Thermoluminescence of shocked granodiorite



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The Hardhat event was an underground nuclear detonation in granodiorite at the Nevada test site. Samples of this rock, representing all stages of peak shock pressure from zero to over 100 kilobars, were Investigated by thermoluminescence to determine whether or not the effects of shock on the quartz and feldspar of the granodiorite could be detected by variations In the shape of the glow curves. Natural thermoluminescence glow curves were obtained In order to detect any changes In the number of electrons trapped In the natural environment. Induced thermoluminescence glow curves were obtained for the detection of possible changes In the total number of electron traps In the crystal structure of the major mineral phases. Glow curves recording the natural thermoluminescence of the Hardhat samples generally displayed a single peak at about 225°C, which decreased In height and area Irregularly with decreasing distance from the shot point. Preshot samples showed the largest natural peak, while highly shocked samples showed essentially no natural thermoluminescence. This effect is attributed mainly to thermal draining of electrons from traps by the heat from the blast. Glow curves recording Induced thermoluminescence, l.e, thermoluminescence of samples which were previously Irradiated with gamma rays In the lab, showed variations In shape which are not, In general, correlated with peak shock pressure. The exact cause fdr this lack of correlation Is not known, but three possible explanations are suggested; compensating effects of shock; effect of heat from the blast on Induced thermoluminescence; and traps not of a type that could be affected by shock.