Signature of bi-modal fission in Uranium nuclei.
We report here, for the first time, the signature of bi-modal fission, one asymmetric and the other symmetric, in all the Uranium nuclei in the mass range A = 230 to 235. The finding is unexpected and striking and is based on analysis of experimental mass distributions at various excitations in the induced fission of 232Th. It has been found that the observed mass distributions, especially the three peaked nature, can be explained in a consistent manner only if one assumes bi-modal fission at lower excitations for all the Uranium nuclei in the range A = 230 to 235, in addition to multi-chance fission. The analysis has also allowed a quantitative estimation of the percentages of the asymmetric and the symmetric component in the bi-modal fission. It is found that the bi-modal fission is predominantly asymmetric (about 90%), which contributes in a major way to the observed asymmetric peaks, while the 10% bi-modal symmetric fission is primarily responsible for the observed narrow symmetric peak in the mass distributions. The unusually narrow symmetry peak in the mass distributions indicates that the symmetric bi-modal fission must have proceeded from a configuration at the bi-modal symmetric saddle which is a highly deformed one with a well-developed neck..
Publisher URL: http://arxiv.org/abs/1810.09209