Measurement and Control of Thermal Radiation Below 6 K

The power absorbed by a surface at 0.2 K illuminated with thermal radiation from a surface at 0.9-6 K has been measured using a variety of materials for these surfaces. Also, the reduction in the absorbed power by the insertion of various thermal shields has been measured. The results are compared with theory and with other measurements. Conclusions as to appropriate design techniques for cryogenic apparatus are discussed.