A study has been made of stars produced by 380-Mev alpha particles in Ilford $G.\mathrm{}5\mathrm{}$ emulsion. The mean free path for star production is 18.4±0.9 cm. The number of prongs per star varies from one to eight. The average number of prongs per star is 3.3. The striking feature of these stars is stripping, or splitting of the incident alpha particle. This is evident in the large number of two-prong stars in which both prongs emerge with high energy at small angles to the beam direction; in the presence of one-prong stars, in which the single prong is a fast proton or deuteron emerging in nearly the forward direction; and in the very narrow angular distribution of the fast prongs.

The star prongs have been divided into two groups, one group consisting almost entirely of cascade prongs, and the other consisting predominantly of evaporation prongs. The properties of the two groups of prongs are examined. It is found that the excitation produced by alpha particles is similar to that produced by protons of the same energy, but the cascade differs in important respects.

By observing the stars with prongs of energy lower than is necessary to escape the barrier of a heavy nucleus, one can identify 27% of the stars as originating in light nuclei. This places a lower limit on the number of events occurring in the gelatin.

• Received 23 August 1955

DOI:https://doi.org/10.1103/PhysRev.101.324