Compound Nucleus Formation Mechanisms in Reaction of Heavy Ions with Medium-Mass Elements

Abstract

Excitation functions and range distributions of heavy products formed by the reaction of ${\mathrm{O}}^{16}$, ${\mathrm{N}}^{14}$, and ${\mathrm{C}}^{12}$ with ${\mathrm{Mn}}^{55}$ and ${\mathrm{Co}}^{59}$ have been measured. Results show that the bulk of products, with mass numbers greater than that of the target, are formed exclusively by decay of a compound nucleus formed by complete fusion of target and projectile. One nuclide, ${\mathrm{Cu}}^{61}$, can also be formed from ${\mathrm{O}}^{16}$ bombardment of ${\mathrm{Co}}^{59}$ (but not from the formally similar compound system ${\mathrm{Mn}}^{55}$+${\mathrm{Ne}}^{20}$) by a mechanism in which only part of the momentum of the projectile is transferred. It appears to be representative of products with mass near that of the target, which can be formed by nucleon transfer in a grazing reaction. No evidence is found for a general type of "buckshot" mechanism. Small yields of ${\mathrm{Na}}^{24}$ and ${\mathrm{P}}^{32}$ appear to result from a fission or fragmentation mechanism.