Study of the long-term stability of peaks 4 and 5 in TLD-100: correlation with isothermal decay measurements at elevated temperatures

Abstract

The long-term fading of peak 5 has been studied using four different annealing regimes in order to isolate the behaviour of peak 5 free from interference effects of peaks 2, 3 and 4. Peak 4 grows over the first nine months of storage and only then begins to decay; peak 5, on the other hand, decays rapidly in the first six months and then stabilizes or even begins to grow. Peaks (4+5) together, however, fade monotonically by approximately 8% per annum. Using thermal cleaning procedures to isolate the behaviour of peak 5, the authors have determined that its mean lifetime at 20 degrees C is 5.8+or-1.2 years (1 SD). This mean lifetime is orders of magnitude smaller than predicted by the exponential extrapolation of the mean lifetimes measured at higher temperatures or via peak shape techniques. The discrepancy suggests that the long-term decay of peak 5 is strongly influenced by other forms of decay not associated with charge carrier detrapping. The short-term fading behaviour of peak 5 alone, on the other hand, does appear to be 'well behaved', at a rate of 3.4+or-0.8% (1 SD) per month (for the first month) irrespective of annealing routine, or the presence of peaks 2 and 3. This suggests the possibility of universal short-term fading corrections in environmental and personnel dosimetry if only peak 5 is used in dosimetric measurements.