Systematic Investigation on Momentum Distributions of Projectile-like Fragments at E/A = 290 MeV

Abstract

A systematic investigation on the longitudinal and transverse momentum (PL and PT) distributions of projectile-like fragments (PLFs) produced at intermediate energies has been performed experimentally. The momentum distributions of PLFs in a broad range of mass and charge, produced from 290 MeV/u Ar-and Kr-beams with various targets (C, Al, Nb, Tb and Au), were observed. The analysis of PL distributions with an asymmetric Gaussian function provides the deceleration e↵ect and the width of the distributions with good precision. A definite systematics is found in both the deceleration e↵ect and the width. The broader width obtained at the low-momentum side indicates the contribution of multi-step processes at this energy. The target and energy dependencies of the induced momentum width are also shown. The analysis of PT distributions with an o↵-centered Gaussian function provides not only the width, but also the orbital-deflection e↵ect. In principle, the width is independent on the target, and is consistently reproduced based on the previously proposed formulation. In contrast, the deflection e↵ect shows a strong target dependence. In the case of one-nucleon removed fragments, the main part of the deflection e↵ect can be understood by the Coulomb repulsion. The systematics of the momentum distributions, shown in the present studies, is important for evaluating the production cross sections of PLFs. Especially, the PT distribution is crucial to deduce production cross sections from the production rates of PLFs, which are observed at the forward angle within the limited angular acceptance.PACS numbers: 29.25.-t, 25.40.-h