Study of fission using multi-nucleon transfer reactions

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

doi:10.1051/epjconf/201716300041

Abstract

It is shown that multi-nucleon transfer reaction is a powerful tool to study fission of exotic neutronrich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multi-nucleon transfer channels of the reactions of 18O+232Th, 18O+238U, 18O+248Cm, and 18O+237Np were used to measure fission-fragment mass distribution for each transfer channel. 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 is shown that mass-asymmetric structure remaining at high excitation energies originates from low-excited and less neutronrich excited nuclei due to higher-order chance fissions.

Highlights

Fission process 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,237Np in normal kinematics to obtain Fission-fragment mass distributions (FFMDs) and their excitation-energy dependence for various isotopes
fission fragments (FFs) masses were determined event-by-event from the kinematic analysis, where the measured ∆T values and incident positions of both FFs were used

Summary

Introduction

Fission process 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. Neutron- and charged particle capture reactions have been used to populate lowexcited compound nuclei (CN) for fission studies [1, 2]. Around 2000, GSI in Darmstadt developed a Coulex-induced fission of relativistic RIBs in inverse kinematics, where comprehensive fission studies were performed for several tens of nuclei in the neutron-deficient Ac-U region [3]. The recent SOFIA experiment at GSI followed the same approach but with a much improved technique [4, 5]. 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 massasymmetric fission [6]

Methods

Results

Conclusion