Superasymmetric fission mode in 254Fm nucleus populated by 16O+238U reaction

Oct 15, 2020, 2:55 PM
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Oral report Section 2. Experimental and theoretical studies of nuclear reactions. Section 2. Experimental and theoretical studies of nuclear reactions

Speaker

Dr Tathagata Banerjee (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia)

Description

The search for super-asymmetric fission, has been receiving increasing interest due to its possible interest in producing exotic neutron rich nucleus [1]. Among the four main fission modes prescribed by Brosa [2], the supershort mode manifests itself only when light and heavy fission fragments are close to the double magic tin with A~132 in their nucleon composition. Though the possibility of the fission asymmetry of the pre-actinides had been predicted in 70’s [3], it took a decade to substantiate this prediction experimentally [4]. Recently, the superasymmetric mode due to the influence of double magic Ca (Z = 20, N = 28) and double magic Pb (Z = 82, N = 126) has been observed at a mass yield level of 10-3 and 10-5, in fission of excited 260No compound nucleus, populated by the reactions 12C+248Cm and 22Ne+238U, respectively [5, 6]. The fission mass distributions of the fermium isotopes showed a marked transition from asymmetric to symmetric as the mass number increases from 254 to 258 [7]. Additionally, Lustig et al. [8] predicted super-asymmetric fission modes in 253Fm(n,f) 254Fm(sf). So, further investigations at the lower excitation energies of Fm isotope and to discern super-asymmetric fission mode and its characteristics out of all other fission modes, was of paramount importance.

The mass-energy distributions of fission fragments of 254Fm compound nucleus formed in the reaction 16O+238U have been measured at two lab energies Elab = 89 and 101 MeV, using the two-arm time-of-flight spectrometer CORSET [9]. The contribution from quasifission is negligible in the reaction 16O+238U [10]. At the energy close to the Coulomb barrier (corresponding excitation energy ECN~ 45 MeV), where the shell effects still exist, the enhancement of the mass yield in the region 60-70 u for the light fragment is observed. This can be explained by the influence of double magic Ni (Z=28, N=50). The mass yield is found to be around 10-2 %. This signature of super-asymmetric fission goes away at the higher excitation energy (ECN~ 56 MeV).

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[9] E.M.Kozulin et al., Instrum. Exp. Tech. 51, 44 (2008).

Primary author

Dr Tathagata Banerjee (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia)

Co-authors

Dr Eduard Michailovich Kozulin (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Dr Kirill Borisovich Gikal (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Dr Iulia Mikhailovna Itkis (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Dr Galina Nikolaevna Knyazheva (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mrs Nina Ivanovna Kozulina (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mr Kirill Vladimirovich Novikov (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mr Ivan Nikolaevich Diatlov (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mr Ivan Valeryevitch Pchelintsev (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mr Andrey Pan (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia) Mr Igor Vladimirovich Vorobiev (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980 Russia)

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