Gold has been bombarded by the 380-Mev proton beam of the Nevis Cyclotron in a study of secondary reactions. Secondary reactions produce nuclei with charges greater than that of a target nucleus by means of an intermediate fragment emitted from one target nucleus and absorbed in a second. The increase in atomic number permits isolation of the effect by chemical separation.

Thallium, lead, and bismuth fractions were separated from irradiated gold bars and carefully purified. The radioactive decay of these samples was followed with a NaI(Tl) crystal scintillation counter. Nuclei produced by secondary reactions were detected for all three elements, the yields decreasing rapidly with increasing atomic number. From the secondary reaction yields of thallium and lead isotopes, it has been possible to calculate the upper portion of the energy distribution of the respective intermediate alpha and lithium fragments. This provides a comprehensive picture of a secondary reaction and demonstrates (1) that the yield of secondary particles is a rapidly increasing function of the bombardment energy for a given target nucleus, (2) that the energy distribution of the secondary fragment possesses an appreciable high-energy tail, and, (3) that secondary reactions can be treated in terms of conventional nuclear reaction theory.

• Received 30 October 1958

DOI:https://doi.org/10.1103/PhysRev.113.1125