Recoil Properties ofSm142from Nuclear Reactions Induced by Heavy Ions. I. Samarium Compound Systems

By means of thin-target differential-range experiments, we have measured the average ranges and range straggling of 72-min ${\mathrm{Sm}}^{142}$ recoils from a number of nuclear reactions induced by heavy ions. Beams of ${\mathrm{Li}}^6$, ${\mathrm{Li}}^7$, ${\mathrm{B}}^{10}$, ${\mathrm{C}}^{12}$, and ${\mathrm{N}}^{14}$ with kinetic energies up to 10.5 MeV per nucleon were used in conjunction with targets of ${\mathrm{Cs}}^{133}$, ${\mathrm{Ba}}^{136}$, ${\mathrm{Ba}}^{137}$, ${\mathrm{Ba}}^{138}$, ${\mathrm{La}}^{139}$, and ${\mathrm{Pr}}^{141}$. A range-energy curve was obtained for ${\mathrm{Sm}}^{142}$ in Al, covering the region 2-10-MeV recoil energy. Strong evidence for a pure compound nucleus reaction mechanism is provided by (a) the uniqueness of the range-energy curve for all the reactions, (b) Gaussian-range distributions, and (c) direct comparison of the experimental ranges with stopping theory. The reaction ${\mathrm{Nd}}^{142}(\alpha , 4n){\mathrm{Sm}}^{142}$ was studied by integral range methods, and the average ranges in Nd were found to be consistent with theoretical expectations when projected ranges were corrected to true ranges. The experimental straggling parameters are compared with theoretical predictions of straggling inherent in the stopping process. For ${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$ experiments, where the recoil velocities are smaller than the Bohr velocity (2.2×${10}^8$ cm/sec), an attempt is made to extract the range straggling due to the nuclear reaction. From this analysis, qualitative information is obtained about the average total energy removed by neutrons and photons.