Ultraviolet radiometry of clinical sources with a miniature multijunction thermopile

Three versions of the Dexter 2M miniature multijunction thermopile were evaluated for the radiometry of clinical ultraviolet radiation (UVR) sources. The acceptance angle had been increased in two of these devices, and one also contained an additional ceramic heat sink under its receiver element. Measurements were made of their absolute sensitivity and linearity, and their response to various UVR sources was compared to that of Hilger Schwarz FT17 and FT32 vacuum compensated thermopiles. Both of the acceptance angle modifications yielded an angular response less than that of the wide-angle FT32 thermopile. The additional ceramic heat sink diminished, but did not eliminate, the initial surge in the 2M thermopile output voltage following exposure. Under constant irradiance, the 2M output voltage was stable after the initial surge had decayed, even without the additional heat sink. It was concluded that irradiance measurements should be made after the output voltage had stabilised. Any version of the 2M thermopile could be used for relative day-to-day monitoring of all UVR sources, and the version with the widest acceptance angle could be used for the absolute radiometry of certain extended sources.