Ionization Energy Loss of Mesons in a Sodium Iodide Scintillation Crystal

The response of a thallium-activated sodium iodide crystal to high-energy charged particles passing through the scintillator has been investigated. Pions and muons produced by the Chicago 450-Mev cyclotron have been used to cover energies ranging from 61 Mev (pions) to 245 Mev (muons). Sea-level cosmic-ray muons have been used to cover energies from 200 Mev to greater than 2 Bev. At each energy, the most probable energy loss is determined from the pulse-height distribution, making use of Po-Be 4.44-Mev $\gamma$ rays for an energy calibration. The distributions from cyclotron data are found from the density variations on photographs of the superposition of many pulses appearing on an oscilloscope. Because the cosmic-ray counting rate is low, each pulse is individually photographed and measured. The results for energies below the occurrence of the minimum in ionization indicate good agreement with the probable energy loss as given by the Bethe-Bloch formula. Beyond the minimum the probable loss is in fair agreement with Sternheimer's calculations for sodium iodide, rising slightly more rapidly than predicted to the Fermi plateau.