Retrospective dosimetry

Retrospective dosimetry is a technique which enables the determination of overexposure doses, either chronical or acute, using common materials which are available in the public domain. The aim is the after-the-fact determination of an overexposure dose from a radioactive source. Overexposures could be due to fallout from a nuclear accident or nuclear terrorist attack, or could be the result from a direct exposure to ionising radiation from a stolen/lost source or an accidently unshielded source while being operated.

Radiation can cause ionisation of electrons, which leads in turn, in various materials, in the trapping of these electrons in pre-existing defects or, in other materials, to the production of free radicals . The trapped electrons can be released using heat (thermal stimulation) or light (optical stimulation), resulting in a luminescent signal, called TL, in the case of thermal stimulation or OSL, in the case optical stimulation was used. In the case of the production of free radicals, the concentration of these radicals can be measured using electron spin resonance (ESR). Using ESR, the trapped charge is measured without releasing it: defects are probed by a constructive interaction between microwave energy and an applied magnetic field.In principle, the intensity of the luminescence and/or ESR signal is proportional to the accumulated dose.

Building materials which are commonly used in retrospective dosimetry include heated materials (ceramics) such as brick and roof tiles. They all contain luminescent minerals such as quartz and feldspar, and these are used as dosemeter. Currently, we are investigating the accuracy/precision and the lower detection limit with which an artificial accident dose or overexposure dose can be measured using TL of heated quartz. Quartz inclusions are extracted from the bulk material by mechanical and chemical separation techniques.

Personal objects can be very useful as fortuitous dosemeter in the case of a radiological incident. Objects such as telephone chip-cards, ID-cards, cellular phones, laptops and related items contain electronic components or modules which might be optically and/or thermally luminescent.

Regenerative dose curve of quartz inclusions extracted from irradiated brick

At present, we are investigating specific ceramic components from cellular phones, USB-sticks and telephone chip cards using both TL and OSL. The following TL/OSL characteristics are being analysed: presence/absence of zero-dose signal, radiation sensitivity, sensitivity changes, thermal stability, fading.

ESR measurements of tooth enamel from human molars offer the possibility to perform retrospective biodosimetry measurements. Tooth enamel is sensitive to ionizing radiation and the resulting defects can be measured with ESR. In optimal circumstances, detection limits of several 10 mGy can be attained. Our research on tooth enamel is directed towards feasibility tests of Q-band retrospective dosimetry.

Contact: Cauwels Vanessa, Vanhavere Filip