Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session CJ: Fission & Light Ion Reactions |
Hide Abstracts |
Sponsoring Units: DNP Chair: Petr Navratil, TRIUMF Room: Junior Ballroom A |
Friday, October 14, 2016 8:30AM - 8:42AM |
CJ.00001: Measurements of Short-Lived Fission Isomers Sean Finch, Megha Bhike, Calvin Howell, Fnu Krishichayan, Werner Tornow Fission yields of the short lived isomers $^{134m}$Te ($T_{1/2}=162$ ns) and $^{136m}$Xe ($T_{1/2}=2.95$ $\mu$s) were measured for $^{235}$U and $^{238}$U. The isomers were detected by the $\gamma$ rays associated with the decay of the isomeric states using high-purity germanium detectors. Fission was induced using both monoenergetic $\gamma$ rays and neutrons. At TUNL's High-Intensity Gamma-ray Source (HI$\gamma$S), $\gamma$ rays of 9 and 11 MeV were produced . Monoenergetic 8 MeV neutrons were produced at TUNL's tandem accelerator laboratory. Both beams were pulsed to allow for precise time-gated spectroscopy of both prompt and delayed $\gamma$ rays following fission. This technique offers a non-destructive probe of special nuclear materials that is sensitive to the isotopic identity of the fissile material. [Preview Abstract] |
Friday, October 14, 2016 8:42AM - 8:54AM |
CJ.00002: Measurement of Angular-Momentum-Dependent Fission Probabilities of $^{240}$Pu Johnathon Koglin, Jason Burke, Igor Jovanovic An experimental technique using the surrogate reaction method has been developed to measure fission probabilities of actinides as a function of angular momentum state of the fissioning nucleus near the fission barrier. In this work, the $^{240}$Pu$(\alpha,\alpha’f)$ reaction was used as a surrogate for $^{239}$Pu$(n,f)$. An array of 12 silicon telescopes positioned at 10 degree intervals from 40 to 140 degrees detect the outgoing reaction particle for identification and measurement of the excitation energy. The angular momentum state is determined by measuring the angular distribution of fission fragments. The expected distributions are predicted from the Wigner d function. An array of 50 photovoltaic (solar) cells detects fission fragments with 10-degree granularity. The solar cells are sensitive to fission fragments but have no response to light ions. Relative contributions from different angular momentum states are extracted from the measured distributions and compared across all $\alpha$ particle scattering angles to determine fission probability at a specific angular momentum state. The first experiment using this technique was recently completed using 37~MeV $\alpha$ particles incident on $^{240)$Pu. First results will be discussed. [Preview Abstract] |
Friday, October 14, 2016 8:54AM - 9:06AM |
CJ.00003: Total Kinetic Energy Release in the Fast Neutron Induced Fission of $^{235}$U Walter Loveland, Ricardo Yanez We have measured the total kinetic energy (TKE) release, its variance and associated fission product mass distributions for the neutron induced fission of $^{235}$U for E$_{n}$=2-90 MeV using the 2E method. The neutron energies were determined,event by event, by time of flight measurements with the white spectrum neutron beam from LANSCE. The TKE decreases with increasing neutron energy. This TKE decrease is due to increasing symmetric fission (and decreasing asymmetric fission)with increasing neutron energy, in accord with Brosa model predictions. Our measurement of the TKE release for $^{235}$U(n$_{th}$,f) is in excellent agreement with the known value, indicating our measurements are absolute measurements. The TKE variances are sensitive indicators of n$^{th}$ chance fission. Due to the occurrence of n$^{th}$ chance fission and pre-fission neutron emission, the average fissioning system and its excitation energy is a complex function of the incident neutron energy. Detailed comparisons of our data with previous measurements will be made. [Preview Abstract] |
Friday, October 14, 2016 9:06AM - 9:18AM |
CJ.00004: Compound-nuclear Reactions with Unstable Isotopes: Constraining Capture Cross Sections with Indirect Data and Theory Jutta Escher Cross sections for compound-nuclear reactions involving unstable targets are important for many applications, but can often not be measured directly. Several indirect methods have recently been proposed to determine neutron capture cross sections for unstable isotopes. These methods aim at constraining statistical calculations of capture cross sections with data obtained from the decay of the compound nucleus relevant to the desired reaction. Each method produces this compound nucleus in a different manner (via a light-ion reaction, a photon-induced reaction, or $\beta$ decay) and requires additional ingredients to yield the sought-after cross section. This contribution focuses on the process of determining capture cross sections from inelastic scattering and transfer experiments. Specifically, theoretical descriptions of the (p,d) transfer reaction have been developed to complement recent measurements in the Zr-Y region. The procedure for obtaining constraints for unknown capture cross sections is illustrated. The main advantages and challenges of this approach are compared to those of the proposed alternatives. [Preview Abstract] |
Friday, October 14, 2016 9:18AM - 9:30AM |
CJ.00005: Entry-Level Spin Distributions of Sm Isotopes from the (p,t) Reaction at 25~MeV using Hyperion and STARLiTeR N. Cooper, P. Humby, C.W. Beausang, E. Wilson, R.O. Hughes, S. Ota, J. Koglin, R.J. Casperson, J. Burke, A. Simon, C. Reingold, M. McCleskey, E. McCleskey, A. Saastamoinen, R. Chyzh, M. Dag The surrogate method has proven to be a useful tool in determining neutron capture cross sections. However, differences in level properties populated in these experimental studies, which are currently being performed near stability, may have an impact on extracted cross sections. This talk will focus on an experiment performed at the Texas A\&M Cyclotron Institute with the Hyperion Si telescope and HPGe detector array. Outgoing particles were detected following the reaction of 25~MeV protons incident on an enriched $^{150}$Sm target. Results from recently developed codes to extract the entry-level spin distributions from experimental data as well as predict this distribution will be presented for $^{148}$Sm as well as $^{150,152}$Sm using past experimental data from STARLiteR. [Preview Abstract] |
Friday, October 14, 2016 9:30AM - 9:42AM |
CJ.00006: The 13C($\alpha $,n)16O reaction: A background source for underground astrophysics measurements and geo-neutrino measurements. Michael Febbraro, Rebecca Toomey, James deBoer, Steven Pain, William Peters, Karl Smith, Fred Becchetti, Michael Wiescher In this study, we present results for a neutron spectroscopic study of the 13C($\alpha $,n)16O reaction between E$\alpha \quad =$ 3.5 and 7.5 MeV performed at the University of Notre Dame Nuclear Science Laboratory. The neutron spectroscopy measurement was performed with deuterated liquid scintillator detectors capable of extracting neutron energy spectra without neutron time-of-flight measurement using spectral unfolding technique [2]. This permitted extraction of the ground state contribution as well as excited state contributions to the total reaction cross section. The usefulness of this technique for the measurement of beam-induced neutron background sources in deep underground nuclear astrophysics measurements will be shown. Results showing the contributions of excited state components to the total cross section will be given and their implication to geo-neutrino measurements will be discussed. [1] S. Harissopulos, et al. Phys. Rev. C. (2005) [2] M. Febbraro, et al., NIM A784 (2015) [Preview Abstract] |
Friday, October 14, 2016 9:42AM - 9:54AM |
CJ.00007: Characterization of NeutronSTARS for Surrogate (n,2n) Measurement Oluwatomi Akindele, Jason Burke, Eric Norman, Robert Casperson NeutronSTARS (neutron silicon telescope array for reaction studies) is a detector apparatus for in beam cross section measurements, specifically (n,2n) reactions on actinides. Both simulations and measurements have been performed to characterize the arrays performance. [Preview Abstract] |
Friday, October 14, 2016 9:54AM - 10:06AM |
CJ.00008: Parameters of Density Distribution of Exotic Nuclei Extracted from a Data on Reaction Cross-section in the Glauber Model Ivan Novikov, Keiti Rueter Parameters of density distribution of exotic nuclei with halo structure were extracted from the experimental data on the interaction cross-section using exact expressions obtained in the Glauber theory. Generally, to do so measured interaction cross-section is compared with a reaction cross-section calculated in optical approximation or using exact expressions of the Glauber theory. It was shown before that the parameters of nuclear density distribution depends on chosen density model (Gaussian, harmonic oscillator or Woods-Saxon) and on the used approximation of the Glauber theory (i.e. optical or rigid target). In the presented paper, we discuss the difference between reaction and interaction cross-sections calculated in various approximations, and how this difference affects the accuracy of the nuclear density parameters determination. As an example, we provide results of the analyzes of experimental data on interaction cross-section of $^{11}$Li, $^{16}$C and $^{31}$Ne nuclei on $^{12}$C target. [Preview Abstract] |
Friday, October 14, 2016 10:06AM - 10:18AM |
CJ.00009: Modernizing the Fission Basis Anton Tonchev, Roger Henderson, Nicolas Schunck, Mark Sroyer, Ramona Vogt In 1939, Niels Bohr and John Wheeler formulated a theory of neutron-induced nuclear fission based on the hypothesis of the compound nucleus [1]. Their theory, the so-called ``Bohr hypothesis,'' is still at the heart of every theoretical fission model today and states that the decay of a compound nucleus for a given excitation energy, spin, and parity is independent of its formation [2]. We propose the first experiment to validate to 1-2{\%} absolute uncertainties the practical consequences of the Bohr hypothesis during induced nuclear fission. We will compare the fission product yields (FPYs) of the same $^{\mathrm{240}}$Pu compound nucleus produced via two different reactions (i) n$+^{\mathrm{239}}$Pu [3] and (ii) $\gamma +^{\mathrm{240}}$Pu. These high-precision FPYs measurements will be extremely beneficial for our fundamental understanding of the nuclear fission process and nuclear reactions from first principles. [1] N. Bohr and J. A. Wheeler, \textit{Phys. Rev.} \textbf{56}, 426 (1939). [2] N. Bohr, \textit{Nature}. \textbf{137}, 344 (1936). [3] M. E. Gooden et al. Nuclear Data Sheets \textbf{119, }324 (2016). [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