Stopping of Energetic Copper Ions in Aluminum

By means of differential-range experiments, we have measured the average ranges and range straggling of 24-min ${\mathrm{Cu}}^{60}$ and 3.3-h ${\mathrm{Cu}}^{61}$ in Al. These species were produced with initial recoil energies from 3 to 18 MeV by bombardment of thin targets of ${\mathrm{Co}}^{59}$ and ${\mathrm{Mn}}^{55}$ with ${\mathrm{Li}}^6$, ${\mathrm{B}}^{10}$, and ${\mathrm{B}}^{11}$ heavy-ion beams. The average ranges increase smoothly with recoil energy and the distributions in range about the average values follow a Gaussian relationship. The experimental range-energy data are in good agreement with theoretical expectations, assuming total momentum transfer over the full energy region investigated. We conclude that the nuclear processes which produced the recoiling ions are pure compound-nucleus reactions. Although theory and experiment yield consistent average-range values, the stopping-theory predictions for range straggling are much smaller than experimental estimates of the straggling inherent in the stopping process. The source of the discrepancy is discussed in terms of the relative contributions of electronic and nuclear stopping.