Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session RN: Nuclear Reactions: Heavy-Ions / Rare Isotope Beams |
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Chair: Dariusz Seweryniak, Argonne National Laboratory Room: Salon K |
Thursday, October 17, 2019 8:30AM - 8:42AM |
RN.00001: Fission Product Chain Yield Measurements at NCERC T.A Bredeweg, E.M. Bond, D.E. Dry, M.E.Gooden Bond, S.K. Hanson, L.A. Hudston, M.R. James, I. May, W.J. Oldham, R.S. Rundberg Fission product chain yields were historically determined by chemical separation and beta counting of fissile samples irradiated in carefully controlled fission chamber experiments$^{1,2}$. These measurements provided the means to extract absolute fission product yields (yield per fission, or $Y_i/f$ for the $i^{th}$ fission product) that are included in the international nuclear data libraries, and ultimately used to model and characterize multiplying systems. However, re-evaluations conducted at Los Alamos National Lab and Lawrence Livermore National Lab in 2005-2009 for neutron-induced fission of $^{235}$U and $^{239}$Pu highlighted disagreement among many of the measurements$^{1,2,3}$. This led to several new, targeted experimental programs to resolve these disagreements. In this presentation we will highlight recent efforts to address these discrepancies using energy-integral measurements at the National Criticality Experiments Research Center (NCERC), and outline our plans to complete the work over the next several years. \\[0.25cm] \noindent $^1$ H.D. Selby, \textit{et al.}, Nucl. Data Sheets 111, 2891 (2010) \\ $^2$ M.B. Chadwick, \textit{et al.}, Nucl. Data Sheets 111, 2923 (2010) \\ $^3$ J. Laurec, \textit{et al.}, Nucl. Data Sheets 111, 2965 (2010) [Preview Abstract] |
Thursday, October 17, 2019 8:42AM - 8:54AM |
RN.00002: Investigating Nuclear Statistical Properties for Indirect Radiative Capture Cross Section Measurements C.S. Reingold, A. Simon, N. Cooper, R.O. Hughes, J.T. Burke, S.P. Burcher, K.A. Chipps, S. Ahn, D.T. Blankstein, J.A. Cizewski, M. Hall, S. Ota, A. Saastamoinen, K. Schmidt, B. Schroeder, S. Upadhyayula Radiative capture reactions between neutrons and lanthanides are of particular importance to nuclear applications, stellar nucleosynthesis, and stockpile stewardship. Experimental constraints, however, can make direct measurements of these cross sections nontrivial. Therefore, it is essential to have a reliable method for predicting $(n,\gamma)$ cross sections. One alternative to direct measurement over the relevant mass and energy regions is to calculate the relevant cross section in Hauser-Feshbach formalism, using experimentally constrained nuclear statistical properties. These statistical properties can be extracted from particle-$\gamma$ coincidence data via the Oslo method. Indirect measurements for $^{145,146}$Sm$(n,\gamma)$ and $^{159,160}$Dy$(n,\gamma)$ have been conducted using the Hyperion detector array at Texas A\&M University. Particle-$\gamma$ coincidence data for $(p,d)$ and $(p,t)$ reactions on self-supporting $^{148}$Sm and $^{162}$Dy targets have been analyzed. Preliminary results will be presented. [Preview Abstract] |
Thursday, October 17, 2019 8:54AM - 9:06AM |
RN.00003: Studies of the angular correlations between complementary fragments in multinucleon transfer reactions Xe-136 $+$ Pt-198 Shaofei Zhu A deep understanding of multi-nucleon transfer reactions is important for the future development in producing the neutron-rich nuclei of interests. The angular correlations of the complementary fragments produced in the reaction of a $^{\mathrm{136}}$Xe beam (8MeV/A) on a $^{\mathrm{198}}$Pt target (1mg/cm2) were measured using the CHICOII detector at ATLAS. The results were simulated by using the quantum molecular dynamics (QMD) model. Different Skyrme interaction parameters were applied. It is found that the effect of reaction Q values almost governs the production of primary fragments with about six or less nucleons being transferred. With the increase of the number of transferred nucleons, the dynamical processes, such as the dissipation of collective motion and the statistical fluctuation of multinucleon transfer, play more important role in the mass distributions. Further detailed study will focus on the mass and isotopic yields with respect to different angles between the target-like and projectile-like fragments. It will provide another direction to improve the model and explore the mechanisms of this type of reactions. [Preview Abstract] |
Thursday, October 17, 2019 9:06AM - 9:18AM |
RN.00004: Energy Dependence of Fission Product Yields from $^{\mathrm{235}}$U, $^{\mathrm{238}}$U and $^{\mathrm{239}}$Pu for Incident Neutron Energies Between 0.5 and 14.8 MeV Matthew Gooden, Todd Bredeweg, David Vieira, Jerry Wilhelmy, Werner Tornow, Jack Silano, Mark Stoyer, Anton Tonchev, Sean Finch, FNU Krishichayan 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) have been measured using quasi-monoenergetic neutron beams for three actinide targets, $^{\mathrm{235}}$U, $^{\mathrm{238}}$U and $^{\mathrm{239}}$Pu, between 0.5 and 14.8 MeV. The FPYs were measured by a combination of fission counting using specially designed dual-fission chambers and $\gamma $-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. [Preview Abstract] |
Thursday, October 17, 2019 9:18AM - 9:30AM |
RN.00005: Observation of dynamics in fusion of neutron-rich oxygen nuclei at above-barrier energies Sylvie Hudan, Romualdo de Souza The recent observation of heavy element nucleosynthesis in the merging of two neutron stars, underscores the importance of better understanding the fusion of neutron-rich nuclei. While the fusion of stable nuclei has been well studied for several decades, only recently have radioactive beam facilities made it possible to systematically investigate fusion for an isotopic chain of nuclei. Investigating the fusion of neutron-rich nuclei with an extended neutron density distribution can reveal whether fusion dynamics for neutron-rich nuclei differs significantly from that of beta stable nuclei. It also allows one to explore the influence of pairing at low density. To address this question the fusion excitation functions for $^{\mathrm{16,17,18}}$O $+ \quad^{\mathrm{12}}$C will be compared to that of $^{\mathrm{19}}$O $+ \quad^{\mathrm{12}}$C. The experimental results will be compared to both simple barrier penetration models as well as the predictions of a density constrained time-dependent Hartree-Fock model (DC-TDHF). [Preview Abstract] |
Thursday, October 17, 2019 9:30AM - 9:42AM |
RN.00006: Measurement of the fusion excitation functions for $^{\mathrm{41,45}}$K $+$ $^{\mathrm{28}}$Si and $^{\mathrm{36,44}}$Ar $+ \quad^{\mathrm{28}}$Si at near-barrier energies James Johnstone, Rekam Giri, Sylvie Hudan, Romualdo deSouza, Dieter Ackermann, Abdou Chbihi, Quentin Hourdille, Austin Abbott, Catherine Balhoff, Andy Hannaman, Alan McIntosh, Maxwell Sorensen, Zachary Tobin, Aditya Wakhle, Sherry Yennello Fusion in neutron-rich environments is presently a topic of considerable interest. Experiments for an isotopic chain allow systematic exploration of the dependence of fusion on neutron number. Recent measurement of the near-barrier fusion excitation functions for $^{\mathrm{39,47}}$K $+$ $^{\mathrm{28}}$Si revealed a 7-fold enhancement in the cross-section for the radioactive isotope relative to the stable isotope. To expand the study of this system away from the closed N$=$20 and N$=$28 shells and to explore the role of proton pairing, Experiment 17002 was conducted at NSCL's ReA3 facility with low-intensity (approximately 10$^{\mathrm{4}}$ ions/s) beams. The experiment measured the fusion cross section for $^{\mathrm{41,45}}$K $+ \quad^{\mathrm{28}}$Si and $^{\mathrm{36,44}}$Ar $+ \quad^{\mathrm{28}}$Si for E/A $=$ 2-3 MeV by detecting and identifying fusion products using E-TOF with high efficiency. Details of the experimental setup as well as the measured experimental fusion excitation functions will be presented. Cross-sections will be compared to the previous $^{\mathrm{39,47}}$K $+$ $^{\mathrm{28}}$Si measurements as well as to coupled channels calculations. [Preview Abstract] |
Thursday, October 17, 2019 9:42AM - 9:54AM |
RN.00007: Experimental Constraints from Heavy-ion Collisions on the Momentum dependence of the Symmetry Potential Kyle Brown Nucleons in dense nuclear matter appear to have reduced inertial masses due to momentum-dependent interactions they experience with other nucleons. This reduction of their masses is often referred to as their effective mass, and at saturation density the masses are reduced to about 70{\%} of their vacuum mass. In asymmetric matter the effective masses of neutrons and protons can be different, leading to an effective mass splitting. The sign and magnitude of this splitting is poorly constrained at densities away from saturation density. Recent experiments at the National Superconducting Cyclotron were performed to help constrain these momentum dependent interactions. By measuring the kinetic energy spectra of neutrons and protons, or analogously using ``pseudo neutrons'' from measured tritons and helium-3, the sign and magnitude of this effective-mass splitting can be extracted, with the help of transport models. Collisions of beams of $^{\mathrm{40,48}}$Ca at 50 and 140 MeV/A impinged on targets of $^{\mathrm{58,64}}$Ni and $^{\mathrm{112,124}}$Sn. Light charged particles up to boron were detected in the upgraded High-Resolution Array and neutrons were detected in the Large-Area Neuron Array. I will present details about the experiment setup and then discuss some first results on the spectral ratios with comparisons to transport model calculations. This research is supported by the National Science Foundation under Grant No. PHY-1565546 and the Department of Energy under Grant No. DE-NA0002923. [Preview Abstract] |
Thursday, October 17, 2019 9:54AM - 10:06AM |
RN.00008: Stability of spectrum unfolding in extraction of neutron spectra for rare isotope beam physics Michael Febbraro, Steven Pain, Rebecca Toomey, Frederick Becchetti, Thomas Massey, Zach Meisel, Richard deBoer, Carl Brune As the FRIB era approaches, it is important that the tools and techniques are in place to maximize scientific capabilities of such facilities. Neutron spectroscopy for transfer reaction physics is one important area which tools and techniques are needed. Traditionally, neutron time-of-flight (ToF) detectors have been used for extraction of neutron energy spectra. While this is a proven technique, the method often suffers from poor energy resolution for short flight paths. This can be improved by increasing the flight path, but at a cost to detection efficiency. An alternative method - based on a combination of short-path ToF and spectrum unfolding - maximizes detection efficiency without sacrificing energy resolution. The stability of the approach for low-statistics data has been investigated using neutron beams from the Edwards Accelerator Laboratory at Ohio University. Application of the technique for the measurement of single nucleon transfer reactions important for nuclear astrophysics will be discussed. [Preview Abstract] |
Thursday, October 17, 2019 10:06AM - 10:18AM |
RN.00009: Confirmation of High Neutron Yields for Ba-Mo from SF of $^{252}$Cf Brooks Musangu, A. H. Thibeault, T. H. Richards, E. H. Wang, J. H. Hamilton, C. J. Zachary, J. M. Eldridge, A. V. Ramayya, J. O. Rasmussen, Y. X. Luo, G. M. Ter-Akopian, Yu. Ts. Oganessian, S. J. Zhu A careful analysis of the yield matrix of coincident pairs of barium (Z = 56) and molybdenum (Z = 42) fission fragments has been made in the present study. The neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd and Nd-Sr have been studied with improved precision by using $\gamma$-$\gamma$-$\gamma$-$\gamma$ as well $\gamma$-$\gamma$-$\gamma$ coincidence data and the latest level scheme structures of these nuclei. The results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8, 9, and 10 neutron evaporation channels are observed. These higher neutron evaporation channels are not observed in other fission pairs. The second mode has an intensity of $\sim$1.3$\%$. This mode can indicate that $^{144}$Ba is likely hyperdeformed at scission to give rise to such high neutron multiplicities. A new experiment is being planned to do fission fragment-$\gamma$-$\gamma$ coincidence studies to investigate details of the fission process and to study new more neutron-rich nuclei. [Preview Abstract] |
Thursday, October 17, 2019 10:18AM - 10:30AM |
RN.00010: Measurements of short-lived fission product yields using a rapid transit system Sean Finch, Calvin Howell, Werner Tornow, Jack Silano, Mark Stoyer, Anton Tonchev, Matthew Gooden, Jerry Wilhelmy A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields from $^{\mathrm{235}}$U, $^{\mathrm{238}}$U, and $^{\mathrm{239}}$Pu. Our goal is to study the energy evolution of fission products by using mono-energetic neutrons from 0.5 to 14.8 MeV. In order to extend our successful fission product yield measurements to include products with shorter half-lifes, a RApid Belt-driven Irradiated Target Transfer System, named RABITTS, was constructed. This system allows us to perform cyclic activation and quantify fission products with $\gamma $-ray spectroscopy using HPGe detectors. Both a 1 meter and 10 meter transfer system have been developed, with transit times of 0.4 and 1.0 seconds, respectively. Using these systems, we have measured sub-second half-lifes. In addition to neutron-induced fission, we have used the 1 meter RABITTS to measure fission product yields from photofission. A detailed characterization of the system's performance will be shown, including preliminary fission product measurements, and the expected sensitivity. [Preview Abstract] |
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