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Study of spontaneous (Cf-252) and neutron-induced (U-235,8) non-binary fission using the fission time projection chamber
Haseman, Mark R.
Haseman, Mark R.
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2023
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In this study, measurements of non-binary fission of 252Cf (sf) and 235,8U (n,f) were performed using the fission time projection chamber (fissionTPC). The neutron source was provided by the Los Alamos Neutron Science Center with a neutron energy spectrum ranging from ∼ 100 keV to ∼ 300 MeV. The study was done to test the feasibility of the fissionTPC to characterize both fission fragments as well as high energy light charged particles (LCP). The fissionTPC was part of the Neutron Fission Fragment Tracking Experiment, which was designed for and employed in high-precision fission cross section measurements. The full characterization of non-binary LCPs was not possible due to design limitations with the detector; however, with the addition of tracking software developed for this study, we were able to extract and compare select non-binary fission data with previous experiments. One such result was the LCP emission angle with respect to the light fission fragment (LFF). The overall results were in good agreement with established values of 252Cf: Θ(LCP−LFF) = 85 ± 1 [deg]; 235U (at the lowest incident neutron energy bin): Θ(LCP−LFF) = 82 ± 1 [deg]; and 238U (at the lowest incident neutron energy bin): Θ(LCP−LFF) = 82 ± 1 [deg]. However, the non-binary fission LCP emission angle as a function of fission fragment mass ratio results did not match some previous experimental results and their theoretical models. For the first time, LCP emission angle data was studied to higher neutron energies. In addition, an attempt was made to extract the relative yield of non-binary fission to binary fission. Here, the non-binary fission yield ratio (efficiency-corrected; with with very confined opening angles) for the 252Cf source was 1:505; this low result is attributed to the poor quality of the 252Cf source. Our 235,8U target was of better quality and produced a relative non-binary fission yield (after adding efficiency corrections) that was in good agreement with previous experimental results at 0.6 and 14 MeV. Additionally, our results showed a nearly flat relative yield across the entire neutron energy range. We also, for the first time, observed dissipative emission of LCPs from 235U and 238U with increasing yield at incident neutron energies above 30 MeV. The study of non-binary fission events can aid us in peeling back the veil that shrouds the dynamics of unstable nuclei as they undergo fission. The results of this work show the promise and potential of using the fissionTPC to investigate non-binary fission, but also point towards improvements that would need to be made to the current design to get the best results.
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