Response function of thallium-activated sodium-iodide scintillation counters

M easurem ents of gamma rays with NaI (TI) crystals yield pulsc height distribu tions related to the true energy spectrum by an integral eq uation whose kern el (response fu nction ) is t he probability t hat an incident photon of energy E will give rise to a pulse of size E'. The response function has been calculated by t he Monte Carlo method for photons with energies from 0.279 to 4.45 Mev. Results are presented for cylind rical crystals ranging in size from 0.25 (radius) by 0.5 inch (length) to 2.5 by 9 inches. They a re based on the a nalysis of 50,000 photon histories sampled wi t h t he use of t he Standards Electronic Automatic Comp uter (SEA C) . Analytical corrections were mad e for t he escape of ann ihilation radiation and bremsstrahlung fr om the crystal.