Low temperature radiative properties of materials used in cryogenics

Radiative heat transfer between two parallel surfaces, a sample surface and a black surface, was measured. One of the surfaces was cooled with liquid helium to about 5 K and the other one was step by step heated to temperatures ranging between 30 and 140 K. As a result, the total hemispherical absorptivity and emissivity of the sample surface were determined in dependence on the temperature of the heat radiation. Aluminium samples were made of Al sheet, Al foil and aluminized mylar. Further measurements were performed on sheets of aluminium alloy, Cu, zinc brass and stainless steel. The influence of different types of sample treatment such as chemical and mechanical surface finishing and material annealing on the radiative properties is presented.