Study of a Fragmentation Reaction by Thin-Target Recoil Techniques; Production ofNa24from Bismuth by 2.9-GeV Protons

Abstract

The angular distribution of ${\mathrm{Na}}^{24}$ nuclei produced by bombardment of thin bismuth targets with 2.9-GeV protons has been measured. The forward-to-backward ratio in the laboratory system was found to be 1.52±0.06. Differential range curves for the ${\mathrm{Na}}^{24}$ nuclei have been obtained at angles of 15, 90, and 165°, with respect to the beam direction. The mean energy of emission at 90° is 47 MeV with a full width at half-maximum of 40 MeV. The mean is only 60% of the energy expected from Coulomb repulsion. Velocity spectra at 15 and 165° are nearly identical to the 90° spectrum linearly shifted by ≈ 10% to higher and lower velocities, respectively. From the analysis of the angular distribution and the range data, we conclude that there is no moving system in which both the angular distribution and velocity spectra of the ${\mathrm{Na}}^{24}$ nuclei are symmetric about the direction perpendicular to the beam. This indicates that this typical fragmentation product is produced by a direct (rapid) process and not by the usual fast nucleonic cascade followed by a slower de-excitation step.