Mass-asymmetric fission of Bi205,207,209 at energies close to the fission barrier using proton bombardment of Pb204,206,208
| Autor: | Edward Simpson, J. Buete, Cedric Simenel, B. M. A. Swinton-Bland, Chandrima Sengupta, T. Tanaka, David Hinde, K. Banerjee, Kaitlin Cook, Mahananda Dasgupta, L. T. Bezzina, K. Vo-Phuoc, Ian Carter, D. Y. Jeung, Annette Berriman, M. A. Stoyer |
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| Rok vydání: | 2020 |
| Předmět: |
Physics
Range (particle radiation) Proton Isotope 010308 nuclear & particles physics Fission Nuclear Theory Fission product yield 01 natural sciences Neutron number 0103 physical sciences Physics::Atomic and Molecular Clusters Atomic physics Nuclear Experiment 010306 general physics Energy (signal processing) Excitation |
| Zdroj: | Physical Review C. 102 |
| ISSN: | 2469-9993 2469-9985 |
| Popis: | 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 $^{205,207,209}\mathrm{Bi}$ 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 $^{204,206,208}\mathrm{Pb}$ were used to study the fission of $^{205,207,209}\mathrm{Bi}$ 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 $\ensuremath{\approx}70$ to $\ensuremath{\approx}40%$ 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 ${Z}_{\mathrm{light}}\ensuremath{\simeq}38$, ${Z}_{\mathrm{heavy}}\ensuremath{\simeq}45$, and ${N}_{\mathrm{light}}\ensuremath{\simeq}56$ 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. Further systematic measurements at these energies offer an opportunity to rigorously test new models of fission in this mass region. |
| Databáze: | OpenAIRE |
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