Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session SQ: Mini-Symposium: New Insights into Fission II |
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Chair: Andrea Mattera, Brookhaven National Lab |
Sunday, November 1, 2020 10:30AM - 10:42AM |
SQ.00001: Prompt Neutron Spectra from Tagged Photofission of $^{235}$U, $^{238}$U, and $^{239}$Pu with a Linearly Polarized 13.5 MeV Photon Beam F.Q.L. Friesen, S.W. Finch, C.R. Howell, C.R. Malone, R.C. Malone, W. Tornow The first angular differential data for prompt neutrons from photofission with a linearly polarized beam have been measured near the peak of the fission cross section for $^{235}$U, $^{238}$U and $^{239}$Pu. A set of active fission ionization chambers were used to tag fission events and isolate the prompt neutrons associated with fission by forming timing coincidences between the ionization chambers and neutron detectors. The energies of the detected neutrons were determined using time-of-flight measurements. Results are presented in units of differential neutron multiplicity as a function of angle, as well as total multiplicity. No azimuthal polarization asymmetries were observed. [Preview Abstract] |
Sunday, November 1, 2020 10:42AM - 10:54AM |
SQ.00002: Measurement of Short-Lived Fission Product Yields for $^{237}$Np via $\gamma$-ray Spectroscopy Sean Burcher, J.T. Harke, S.W. Padgett, N. Gharibyan, N. Howard, K. Roberts, G. Slavik, P. Zhao, A.S. Tamashiro, B.D. Pierson, L. Greenwood, J. Goda, D. Hayes, J. Hutchinson, J. Walker Accurate fission product yields (FPYs) for neutron-induced fission of $^{237}$Np are important for applied nuclear science. The yields of short-lived fission products $(t_{1/2}$ $\lesssim$ hours$)$ are of particular interest, and are experimentally challenging to measure. High-resolution $\gamma$-ray spectroscopy can be used to determine the amount of various fission fragments produced by the unique $\gamma$-ray signatures of their decay, and does not require time-consuming chemical separation processes. Samples of $^{237}$Np have been irradiated in the Godiva-IV critical assembly, and then measured in a $\gamma$-ray counting setup for approximately 7 days. Hundreds of unique $\gamma$-rays were observed, allowing for the measurement of FPYs for many short-lived isotopes. [Preview Abstract] |
Sunday, November 1, 2020 10:54AM - 11:06AM |
SQ.00003: Fission product mass yields from fast neutron-induced fission of $^{237}\mathrm{Np}$ Devin Connolly, Kristina Montoya, Dana L. Duke, Uwe Greife, Walter Loveland, Shea Mosby, Christopher Prokop, Kyle Schmitt, Jack Winkelbauer $^{237}\mathrm{Np}$ is produced in significant quantities in the nuclear fuel cycle. Its presence in spent reactor fuel coupled with its $\sim 2\times10^6$ year half life make a complete and precise understanding of its nature critical to reactor design, particularly that of fast reactors. Although the fission cross section of $^{237}\mathrm{Np}$ has been measured for a wide range of incident neutron energies, little total kinetic energy (TKE) data exists for $^{237}\mathrm{Np}(n,f)$, and there are no TKE nor mass yield data for incident neutron energies above $E_n = 5.55$MeV. Measurements of the TKE of correlated fission fragments from $^{237}\mathrm{Np}(n,f)$ at incident neutron energies from $E_n = 0.5 - 40$MeV have been performed at the Los Alamos Neutron Science Center Weapons Neutron Research facility using using a twin Frisch-gridded ionization chamber and a thin-backed $^{237}\mathrm{Np}$ target. Fission mass yields have been extracted from the data using the double energy method. In this talk, experimental methods, analysis techniques and preliminary results will be discussed. [Preview Abstract] |
Sunday, November 1, 2020 11:06AM - 11:18AM |
SQ.00004: Short-lived fission product-yield measurements from $^{\mathrm{238}}$U(n,f) at E$_{\mathrm{n}}=$4.6 MeV Anthony Ramirez, Chris Hagmann, Jack Silano, Mark Stoyer, Anton Tonchev, Matthew Gooden, Todd Bredeweg, David Vieira, Jerry Wilhelmy, Vanessa Linero, Sean Finch, Werner Tornow, Calvin Howell, FNU Krishichayan, Innocent Tsorxe There is currently an ongoing effort by the LLNL-LANL-TUNL collaboration to measure high quality fission product yield (FPY) data from neutron-induced fission on $^{\mathrm{235,238}}$U, and $^{\mathrm{239}}$Pu. The goal is to study the energy dependence of the fission products using monoenergetic and pulsed neutron beams at the TUNL tandem accelerator for incident energies between 0.5 and 15 MeV. Previous data have focused on long-lived cumulative FPYs with half lives of hours to days [1,2]. In order to provide consistent data of the FPY distributions, there is a need to extend the measurements to shorter-lived fission products. Hence, a rapid belt-driven irradiated target transfer system (RABITTS) was developed at TUNL to allow cyclic neutron activation on the actinide targets. This technique permits the measurement of fission products with half lives as short as a fraction of a second. An overview of the experimental procedure and data analysis, as well as preliminary results, using the recent $^{\mathrm{238}}$U(n,f) measurements at E$_{\mathrm{n}}=$4.6 MeV with the RABITTS will be presented. [1] M. Gooden et al., Nucl. Data Sheets 131, 319 (2016). [2] A. Tonchev et al., LLNL-CONF-788565-986272. [Preview Abstract] |
Sunday, November 1, 2020 11:18AM - 11:30AM |
SQ.00005: Fission product-yield measurements of importance to the bump in the reactor antineutrino energy spectrum Sean Finch, Werner Tornow, Calvin Howell, FNU Krishichayan, Todd Bredeweg, Matthew Gooden, David Vieira, Jerry Wilhelmy, Anthony Ramirez, Jack Silano, Mark Stoyer, Anton Tonchev Using the rapid belt-driven irradiated target transfer system (RABITTS), cyclic activation was performed to measure cumulative fission yields for products with half-lives between 0.5 s and 50 s. Fission was induced on $^{238}$U using 2 MeV neutrons, and the resultant products were identified and quantified with $\gamma$-ray spectroscopy using HPGe detectors. Emphasis was placed on fission products which are known to contribute to the antineutrino energy spectrum in the 5 to 6 MeV energy range [1-3]. This region of the reactor antineutrino spectrum is commonly referred to as the ``bump,'' and is one component of the reactor antineutrino anomaly. In contrast to research reactors using highly enriched $^{235}$U, $^{238}$U is expected to contribute significantly to the antineutrino spectrum at the power reactors Daya Bay, RENO, and Double Chooz. Preliminary results will be presented for the most important fission products of interest, in addition to other short-lived fission products. [1] D.A. Dwyer and T.J. Langford, Phys. Rev. Lett. 114, 012502 (2015). [2] A.A. Sonzogni, T.D. Johnson, and E.A. McCutchan, Phys. Rev. C 91, 011301(R) (2015). [3] A.C. Hayes et al., Phys. Rev. D 92, 033015 (2015). [Preview Abstract] |
Sunday, November 1, 2020 11:30AM - 11:42AM |
SQ.00006: $^{239}$Pu Cumulative Fast Fission Product Yield Analysis Aaron S. Tamashiro, C.J. Palmer, J.T. Harke, S. Burcher, S.W. Padgett, G. Slavik, N. Harward, N. Gharibyan, R. Henderson, B. Pierson, L. Greenwood, J. Goda, D. Hayes, J.A. Bounds Precise integral measurement of fast neutron-induced fission product yields for various actinides is of high interest for applied nuclear science. The goal of this effort is to improve uncertainties in fission product yield values of $^{239}$Pu. Fission was induced in a pure $^{239}$Pu ($>99\%$) target using the Godiva-IV critical assembly in burst mode. The irradiated sample was transferred to a high-resolution $\gamma$-ray detector within 45 minutes. $\gamma$-ray list mode data was collected from 45 minutes to 1 week after the irradiation. $\gamma$-ray spectroscopy was performed to analyze the time dependent $\gamma$-ray yields using an automated peak search algorithm to identify isotopes by their decay $\gamma$-ray energy and half-life. The initial activity for each isotope identified was used to calculate their fission product yield. [Preview Abstract] |
Sunday, November 1, 2020 11:42AM - 11:54AM |
SQ.00007: Measurements of the short-lived (minutes $\le $ T$_{\mathrm{1/2}} \quad \le $ hours) photon-induced fission product yields using monoenergetic photon beams Fnu Krishichayan, S. Finch, C.R. Howell, J. Silano, A.P. Tonchev, W. Tornow, I. Tsorxe A program has been initiated at TUNL to bridge the gap between ongoing fission product yield (FPY) measurements of isotopes with half-lives (T$_{\mathrm{1/2}})$ close to seconds (fission products pretty close to the initial distribution produced directly by fission) and those with T$_{\mathrm{1/2}} \quad \ge $ 1 hour (longest-lived radioactive members of the beta-decay chain). The focus is on fission products with T$_{\mathrm{1/2\thinspace }}$between these two time regions. The ``big three'' actinide samples ($^{\mathrm{235}}$U, $^{\mathrm{238}}$U, and $^{\mathrm{239}}$Pu) were irradiated for 2 hours with a monoenergetic photon beam of E$_{\mathrm{\gamma }} \quad =$ 11.2 MeV at the HIGS facility. The samples were gamma-counted for a week post irradiation. In the present talk, details of the experimental setup and data analysis procedures will be discussed. The techniques employed in these measurements do not require absolute determination of the gamma-ray beam flux, thus significantly reducing the systematic uncertainties. [Preview Abstract] |
Sunday, November 1, 2020 11:54AM - 12:06PM |
SQ.00008: Total Kinetic Energy and Mass Yield Curves from the Fast Neutron-Induced Fission of $^{\mathrm{239}}$Pu Alexander Chemey, Ashley Pica, Walter Loveland, Larry Yao, Hye Young Lee, Sean Kuvin The total kinetic energy (TKE) release in fission constitutes the bulk of the energy released (Q$_{\mathrm{f}} \quad \approx $ 200 MeV). While TKE release in the $^{\mathrm{239}}$Pu(n,f) reaction was previously measured from 0.5 to 50 MeV (Phys. Rev. C \textbf{94}, 034611 (2016)), the highest energies in the evolution of TKE(E$_{\mathrm{n}})$ were puzzling. Notably, there was a high incident neutron energy flattening of TKE from E$_{\mathrm{n}} \quad =$ 30 to 50 MeV, contra the clear trend of decreasing TKE observed in the range of 0 to 30 MeV. Presented herein are measurements of TKE in $^{\mathrm{239}}$Pu(n,f) from E$_{\mathrm{n}} \quad =$ 2.5 to 100 MeV using PIN detectors, mass-yield curves using the 2E-method, and discussions of the symmetric fission contribution to TKE at high energies. [Preview Abstract] |
Sunday, November 1, 2020 12:06PM - 12:18PM |
SQ.00009: New Short-Lived Fission Product Yield Experiment at Oregon State University Aaron S. Tamashiro, C.J. Palmer, J.T. Harke, S. Burcher, S.W. Padgett A new experimental setup at the Oregon State University (OSU) TRIGA reaction is being designed, with the goal of measuring short-lived fission product yields and investigating discrepancies in fission product $\gamma$-ray branching ratios. ${}^{238}$U cumulative fast fission product yields were recently measured using Godiva-IV. The fission product yields were extracted by analyzing fission product $\gamma$-rays which rely on $\gamma$-ray branching ratios. This method relies on the accuracy of $\gamma$-ray branching ratios, some of which may not be reliable. Measurements at Godiva-IV are limited to begin $\sim$1 hour post-irradiation. The OSU rabbit system allows the rapid transport of samples from the core to the counting setup within 3 seconds. The new setup will consist of four Compton-suppressed HPGe clover detectors providing high efficiency for $\gamma$-ray detection, and the high segmentation of the array will increase the $\gamma$-$\gamma$ coincidence detection efficiency and enable the investigation of gamma-ray branching ratios. Results from a preliminary proof-of-principle measurement at the OSU TRIGA reactor will be presented along with the current status of preparations for the future campaign. [Preview Abstract] |
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