New Results on the Ternary Fission of cm and cf Isotopes

Recently, the influence of the excitation energy of the fissioning nucleus on the ternary triton emission probability (noted t/B) has been investigated for ²⁴⁸Cm. This was done by comparing the (t/B)-data obtained from the ²⁴⁷Cm(n_th,f) reaction (where the excitation energy of the fissioning nucleus corresponds to the neutron binding energy) and from ²⁴⁸Cm(sf) decay (where the excitation energy is zero). This study has revealed a slight increase of t/B with the excitation energy indicating that tritons do not behave in the same way as ternary alpha particles. The aim of this paper is to study this effect on the ²⁴⁶Cm compound nucleus and on various Cf-isotopes.

For that purpose, the energy distributions and yields of the ternary triton and alpha particles emitted from ²⁴⁶Cm(sf) have been measured, using a double telescope consisting of a twin ionization chamber coupled to two surface barrier detectors. The corresponding ²⁴⁵Cm(n_th,f) data are available from a previous experiment. For the investigation of the Cf-isotopes, a ²⁵¹Cf-sample also containing ²⁴⁹Cf, ²⁵⁰Cf and ²⁵²Cf has been used. The measurement was performed at the high flux reactor of the Institute Laue Langevin in Grenoble (France), using a vacuum chamber with a single ΔE-E telescope, consisting of two suited surface barrier detectors. This measurement was performed respectively with the neutron beam closed and opened in order to investigate contributions from (sf)-decays as well as (n_th,f)-reactions.

For each fissioning nucleus studied, a comparison of the spontaneous and thermal neutron induced fission data confirms the previously observed behaviour for the ²⁴⁸Cm compound nucleus, namely: a decrease of the ternary alpha emission probability and an increase of the triton emission probability with the excitation energy of the compound nucleus.