Behavior of nuclear projectile fragments produced in collisions of 14.5A GeV 28Si with Pb and Cu targets.

Abstract

Using CR-39 nuclear track detectors and an automated scanning system, we have studied the behavior of projectile fragments with charges 8\ensuremath{\le}${\mathit{Z}}_{\mathit{F}}$\ensuremath{\le}13 produced in interactions of 14.5A GeV $^{28}\mathrm{Si}$ nuclei with Pb and Cu targets. Both nuclear and electromagnetic spallation contribute to fragmentation of beam nuclei in Pb and Cu. The total charge-changing cross sections of nuclear projectile fragments with 9\ensuremath{\le}${\mathit{Z}}_{\mathit{F}}$\ensuremath{\le}13 interacting in Pb are found to be enhanced by 10 to 30 % relative to charge-changing cross sections of stable nuclides. The enhancement occurs primarily in interactions with large loss of charge. In Cu the charge-changing cross sections of secondaries show no significant excess. The mean free path of secondary fragments shows no dependence on the distance from the point of origin. This result rules out at 95% confidence level the production of nuclear fragments with interaction cross sections enhanced by a large factor as conjectured by some workers, but the result is consistent with a two-component model in which \ensuremath{\sim}30% of secondary beams are off-stability isotopes with total cross sections enhanced by \ensuremath{\sim}25%. Our measurements of angular distributions of projectile fragments showed that the transverse momentum distributions are similar to those measured at (1--2)A GeV. The charge pickup cross section of 14.5A GeV Si is measured to be 0.07--1.3 mb in Pb and \ensuremath{\le}0.9 mb in Cu, which is of the same order of magnitude as that measured at \ensuremath{\sim}1A GeV.