Clustering pre-equilibrium model analysis for nucleon-induced alpha-particle spectra up to 200 MeV

The clustering exciton model of Iwamoto and Harada is applied to the analysis of pre-equilibrium alpha-particle energy spectra. The model describes the pickup process within the exciton model framework, where the alpha-particle formation factor is calculated by the overlap of wave functions between the alpha-particle and four excitons. In the present work, The formation factor is calculated exactly, while the original Iwamoto-Harada model employed a root-mean-square approximation where no correlation exists between the coordinates in the phase-space. The model is incorporated into the GNASH code to obtain the alpha-particle energy spectra that are consistent with the (N, xα) cross sections. The exciton model parameters are independently obtained to reproduce experimental (N, xN) pre-equilibrium spectra, while the pickup radius ΔR is determined to describe measured (N, xα) spectra. According to this analysis, the model gives a global description of experimental spectra with a simple parameterization up to 150 MeV, although it tends to underestimate the measured data at higher energies. In this talk, we show the difference between the exact and the approximation calculations. The calculated spectra are presented for the nucleon incident energies up to 200 MeV, and behavior of the major parameters are investigated. (author)