D2 Physical dosimetry: instruments for direct dose measurement

Topic

This same absorbed dose—which the cellular biological damage model has already established as the central physical quantity—is measured in three different ways, depending on the timing and the available instrumentation. A thermoluminescent dosimeter accumulates energy within a crystal in proportion to the dose received; this energy remains stored until it is released as light when the crystal is heated in a laboratory, meaning the reading is obtained after the fact but with high precision. In contrast, an electronic personal dosimeter provides a real-time reading; it is therefore the standard instrument for emergency responders and occupationally exposed workers, who need to know their dose level while they are being exposed, rather than afterwards.

When no active dosimeter was present at the time of exposure, retrospective dosimetry offers a third approach: techniques such as electron paramagnetic resonance—applied to construction materials or even a person's tooth enamel—allow the received dose to be estimated long after the event based on physical changes the radiation left in the material.

Thus, this model—which begins with three distinct ways of measuring the same absorbed dose—complements the biological dosimetry of the subsequent model rather than competing with it: physical dosimetry is more precise when instrumentation is available, whereas biological dosimetry is the only option when the exposure was unanticipated and no physical instrument was present.

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