Scintillation Response of Aikali Iodides to Alpeha Particles and Protons

The relative pulse height for all alkali iodide crystals, with and without activation, in response to alpha particles and protons was measured as a function of the incident particles energy at both liquid nitrogen and room temperatures. In all cases the response curve is linear for protons of an energy range from 1 to 10 Mev, linear for alpha particles of high energies, but clearly nonlinear generally below 15 Mev. The response curve of activated crystals at liquid nitrogen temperature is generally flatter than that at room temperature. Unactivated crystals have a unique response only at liquid nitrogen temperature. For all crystals the proton scintillation efficiency curve lies slightly below the linear portion of the alpha particles curve. A sharp change in dL/dE is observed in the region of 130 < dE/dx < 160 kev/mg-cm-2, indicating a threshold for a process which has a decreased probability of exciting luminescence.