SUPER-ASYMMETRIC COLD FISSION AND EXOTIC CLUSTER-DECAY

Cold fission of radioactive nuclei is studied in the super-asymmetric mass region of exotic cluster radioactivity, using the quantum-mechanical fragmentation theory (QMFT) based saddle-point fission (SPF) model for calculating the decay half-life times. The calculations show that cold fission also prefers light fragments like ^24–26Ne, ^28,30Mg, ^32,34,36Si, ³⁷P ³⁸S, ⁴⁶Ar and ^48,50Ca, some of which are observed in exotic cluster radioactivity. The predictions of the SPF model calculations are compared with the available exotic cluster-decay experimental data and the calculations based on the preformed-cluster model (PCM). The SPF model calculations show large disagreements with both the PCM and cluster-decay experimental data. For clusters of mass A₂<46, the predicted half-lives for the SPF model are much smaller than for the PCM, which apparently means predicting the cold fission as a more probable process than the cluster-decay. The cold fission predicts some new decay modes which are far more probable (smaller log₁₀ T_1/2-values) as cold fission fragments than as cluster-decay products. For heavier clusters (A₂≥46), the two models (SPF and PCM) make nearly identical predictions, which means predicting an overlap of two processes (cold fission and cluster-decay) for A₂>46. Also, cold fission is found to be more probable than hot fission and a new fission mode (known as bimodel fission) is identified in the neighbourhood of the doubly magic fragment. Our calculations are made for ²³⁴U, ²³⁸Pu, ²⁴¹Am and ²⁵²Cf.