Recoil Range Measurements of Reactions Induced inNi58with 46- to 68-MeV Helium Ions

Abstract

Ranges in ${\mathrm{Ni}}^{58}$ are reported for ${\mathrm{Ni}}^{56}$, ${\mathrm{Ni}}^{57}$, ${\mathrm{Co}}^{55}$, ${\mathrm{Co}}^{56}$, ${\mathrm{Co}}^{57}$, and ${\mathrm{Co}}^{58}$ recoil ions resulting from the bombardment of ${\mathrm{Ni}}^{58}$ with 46- to 68-MeV helium ions. The thick target-thick catcher method was used to obtain average recoil ranges in the beam direction. Measured ranges have been compared with theoretical range predictions, calculated assuming full momentum transfer from the incident helium ions to the recoil ions. Theoretical range curves were corrected for the influence of $\alpha$ particle and nucleon evaporation. Experimental ranges measured from reaction thresholds to excitation function peaks agree with the corrected theoretical curves to within 10%. Recoil ranges for ${\mathrm{Co}}^{57}$ and ${\mathrm{Ni}}^{57}$ are shown to have predominate contributions from a low-momentum-transfer process in the energy range corresponding to the high-energy tail of the excitation functions. At higher energies the ranges and excitation functions are shown to increase, consistent with contributions from the onset of ${\mathrm{Ni}}^{58}$ ($\alpha$, 5 nucleon) compound-nucleus reactions. Recoil ranges for ${\mathrm{Co}}^{55}$, ${\mathrm{Co}}^{56}$, and ${\mathrm{Co}}^{58}$ are consistent with full momentum transfer over the entire energy range studied, including those ranges corresponding to the high-energy tail of the ${\mathrm{Co}}^{56}$ excitation function. Recoil ranges for ${\mathrm{Ni}}^{56}$ are consistent with full momentum transfer up to the peak of the excitation function, after which the range decreases sharply as a competing low momentum-transfer reaction becomes predominant. We discuss the details of the reaction mechanism responsible for the high-energy tails of the ${\mathrm{Ni}}^{57}$, ${\mathrm{Co}}^{57}$, and ${\mathrm{Ni}}^{56}$ excitation functions. In the case of the tail of the excitation-function for the formation of ${\mathrm{Ni}}^{56}$ we present evidence that the interaction is between the incident helium ion and one or two neutrons, rather than an ($\alpha , {\alpha }^{\prime }$) inelastic scattering followed by nucleon evaporation. We conclude that we cannot differentiate between these two mechanisms in the case of the reactions forming ${\mathrm{Ni}}^{57}$ and ${\mathrm{Co}}^{57}$.