Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session JG: Nuclear Reactions: Heavy-Ions/Rare Isotope Beams I |
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Chair: Jorgen Randrup, LBNL Room: Copley & Kenmore |
Wednesday, October 13, 2021 9:30AM - 9:42AM |
JG.00001: Fission in the neutron-deficient lead region Adam K Anthony, Joseph M Wieske, Chenyang Niu, Kyle W Brown, Zbigniew Chajecki, William G Lynch Rare isotope beam facilities offer the opportunity to study the physics of isotopes far from stability. Following the discovery of an unexpected region of asymmetric beta-delayed fission in the neutron deficient mercury region, there has been a flurry of work to study fission properties of other nuclei in the region. At the National Superconducting Cyclotron Laboratory (NSCL), an experiment was designed to measure the fission properties of nuclei in the transition region from asymmetric to symmetric fission. A radioactive beam centered around Pb197 was produced by the coupled cyclotrons at the NSCL. Helium-induced fusion-fission properties were measured as a function of beam energy. The Active-Target Time Projection Chamber (AT-TPC) served as the helium gas target and was used to separate fusion-fission events from the background. In this talk, we will discuss preliminary results from the experiment. |
Wednesday, October 13, 2021 9:42AM - 9:54AM |
JG.00002: Resolution of the discrepancy in the 17O + 12C fusion excitation function Benjamin W Asher, Sergio J Almaraz-Calderon, Kirby W Kemper, Nicholas Keeley, Lagy T Baby, Eilens Lopez-Saavedra, Ashton B Morelock, Jesus F Perello, Vandana Tripathi Measurements of the total fusion cross section around the Coulomb barrier can provide insight into different underlying mechanisms that makeup the structural properties of the fusion excitation function. Couple channel calculations are typically used to understand the measurements. However, for the case of fusion in light symmetric systems, unique interpretations are needed to explain, for example, the observed oscillatory structures found in their fusion excitation functions. At Florida State University we used the novel Encore detector to measure the 17O + 12C fusion excitation function in order to resolve a long-standing discrepancy around E = 14 MeV in the existing data. Details of the detector, results of the measurement and possible implications will be discussed in this talk. |
Wednesday, October 13, 2021 9:54AM - 10:06AM |
JG.00003: Influence of shell structure on the fusion of neutron-rich mid-mass nuclei Romualdo T Desouza, James E Johnstone, Rekam Giri, Sylvie Hudan, Jessica Vadas, Jesus Lubian, Hugo Soler The influence of shell effects on fusion of mid-mass nuclei is explored using isotopic chains of K and Ar ions on an oxygen target. Calculation of reduced excitation functions from the measured cross-section eliminates trivial size and barrier effects. Comparison of the reduced excitation functions reveals that the fusion cross-section for the open neutron shell projectile nuclei 41K and 45K is systematically larger than for the closed neutron shell projectiles 39K and 47K. The Sao Paulo fusion model using one-body matter densities from systematics fails to describe the measured excitation functions. Use of more realistic densities calculated within a Dirac-Hartree-Bogoliubov (DHB) approach performs significantly better though it still overpredicts the closed shell nuclei. |
Wednesday, October 13, 2021 10:06AM - 10:18AM |
JG.00004: Measurements of beta-delayed neutrons from photofission of 238U Sean W Finch, Mohammad Ahmed, Calvin R Howell, Jack A Silano, Werner Tornow Many fission products emit neutrons following β- decay, seconds to minutes after fission has occurred. Because of this unique signature, β-delayed neutrons play an important role in applications such as nuclear security and reactor modeling. Photofission of 238U may be used as a surrogate reaction to probe the β-delayed neutron spectra of the neutron-induced fission of 237U, which is difficult to experimentally measure. Fission is induced using mono-energetic γ-rays produced by Compton backscattering of free-electron laser light at HIγS. The 238U target is transported by a rabbit system from an in-beam irradiation position to the center of a moderated array of 3He neutron detectors, where the time spectra of β-delayed neutrons is measured. Preliminary results will be presented, and comparisons will be made to previous measurements using bremsstrahlung beams [1]. |
Wednesday, October 13, 2021 10:18AM - 10:30AM |
JG.00005: Energy Dependence of Fission Product Yields Matthew E Gooden, Todd A Bredeweg, David Vieira, Jerry B Wilhelmy, Anton P Tonchev, Jack A Silano, Mark A Stoyer, Anthony Paul Ramirez, Sean W Finch, Werner Tornow Under a joint collaboration between TUNL-LANL-LLNL, a set of absolute fission product yield measurements has been performed. The energy dependence of a number of cumulative fission product yields (FPY), for long lived (days-to-months) isotopes, have been measured using quasi-monoenergetic neutron beams for three actinide targets, 235U, 238U and 239Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and γ-ray counting. Each dual-fission chamber is a back-to-back ionization chamber encasing an activation target in the center with thin deposits of the same target isotope in each chamber. This method allows for the direct measurement of the total number of fissions in the activation target with no reference to the fission cross-section, thus reducing uncertainties. Reported are absolute cumulative fission product yields for incident neutron energies of 0.5, 1.37, 2.4, 3.6, 4.6 and 14.8 MeV. New data in the second chance fission region of 5.5 – 11 MeV are included to complete the measurements in the energy range of interest. These results are compared to previous measurements and theoretical estimates. |
Wednesday, October 13, 2021 10:30AM - 10:42AM |
JG.00006: Fission Product Yields of 238U Samples Irradiated Using the Flattop Critical Assembly Vanessa Linero, Jessica Jackson, Jenifer Shafer, Todd A Bredeweg, Matthew E Gooden, Jesson D Hutchinson Integral fission yield measurements were performed on the Flattop critical assembly at the National Criticality Experiments Research Center (NCERC) located at the Nevada National Security Site. Four DU samples, along with dosimetry foils, were positioned at two different positions within the glory hole passing through the natural uranium outer reflector and into the HEU core of the Flattop assembly. The samples were each irradiated in sets of two in separate low-power and high-power irradiations, along with a fission chamber designed especially for use in Flattop, to determine the absolute number of fissions in the samples. These measurements were designed to look at variations in the 238U fission product yields as a function of neutron energy, by having samples at different positions within the assembly and hence seeing different neutron spectra. Select fission products were isolated in duplicate from each DU target via radiochemical separations and measured for beta and gamma decay. This talk will highlight the yields measured from Sr, Mo, Zr, Cd, Ag, Cs, Ba, and Nd fission products and will compare the results to current ENDF measurements. The number of fissions measured from 99Mo will also be compared against fission chamber counts during the low-powered run. |
Wednesday, October 13, 2021 10:42AM - 10:54AM |
JG.00007: Abstract Withdrawn
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Wednesday, October 13, 2021 10:54AM - 11:06AM |
JG.00008: Development of the LISE++ code to simulate rare isotopes production Oleg B Tarasov, Daniel Bazin, Marc Hausmann, Michelle P Kuchera, Peter N Ostroumov, Mauricio Portillo, Bradley M Sherrill, Ksenia V Tarasova, Tong Zhang LISE++ [1,2], the standard software package used at in-flight separator facilities for predicting beam intensity and purity, was recently ported to Qt-framework. The benefits of this porting include: |
Wednesday, October 13, 2021 11:06AM - 11:18AM |
JG.00009: Shell effects in quasifission and implications for fission Sait A Umar, Kyle Godbey, C. Simenel Quasifission reactions have been of great interest in recent years particularly in connections with the formation of superheavy elements and a source for producing neutron rich nuclei. Such reactions proceed through regions of periodic table where the dynamical evolution of quantal shell effects influence the formation of final fragments. The time-dependent density functional theory (TDDFT) has been found to be an excellent theoretical tool to study these reactions microscopically [1-4]. In this talk we discuss the recent results for quasifission reactions obtained using the TDDFT. In, particular we focus on the observed shell effects in these calculations and their relevance and/or relationship for shell effects in fission dynamics. |
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