Lifetime and Fission-probability Estimates

Abstract

Fission lifetime distributions and fission cross sections are investigated using an analytic approximation to the level density containing shell effects and including collective rotational states. The observed particle induced fission probabilities are reasonably well reproduced. The compound nucleus fission is investigated for the reactions oxygen on gold and tungsten. The fission probability and lifetime distribution are estimated and compared with available experimental data. Fission probabilities are sensitive to model parameters, e.g., extrapolated barrier heights. For each energy, the theoretical uncertainty limits include the observed values but the calculated energy dependence is too fast compared to observations. It is found that higher-order fission dominates. The lifetime distribution is fairly insensitive to the model parameters with short lifetimes of less than 10-17 s being dominant. However, in agreement with experiments, a significant contribution from lifetimes longer than 10-17 s is found. The size of the long components is consistent with the lifetime experiments for oxygen on gold and too small for oxygen on natural tungsten.