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 BG: Mini-Symposium on Nuclear Physics in Stars I |
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Chair: Tatsushi Shima, Osaka University Room: Kings 2 |
Wednesday, October 14, 2009 7:00PM - 7:30PM |
BG.00001: Constraints on Nuclear Astrophysics from Presolar Stardust in Meteorites Invited Speaker: Meteorites contain presolar grains of stardust, solid condensates from previous generations of stars that survived destructive processes in interstellar space and the early solar system and can now be studied in detail in the laboratory. They are identified on the basis of extremely unusual isotopic compositions, which directly reflect nuclear processes in their parent stars as well as Galactic Chemical Evolution. They thus can provide important information for nuclear astrophysics, complementary to astronomical observations, but in many cases with much higher analytical precision. A large number of types of presolar grains, including elemental C and various carbides, oxides and silicates have now been identified. Based on comparisons with astronomical observations and theoretical models, a diversity of stellar sources has been identified for the grains including AGB stars, supernovae, and novae. The grain isotopic compositions have provided a wealth of new constraints on nuclear processes in these environments as well as on stellar and galactic evolution. This talk will review the current status of presolar grain studies as they apply to nuclear astrophysics. [Preview Abstract] |
Wednesday, October 14, 2009 7:30PM - 7:45PM |
BG.00002: Study of the $^{14}$O~+~$\alpha$ reaction at low energy T. Hashimoto, S. Kubono, H. Yamaguchi, S. Hayakawa, N.B. Dam, D. Kahl, T. Kawabata, Y. Wakabayashi, N.H. Lee, A. Kim, M.H. Han, J.S. Yoo, K.I. Hahn, Y.K. Kwon, C.S. Lee, T. Teranishi, S. Kato, T. Komatsubara, B.X. Wang, B. Guo, G. Bing, Y.B. Wang, W.P. Liu The $^{14}$O($\alpha$,~p)$^{17}$F stellar reaction is one of the key reactions for the breakout from the Hot--CNO cycle to the rp--process. Since the cross sections depends on the product of $\alpha$ and proton widths of the intermediate states in $^{18} $Ne, it is important to determine these widths. We performed an experiment of the $^{14}$O~+~$\alpha$ scattering with a thick target method at the CNS Radioactive Ion Beam (CRIB) facility. The experiment was carried out using a thick Helium gas target and position sensitive silicon telescopes. This measurement provides an excitation function of $^{14}$O~+~$\alpha$ scattering for an energy range of E$_{\textrm{cm}}$~=~1.7~--~5.9~MeV. We will concentrate on the elastic scattering channel in this presentation, since the $\alpha$-cluster structure in $^{18}$Ne above the $\alpha$~--~threshold would play an important role for the stellar reaction. Several $\alpha$~--~resonances were observed in the present experiment. The experimental result will be presented, and the $\alpha$ cluster structure in $^{18}$Ne and the significance to the stellar reaction will be discussed. [Preview Abstract] |
Wednesday, October 14, 2009 7:45PM - 8:00PM |
BG.00003: Triple-$\alpha$ Process in Hot Astrophysical Scenarios N.R. Patel, U. Greife, K.E. Rehm, C.M. Deibel, J. Greene, D. Henderson, C.L. Jiang, B.P. Kay, H.Y. Lee, R. Pardo, K. Teh, S.T. Marley, M. Notani, X.D. Tang The production of carbon in red giant stars relies significantly on the 1$^{st}$ 0$^{+}$ excited state of $^{12}$C at 7.65 MeV (the Hoyle state). The recent NACRE listing assumes a 2$^{+}$ resonance at 9.1 MeV,\footnote{Angulo \textit{et al}, Nucl. Phys. \textbf{A656} (1999)} which could be considered as the 2$^{+}$ member of a deformed rotational band built on the Hoyle state. At temperatures of several billion Kelvin in explosive scenarios like supernovae where the 3$\alpha $ process is also relevant, this state would increase the astrophysical reaction rate by an order of magnitude.\footnote{Fynbo \textit{et al}, Nature \textbf{433} (2005)} In order to determine this experimentally, the states of $^{12}$C were populated through $\beta $-decay of $^{12}$B and $^{12}$N mirror nuclei produced at the ATLAS in-flight facility at Argonne. The decay of $^{12}$C* into three alphas were detected in a twin ionization chamber, acting as a 4$\pi $ calorimeter. This minimized the effect of $\beta $-summing and allowed us to investigate the minimum between the 1$^{st}$ and the 2$^{nd}$ 0$^{+}$ state with much better accuracy than previously possible. An R-Matrix analysis was performed to determine an upper limit on the 2$^{+}$ resonance in the 8-11 MeV region. Our data analysis thus far shows no evidence of a 2$^{+}$ state in this region. This work is supported by U.S. DOE, and NSF grants. [Preview Abstract] |
Wednesday, October 14, 2009 8:00PM - 8:15PM |
BG.00004: Present status of direct $^{4}$He($^{12}$C,$^{16}$O)$\gamma $ measurement near stellar energy at KUTL Kunihiro Fujita, Kenshi Sagara, Takashi Teranishi, Takashi Goto, Rie Iwabuchi, Sayaka Matsuda, Keiju Nakano, Nozomi Oba, Masahiko Taniguchi, Hiroyuki Yamaguchi A $^{12}$C + $^{4}$He $\to \quad ^{16}$O + $\gamma $ reaction plays a very important role in evolution of heavy stars. The cross section is, however, still unknown in spite of more than 40 years experiment in the world because of its quite low value. We are planning to measure the cross section with the direct detection of the produced $^{16}$O from E$_{cm}$= 2.4 down to 0.7 MeV by using a pulsed $^{12}$C beam and a windowless $^{4}$He gas target. Detection of $^{16}$O is the most possible method since detection efficiency of $^{16}$O recoils is very high. A new blow-in gas target was developed to achieve $^{4}$He pressure of 24 Torr, and the target thickness along the beam axis was measured by p+$^{4}$He scattering. Using many movable slits installed in a recoil mass separator, backgrounds generated by the $^{12}$C beam were eliminated effectively. Present experiment at E$_{cm}$ = 1.5MeV is reported. [Preview Abstract] |
Wednesday, October 14, 2009 8:15PM - 8:30PM |
BG.00005: Thick target measurement of the 40Ca(a,g)44Ti reaction rate S.A. Sheets, J.T. Burke, D. Blueul, T.A. Brown, P.G. Grant, R.D. Hoffman, A.M. Hurst, J.L. Fisker, E.B. Norman, L.W. Phair, N.D. Scielzo, S. Tumey The thick-target yield for the $^{40}$Ca($\alpha$,$\gamma$)$^{44}$Ti reaction has been measured for $E_{\rm beam}$ = 4.13, 4.54, and 5.36 MeV using $\gamma$-ray spectroscopy. At the highest beam energy, an activation measurement was performed. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than current statistical-model calculations. This implies a smaller $^{44}$Ti production in supernova compared to recently measured $^{40}$Ca($\alpha$,$\gamma$)$^{44}$Ti reaction rates. [Preview Abstract] |
Wednesday, October 14, 2009 8:30PM - 8:45PM |
BG.00006: Astrophysical measurements with radioactive $^{17}$F beams at HRIBF D.W. Bardayan, C.D. Nesaraja, S.D. Pain, M.S. Smith, K.A. Chipps, U. Greife, J.C. Blackmon, K.Y. Chae, B.H. Moazen, S.T. Pittman, R. Hatarik, W.A. Peters, R.L. Kozub, J.F. Shriner, Jr., C. Matei The astrophysical rates of the $^{14}$O($\alpha,p$)$^{17}$F and $^{17}$F($p,\gamma$)$^{18}$Ne reactions affect the transition to the $\alpha p$-process in x-ray bursts and $^{18}$F production in novae, respectively. Both reactions have been studied in the laboratory with the intense radioactive $^{17}$F beams delivered at HRIBF. Recently beam intensities greater than 10$^7$ $^{17}$F ions/s have become available, making possible the first direct measurement of the $^{17}$F ($p,\gamma$)$^{18}$Ne cross section [K. A. Chipps et al., Phys. Rev. Lett. 102, 152502 (2009)]. These high beam intensities also provide an opportunity to make the first precise determination of the resonance strength of the 1$^-$ $^{14}$O ($\alpha,p$)$^{17}$F resonance near E$_{c.m.}$=1 MeV. Recent results and upcoming plans for measurements with $^{17}$F beams at the HRIBF will be presented. [Preview Abstract] |
Wednesday, October 14, 2009 8:45PM - 9:00PM |
BG.00007: Probing Nucleosynthesis in Novae: $^{22}$Na(p,$\gamma$)$^{23}$Mg A.L. Sallaska, D.W. Storm, T.A.D. Brown, A. Garcia, C. Ruiz, D.F. Ottewell, C. Wrede, K. Snover, K. Deryckx, D.A. Hutcheon, L. Buchmann, C. Vockenhuber, J.A. Caggiano Orbiting gamma ray telescopes have yet to observe the elusive $^{22}$Na isotope. More sensitive observatories are planned. Present uncertainties in the dominant destructive reaction, $^{22}$Na(p,$\gamma$), suggest new measurements in the proton energy range of 150 to 300 keV are needed to clarify the predictions of the amount of $^{22}$Na expected in novae explosions. In particular, Ref [1] suggested that a possible resonance at $E_p$ = 198 keV could be significant. We have measured the $^{22}$Na(p,$\gamma$) resonance strengths and energies directly by using protons from the University of Washington accelerator with a specially designed beamline, which included rastering and cold vacuum protection of the $^{22}$Na implanted targets, fabricated at TRIUMF. Utilizing two high-purity germanium detectors with anticoincidence shields to reduce cosmic backgrounds, measurements have been performed on known resonances of $^{22}$Na+p, as well as on the proposed new resonance. Results will be presented. These indicate that the dominant contribution to the reaction rate in the temperature region of interest to novae is the resonance at $E_p$ = 214 keV, rather than the suggested new resonance at $E_p$ = 198 keV. [1] Jenkins $\it{et}$ $\it{al}$., PRL $\bf{92}$ (2004) 031101 [Preview Abstract] |
Wednesday, October 14, 2009 9:00PM - 9:15PM |
BG.00008: First direct measurement of $^{23}$Mg$(p,\gamma)^{24}$Al with DRAGON L. Erikson During explosive nucleosynthesis, the $^{23}$Mg(p,$\gamma)^{24}$Al capture reaction may function as a breakout from the NeNa to the MgAl cycles. Depending on the resonance strength and energy, such a breakout could substantially affect the production of $^{26}$Al and $^{22}$Na which have been detected by orbital satellite. This important reaction was directly studied at astrophysically relevant energies ($E_{lab} \simeq 490$ keV/u) by the DRAGON collaboration during the summer and fall of 2008. However, due to limitations of the ISAC facility, the experiment was complicated by a $^{23}$Na contamination ranging from 2 to 5000 times more intense than the $^{23}$Mg component. To compensate, a new local time-of-flight system and a multi-segmented ion chamber were used for particle identification. This talk will present and discuss some details of the experiment and the results to date. [Preview Abstract] |
Wednesday, October 14, 2009 9:15PM - 9:30PM |
BG.00009: Photoexcitation of Astrophysically Important States in $^{26}$Mg Richard Longland, Richard deBoer, Christian Iliadis, Gencho Rusev, Anton Tonchev, Michael Wiescher The $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction is an important source of neutrons for the s-process in massive stars and Asymptotic Giant Branch (AGB) stars. Spin-parity ambiguities of levels in the $^{26}$Mg compound nucleus result in large uncertainties in the reaction rates at temperatures relevant to these environments. We report the results of a nuclear resonance fluorescence experiment at the High Intensity $\gamma$-ray Source (HI$\gamma$S) that used a linearly polarised photon beam to populate levels in $^{26}$Mg at astrophysically important excitation energies. High precision excitation energies, branching ratios, and unambiguous spin-parities were assigned to five levels between $E_{x}=10.5$ and $11.2$\ MeV. We will discuss the $E_{r}=630$\ keV resonance, which, contrary to previous findings, has been found to have unnatural parity, and thus does not contribute to the $^{22}$Ne$+\alpha$ rates. In addition, two natural parity states, located below the neutron threshold, are expected to reduce rate uncertainties for the competing $^{22}$Ne($\alpha$,$\gamma$)$^{26}$Mg reaction significantly. [Preview Abstract] |
Wednesday, October 14, 2009 9:30PM - 9:45PM |
BG.00010: Investigation of the $^{30}$S($p,\gamma$)$^{31}$Cl reaction via Coulomb dissociation Yasuhiro Togano The Stellar reaction $^{30}$S($p,\gamma$)$^{31}$Cl was studied via Coulomb dissociation. The nucleus $^{30}$S is a candidate for the waiting point, which the reaction flow temporary stops at this nuclei, in the rapid proton capture ({\em rp}) process. The $^{30}$S($p,\gamma$)$^{31}$Cl reaction decreases the amount of $^{30}$S, and thus speeds the reaction flow of the {\em rp} process up. Therefore the strength of this reaction affects the resultant abundance and energy production in the {\em rp} process. No direct measurement of the $^{30}$S($p,\gamma$)$^{31}$Cl reaction has been made so far. The aim of the present work is to determine the resonant capture reaction rate of $^{30}$S($p,\gamma$)$^{31}$Cl from the result of Coulomb dissociation of $^{31}$Cl. The experiment was performed at the RIKEN Nishina Center. The secondary beam of $^{31}$Cl at 58~MeV/nucleon was produced and separated using the RIKEN Projectile Fragment Separator (RIPS). The beam of $^{31}$Cl bombarded a $^{208}$Pb target. The momentum vectors of the breakup products, the isotopes $^{30}$S and protons, were determined using the detectors located at downstream of the target. The relative energy spectrum of $^{30}$S + $p$ system was extracted using invariant-mass method. In this presentation, we discuss the unbound state of $^{31}$Cl which is relevant to the resonant capture in the $^{30}$S($p,\gamma$)$^{31}$Cl reaction. [Preview Abstract] |
Wednesday, October 14, 2009 9:45PM - 10:00PM |
BG.00011: Beta-decay of proton-rich $^{31}$Cl and its relevance for explosive H-burning L. Trache, A. Banu, J.C. Hardy, V.E. Iacob, M. McCleskey, B. Roeder, E. Simmons, G. Tabacaru, R.E. Tribble, T. Davinson, G. Lotay, P.J. Woods, A. Saastamoinen, A. Jokinen, J. Aysto We produced and separated proton-rich nucleus $^{31}$Cl with the MARS recoil separator at TAMU. Then studied its beta-gamma and beta-delayed proton-decay using techniques designed for low-intensity, short-lived sources. The states populated in the daughter nucleus $^{31}$S above the proton threshold at S$_{p}$=6133 keV are resonances in the proton capture reaction $^{30}$P(p,$\gamma )^{31}$S, crucially important for the explosive H-burning novae. The setup consisted of a telescope made of a thin double sided Si strip detector (p-detector) BB2-45 and a thick Si detector ($\beta $-detector). A HpGe detector outside the chamber detected $\gamma $-rays. The source nuclei produced at about 32 MeV/u were slowed down and implanted in the middle of the thin Si strip detector. The technique allowed us to measure very low proton energies (down to 2-300 keV), has shown a remarkable selectivity to $\beta $-delayed charged particle emission, and would work even at radioactive beam rates of a few pps. Furthermore, the half-life of $^{31}$Cl was measured with under 1{\%} accuracy, its Isobar Analog State was located and from IMME its mass excess better determined. [Preview Abstract] |
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