Dispersion of longitudinal momentum distributions induced in fragmentation reactions

Abstract

On the basis of systematic measurements of fragmentation reactions, which provide a detailed overview on the velocity distributions of residual nuclei, an improved description of the kinematical properties of the fragmentation residues is established. This work is dedicated to the fluctuations of their momentum distributions. In contrast to previous investigations, limited to close-to-projectile fragments, we extended our study to the entire production range, down to the lightest observed fragments. In this context, beside the contribution of abrasion and evaporation processes, we considered the effect of the thermal break-up on the width of the momentum distributions. Using approximated theoretical descriptions of the different reaction stages, a new analytical formula for the variance of the momentum distribution is derived, which is well adapted to technical applications.

Evaluation of nuclear reaction cross-sections and fragment yields in carbon beams using the SHIELD-HIT Monte Carlo code. Comparison with experiments

“…In Goldhaber's model the Fermi motion is considered to be the major contribution to the fragment momentum distribution (Bacquias et al, 2012). (Morrissey, 1989) derives a similar scaling formula from experimental data and valid in the approximation of small mass losses: i…”

“…� is a constant which should be fitted from experimental data, values of the constant are reported, for example, by (Meierbachtol et al, 2012). Alternative semi-empirical or fully theoretical models are also described in the literature in order to determine the dispersion of the longitudinal momentum distribution (Tarasov, 2004;Bacquias et al, 2012). Tarasov and co-workers introduce a "universal parameterization" model where a semi-empirical formula is used to calculate the momentum distribution of the fragments.…”

“…Bacquias and co-workers describe a model fully based on theoretical considerations, which takes into account the different fragmentation reaction processes. They define a mass limit for multifragmentation and derive different equations according to the fragment mass with respect to mass limit value (Bacquias et al, 2012). When fragments having a mass close to the projectile are produced the multifragmentation do not occur and the total momentum dispersion is the sum in quadrature of the Fermi motion contribution and the recoil induced by evaporation (Bacquias et al, 2012).…”