Recoil Properties ofSm142from Nuclear Reactions Induced by Heavy Ions. II. Europium and Gadolinium Compound Systems

Using thin-target recoil techniques, we have measured the average ranges and range straggling, in aluminum, of 72-min ${\mathrm{Sm}}^{142}$ produced in heavy-ion induced nuclear reactions. Eight different combinations of target and beam projectile were studied, five leading to Eu compound systems and three leading to Gd compound systems. In all cases the recoil-range distributions could be fitted by Gaussian functions. Comparison of the average ranges with a range-energy curve for ${\mathrm{Sm}}^{142}$ in Al provides evidence for a compound-nucleus mechanism in these reactions. The straggling parameters observed in reactions leading to Eu compound systems are in good agreement with those obtained for (HI, $\mathrm{xn}$) reactions. In reactions leading to Gd compound systems, the straggling parameters are found to be anomalously large. It is suggested that these effects are due to alpha-particle emission from highly excited Gd compound nuclei, and an attempt is made to infer the kinematics associated with this process. The results of a relatively simple analysis of the straggling-parameter data show that the average kinetic energies of the emitted alpha particles are reasonable, but somewhat different for the several reactions investigated.