The Response of Sodium Iodide Crystals to High Energy Protons

For the purpose of analyzing the energy spectrum of high energy protons, a scintillation counter particle spectrometer has been constructed employing thallium activated sodium iodide crystals, as described in the accompanying letter. To make such a device useful for energy determinations, it is necessary to know the relationship between the size of the light flash produced in the crystal and the energy of the particle striking it. Previous studies have Indicated that this relationship is approximately linear for protons incident on sodium iodide. We have reinvestigated this question with careful attention to the sources of error that may influence the result obtained.