Irradiation disordering ofNi3Mn by replacement collision sequences

Abstract

Replacement collision sequences have been investigated in ordered ${\mathrm{Ni}}_3$Mn during thermal-neutron irradiation near liquid-helium temperature. Decreases in saturation magnetization were measured as a function of increasing neutron fluence in samples with different degrees of long-range order. These magnetic changes are related, through a unique dependence on sample order, to the production of replacement collision sequences by irradiation. This dependence has been determined by computer model calculation. The results of four irradiations on samples of different degrees of long-range order yield an average of 132 ± 10 replacements in sequences per 450 eV ($n,\gamma$) recoil. Arguments are presented which suggest these 132 replacements are produced in one or two long sequences rather than in many short sequences. These results are compared with previous experiments and computer calculations on replacement collision sequences.