Ordered alloys reveal fundamental mechanisms of neutron damage production

Abstract

Ordered alloys have historically played an important role in investigating basic mechanisms of neutron irradiation damage. We have been particularly active in this field at Argonne National Laboratory, and in this paper we will review four different areas of our experimentation using ordered alloys. We will briefly review and critically re-examine our magnetic saturation measurements performed on Ni 3Mn during neutron irradiations. Disordering during thermal-neutron bombardment at 5 K uniquely revealed the existence, number and average length of replacement collision sequences. Confirmation of our analysis by others will be presented; some refinements will be introduced; comparisons with recent molecular-dynamic calculations will be drawn; and the (n, γ) recoil spectrum in Ni 3Mn will be reanalyzed. Overall, we conclude that 112 to 150 〈110〉 replacements occur, within one or two sequences, per (n, γ) recoil with an average energy of 492 eV. Similar measuremens on Ni 3Mn during fast-neutron bombardment at 5 K yielded the total number of replacements per typical 30 keV cascade and demonstrated that very few interstitials were produced at large distances from the cascade by 〈110〉 replacement sequences. We will discuss our very recent results on high-resolution TEM measurements of disordered zones in fast-neutron irradiated Cu 3 Au. These results have been compared with damage calculations for the accurately measured fast-neutron flux and energy spectrum in CP5 and reveal the spatial characteristics of the deposited energy in individual cascades. Resistivity measurements of Cu 3Au during fast-neutron bombardment at 150°C have revealed both the disordering process within cascades and ordering by irradiation-enhanced vacancy diffusion. These experiments provide a means of comparing different neutron energy spectra and studying irradiation-enhanced diffusion in a system amenable to theoretical treatments.