Comparative Gamma Radiation and Temperature Effects on SiO2 and MgO Insulated Nuclear Instrument Cable

The relative merits of SiO2 and MgO as insulation for nuclear instrument cables are investigated. The insulation resistance of SiO2 cable was between one and two decades higher than that of MgO cable under the combined effects of temperature and gamma radiation (5.3 × 105 R/hr). The insulation resistivity of the SiO2 cables tested exceeded 1011 ¿·ft. at 400°C in the gamma fluence. MgO cables maintained superior pulse voltage breakdown thresholds (> 800 Vdc at 500°C, 105 R/hr) to SiO2 cables in testing. Spontaneous current signals, generated during thermal cycling, were characterized. Although these currents were a decade higher in SiO2 cable, their magnitude did not exceed 2 × 10-10 amps.