Study of the radiative decay of 252Cf fission fragments

This work is focused on the study of the excitation energy repartition and the angular momentum of ²⁵²Cf  fission fragments in cold fission events, ie. without any neutron emission. In these rare events, studying the emitted photons can address these two open questions of the fission. The experimental setup is made of 54 NaI detectors in order to measure the emitted gammas with high efficiency. It is coupled to a Frisch-gridded twin ionization chamber allowing a mass resolution of 0.68 a.m.u. in cold fission.

Two cold fragmentations have been perfectly identifed: ¹²⁰Cd/¹³²Sn et ¹¹⁸Pd/¹³⁴Te. In the first one,  ¹³²Sn is observed in its ground state, allowing for the first measurement of the excitation energy distribution of a fission fragment (ie. ¹²⁰Cd). The reproduction of the associated prompt-γ spectrum was very sensitive to the initial spin distribution of ¹²⁰Cd, allowing its experimental determination for the first in cold fission. For the second studied fragmentation, (¹¹⁸Pd/¹³⁴Te) the excitation energy repartition was the most sensitive quantity in order to reproduce the prompt-γ spectrum. It was determined through a genetic algorithm.