Inadequacy of the statistical model: some evidence for compound nuclei in the A ~ 150 and Ex ~ 100-200 MeV region

Light charged-particle multiplicities in the evaporation residue (ER) and fission (FF) channels from the reaction 200 MeV 32S+100Mo as well as ER and FF channel cross sections have been measured and compared to the predictions of the statistical model(SM) to estimate the fission time scale. The statistical model fails in reproducing the whole set of data and no convincing estimate is possible. In particular, while pre-scission multiplicities can be reproduced, the model strongly overestimates proton and alpha particle multiplicities in the ER channel, irrespective of the SM input parameters and prescriptions used for the level density and the transmission coefficients. Same calculations performed on data from literature in the A≈150 and excitation energy Ex≈100–200 MeV region, for the ER channel, provide similar conclusions. These findings repropose the problem of the reliability of the SM in describing the compound-nucleus decay and have a relevant impact on the extraction of the fission delay time through the use of the SM.