A LOW TEMPERATURE STANDARD OF TOTAL RADIATION

Abstract

A standard of total radiation used for the calibration of thermal radiation detectors is described. The black body source is a modified cone operating over the temperature range 40 °C to 150 °C; the detector is located in an isothermal (better than 0.01 °C) environment. For the detectors used a decrease in sensitivity of approximately 1% during the first 24 hours was observed. This is probably due to the slow drying of the receiver surface by the gas used to displace the air. The day-to-day reproducibility of results is about 0.1%, and an over-all accuracy of 0.3% is claimed for radiation measurements made with the instrument. The scale of total radiation defined by four National Bureau of Standards carbon filament standards of thermal radiation probably differs from that defined here by −0.3%.