Ranges ofBa126andBa128Recoil Fragments in Aluminum

Abstract

Using thin-target, thin-catcher recoil techniques, we have measured the average ranges and range straggling of 97-min ${\mathrm{Ba}}^{126}$ and 2.4-day ${\mathrm{Ba}}^{128}$ in Al. The Ba ions were produced with initial energies from 3 to 14 MeV by bombardment of ${\mathrm{Sn}}^{120}$, ${\mathrm{Sb}}^{121}$, and ${\mathrm{Sb}}^{123}$ targets with ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, and ${\mathrm{N}}^{14}$ ion beams. The assumption of a compound-nucleus mechanism in the nuclear reactions leads to a smooth relationship between average range and recoil energy. Theoretical predictions are in good agreement with the observed ranges, but relatively small (10%) systematic deviations become apparent at the higher energies. The range distributions are consistent with a Gaussian representation, and yield straggling parameters which are substantially larger than theoretical estimates of straggling inherent in the stopping process. Possible sources of the discrepancy are discussed. In one experiment, the product Ba ion is believed to be formed in a reaction involving emission of an alpha particle, and an abnormally large straggling parameter is observed.