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THERMO- 



LUMINESCENCE 



ANALYSIS 



Farrington Daniels 



Some crystals emit light when heated after previous exposure to X-rays or 

 gamma rays. This thermoluminescence has been studied in this laboratory for 

 several years (Daniels, and others, 1949; Daniels and Saunders, 1951). When 

 the intensity of the light is plotted against the temperature, a glow curve results 

 with a series of peaks at definite temperatures. A typical glow curve is shown in 

 Figure 10-1. These glow curves are reproducible for a given sample, but they de- 

 pend on the chemical impurities, the physical defects, and the amount of ex- 

 posure to the high-energy radiation. The glow curves can be used for identifica- 

 tion and comparison in a manner similar to that used in spectral analysis and 

 X-ray diffraction patterns. The fact that they depend so greatly on traces of im- 

 purities and on previous treatments makes thermoluminescence analysis much 

 less specific and precise than spectrographic analysis, but on the other hand, it 

 provides a tool for comparing crystals of different origins and rocks of different 

 geological histories. It should be useful in stratigraphic analyses. 



Many minerals possess natural thermoluminescence and emit light when 

 heated even without exposure to X-rays or other high-energy radiation. This 

 thermoluminescence is usually due to the presence of a trace of uranium (about 

 1 part per million) in the sample which, over the millions of years since the last 

 crystallization process, gives an accumulated effect that, is detectable. Limestones, 

 fluorites, and granites are among the rocks which exhibit this natural thermo- 



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