energies of 4.4 AMeV and 4.0 AMeV, respectively. At scattering angles of $\theta _{lab}$= 4\r{ }, 17\r{ } and 23\r{ }, the recoiled particles were measured by three sets of $\Delta $E-E Si telescopes. As for nucleus $^{23}$Al (via $^{22}$Mg+p), several new resonant states were observed. As for nucleus $^{22}$Mg (via $^{21}$Na+p), the previously observed resonant states were confirmed. The states above the alpha threshold were observed, which are related to the $^{18}$Ne($\alpha $, p)$^{21}$Na reaction. The resonant parameters were deduced from an R-matrix code. The nuclear structures and the astrophysical implications are discussed. [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
EH.00007: Excited states in $^{22}$Mg and the $^{21}$Na(p,$\gamma$)$^{22}$Mg reaction Cybele Jewett, Uwe Greife, Kelly Chipps, Fred Sarazin, Shawn Bishop, John D'Auria, Michael Lamey, Michael Trinczek, Dave Hutcheon, Dave Ottewell, Art Olin, Lothar Buchmann, Jonathan Pearson, Sabine Engel, Dario Gigliotti, Chris Ruiz, Gotz Ruprecht, Christof Vockenhuber, Carl Gross, David Radford, Chang-Hong Yu, Jeff Blackmon, Daniel Bardayan, Michael Smith, Ray Kozub In explosive astrophysical scenarios like novae or x-ray bursts, the $^{21}$Na(p,$\gamma$)$^{22}$Mg reaction is believed to play an important role. The proton capture proceeds predominantly via isolated states in the $^{22}$Mg nucleus. This talk will present results from a search for excited states in $^{22}$Mg via the $^{12}$C+$^{12}$C reaction measured at HRIBF (ORNL). A direct measurement of $^{21}$Na(p,$\gamma$)$^{22}$Mg was performed with a radioactive ion beam at ISAC (TRIUMF), using the DRAGON separator. We also used the DRAGON's BGO array to measure the $\gamma$-branching ratios of the excited states in $^ {22}$Mg, and compared their J$^{\pi}$ assignments with previously published values. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
EH.00008: Breakup of loosely bound nuclei as indirect method in nuclear astrophysics: $^{8}$B, $^{9}$C, $^{15}$C, $^{23}$Al L. Trache, C.A. Gagliardi, R.E. Tribble, F. Carstoiu We discuss the use of one-nucleon breakup reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. These are peripheral processes, therefore we can extract asymptotic normalization coefficients (ANC) from which astrophysical S-factors and rates for radiative proton capture reactions can be precisely determined. In particular, the breakup of $^{8}$B and $^{9}$C is described in terms of an extended Glauber model. Existing experimental data for the breakup of $^{8}$B and of $^{9}$C on light through heavy targets are analyzed. We show that there exists a favorable kinematical window in which breakup reactions are highly peripheral. In this regime the ANC is the better spectroscopic information to be extracted. Glauber model calculations in the eikonal approximation and the optical limit using different effective interactions give consistent, though slightly different results. This shows the possibilities and the limits of the precision of the method. Breakup reactions can be measured with radioactive beams as weak as a few particle per second, and can be used for cases where no direct measurements or other indirect methods for nuclear astrophysics can be applied. We discuss also the use of one-neutron-removal to assess (n,$\gamma )$ rates using $^{15}$C as example, and the proposed use of the breakup of proton drip line nucleus $^{23}$Al to obtain the stellar reaction rate for $^{22}$Mg(p,$\gamma)^{23}$Al. [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
EH.00009: Coulomb Dissociation of $^{27}$P for Study of $^{26}$Si(p,$\gamma$)$^{27}$P Reaction Yasuhiro Togano The $^{26}$Si(p,$\gamma$)$^{27}$P reaction was investigated by the Coulomb dissociation of $^{27}$P. This reaction is suggested to be relevant to the synthesis of $^ {26}$Al whose 1.8~MeV $\gamma$-line distribution in the Galaxy is observed by satellite telescopes. In order to estimate the reaction flow around $^{26}$Al, we determined the gamma decay widths of excited states in $^{27}$P, which mainly determine the resonant capture reaction rate. The experiment was performed at RIPS beam line in RIKEN. A beam of the unstable $^{27}$P nucleus at 57~MeV/nucleon was produced by the fragmentation of a 115-MeV/nucleon $^{36}$Ar beam. The $^{27}$P beam bombarded a Pb target. The excitation energy of $^{27}$P was extracted by combining the momentum vectors of $^{26}$Si and proton. The three known excited states in $^{27}$P [1] as well as a new excited state at around 2.0~MeV were observed. The gamma decay width of the first excited state was deduced to be (1.3 $\pm$ 0.8) $\times$ 10$^{-3}$ eV. Details of experiment and astrophysical implications of the measured gamma decay widths will be presented.\\ \vspace*{0.5cm} \setlength \parindent{0 cm} [1] J.A. Caggiano {\em et al}., Phys. Rev. C {\bf 64}, 025802 (2001). [Preview Abstract] |
Wednesday, September 21, 2005 11:30AM - 11:45AM |
EH.00010: Lifetime of the 4.033 MeV state in $^{19}$Ne Barry Davids, Gordon Ball, Rituparna Kanungo, Mythili Subramanian In astrophysical environments the $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction proceeds predominantly through resonances lying just above the $^{15}$O + $\alpha$ threshold at 3.529 MeV in $^{19}$Ne. The reaction rate in novae is determined by the resonance strength of the 4.033 MeV 3/2$^+$ state. This state may also make the largest contribution to the reaction rate at the higher peak temperatures reached in x-ray bursts. By populating these states and observing the subsequent $\alpha$- and $\gamma$-decays, one can deduce the branching ratio B$_{\alpha}\equiv\Gamma_{\alpha}/(\Gamma_{\alpha}+\Gamma_{\gamma})$. If $\Gamma_{\gamma}$ is also known, one can then calculate the resonance strength and thereby the contribution of each state to the astrophysical rate of the $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction. Experimental data on the radiative widths of these states are sparse. An effort to measure the lifetime of the 4.033 MeV state by the Doppler shift attenuation method (DSAM) resulted in an upper limit. A complementary measurement of the Coulomb excitation to this state at intermediate beam energies resulted in an upper limit on the radiative width, corresponding to a lower limit on the lifetime. The 95\% confidence level allowed region for the lifetime, and therefore the reaction rate, spans two orders of magnitude. We are planning to measure the lifetime of this state using the DSAM, populating it via the $^3$He($^{20}$Ne,$\alpha$)$^{19}$Ne reaction at a $^{20}$Ne beam energy of 34 MeV. [Preview Abstract] |
Wednesday, September 21, 2005 11:45AM - 12:00PM |
EH.00011: Computational Infrastructure and Nuclear Data Activities for Nuclear Astrophysics at Oak Ridge National Laboratory C.D. Nesaraja, M.S. Smith, D.W. Bardayan, J.C. Blackmon, E.J. Lingerfelt, J.P. Scott, K. Chae, R.L. Kozub, J.S. Thomas, R.A. Meyer A \textbf{Computational Infrastructure for Nuclear Astrophysics} has been developed to enable rapid incorporation of the latest nuclear physics data in astrophysics models. The infrastructure is a platform-independent suite of computer codes and is available online at \textbf{nucastrodata.org}. The user-friendly interface enables users to easily upload their data, create reaction rates, easily access and manage libraries of cross sections and rates, perform simple data evaluation tasks, run element synthesis calculations, and visualize them with animations. The suite's new features and its utilization for nova and X-ray burst modeling will be discussed. Other nuclear data activities at ORNL include evaluating properties and reactions of unstable nuclei being measured at ORNL's HRIBF. Reactions with radioactive beams of $^{18}$F, $^{82}$Ge, and $^{84}$Se are among those being studied. A survey of evaluation results and plans for additional work will be presented. [Preview Abstract] |
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