Direct Radiation Effects on Thermocouples

Sheathed Chromel/Alumel and iron/Constantan thermocouples of various geometries were exposed to varying radiation levels from a nuclear reactor while immersed in a constant-temperature medium. Emf measurements indicated transient changes in thermocouple calibration of as much as 18°F occurring over periods of several hours after a change in radiation level. After further exposure (1 × 10¹⁸ n/cm² for fast neutrons), the magnitude of the transient decalibration effect had diminished. This behavior is consistent with a mechanism involving changes in electron mobility in the two thermoelectric materials due to the appearance of radiation-produced scattering centers followed by self-annealing.