Mass-asymmetric fission in the40ca+142Nd reaction

E Prasad ,K Ramachandran,D C Rafferty,D Y Jeung,C S Palshetkar,E Williams,J Khuyagbaatar,David Hinde ,Ch E Düllmann ,M Dasgupta ,K J Cook ,I P Carter ,B Lommel ,C Simenel ,Steven Mcneil ,D H Luong ,A Wakhle ,B Kindler

doi:10.1051/epjconf/201612303006

Abstract

Shell effects play a major role in fission. Mass-asymmetric fission observed in the spontaneous and low energy fission of actinide nuclei was explained by incorporating the fragment shell properties in liquid drop model. Asymmetric fission has also been observed in the low energy fission of neutron-deficient 180 Hg nuclei in recent β -delayed fission experiments. This low-energy β -delayed fission has been explained in terms of strong shell effects in pre-scission configurations associated with the system after capture. Calculations predicted asymmetric fission for heavier Hg isotopes as well, at compound nuclear excitation energy as high as 40 MeV. To explore the evolution of fission fragment mass distribution as a function of neutron and proton numbers and also with excitation energy, fission fragment mass distributions have been measured for the 40 Ca+ 142 Nd reaction forming the compound nucleus 182 Hg at energies around the capture barrier, using the Heavy Ion Accelerator Facility and CUBE spectrometer at the Australian National University. Mass-asymmetric fission is observed in this reaction at an excitation energy of 33.6 MeV. The results are consistent with the β -delayed fission measurements and indicate the presence of shell effects even at higher exciation energies.

Highlights

Nuclear fission is a dynamic process involving large scale collective motion, often affected by a subtle interplay of macroscopic and microscopic effects during the transition of the fissioning nucleus from its ground state deformation to the scission point
The experimental observations were explained by incorporating the fragment shell properties near the scission configuration, the spherical shell closure (Z = 50, N = 82) or deformed neutron shells (N = 88) [1, 3], within the liquid drop model (LDM) frame work
The fission fragment mass ratio (MR) distribution shows an asymmetric mass division with peaks centered around MR values 0.45 and 0.55 at E∗=33.6 MeV

Summary

Introduction

Nuclear fission is a dynamic process involving large scale collective motion, often affected by a subtle interplay of macroscopic and microscopic effects during the transition of the fissioning nucleus from its ground state deformation to the scission point. Fragment mass distributions are an important observable in fission which provides crucial information about the potential-energy landscape of the fissioning system. Fragment mass distributions have been observed to be predominantly asymmetric in the spontaneous or low energy fission of most of the actinide nuclei [1], which could not be explained solely by using the liquid drop model (LDM) [2]. The low yield of symmetric fission in 180Hg populating 90Zr (Z = 40, N = 50) led to the speculation that fragment shell effects, though significant in the potential energy surface near scission, must not play a major role in determining the mass split in this nucleus

Results

Discussion

Conclusion