Thermoluminescence of chip inductors and resistors in new generation mobile phones for retrospective accident dosimetry

Luminescence dosimetric properties of inductors and resistors in mobile phones have attracted wide attention for their use in retrospective accident dosimetry. Thermoluminescence (TL) signal following optically stimulated luminescence (OSL) readout, which has been recently shown to be useful for dose re-estimation (Lee et al., 2016), when measured by a Risoe OSL reader without a Hoya U-340 optical filter, was found to be up to 85 times of that recorded with the Hoya filter (with transmission window 270–380 nm, necessary for recording the usual OSL signal) placed in front of the photomultiplier tube (PMT) in the reader. In view of this, a study of dosimetric TL properties, namely sample-to-sample variation, fading, zero-dose signal, minimum measurable dose, effect of room light, dose response and emission spectrum, was undertaken to explore the use of TL of inductors and resistors in new generation mobile phones for accident dosimetry. The hitherto unknown TL emission spectrum was found to exhibit an intense emission beyond 550 nm (peaking at 700 nm) when recorded in the range from 250 nm to 750 nm. Emission below 500 nm was smaller by orders of magnitude than that at 700 nm. As the TL and OSL signals have been attributed to alumina substrates of inductors and resistors, the TL emission spectrum was compared with that of dosimetry grade Al2O3:C. The emission spectra of inductors and resistors were found to differ significantly, not only from that of Al2O3:C, but also from each other. Although the differences in TL glow curves, optical emission spectra, fading, etc. Indicated a lack of universality in luminescence properties of alumina substrates in different electronic components, it was concluded that the TL of inductors and resistors in new generation mobile phones offers a better option for accident dosimetry than OSL, with the specific advantage of much lower post-irradiation fading.