Mass-asymmetric fission of 205,207,209Bi at energies close to the fission barrier using proton bombardment of 204,206,208Pb

Swinton-Bland, B. A.; Stoyer, M. A.; Berriman, A. C.; Hinde, D. J.; Simenel, C.; Buete, J.; Tanaka, T.; Banerjee, K.; Bezzina, L. T.; Carter, I. P.; Cook, K. J.; Dasgupta, M.; Jeung, D. Y.; Sengupta, C.; Simpson, E. C.; Vo-Phuoc, K.

doi:10.1103/physrevc.102.054611

Title: Mass-asymmetric fission of ^205,207,209Bi at energies close to the fission barrier using proton bombardment of ^204,206,208Pb

Journal Article · Tue Nov 24 00:00:00 EST 2020 · Physical Review C

DOI:https://doi.org/10.1103/physrevc.102.054611· OSTI ID:1814102

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^[4]; Dasgupta, M. ^[1];

^[1]; Sengupta, C. ^[5];

^[1]; Vo-Phuoc, K. ^[1]

Australian National Univ., Canberra, ACT (Australia)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Australian National Univ., Canberra, ACT (Australia); Variable Energy Cyclotron Centre, Kolkata (India)
Australian National Univ., Canberra, ACT (Australia); Michigan State Univ., East Lansing, MI (United States)
Australian National Univ., Canberra, ACT (Australia); Univ. of Sydney, NSW (Australia)

Background: Recent observation of mass-asymmetric fission in neutron-deficient Hg and Pt nuclei has reignited interest in fission fragment mass distributions close to Pb. Investigations at energies close to the fission barrier, where mass-asymmetric fission is expected to be most obvious and the sensitivity to shell effects is maximized, are limited in this mass region. Purpose: To measure fission mass distributions for ^205,207,209Bi nuclei at the lowest possible excitation energies to determine how the mass distributions change with excitation energy and the neutron number of the compound nucleus. Method: Proton beams bombarding targets of ^204,206,208Pb were used to study the fission of ^205,207,209Bi at energies from just above to 10 MeV above their fission barriers. Fission fragments were measured using the CUBE fission spectrometer. Fission fragment mass distributions were determined using a newly developed time difference analysis method. Mass distributions were characterized by triple-Gaussian fits to determine the systematic trends across each isotope with excitation energy. Results: Measured mass distributions of all three Bi isotopes exhibit a component of mass-asymmetric fission at all energies studied. The probability of mass-asymmetric fission decreases significantly with increasing excitation energy, from ≈70 to ≈40% over a 10-MeV range. Comparisons between the three Bi isotopes hint at an increase in the mass-symmetric fission yield with increasing neutron number, which could be due to a decrease in the difference between the symmetric and asymmetric fission barriers. The centroids of the mass-asymmetric peaks suggest that several deformed shell gaps in the fission fragments could be contributing to the presence of the mass-asymmetric fission mode with Z_light ≃ 38, Z_heavy ≃ 45, and N_light ≃ 56 all present in the fission fragments. Conclusions: Measurements of fission mass distributions at the lowest possible excitation energies above the fission barrier provide an excellent platform to investigate the origins of the mass-asymmetric fission mode. Finally, further systematic measurements at these energies offer an opportunity to rigorously test new models of fission in this mass region.

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Research Organization:: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); Australian Research Council

Grant/Contract Number:: AC52-07NA27344; DP170102318; DP170102423; DP190100256; DP200100601

OSTI ID:: 1814102

Report Number(s):: LLNL-JRNL-814630; 1023163; TRN: US2213402

Journal Information:: Physical Review C, Vol. 102, Issue 5; ISSN 2469-9985

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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Title: Mass-asymmetric fission of ^205,207,209Bi at energies close to the fission barrier using proton bombardment of ^204,206,208Pb