Studies of Properties of Fission Fragments by Cyclic-Time Optimization Method.

The half-lives of some of the radioactive fission fragments from the spontaneous fission of Californium-252 have been determined from the study of the time variation of the K x-ray yields of these fragments. These half-lives have been used for the mass identification of the decaying fragments. The method of cyclic time optimization was used in conjunction with a beta-K x-ray coincidence technique to obtain the beta spectrum of decaying cerium isotopes. A Kurie plot of the beta spectrum revealed at least four beta groups. From the relative isotopic yields of K x -rays the mass origin of each group has been determined. The end point energies and mass origin of these groups were as follows: 2.349 ((+OR-) 0.100) MeV, ('145)Ce; 1.715 ((+OR -) 0.013) MeV, ('145)Ce and ('148)Ce; 1.267 ((+OR-) 0.103) MeV, ('145)Ce; 0.748 ((+OR-) 0.109) MeV, ('146)Ce.