Overcoming fading in passive dosimetry: A combined persistent-luminescence and residual-thermoluminescence method

Thermoluminescence (TL) and optically stimulated luminescence are widely used in radiation dosimetry. In applying these methods, signal fading is a major source of error in dose estimation. Hypothetically, a material whose conventional TL fades significantly due to spontaneous detrapping of electrons should produce persistent luminescence (PerL) as the electrons recombine radiatively with holes. If the material is heated after measurement of PerL, the resulting TL (RTL) is due to the residual population of trapped electrons. Therefore, combining PerL and RTL may provide reliable information on radiation dose. This paper proposes a versatile method of evaluating radiation dose intended to overcome the issue of fading. The hypothesis was tested using (BaAl2O4–BaAl12O19):Eu2+, a mixed-phase phosphor. This phosphor has a continuous distribution of electron traps with an energy depth range 0.59–1.17 eV below the conduction band. In addition to conventional TL, the phosphor produces intense PerL as well as RTL and has a linear dose response between 1 and 15 Gy. The hypothesis was, thus, tested for five test doses, namely, 2, 4, 8, 11, and 14 Gy. The values of these test doses as estimated using conventional TL are 2.17 ± 0.01, 4.08 ± 0.01, 7.95 ± 0.01, 10.96 ± 0.01, and 14.12 ± 0.01 Gy, respectively. In comparison, the combined use of PerL and RTL retained them as 2.05 ± 0.02, 4.04 ± 0.02, 8.02 ± 0.02, 10.98 ± 0.02, and 13.99 ± 0.02 Gy, respectively. For all test doses, the discrepancies in doses recovered using conventional TL exceed those estimated using combined PerL and RTL, thus making the later a reliable alternative method for dosimetry.