Energy Loss of Cosmic-Ray Mu-Mesons in Sodium Iodide Crystals

A scintillation counter telescope, employing three NaI(Tl) crystals in coincidence, has been used to study the energy losses experienced by mu-mesons in traversing one of the crystals. The magnitude of the light flash in NaI(Tl) has been assumed to be proportional to the energy lost in the crystal by the meson. The observed pulse distribution is compared with one calculated on the basis of the Bethe-Bloch theory without the density correction and also with the Halpern-Hall theory which includes the effect of the dielectric shielding. Each calculated curve employs a fold of the Landau straggling theory with the cosmic-ray mumeson spectrum. Comparison of the data with the two theories definitely favors the Halpern-Hall theory both in respect to absolute value of the most probable energy loss as well as the shape of the distribution.