Irradiation of Magnetic Materials with 1.5- and 4-MeV Protons

Abstract

Pure iron and 5% molybdenum Permalloy samples, 0.01 in. thick, were irradiated with 1.5‐ and 4‐MeV protons at total incident integrated fluxes of 10¹⁶ and 10¹⁷ protons per cm². The actual shapes used were a ring $\frac{\text{1 3}}{\text{1 6}}-\mathrm{in}$ . o.d.×⅝‐in. i.d. and a disk of ⅝‐in. diameter. The ring was utilized for dc magnetic property measurements (before and after irradiation) while the disk was used for magnetic anisotropy torque measurements. The remanence (B_r) and maximum permeability (μ_m) of molybdenum Permalloy decreased by about 35%. This is of the same order of change produced by neutron irradiation of 10¹⁷ neutrons/cm² in this material. However, measurements to date indicate that changes in coercive force and initial permeability due to proton irradiation are relatively small as compared with neutron irradiation effects. The decreases in B_r and μ_m of the pure iron samples were of the order of 10 to 20% for irradiations of both ∼10¹⁶ and ∼10¹⁷ protons/cm². Both materials were essentially isotropic initially. Post irradiation torque measurements showed that the materials became slightly more isotropic. No changes were observed in saturation magnetization. Heating of control samples to 250°C did not produce changes in magnetic properties, showing that temperature alone is not a factor in producing the permanent changes which occurred under irradiation. All irradiations were performed at temperatures below 250°C. The changes due to proton irradiation are thought to be due to proton‐induced disordering.