A long-term fading study for ESR intensity measurement and dose evaluation on fossil tooth enamel

Two sets of samples, originally measured in 1989 and 1995, respectively, were re-measured in 2001 to assess long-term fading of the ESR signal in fossil tooth enamel. About half of the samples of the 1989 set showed some fading of the central ESR signal, the average intensity of the irradiated aliquots of a sample decreasing by between 3% and 10%. The resulting dose values were on average between 2% and 6% larger than the original estimates. The 1995 sample set did not contain any quantifiable fading component. We infer that there may be a fading component which saturates at relatively low intensities. However, at present we are not confident that any prescribed post-irradiation annealing procedure is capable of eliminating the unstable component without affecting any other ESR parameters.