Radiation stability of bead thermistors of NR 09 type

Radiation stability was studied of bead thermistors 13 NR 09 under irradiation in the mixed neutron-gamma field of a 252Cf source with an overall fast neutron flux of 2.1x109 n.s-1. The electrical parameters of the thermistors were measured two days prior to irradiation and after 30, 60, and 90 days of irradiation at temperatures of 25 and 80 degC. At a total integral neutron dose of 1.2x104 Gy and a total photon radiation exposure of 232.5 C.kg-1, ie., 9x105 R, the rated thermistor resistance decreased by 0.3% and constant B given by the relation B=4406xlog(R25/R80) decreased by 1.5%. After long-term irradiation, the thermistors showed an induced activity of 104 Bq which dropped to background level after 120 hours. Considering the maximum measurement error of 0.5%, it is evident that the measured values of rated resistance and constant B show good radiation stability of Czechoslovak bead thermistors of the 13 NR 09 type in a fast neutron field and indicate their possible applications in measuring and controlling temperature in an intense ionizing radiation environment. (B.S.)