Peripheral collisions of 2 GeV/nucleon Fe nuclei in nuclear emulsion. I. Light projectile fragments

Observations on 374 collisions of 1.88-GeV/nucleon Fe nuclei in Ilford G-5 nuclear track emulsion, in which at least one projectle fragment of Z > = 3 was emitted within a 60 cone, revealed several features of projectile breakup. The onset of copious multiple fragmentation was observed. The relatively high α-particle multiplicities allowed for the first time a study of the α multiplicity distribution; a Poisson distribution gave an excellent fit. The data showed a significant enhancement of α-particle pairs with very small relative momenta. The transverse momentum distributions, which should reflect best the thermal motion in the projectile system, are in flagrant discrepancy with theoretical predictions; the distributions show a marked target dependence. The charges of all projectile fragments up to B were determined by measurement of gap-length distributions. Events with N/sub h/ = 0 are a class apart from the rest of the events; between N/sub h/ = 1 and N/sub h/ = 9 there is surprisingly little change in most parameters. 4 figures