Simultaneous estimation of exposure and time elapsed since exposure using multipeaked thermoluminescent phosphors.

Knowledge of the time elapsed since a radiation exposure may be useful in personnel monitoring, as for example in determining the time for occurrence of an over exposure or a nuclear accident, or in the choice of a therapy procedure, etc. This paper describes the application of the multipeaked thermoluminescent phosphors, such as natural CaF2, and Harshaw's type of LiF, for the simultaneous estimation of the exposure and the time elapsed since this exposure. Natural CaF2 used for this purpose has three types of traps, so that the glow curve shows three maxima at about 100, 180 and 260 degrees C. These can easily supply data for the computation of both results. From the area under the 260 degrees peak the exposure can be calculated with good precision within the range from a few millirads to some kilorads. The spontaneous decay of the electrons from shallow traps at normal temperatures (fading) with time after exposure leads to the decrease of the peak areas. The 100 degree peak decays most rapidly, and after about a month the decay of the 180 degree peak is observable. By measuring the ratios of the areas under the peaks, or of the peak heights, the time elapsed since the exposure may be assessed with a precision of about 10% for the range from a few hours up to a thousand days. These ratios are independent of the exposure, the LET, and the dose rate. LiF phosphor offers similar possibilities.(ABSTRACT TRUNCATED AT 250 WORDS)