Collective spectra along the fission barrier

T. M. Shneidman^1a, A. V. Andreev¹, M. T. Pigni², C. Massimi^3,4, G. Vannini^3,4 and A. Ventura^4,5

¹ Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia
² Nuclear Data Criticality Safety, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
³ Dipartimento di Fisica dell’ Università di Bologna, 40126 Bologna, Italy
⁴ INFN, Sezione di Bologna, 40126 Bologna, Italy
⁵ ENEA, Centro Ricerche Ezio Clementel, 40126 Bologna, Italy

^a e-mail: shneyd@theor.jinr.ru

Abstract

Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states) and in the intermediate wells (superdeformed and hyperdeformed states) play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster configurations in a dynamical way, permitting exchange of upper–shell nucleons between clusters. The impact of theoretical spectra on neutron–induced fission cross sections and, in combination with an improved version of the scission–point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.