Deriving Correction Factors for a Primary Standard for Radiation Dosimetry

R. Tosh, and H. Chen-Mayer
NIST
Gaithersburg, MD

Accurate metrology of radiotherapeutic absorbed dose to water requires assessing the radiation induced temperature change. The most direct method for doing this is water calorimetry, for which the established technique involves the use of slender thermistor probes that are sealed within a glass vessel containing high-purity water.

The probes and vessel perturb the radiation field, via scattering/absorption processes, and, because their thermal properties differ from that of water, introduce spurious heat-transport effects. In addition, trace quantities of dissolved gases and residue from distillation processes produce a measurable heat defect due to photolytic reactions. We shall discuss using COMSOL to model both the heat transport and chemistry for purposes of correcting the data.

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