Photonic Dosimeter

Radiation-induced materials modification is ubiquitous. These applications rely on dosimetry to reliably deliver the desired amount of radiation to the right place. Currently, the dosimetry standard is based on calorimetry of a large water phantom irradiated exclusively by Co-60 gamma rays. The thermistor used is large, half a millimeter. The current dosimetry standards permit traceable dosimetry that is limited by the size of the probes used in primary standard calorimeters and the requirement of field uniformity over the probe (thus, field ~ 10x∙probe diameter). This works for bulk sterilization, but for surfaces or small dimensions, this existing dose standard is too crude by several orders of magnitude. While higher-energy electron beams can penetrate matter, beams of low-energy electrons have the opposite characteristic: they penetrate no more than 100 microns or so into most materials. This makes them valuable for industrial processes like surface sterilization of medical instruments and bandages or curing of inks used on labels for food items – wherever the benefits of radiation dose are confined to the outside of something (and could harm what’s inside). Lack of traceability thus leaves huge industries without the support needed to meet regulatory requirements. Thus, NIST has developed a chip-scale calorimeter for radiation dosimetry that could serve as a new standard to extend traceability and allow quantitative dosimetry on a micron scale.