Speaker
Description
Pawan Singh 1,2, Y. K. Gupta 1,2, G. K. Prajapati 1,2, N. Sirswal 1,2, B. N. Joshi 1,2, Harshad Vyas 1,2, K. Ramachandran 1, and V. V. Desai 3
1 Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
2 Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
3 SIES College of Arts, Science and Commerce, Sion, Mumbai - 400022, India
Since the discovery of nuclear fission by Hahn and Strassmann in 1939, it has remained a subject of sus-tained research interest. Nuclear fission is a fascinating example of large-scale rearrangement of strongly interacting nucleons within a finite many-body system. Despite decades of extensive experimental and theoretical efforts, several aspects of the fission process are still not fully understood. In this context, the emission of light charged particles serves as an potential probe to get fine details about the subtle aspects of the process. It offers valuable insight into the interplay between nuclear structure, dissipation, and collective motion.
α-particle multiplicities specta were measured for the reactions 12C+209 Bi at a beam energy of 75 MeV
and 19F +209 Bi at 99 MeV, leading to the formation of the compound nuclei 221Ac∗ and 228U∗, respec-tively. The experiments were carried out at the BARC-TIFR Pelletron/LINAC facility, Mumbai, using a dedicated detector setup optimized for the detection of light charged particles in coincidence with fis-sion fragments. After correcting for random coincidences, the normalized α-particle multiplicity spectra
were obtained by dividing the coincidence energy spectra by the total number of fission single events.
The Moving Source Disentangling Analysis (MSDA) was then employed to calculate the contributions from different emission stages, namely pre-scission, near-scission, and post-scission emissions.
A pronounced difference is observed in the pre-scission α-particle multiplicities for the two systems.
The multiplicity associated with the 221Ac∗ compound nucleus is nearly an order of magnitude lower than that observed for the 228U∗ compound nucleus, despite the excitation energies being comparable
(37.4 MeV for 221Ac∗ and 40.2 MeV for 228U∗). This substantial reduction in α-particle multiplicity cannot be explained solely by the modest difference in excitation energy.
To quantitatively understand this behavior, statistical model calculations were performed using the JOANNE2 code. The model incorporates deformation-dependent particle binding energies and trans-
mission coefficients and treats the fission process in two distinct stages: from the compound nucleus
to the saddle point and from the saddle point to scission. The calculated α-particle multiplicities are in good agreement with the experimentally extracted values. Thus, a supression of pre-scission alpha particle multiplicity in the pre-actinide region at a similar excitation energy of around 40 MeV is es-tablished from experimental and theoretical investigations.
Detailed results will be presented during the workshop.
| Type of contribution | Regular Abstract |
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