Stars in Photographic Emulsions Initiated by Alpha-Particles

A study has been made of stars in photographic emulsions initiated by alpha-particles from the 184-inch Berkeley cyclotron. These stars are similar to stars initiated by deuterons, which were described in an earlier paper. Eastman NTA plates were used. Plates from the emulsion number used will record alpha-particles of energy about 200 Mev and lower and protons of about 10 Mev and lower. The contribution of the high energy protons may be missing from the results given. The average number of prongs observed is close to 3. The ratio of the number of prongs in the three sectors in the forward direction of the beam to the number in the three backward sectors is about 6. The cross section for the formation of stars has been estimated by counting sections of alpha-particle tracks and the stars associated with these tracks. For alpha-particles of energy 130 Mev we obtain a value of the cross section, averaged over all of the atoms in the emulsion, of 3×${10}^{-25\mathrm{}}$ ${\mathrm{cm}}^2$ with an estimated uncertainty of 30 percent.