Mass distribution in 36.2 MeV alpha induced fission of $$^{232}\hbox {Th}$$ 232 Th
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Regular Article - Experimental Physics
Mass distribution in 36.2 MeV alpha induced fission of 232 Th D. Banerjee1,a , T. N. Nag2 , R. Tripathi2 , S. K. Wasim Raja1, S. Sodaye2 , P. K. Pujari2 , A. Chakrabarti3 , M. Bhattacharjee3 , L. K. Doddi3 , V. Naik3 1
Radiochemistry Division (BARC), Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064, India Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India 3 Radioactive Ion Beam Group, Variable Energy Cyclotron Centre and HBNI-Kolkata, 1/AF, Bidhan Nagar, Kolkata 700064, India
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Received: 6 September 2019 / Accepted: 9 July 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Communicated by Jose Benlliure
Abstract Mass distribution of fission products has been determined in α+232 Th reaction at E lab = 36.2 MeV using α particles from the cyclotron at the Variable Energy Cyclotron Centre (VECC), Kolkata. Yields of 64 fission products having half-lives in the range of about ∼ 1 min to several days have been measured using gamma ray spectrometry. The mass distribution shows a clear triple humped structure indicating the contribution from both asymmetric and symmetric modes of fission. The experimental mass distribution was well reproduced by the calculation from the GEF code, which takes into account the multi-chance fission.
1 Introduction Historically, nuclear fission has been described using a macroscopic approach, where the potential energy of a liquid drop is traced as a function of deformation of the nucleus undergoing fission [1–3]. However, the observed asymmetric mass distribution in the fission of actinides, especially in thermal neutron induced fission of 235 U at low excitation energies, could only be explained by incorporating the shell effects in the macroscopic liquid drop approach [4]. The spherical shell corresponding to N = 82 and deformed shell corresponding to N = 88 appear to play a major role in the asymmetric split. The shell effect is expected to play a role only at low excitation energies and one would expect a gradual washing out of the shell effect with increasing excitation energy [5–7], resulting in a gradual shift from asymmetric to a completely symmetric split. The asymmetric peak to symmetric valley ratio, 600, for thermal neutron induced fission changes to 6 when neutron energy is increased to 14 MeV. More studies are required to understand the role of shell effects in governing the mass distribution with varia e-mail:
ation in excitation energy of the compound nucleus. The compound nucleus, 236 U, can be produced in n +235 U as well as in α +232 Th reaction. Due to the availability of αparticles of different energies from different types of accelerators, a number of studies on fission product mass distribution at higher excitation energies of the 236 U compound nucleus have been carried out by different groups using the α+232 Th reaction [8–12]. In two of the earlier studies involving α +232 Th reaction, the mass distributions were found to have three
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