Analysis of Secondary Particles Resulting from High-Energy Nuclear Bombardment

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Abstract
Experimental studies have been made of the low-energy yields of secondary particles resulting from high-energy bombardment. For this purpose, thin foils of Be, Al, Ni, Ag, Au, and U have been bombarded by an internal beam of 375-Mev alphas, 332-Mev protons, and 187-Mev deuterons. Secondary particles emerging from the disintegration of the nucleus at 0° to the incident beam direction are magnetically analyzed and detected in nuclear emulsions located beneath the median plane of the 184-inch cyclotron. There are three specific positions for these emulsions corresponding to energies of the secondary protons and of alpha particles of approximately 6, 10, and 20 Mev. This apparatus was modified to make a special study of the secondary alpha and proton yields by including two extra plates so that 10 energy points could be taken in the range from approximately 5 to 22 Mev. The angular distribution of secondary particles has also been measured for 240-Mev alpha bombardment of Be, Al, Ni, and Ag. Here, secondary particles emitted at 0°, 45°, and 135° are detected in nuclear emulsions at positions for which the secondary proton and alpha energy is approximately 6 Mev. A secondary particle is identified by measurement of its radius of curvature upon entering the emulsion and its range and specific ionization in the emulsion. A considerable yield of hydrogen and helium isotopes as well as of particles of higher atomic number is found. The relative yields of the secondary protons and alpha particles for each element and for each bombardment are shown as a function of energy. The results, while found to be consistent with the predictions of an evaporation model, also indicate that a large percentage of secondary protons and alphas are directly knocked out of the nucleus.