High-resolution measurements of initial kinetic energy of fragment ions produced in fast heavy ions - C-60

High-resolution data are presented for initial kinetic energy distributions (KEDs) of fragment ions from C-60 bombarded by 1.5-MeV Li+ and 6.0-MeV Si3 + ions. The KEDs were obtained by means of a peak profile analysis of time- of-flight spectra measured in coincidence with secondary electrons emitted simultaneously. It is found that the values of K-E decrease monotonically w ith increasing cluster size; e.g., mean values are about 12 eV (C-1(+)) and 1 eV (C-11(+)) for Si3+ impacts. Also, we found that the KEDs for small io ns C-n(+) (n > 1) showed single-peak distribution patterns. The most import ant result obtained in this work is the double peak distribution pattern ob served for C-1(+) ions. This newly observed structure suggests clearly that two different production mechanisms must be taken into account for the pro duction of C-1(+) ions in C-60-multifragmentation process.