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 LN: Fission Physics |
Hide Abstracts |
Chair: Andrea Mattera, BNL Room: Studio 1 |
Wednesday, October 13, 2021 2:00PM - 2:12PM |
LN.00001: Generation of Fragment Angular Momentum in Fission Jorgen Randrup, Ramona L Vogt A recent analysis of experimental data published in Nature found that the angular momenta of nuclear fission fragments are uncorrelated. Based on this finding, the authors concluded that the spins are therefore determined only {\em after} scission has occurred. We show here that the nucleon-exchange mechanism, as implemented in the well-established event-by-event fission model FREYA, while agitating collective rotational modes in which the two spins are highly correlated, nevertheless leads to fragment spins that are largely uncorrelated. This counter example invalidates the conclusion in the Nature paper that uncorrelated spins must necessarily have been generated after scission (a potentious conclusion that would rule out all models that generate the fragment spins prior to scission). Furthermore, they reported that the mass dependence of the average fragment spin has a sawtooth structure. We demonstrate that such a behavior naturally emerges when shell and deformation effects are included in the moments of inertia of the fragments at scission. |
Wednesday, October 13, 2021 2:12PM - 2:24PM |
LN.00002: Measuring the 235U(n,f)/6Li(n,t) cross section ratio in the NIFFTE fissionTPC Maria Anastasiou While nuclear data play an important role in nuclear physics applications, it has become important to have a better understanding and try to minimize their uncertainties. In particular, there is a need for precision neutron-induced fission cross section measurements on fissile nuclei. Neutron-induced fission cross sections are typically measured as ratios, with a well-known standard in the denominator. While the 235U(n,f) standard is well measured, some light particle reactions are also well-known and their use as reference can provide information to remove shared systematic uncertainties that are present in an actinide-only ratio. The NIFFTE collaboration’s fission time projection chamber (fissionTPC) is a 2×2π charged particle tracker designed for measuring neutron-induced fission. Detailed 3D track reconstruction of the reaction products enables evaluation of systematic effects and corresponding uncertainties which are less directly accessible by other measurement techniques. This work focuses on the recent measurement of the 235U(n,f) using as a reference the standard 6Li(n,t) reaction. Preliminary data of the 235U(n,f)/6Li(n,t) measurement deployed at the Los Alamos Neutron Science Center will be presented. |
Wednesday, October 13, 2021 2:24PM - 2:36PM |
LN.00003: Fission-product Yields from Photon-induced Fission of 240Pu and Neutron-induced Fission of 239Pu as a Function of Incident Energy Jack A Silano, Anthony Paul Ramirez, Anton P Tonchev, Mark A Stoyer, Roger Henderson, Nicolas Schunck, Werner Tornow, Calvin R Howell, FNU Krishichayan, Sean W Finch, Matthew E Gooden The Bohr Hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation1. Using fission product yields (FPYs) as a sensitive probe, we have performed novel high-precision test of the combined effects of the entrance channel, spin and parity on the fission process. Two different reactions were used in a self-consistent manner to produce a compound 240Pu nucleus with the same excitation energy: neutron induced fission of 239Pu and photon-induced fission of 240Pu. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator2 and quasimonenergetic photon beams from the HIGS facility. A comparison of the FPYs from 239Pu(n,f) at En=1.5 and 4.6 MeV with those from 240Pu(γ,f) at Eγ=8 and 11.2 MeV will be presented. |
Wednesday, October 13, 2021 2:36PM - 2:48PM |
LN.00004: Measurement of Independent Fission Product Yields with the SPIDER Detector System at LANSCE Panagiotis Gastis, Jack R Winkelbauer, Devin S Connolly, Sean A Kuvin, Shea Mosby, Christopher J Prokop Independent fission product yields (FPY), i.e., yields of fission products right after the prompt neutron emission, but before beta decay, are an important piece of data for nuclear fission modeling and fission applications. Presently, measurements of FPYs are performed using various techniques, such as the 2E method (gridded ionization chambers), the 2E-2v method, radiochemical separation, and magnetic separators. Among these techniques, the 2E-2v is considered the most robust in terms of combining high resolution (< 3 amu), accuracy, and relatively high efficiency. In the 2E-2v method, the mass of fission fragments is determined by measuring the kinetic energy and velocity (via time-of-flight) of both fragments in coincidence. To accurately extract the mass, however, the energy loss of the fission fragments inside the conversion foils of the time-of-flight detectors and the windows of the energy detectors must be well known. In the past, energy loss corrections have been based on theoretical stopping power models, inserting systematic uncertainties in the extracted mass distribution. The Spectrometer for Ion Determination in fission Research (SPIDER), was developed at Los Alamos Neutron Science Center (LANSCE) for measuring FPYs from neutron-induced fission using the 2E-2v method, eventually spanning from thermal up to 20 MeV in incident neutron energy. SPIDER has recently undergone various improvements for increasing the fidelity and resolution of the extracted data. In particular, a gamma-ray tagging system has been implemented for improving the accuracy of the mass calibration by measuring strong gamma-ray transitions from isotopes of known mass. In this presentation, an overview of the upgraded SPIDER system and preliminary results from FPY measurements on 252Cf(sf), 235U(nth,f), and 239Pu(nth,f) will be discussed. |
Wednesday, October 13, 2021 2:48PM - 3:00PM |
LN.00005: New approach to precisely measure gamma-ray intensities for long-lived fission products Daniel E Hoff, Kay Kolos, Miguel Bencomo, Nicholas D Scielzo, Wei Jia Ong, Mary Burkey, Jason A Clark, Victor Iacob, Dan G Melconian, Eric B Norman, Rodney Orford, Daniel Santiago-Gonzalez, Guy Savard, Anton P Tonchev, Mark A Stoyer The distribution of fragment masses following fission, called fission yields, is one of the most basic quantities of nuclear fission. These fission yields play an important role in many applications such as estimation of decay heat and delayed neutron emission in nuclear reactors, the reactor neutrino study, the radio-isotope production for medical applications, stockpile stewardship, and national security. One of the most straightforward and reliable ways to determine the number of fissions that occurred in a chain reaction is done via detection of the characteristic γ-rays emitted during the β decay of the long-lived fission products. A lot of nuclear data suffer from high uncertainties, which contribute to the uncertainties in the determined fission yields. We developed a new experimental method [1] that takes advantage of radioactive ions beam at CARIBU, and very well characterized detection system [2], to performed precision. We will present results for 144Ce and 147Nd decay properties determined to fractional precisions of ~1%, and discuss plans for future measurements. |
Wednesday, October 13, 2021 3:00PM - 3:12PM |
LN.00006: Fission Product Yields from Neutron-Induced Fission of Major Actinides at 6.5 MeV Ronald C Malone, Anthony Paul Ramirez, Jack A Silano, Anton P Tonchev, Mark A Stoyer, Sean W Finch, Calvin R Howell, FNU Krishichayan, Werner Tornow, Matthew E Gooden, Jerry B Wilhelmy Fission product yields (FPY) are an important observable for fundamental and applied nuclear physics. We are conducting a comprehensive study of the cumulative FPY from neutron-induced fission of 235U, 238U, and 239Pu between 0.5 and 15 MeV at the Triangle Universities Nuclear Laboratory. Actinide foils are irradiated by monoenergetic neutron beams produced with a tandem accelerator. A dual fission chamber is employed to determine the number of fission events induced in the target. After irradiation the samples are assayed using high-purity germanium detectors in a low-background counting facility to identify and determine the yield of fission products. Details of the experiment setup and preliminary results for FPY at a neutron energy of 6.5 MeV will be presented. |
Wednesday, October 13, 2021 3:12PM - 3:24PM |
LN.00007: Precision Gamma-ray Spectroscopy of Fission Fragments Libby McCutchan, Andrea Mattera, Shaofei Zhu, Chris Morse, Adam Hayes, Marian Jandel, Peter C Bender, John P Greene, Matt D Gott, Michael P Carpenter, Jenna Ocheltree The decay data on fission fragments plays an important role in non-proliferation and reactor science, and forms the foundation for many fission yield measurements. Many isotopes, however, were last studied at a time when gamma-ray spectroscopy was in its infancy. A new campaign of measurements to improve decay data related to fission fragments will be described. It involves measurements using the Gammasphere array at Argonne National Laboratory as well as a new detector system being built at Brookhaven National Laboratory. Capabilities and initial commissioning of the new detector system will be presented. A fission fragment of interest is 140La, a well-known nuclear chronometer and particulate fission fragment monitored as part of CTBTO. A source of 140La was produced through neutron irradiation at UMASS, Lowell and studied with Gammasphere. Preliminary results on the measurement of precision intensities will be presented. |
Wednesday, October 13, 2021 3:24PM - 3:36PM |
LN.00008: Short-lived fission products from 235U using monoenergetic neutrons Anthony Paul Ramirez, Jack A Silano, Mark A Stoyer, Anton P Tonchev, Matthew E Gooden, Todd A Bredeweg, David Vieira, Vanessa Linero, Sean W Finch, Werner Tornow, Calvin R Howell, FNU Krishichayan Fission product yields (FPYs) are among the fundamental fission observables that play crucial roles in basic and applied nuclear physics. Accurate knowledge of the FPYs is necessary for addressing questions relevant to nucleosynthesis in the cosmos, resolving the reactor antineutrino anomaly, decay heat release in nuclear reactors, and national security applications. In this talk, I will discuss an ongoing campaign by the LLNL-LANL-TUNL collaboration to measure the cumulative FPYs from neutron-induced fission of 235,238U and 239Pu at the Triangle Universities Nuclear Laboratory (TUNL). Emphasis will be given on our recent experimental effort utilizing the RApid Belt-driven Irradiated Target Transfer System (RABITTS) to measure short-lived (T1/2 ~ minutes to seconds) fission products extending our previous long-lived (T1/2 > 1 hour) FPY measurements[1]. An overview of the experimental methods with the RABITTS and some preliminary data for the 235U(n,f) reaction at En=4.6 MeV will be presented. |
Wednesday, October 13, 2021 3:36PM - 3:48PM |
LN.00009: Simultaneous calculation of fission fragment charge and mass yields with the Enhanced Finite-Range Liquid-Drop Model (eFRLDM) Matthew R Mumpower, Marc Verriere, Trevor Sprouse, Ionel Stetcu We present model improvements to the macroscopic-microscopic approach to nuclear fission. We have magnified the resolution of the Lipkin-Nogami equations and strengthened the Strutinksy procedure, reducing spurious effects from the continuum. We further calculate scission configurations using particle number projection which affords the simultaneous calculation of both mass and charge yield distributions. We discuss our predicted yields in the actinide region. |
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