Interaction Lengths of Energetic Pions and Protons in Iron

Abstract

The interaction lengths of pions and protons in iron have been measured using an ionization spectrometer composed of alternating layers of iron and plastic scintillator. These measurements cover an energy range from 9.3 to 18 GeV. The interaction lengths were determined by accurate statistical analyses of the experimental data using the maximum-likelihood method. The dependence of the interaction length on the parameters used to define an interaction was studied, and the results reported employ parameters chosen to minimize the percentage uncertainty in the interaction length. The mean interaction length of pions was found to be approximately 20% greater than that of protons. No significant dependence on the energy of the incident primary was found in the range measured. Consistency was found with the great variety of accelerator measurements made to date, all of which report greater interaction lengths than those reported by the cosmic-ray measurements.