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 DF: Nuclear Astrophysics II |
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Sponsoring Units: DNP JPS Chair: Grant Mathews Room: Ritz-Carlton Hotel Plantation 3 |
Tuesday, September 20, 2005 7:00PM - 7:15PM |
DF.00001: Measurements of $^{7}$Be + p elastic and inelastic scattering R.J. Livesay, U. Greife, F. Sarazin, R.L. Kozub, K. Chae, B.H. Moazen, C.D. Nesaraja, D.W. Bardayan, J.C. Blackmon, M.S. Smith, D. Stracener, K.L. Jones, S.D. Pain, J.S. Thomas, M.S. Johnson, C. Deibel, C. Wrede Measurements of the $^{7}$Be+p elastic and inelastic scattering cross sections have been made at the HRIBF at ORNL, with a combined angular coverage of up to 60 degrees in the center of mass. Thin CH$_{2}$ foils were bombarded by a fully stripped radioactive $^{7}$Be beam. Scattered protons were detected in the SIlicon Detector ARray (SIDAR) and recoiling $^{7}$Be in a gas ionization chamber. Results will be presented and compared with previous measurements. [Preview Abstract] |
Tuesday, September 20, 2005 7:15PM - 7:30PM |
DF.00002: Study of excited states in nuclei of astrophysical interest via the $(^3He,p)$ reaction K. Chipps, L. Erikson, U. Greife, F. Sarazin, J. Blackmon, D. Bardayan, M. Smith, J. Pearson The $(^3He,p)$ reaction may be used to populate excited states in nuclei of astrophysical interest due to its high Q value. To this end, a $^{3}He$ gas cell target has been designed and constructed for use with radioactive ion beams. Simulations were run using GEANT for several different beams, and experiments using $^{17}O$ and $^{17}F$ beams are in preparation at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. [Preview Abstract] |
Tuesday, September 20, 2005 7:30PM - 7:45PM |
DF.00003: Extracting ANCs in neutron transfer reactions to determine proton capture reaction rates Tariq Al-Albdullah, X. Chen, C.A. Gagliardi, Y.-W. Lui, G. Tabacaru, Y. Tokimoto, L. Trache, R.E. Tribble, F. Carstoiu The high temperatures ( $>$10$^{8}$ K) in novae outbursts enable unstable nuclei to leak out from the hot CNO cycle to the rp-process, where heavier nuclei such as $^{18}$F and $^{22}$Na are synthesized and might be ejected. Their abundances can be influenced by the $^{17}$F(p,$\gamma )^{18}$Ne and $^{22}$Mg(p,$\gamma )^{23}$Al reactions respectively. The first reaction connects the CNO and NeNa cycles, while the second may explain the unobserved $\gamma $-ray emission from $^{22}$Ne due to the $\beta $ decay in $^{22}$Na. We have applied an indirect technique to determine the above reaction rates at stellar energies. We have measured the neutron transfer reactions $^{13}$C($^{17}$O,$^{18}$O)$^{12}$C and $^{13}$C($^{22}$Ne,$^{23}$Ne)$^{12}$C to determine the asymptotic normalization coefficients (ANCs) for the ground and first excited states in $^{18}$O and $^{23}$Ne. These ANCs can be transposed to the corresponding states in the mirror nuclei $^{18}$Ne and $^{23}$Al respectively. As a part of these experiments, we have measured the elastic scattering data to obtain the optical model parameters that are used in DWBA calculations, and hence to extract the ANCs. [Preview Abstract] |
Tuesday, September 20, 2005 7:45PM - 8:00PM |
DF.00004: Development of a high-precision method for alpha resonant scattering measurements for nuclear astrophysics Hisashi Fujikawa, S. Kubono, A. Saito, G. Amadio, J.J. He, H. Yamaguchi, Y. Wakabayashi, S. Nishimura, L.H. Khiem, H. Ohta, A. Ozawa, M. Yamaguchi, T. Yasuno An experiment was performed for a development on the experimental method to measure heavy ion + $\alpha$ resonant scattering. This method should be useful for studies of astrophysical ($\alpha$,p) reaction and $\alpha$-cluster structures. The experiment was performed using $^{16}$O beams at 40 and 60 MeV, supplied by a tandem accelerator at Univ. of Tsukuba. The goal of this development is to obtain with high precision the resonant scattering data with the thick target method that use a gaseous helium of a large volume at room temperature. We used a 300-mm long helium target at a pressure of 600 Torr to stop the beam fully in the gas. We set the telescope of position sensitive silicon detectors inside the same gas target at several angles, and identified emitted alpha particles and protons by $\delta$E-E method. In order to obtain the angular information, in addition to the position of detectors, the position where the corresponding reaction occurred has to be determined precisely by taking into account the energy and the energy loss of emitted particles in the gas as well as kinematics. The experimental result and the analysis will be discussed. [Preview Abstract] |
Tuesday, September 20, 2005 8:00PM - 8:15PM |
DF.00005: Coulomb Dissociation of $^{12}$N and $^{13}$O Toshiyuki Minemura T.\ Minemura$^A$, T.\ Motobayashi$^A$, S.\ Shimoura$^D$, H.\ Murakami$^B$, Y.\ Ando$^B$, Y.\ Yanagisawa$^A$, Y.\ Iwata$^B$, S.\ Ozawa$^A$, S.\ Takeuchi$^A$, Y.\ Higurashi$^A$, K.\ Yamada$^B$, T.\ Gomi$^B$, M.\ Serata$^B$, H.\ Kobayashi$^B$, N.\ Aoi$^A$, M.\ Hirai$^C$, H.\ Iwasaki$^C$, K.\ Yoshida$^A$, N.\ Iwasa$^E$ M.\ Kurokawa$^D$, H.\ Akiyoshi$^A$, Zs.\ F\"ul\"op$^{A,}$ H.\ Sakurai$^C$, T.\ Teranishi$^D$, Z.\ Liu$^A$, M.\ Ishihara$^A$ $^A$RIKEN $^B$Department of Physics, Rikkyo University $^C$Department of Physics, University of Tokyo $^D$Center for Nuclear Study (CNS), University of Tokyo, $^E$Department of Physics, Tohoku University ---The Coulomb breakup technique was employed to determine the radiative width of excited levels in $^{12}$N and $^{13}$O, which dominate the low-energy cross sections of the $^ {11}$C(p,$\gamma$)$^{12}$N and $^{12}$N(p,$\gamma$)$^{13}$O reactions. The $^{12}$N and $^{13}$O radioactive beams were produced through transfer and fragmentation reactions of aprimary 135~MeV/nucleon $^{16}$O beam at RIKEN. For the $^{12}$N-dissociation experiment, the radiative width of the 2$^-$ state at $E_{\rm{ex}}$=1.19~MeV in $^{12}$N was extracted to be $\Gamma_{\gamma}$=29.0$\pm$4.1~meV, the accuracy of which has been much improved compared with earlier studies. For $^{13}$O, large E1 strength was found for the first time at around $E_{\rm x}$=2.5~MeV. By the present study, the accuracy of the low-energy photo- capture cross sections for $^{11}$C and $^{12}$N have been improved, and reaction rates are now calculable based on more reliable experimental informations. [Preview Abstract] |
Tuesday, September 20, 2005 8:15PM - 8:30PM |
DF.00006: CRIB enhanced with a Wien Filter for Astrophysical studies H. Yamaguchi, A. Saito, J.J. He, Y. Wakabayashi, G. Amadio, H. Fujikawa, S. Kubono, N. Yamazaki, T. Teranishi, M. Niikura, Y. Yanagisawa, S. Michimasa, S. Nishimura, M. Nishimura, Z. Fulop, Z. Elekes CRIB (CNS Radioactive Ion Beam separator) is a facility at which low-energy and pure radioactive ion (RI) beams can be produced by in-flight separation method. Many astrophysical reactions have been studied at CRIB, mainly by the proton elastic resonance scattering method. In the recent few years, we have developed a Wien filter system for CRIB, in order to have a better separation power for the RI beams. The design and structure of the Wien filter, results of beam separation tests using it, and latest applications for nuclear astrophysics will be presented in this talk. [Preview Abstract] |
Tuesday, September 20, 2005 8:30PM - 8:45PM |
DF.00007: Recent results for capture reactions of interest in nuclear astrophysics Gerald M. Hale We report recent results for the $^1$H($n,\gamma)^2$H and $^{12}$C($\alpha,\gamma)^{16}$O capture reactions that are of interest to nucleosynthesis in the Big Bang, and during the Helium Burning phase of red giant stars, respectively. New data for these reactions are being analyzed in $R$-matrix analyses of the $^2$H and $^{16}$O systems that use a new approach to including photon channels in the theory. Results for the E1 part of the $^{12}$C($\alpha,\gamma)$ reaction are also constrained by measurements of the $\beta$-delayed $\alpha$ spectrum from the decay of $^{16}$N. Comparisons with previous results will be made, and uncertainty estimates will be given for both types of capture cross sections. [Preview Abstract] |
Tuesday, September 20, 2005 8:45PM - 9:00PM |
DF.00008: Determination of the $^{12}$N$\to ^{11}$C+p asymptotic normalization coefficient from the indirect $^{11}$C(d,n)$^{12}$N transfer reaction. Dongwon Lee, James Powell, Kari Perajarvi, Fanqing Guo, Dennis Moltz, Jim O'Neil, Joseph Cerny The $^{11}$C(p,$\gamma )^{12}$N reaction has been known to be an important branch point in supermassive low-metallicity stars because it could produce CNO seed nuclei before the traditional triple-alpha process turns on. In the present work, the $^{11}$C(d,n)$^{12}$N transfer reaction was employed with a radioactive ion beam of 150 MeV $^{11}$C with 6$\times $10$^{5}$ ions/s on target from the BEARS project at the 88'' cyclotron at LBNL. Excellent agreement was obtained between the experimental cross sections ($\theta _{cm}$=10.9\r{ } to 71.5\r{ }) and DWBA calculations. The asymptotic normalization coefficient (ANC) was deduced to be $(C_{eff}^{12N} )^2=(C_{p1/2}^{12N} )^2+(C_{p3/2}^{12N} )^2=1.85\pm 0.27fm^{-1}$, which is in good agreement with the published result from $^{14}$N($^{11}$C,$^{ 12}$N)$^{13}$C. The astrophysical S-factor at zero-energy,$S(0)=0.099\pm 0.020\mbox{ }keV\mbox{ }b$, was also calculated based on the extracted ANC value. These results confirm that the $^{11}$C(p,$\gamma )^{12}$N reaction occurs at lower temperatures and densities than previously believed. [Preview Abstract] |
Tuesday, September 20, 2005 9:00PM - 9:15PM |
DF.00009: Cross section measurements of the $^{152}$Sm($\gamma$,n)$^{151}$Sm reaction near threshold Kaoru Y. Hara, H. Harada, F. Kitatani, H. Akimune, S. Goko, S. Hohara, T. Kaihori, A. Makinaga, H. Utsunomiya, T. Yamagata, H. Toyokawa, K. Yamada Neutron capture cross sections of the unstable nucleus $^{151}$Sm (t$_{1/2}$=90~yr) are the fundamental data for nuclear transmutation and nuclear astrophysics. The $^{151}$Sm is one of radioactive fission products in the nuclear waste. In order to determine the (n,$\gamma$) transmutation rate of this nucleus, the experimental data are desired to be available in the energy range from thermal to MeV. On the other hand, the branching point nucleus $^{151}$Sm is important for characterizing the s-process nucleosynthesis in AGB stars. The inverse $^{152}$Sm($\gamma$,n)$^{151}$Sm reaction was measured near threshold at the AIST facility. Beams of quasi-monochromatic photons from laser Compton scattering (LCS) irradiated an enriched $^{152}$Sm sample. We present the experimental method with the LCS $\gamma$ beam and photoneutron cross sections for $^{152}$Sm. The present data will be used to evaluate the capture cross section of $^{151}$Sm with the Hauser-Fechbach statical model. [Preview Abstract] |
Tuesday, September 20, 2005 9:15PM - 9:30PM |
DF.00010: Proposed Measurement of the 242mAm(n,g) cross section using DANCE/LANSCE R.A. Macri, U. Agvaanluvsan, J.A. Becker, R.R.C. Clement, D. Dashdorj, K. Moody, W. Parker, P. Wilk, C. Wu, T.A. Bredeweg, M.B. Chadwick, J. O'Donnell, R. Reifarth, R.S. Rundberg, J. Schwantes, J. Ullmann, D.J. Vieira, J. Wilhelmy, J.M. Wouters, M. Fowler Radiochemists at LLNL have produced a 98{\%} enriched sample of $^{242m}$Am (t$_{1/2}$ = 141 y) via $^{241}$Am(n,g) in the Hi-Flux reactor at ORNL and subsequent calutron enrichment. The availability of such a rare sample provides a unique opportunity to study properties of $^{242m}$Am . A proposal has been submitted to use the DANCE array at the LANSCE to measure the (n,g) cross section on the $^{242m}$Am isomer. At DANCE, capture cross sections can be measured for neutron energies ranging from thermal to about 100 keV on milligram-size radioactive targets. LLNL and LANL collaborators are currently working to build and install a fission-tagging detector in DANCE. With this extended capability, fission and capture events can be discriminated, leading to a better signal-to-noise ratio for the (n, g) measurement and enabling a simultaneous measurement of the (n,f) cross section. Progress on the implementation of the fission-tagging detector at DANCE and details of the proposed $^{242m}$Am(n,g) experiment will be presented. *Work performed under the auspices of the U.S.DOE. by the University of California, LLNL, and LANL under contracts W-7405-ENG-48 and W-7405-ENG-36. [Preview Abstract] |
Tuesday, September 20, 2005 9:30PM - 9:45PM |
DF.00011: The neutron capture cross section of $^{151}$Sm Rene Reifarth The Detector for Advanced Neutron Capture Experiments (DANCE) is a 160-element 4$\pi $ barium fluoride array designed to study neutron capture on small quantities of radioactive material. It is located on a 20 meter neutron flight path, which views an ``upper tier'' water moderator at the Manuel J. Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science Center (LANSCE). The first radioactive isotope under investigation was $^{151}$Sm with a half-life of 100 years. $^{151}$Sm is an important branch point during the slow neutron capture nucleosynthesis. During the talk the detector will be described, and results for the neutron capture cross section on $^{151}$Sm between 10 meV and 100 keV will be presented. [Preview Abstract] |
Tuesday, September 20, 2005 9:45PM - 10:00PM |
DF.00012: Studying close proximity nucleons in nuclei via triple-coincidence measurement of the (e,e$'$pN) reaction Ran Shneor This is a proposal to use the (e,e$'$pN) reaction to study short range nucleon-nucleon correlations (NN SRC) in nuclei. In the context of this proposal we refer to NN SRC as a pre-existing pair of nucleons which have back-to-back high momenta balancing each other. The two existing magnetic spectrometers in Hall A of Jefferson lab (JLab) were used to measure the (e,e$'$p) part of the reaction. The measurement required a third spectrometer (BigBite) and an array of scintillator counters, to simultaneously measure neutrons and protons in coincidence with the outgoing high momenta electron and proton. We chose kinematical conditions that will allow us to determine the fraction of (e,e$'$p) events which are associated with NN SRC. This was done as a function of the momentum of the proton in the nucleus in the range 250-600 MeV/c. This experiment expands the existing limits to large$Q^2$, x $>$ 1 and ``exclusiveness'' which were not covered by earlier data or other proposals to JLab. The proposal was approved by the program advisory comity at JLab in Jan 2001 as experiment E01-015. Over 5 years were devoted to the design and the assembly of the two dedicated new detectors (BigBite and the neutron array), various tests and calibrations were conducted which where then followed by final commissioning in the experimental hall, during Dec 2004. The experiment took data from Jan to April 2005. [Preview Abstract] |
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