RELATIVISTIC ENERGY LOSS BY IONIZATION IN NUCLEAR EMULSIONS

The variation in grain density in the tracks of 5-, 8-, 12-, and 24-GeV/c protons and 5-GeV/c pions has been investigated as a function of velocity in the same plate of an Ilford K-5 nuclear emulsion. About 80 000 blobs were counted for each beam. The pion-to-proton ratio of grain densities at 5 GeV/c is 1.114 ±0.006. The results are in agreement with the Sternheimer formula using a mean ionization potential for AgBr of 434 eV and a cutoff energy T0 of 2-5 keV. Comparison of these data with an earlier experiment in a G-5 emulsion shows no dependence of the rate of the relativistic rise in grain density on type of emulsion. The combined data from the two experiments are in excellent agreement with Sternheimer's formula with I=434 eV and T0=5 keV with no correction due to secondary ionization. A correction for secondary ionization corresponding to a 10% contribution due to secondary ionization at minimum ionization gives excellent agreement with I=434 eV and T0=2 keV. © 1968 The American Physical Society.