Study of fission using multi-nucleon transfer reactions

Katsuhisa Nishio,Tsutomu Ohtsuki,Kentaro Hirose,Atsushi Toyoshima,Yuichiro Nagame,Masato Asai,Igor Tsekhanovich,Mark Vermeulen,Tetsuya K Sato,Riccardo Orlandi,Hiroyuki Makii,Andrei Andreyev,Shouya Tanaka,Kazuaki Tsukada,Yoshihiro Aritomo,Satoshi Chiba,Costel M Petrache

doi:10.1051/epjconf/201816900013

Abstract

Multi-nucleon transfer channels of the reactions of 18O+232Th, 18O+238U, 18O+248Cm were used to measure fission-fragment mass distribution for various nuclides and their excitation energy dependence. Predominantly asymmetric fission is observed at low excitation energies for all the studied cases, with an increase of the symmetric fission towards high excitation energies. Experimental data are compared with predictions of the fluctuation-dissipation model, where effects of multi-chance fission (neutron evaporation prior to fission) was introduced. It was shown that a reliable understanding of the observed fission fragment mass distributions can be obtained only invoking multi-chance fissions.

Highlights

Nuclear fission is usually described as an evolution of a nuclear shape on a potential-energy surface which results from the subtle interplay of macroscopic nuclear properties and microscopic shell effects
At the tandem accelerator facility of the Japan Atomic Energy Agency (JAEA), we studied the Multi-nucleon transfer (MNT) channels of the reactions 18O + 232Th,238U,248Cm in normal kinematics to obtain Fission-fragment mass distribution (FFMD) and their excitation-energy dependence for various isotopes
For the event-by-event identification of the transfer channel and of respective coincident fission fragments (FFs), a detection system consisting of a ∆E - E silicon detector telescope and four multiwire proportional chambers (MWPC) were used, see Fig. 1

Summary

Introduction

Nuclear fission is usually described as an evolution of a nuclear shape on a potential-energy surface which results from the subtle interplay of macroscopic nuclear properties and microscopic shell effects. New experimental techniques and associated new data are indispensable to further understand fission mechanism. Fission-fragment mass distribution (FFMD) is one of the most fundamental data, which exhibits asymmetric shape at low excitation energy due to shell structures. Neutron- and charged particle capture reactions as well as spontaneous fission have been used to study low-energy fissions. Β/EC delayed fission was investigated for the very proton-rich nucleus using radioactive beams, and 180Hg was found to show an asymmetric fission as a new region of mass-asymmetric fission [3]. Advancement of new technique for fission studies is reviewed in [4]

Methods

Results

Conclusion