In-Pile Measurements of Radiation Effects in Magnetic Materials

Abstract

Experiments have been performed at Brookhaven National Laboratory to determine the effects of nuclear reactor radiation upon the characteristics of ferrites and metallic magnetic materials. Photographs of 60 cycle hysteresis loops and bridge measurements of 1000 cycle inductance were made before irradiation, periodically during irradiation, and after reactor shutdown. The samples were irradiated for 12 days, resulting in an integrated fast flux of 1.6×1017 neutrons/cm2. No permanent effect was observed in any ferrite. In-pile changes in ferrite properties are identified with changes due to temperature variations resulting from gamma ray absorption. Permanent damage was observed in all metallic samples tested. Supermendur and Deltamax were least affected, showing increases of the order of 50% in coercive force and small decreases in initial permeability. Various samples of 4–79 Mo-Permalloy were affected differently, but all showed change in shape of hysteresis loop, several hundred percent increase in coercive force, and about 80% decrease in initial permeability. Supermalloy was most damaged by radiation, showing marked effects after 24 hr, and progressively greater effects throughout the exposure period.