Scintillation Studies on Potassium Iodide

Scintillation studies have been conducted on the effect of thallium impurity on the fluorescence properties of potassium iodide. Coincidence techniques have demonstrated the presence of single photon emission as expected from electron trapping at impurity sites. It has been possible to distinguish between the characteristic radiation due to the impurity and the fundamental or lattice radiation from the pure potassium iodide crystal. The fluorescence efficiencies of both types of emission have been determined as a function of temperature. Measurements of the ${\mathrm{K}}^{40}$ radioactivity in the crystal result in the values $\lambda \left(\beta \right)=3.90\mathrm{}\times {10}^{-10\mathrm{}}$ per year and $\frac{\lambda \left(\gamma \right)}{\lambda \left(\beta \right)}\cong 0.05$. Comparison of pulse height distribution with that from ${\mathrm{Cs}}^{137}$ activity gives a provisional $E_{max}\left(\beta \right)\cong 1.3$ Mev.