been studied in some detail (Rieke and Daniels, 1957) and the thermolumines- 

 cence glow curve depends on the extent of dehydration as determined by the tem- 

 perature to which the oxide is heated. In aluminum oxide which has been heated 

 above 1000C to remove all the water, the peaks appear to be associated with im- 

 purities of sodium. By far the brightest thermoluminescence is found in the 

 fused and recrystallized aluminum oxide (sapphire). 



The sulfates give definite thermoluminescence patterns (Moore, 1957). Sodi- 

 um sulfate recrystallized many times still gives the same peaks, although there 

 is a tendency to decrease in intensity with purification. The addition of 75 parts 

 per million of lead introduces a prominent new thermoluminescence peak at a 

 higher temperature. The speed of dehydration of the Na 2 S0 4 • 10H 2 O affects the 

 glow curves. Rapid dehydration with heating gives more thermoluminescence 

 peaks and higher intensities than long, slow dehydration at room temperatures. 



Many common inorganic chemicals do not give gamma-radiation-induced 

 thermoluminescence, but many others do. In general, thermoluminescence is 

 most likely to be exhibited by brittle, transparent crystals having low atomic 

 weights, occurring in simple crystal forms, and containing some impurities. An 

 examination of over fifty inorganic crystals leads to the following generaliza- 

 tions (Rieke, 1957). 



( 1 ) High thermoluminescence efficiences are often obtained with fluor- 

 ides, chlorides, carbonates, sulfates, oxides, and silicates, and the 

 cations of Li, Na, K, Mg, Ca, Sr, and Al. 



(2) Intermediate thermoluminescence is given by phosphates, bro- 

 mides, iodides, and the cations of Pb, Cd, and Ba. 



(3) Low-efficiency thermoluminescence is obtained from chromates, 

 persulfates, ferricyanides, permanganates, nitrates, and the cations 

 of Cr, Fe, Mn, Co, Ni, Cu, Ag, and NH 4 . 



LIMESTONES Practically all limestones exhibit natural ther- 



moluminescence and give a yellow or white 

 light. Some limestones and dolomites give an orange light. The colors of the 

 light are probably determined by impurities such as manganese and magnesium. 



The temperatures of thermoluminescence peaks and the general pattern of 

 glow curves vary greatly with the limestone deposit, the chemical impurities, and 

 previous geological history. Glow curves are given in Figures 10-4 and 10-5 for 

 different types of limestones. Many limestones have three peaks or maxima in 

 the glow curves. 



The low-temperature peaks can be annealed out without affecting the high- 

 temperature peaks if the annealing temperature is kept low enough, as indicated 

 in Figure 10-6. At earth temperatures, the electrons, which are trapped in imper- 



188 



