Many materials originally inactive are made thermoluminescent by exposure to x-rays. Calcium sulphate containing a small amount of manganese in solid solution shows this effect strongly and has been previously studied by the authors. The present report gives a continuation of this work upon sulphates of cadmium, calcium, sodium and zinc containing a small amount of manganese.
Exposure to x-rays produces two kinds of change in the material. One of these results in a thermoluminescence which comes up quickly upon heating and lasts for a very short time while the other is shown by a luminescence which comes up more slowly and lasts longer. If the material is allowed to stand at room temperature after exposure the first effect disappears in a few hours while the second may last for months. Both of the effects may be preserved indefinitely by keeping the specimen in liquid air after exposure.
The decay of thermoluminescence was studied using different temperatures of observation, different temperatures of exposure and different voltages on the x-ray tube. Exposure to ultraviolet light of a definite frequency was found to suppress the effect produced by exposure to x-rays. The results obtained are compared with effects of exposure to cathode rays as described by Wiedemann and Schmidt.
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