The delayed proton emission in the A ~ 65-77 mass region, statistical aspects and structure effects ISOLDE Collaboration

The alfa-particle energy spectra have been measured at different laboratory angles from the fusion reaction 12C + 45Sc at 83 and 97 MeV incident energies. These spectra are consistent with the predictions of the statistical model calculations using the Rotating Liquid Drop Model (RLDM) values of the moment of inertia and the optical model transmission coefficients for the respective inverse absorption channels. The results of 12C + 45Sc asymmetric system were compared with the 28Si + 27Al symmetric system at 140 MeV studied earlier as both the systems lead to the formation of nearly same compound nucleus (Z = 27) with the same angular momentum and the excitation energy. The comparison was made in order to understand the symmetric and the asymmetric entrance channel effects in the formation and the decay of the compound system. In the case of 28Si + 27Al symmetric system, the experimental spectra deviate at higher as well as at lower energies from the statistical model calculations. Alterations were required in the moment of inertia as well as in the calculation of the transmission coefficients to explain the experimental data. However, in the case of 12C + 45Sc asymmetric system there was no need for such changes and the experimental spectra can be well explained by the statistical model calculation using RLDM values of moment of inertia and the optical model transmission coefficients. The dynamical trajectory model calculations are done to explain the experimental data. The comparison of the decay times with the formation times implies that the light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus in the case of 28Si + 27Al symmetric system. The results of the present study suggest an entrance channel dependence in the formation and the decay of the compound nucleus.