Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session EE: Nuclear Astrophysics II |
Hide Abstracts |
Chair: J.C. Blackmon, Louisiana State University Room: Newport News Marriott at City Center Grand Salon V |
Friday, October 12, 2007 2:00PM - 2:12PM |
EE.00001: $^{30,31}$S level structure measured via ($p,t$) and ($p,d$) reactions on $^{32}$S D.W. Bardayan, J.C. Blackmon, W.R. Hix, J.F. Liang, L.F. Roberts, M.S. Smith, Z. Ma, R.L. Kozub, K.L. Jones, J.S. Thomas, R.J. Livesay, R.P. Fitzgerald, D.W. Visser An accurate knowledge of the level structure of $^{30,31}$S above the proton threshold is important for calculating the astrophysical rates of proton capture on $^{29,30}$P respectively. These proton captures affect the Si abundances observed in meteoritic presolar grains and the reaction flow to heavier nulcei in novae. We have studied $^{30,31}$S by bombarding ZnS targets with $\sim$40-MeV proton beams from the Holifield Radioactive Ion Beam Facility and detecting reaction tritons and deuterons in the Silicon Detector Array (SIDAR). A total of 13(26) states were observed in $^{30}$S($^{31}$S) including 9(17) above the proton threshold. The spins of strongly-populated levels were constrained through a DWBA analysis of the measured angular distributions. The method and results will be presented. [Preview Abstract] |
Friday, October 12, 2007 2:12PM - 2:24PM |
EE.00002: The $^{40}$Ca( $\alpha $,$\gamma $ )$^{44}$Ti Reaction Using DRAGON C. Ouellet, C. Vockenhuber, L.S. The, L. Buchmann, J. Caggiano, A. Chen, H. Crawford, J. D'Auria, B. Davids , D. Frekers, A. Hussein, D. Hutcheon, W. Kutschera, A. Laird, R. Lewis, E. O'Connor, D. Ottewell, M. Paul, M. Pavan, J. Pearson, C. Ruiz, G. Ruprecht, M. Trinczek, B. Wales, A. Wallner $^{44}$Ti is one a handful of short lived nuclei believed to be a signature of explosive nucleosynthesis, a product of $\alpha $-rich freezeout following a core collapse supernova. To understand the production of 44Ti a key reaction, $^{40}$Ca( $\alpha $,$\gamma $ )$^{44}$Ti, has been studied in inverse kinematics using the DRAGON recoil separator located at ISAC/TRIUMF in Vancouver B.C. The coincidence detection of the recoils and $\gamma $-rays coupled with a time of flight technique provided an accurate determination of the excitation function over a range of beam energies of 0.6 -- 1.14 MeV/u. Direct measurement of the stopping power permitted an accurate measure of the stellar reaction rate. The excitation function hints towards previously undiscovered resonances and the new rate results in increased $^{44}$Ti production from supernovae judging from prompt $\gamma $-ray studies alone. [Preview Abstract] |
Friday, October 12, 2007 2:24PM - 2:36PM |
EE.00003: High precision mass measurement of sulfur near N = 28 Amanda Prinke, C. Bachelet, M. Block, G. Bollen, M. Facina, C.M. Folden III, C. Guenaut, A.A. Kwiatkowski, D.J. Morissey, G.K. Pang, R. Ringle, J. Savory, P. Schury, S. Schwarz High-precision mass measurements have been performed on the neutron-rich sulfur isotopes 40-44S using the Low Energy Beam and Ion Trap (LEBIT) 9.4 T Penning trap at the NSCL. Produced via projectile fragmentation with a 48Ca primary beam, the ions were converted into a low-energy beam via gas stopping and then transferred into a 9.4 T Penning trap mass spectrometer. Mass uncertainties as low as 20 keV have been achieved in a mass region with important nuclear structure effects like the disappearance of the N=28 shell closure and the appearance of a strong subshell closure in neighboring Z=14. The experiments were of further technical interest because of the type of beams that can be extracted from gas stoppers. Not only atomic sulfur ions but also several different radio-molecules were used for the mass determination. [Preview Abstract] |
Friday, October 12, 2007 2:36PM - 2:48PM |
EE.00004: Technique and study of $\beta $-delayed p-decay of proton-rich nuclei L. Trache, T. Al-Abdullah, A. Banu, C. Fu, V. Golovko, J.C. Hardy, V.E. Iacob, H.I. Park, G. Tabacaru, R.E. Tribble, Y. Zhai, J. Aysto, A. Saastamoinen, P.J. Woods, T. Davinson, M.A. Bentley, D. Jenkins We developed a technique to measure beta-delayed proton-decay of proton-rich nuclei produced and separated with the MARS recoil separator at TAMU. In particular we studied the case of $^{23}$Al produced in inverse kinematics. Its $\beta $-decay was studied before, using $\beta -\gamma $ coincidence techniques. The states populated in $^{23}$Mg above the proton threshold at S$_{p}$=7580 keV may proton decay. They are resonances in the proton capture reaction $^{22}$Na(p,$\gamma )^{23}$Mg, crucially important for the depletion of $^{22}$Na in ONe novae. A setup consisting of a thin Si strip detector (p-detector) and a thick Si detector ($\beta $-detector) was designed. A HpGe detector outside the chamber detected $\gamma $-rays. A rotating energy-degrader was used to implant the source nuclei (from 40 MeV/u) in the middle of the thin p-detector. We have pulsed the beam from the cyclotron, implanted the source, then measured $\beta -$p and $\beta -\gamma $ coincidences off-beam. The technique has shown a remarkable selectivity to $\beta $-delayed charged particle emission and would work even at radioactive beam rates of a few pps. [Preview Abstract] |
Friday, October 12, 2007 2:48PM - 3:00PM |
EE.00005: Consequences of Heavy-Ion Fusion Hindrance on Explosive Astrophysical Processes. B.B. Back, C.L. Jiang, R.V.F. Janssens, K.E. Rehm Recent measurements of sub-barrier fusion of $^{60}$Ni+$^{89}$Y[1], $^{64}$Ni+$^{64}$Ni[2], $^{64}$Ni+$^{100}$Mo[3], and $^{28}$Si+$^{64}$Ni[4], as well as a re-analysis of older data from the literature, has unambiguously demonstrated that fusion cross sections at sub-barrier energies are substantially lower than predicted by present fusion models. Recently, it has been proposed that the additional compression energy inside the touching point of the fusing nuclei causes the observed fusion hindrance [5]. A close examination of published data on fusion reactions involving carbon and oxygen indicates that also these light systems are subject to the sub-barrier hindrance. This renders the standard extrapolations to the even lower energies, which come into play in explosive astrophysical processes, unreliable, and an extrapolation method, which is guided by the observed fusion hindrance, is therefore proposed [6]. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. [1] C.L. Jiang \textit{et al.}, Phys. Rev. Lett. \textbf{89}, 52701 (2002) [2] C.L. Jiang \textit{et al.}, Phys. Rev. Lett. \textbf{93}, 12701 (2004) [3] C.L. Jiang \textit{et al.}, Phys. Rev. C\textbf{ 71}, 44613 (2005) [4] C.L. Jiang \textit{et al.}, Phys. Lett. \textbf{B640, }18 (2006) [5] S. Misicu and H. Esbensen, Phys. Rev. Lett. \textbf{96},112701 (2006) [6] C.L. Jiang \textit{et al.}, Phys. Rev. C\textbf{ 75}, 015803 (2007) [Preview Abstract] |
Friday, October 12, 2007 3:00PM - 3:12PM |
EE.00006: MANTIS, in Gas-Filled Mode -- AMS for nuclear astrophysics at Notre Dame, first results Philippe Collon, Chris Schmitt, Daniel Roberston, Dale Henderson, Brent Schumard, Larry Lamm, Edward Stech, Steven Kurtz Over the past 2.5 years the Browne-Buechner spectrograph at the Nuclear Science Laboratory (NSL) at the University of Notre Dame has been renovated and its system upgraded to enable operations in the gas-filled mode. In addition to this, a new position sensitive PPAC detector and Ionization counter were developed as the focal plane detector of this system. The upgrade enables operation of the magnet both in the standard as well as in the gas-filled mode for the measurement of specific nuclear reactions of interest in stellar nucleosynthesis. The presentation will focus on the upgrade work that has involved both graduate and undergraduate students as well as the first tests of the system using the separation of the $^{58}$Fe-$^{58}$Ni isobars as a benchmark measurement. First results on $^{40}$Ca($\alpha $, $\gamma )^{44}$Ti as well as the detection of $^{36}$Cl using AMS in conjunction with the gas-filled technique at Notre Dame will also be presented. [Preview Abstract] |
Friday, October 12, 2007 3:12PM - 3:24PM |
EE.00007: Equation of State of the Nuclear Pasta Jutri Taruna, Jorge Piekarewicz Pasta phase -- the neutron-rich matter at subnuclear densities present in the core-collapse supernovae and the crust of neutron stars -- displays fascinating complex structures. The equation of state and the two-body spin-isospin dependent correlation function in the nuclear pasta are computed via semi-classical Monte Carlo simulation that incorporates a ``semi classical'' short-range spin-dependent term to simulate Pauli correlations. [Preview Abstract] |
Friday, October 12, 2007 3:24PM - 3:36PM |
EE.00008: Spin response for partially magnetized neutron matter Angeles Perez-Garcia The spin response function is studied for a neutron plasma partially polarized by the existence of a magnetic field, $B$. By using Skyrme and Gogny interaction potentials we will analize the monopolar Landau approximation and the modified Lindhart function in the polarized plasma. [Preview Abstract] |
Friday, October 12, 2007 3:36PM - 3:48PM |
EE.00009: Logical Aspect of Quantum Tunnelling Shantilal Goradia I am postulating that every particle communicates to the rest of the universe via a quantum mouth as shown in Fig 2, physics/0210040 v3 (What is Fine-structure Constant?). A question is raised ``How can it explain quantum tunneling?'' The neck like portion of the connection between the particle and its mouth can stretch as it has no classical counterpart of any fixed length. When the mouths of the alpha particle appear outside the potential well as they will do consistent with quantum probabilities, observing particles positioned outside the potential well can create enough force to drag the alpha particle over the peak of the well and outside. There is no constraint of the stretch of the neck, invisible to us. This logic has a potential to throw light on the issue of EPR. [Preview Abstract] |
Friday, October 12, 2007 3:48PM - 4:00PM |
EE.00010: Can thermal input from a prior universe account for relic graviton production?: Implications for the cosmological landscape Andrew Beckwith The author presents how one can answer if Sean Carroll's supposition of a pre inflation state of low temperature-low entropy pre inflation state provides a bridge between two models. Note, loop quantum gravity gives us thermal input permitting large scale relic graviton production. Brane world models as constructed by Randall and Sundrum permit the low entropy conditions Carroll and Chen predicted in 2005. Then we make a linkage from the brane world model to the 10 to the 32 Kelvin conditions stated by Weinberg in 1972 as necessary for quantum gravity. Afterwards, we have a transition to Guth style inflation. We also discuss a difference in values of the cosmological constant between a huge upper bound dependent upon temperature, and a lower bound predicted by Barvinsky et al. in late 2006 with the difference in values as an energy input into relic graviton production. This introduce quantization via a shift in values of the Hartle-Hawking wave function from a lower value of zero to one which is set via a cosmological constant 360 times the square of the Planck's mass. [Preview Abstract] |
Friday, October 12, 2007 4:00PM - 4:12PM |
EE.00011: Nuclear Recoil Background Evaluation for WIMP Searches Dongming Mei, Andrew Hime, Christina Keller, Zhongbao Yin Nuclear recoils produced by neutrons, alphas and neutrinos as they scatter from target nuclei are important sources of background which must be considered in WIMP searches. PMTs and other detector components may contribute neutrons which generate a source of background. Alphas on the surface of the vessel can also be a serious issue for some of the experiments. And, neutrino-induced recoils represent a background to low-threshold experiments. We present a comprehensive study of nuclear recoil events induced by neutrons, alpha particle and neutrinos. The sources of neutrons, alphas and neutrinos are discussed. We also show the background reduction techniques for different type of detectors. [Preview Abstract] |
Friday, October 12, 2007 4:12PM - 4:24PM |
EE.00012: The implementation of a $4\pi$ $\gamma$-summing method in capture reaction cross section measurements with relevance to astrophysical processes. A. Spyrou, A. Lagoyannis, S. Harissopulos, H.-W. Becker, C. Rolfs A new method, employing a $12'' \times 12''$ $\gamma$-summing single NaI crystal, was developed for cross section measurements of astrophysically relevant capture reactions on medium-mass nuclei. The large volume and the timing response of such a detector enables the summing of all $\gamma$ rays of a capture reaction. As a result, a single peak, the so-called sum peak, arises in the spectra. Its intensity can be used to obtain cross sections of capture reactions, as long as it is corrected for the detector's sum peak efficiency. This efficiency is highly affected by the multiplicity of the reaction under study. The method enables to first determine this multiplicity, which is then used to derive the corresponding sum peak efficiency by means of Monte Carlo simulations. Cross sections are finally obtained from the sum-peak intensity with an average uncertainty of $\approx$15\%. The method was first applied to the $^{62}$Ni($\alpha,\gamma$)$^ {66}$Zn reaction. The results obtained are in excellent agreement with those reported in literature. The new method was also employed to determine cross sections of 23 capture reactions in the Ge-- Sb region. [Preview Abstract] |
Friday, October 12, 2007 4:24PM - 4:36PM |
EE.00013: Feasibility of Direct (n,$\gamma$) TOF Experiments on s-Process Branch Points Aaron Couture, Rene Reifarth We have simulated the response of a 4-$\pi$ calorimetric detector to radioactive isotopes on the s-process path. From these simulations, a maximum tolerable sample size has been determined. In addition, the estimated neutron flux needed for a direct time-of-flight measurement on these branch-point isotopes has been determined. These calculations should aid in the planning of future experiments on these critical isotopes. The methodology of the simulations as well as the determination of the maximum sample size will be discussed. [Preview Abstract] |
Friday, October 12, 2007 4:36PM - 4:48PM |
EE.00014: Some remarks about the $\beta$-delayed $\alpha$-decay of $^{16}$N Lothar Buchmann, G. Ruprecht, C.A. Barnes, C. Ruiz The $\beta$-delayed $\alpha$-decay of $^{16}$N has been used to restrict the E1 fraction of the ground state in the key $^{12}$C($\alpha$,$\gamma$)$^{16}$O reaction. A review of the measurements is given and new R-Matrix and GEANT calculations are presented to further elucidate the observed $\alpha$ spectra. A clear response tail from scattering of $\alpha$-particles in the catcher foil is observed in these simulations for thick foils. The simulations show that the TRIUMF measurement and those performed at Yale originate from the same underlying spectrum. The $R$-matrix calculations reveal, in addition, that the S$_{E1}$(300) is relatively insensitive to details of the spectrum. It is concluded that the TRIUMF measurement represents most likely the closest approximation to the natural $\beta$-delayed $\alpha$-decay spectrum of $^{16}$N. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700