The Response of Crystal Phosphors to Nuclear Radiation
Report Number: AFOSR-TN-57-313 Author(s): Reiffel, L. Corporate Author: Illinois Inst. of Tech. Armour Research Foundation Date of Publication: 6/4/1957 Pages: 52 Contract: AF 49(638)113 AD Number: AD0132384 Original AD Number: AD 132384
Abstract: The utility of a parameter other than temperature is being investigated for its effect on luminescence behavior of the simple alkali halide phosphors. The effect of pressure on luminescent systems is examined with particular reference to the phosphorescent decay of long-lived traps in Tl-activated NaI. Important parameters of the trapping centers may be obtained by subjecting the phosphor to hydrostatic stress during phosphorescent decay. Increased pressure tends to favor configurational coordinate distances smaller than equilibrium values, while thermoluminescence experiments and other techniques which rest on variations in temperatures carry the system with equal probability to larger and smaller than equilibrium values of configurational coordinates. The critical displacement of I~ from their equilibrium position which allows thermal collapse of a specific trap, in NaI (T1) is +0.19A (an outward displacement). For another trap in the same material, thermal collapse sets in with the ions moved inward by -0.046A. The effect of these displacement values is observed as a change in phosphorescent lifetime under pressure. As a second illustration of the utility of pressure, a type'of experiment, termed the pressure break, was devised which is essentially equivalent to experiments where the temperature of the phosphor is changed over large ranges, almost instantaneously. The ability of the phosphor to stand rapid pressure changes permits experiments to be conducted at essentially constant light sum in the crystal. The technique is still in the early stages of development.
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