The inelastic-interaction mean free paths $\lambda$ of 5-, 10-, and 15-GeV/c pions have been measured by determining the distribution of first-interaction locations in a modular tungsten-scintillator ionization spectrometer. In addition to commonly used interaction signatures of a few (2-5) particles in two or three consecutive modules, we have used a ${\chi }^2$ distribution to calculate the probability that the first interaction occurred at a specific depth in the spectrometer. This latter technique seems to be more reliable than use of the simpler criteria. No significant dependence of $\lambda$ on energy has been observed. In tungsten, $\lambda$ for pions is 206 ± 6 g/${\mathrm{cm}}^2$.

• Received 10 June 1975

DOI:https://doi.org/10.1103/PhysRevD.12.2587