0 degrees measurements of momentum distributions of projectile-like fragments.

Abstract

The results of momentum distribution measurements at 0\ifmmode^\circ\else\textdegree\fi{} for projectile-like fragments produced by several intermediate-energy beams and separated using the A1200 beam-analysis device are described. The most detailed measurements were performed for neutron-rich fragments from the reaction of $^{18}\mathrm{O}$ (E/A=80 MeV) projectiles with $^{27}\mathrm{Al}$ and $^{181}\mathrm{Ta}$ targets. The analysis of the centroids and widths of the parallel momentum distributions of the fragments indicated that no ``pure'' fragmentation occurs, but rather, along with fragmentation, direct stripping and/or pickup channels contribute significantly to the production mechanism, especially for fragments close in mass to the projectile. Apart from nucleon-removal products, nuclei with a net number of nucleons picked up from the target were observed with momentum distributions peaked at velocities considerably lower than that of the beam. These distributions are consistent with momentum conservation and the previously established feature of lower energy transfer reactions that the excitation energy is preferentially given to the nucleon acceptor.