Investigation of the structural changes taking place in a uranium-molybdenum alloy under the action of neutron irradiation

Abstract

An alloy of uranium with 9 wt.%molybdenum was subjected to neutron irratiation, after which the electrical resistivity was measured and the structure studied by x-ray and microposcopic analysis. Preliminary heat treatment allowed specimens to be obtained with an α +γ′ eutectoid structure having various grain sizes. It was established that the rate of diffusion leading to homogenization under the action of irradiation in annealed specimens is inversely proportional to the square of the grain size (the period of the lamellar eutectoid). In a homogeneous specimen (γ-phase) irradiation causes a change in properties and structure which rapidly (in 2–4 hours) attains a limiting value, which is explained as being due to radiation annealing. Disordering was found in the γ′-phase, with a transition to the cubic lattice which took place under the influence of irradiation during the first hours of exposure.

All these phenomena are satisfactorily accounted for on the basis of the theory previously developed [2], although the magnitudes of the thermal-spike region and of the energy liberated in it, equal respectively to 2.5 · 10⁻¹⁷ cc and approximately 2 Mev, are less than were determined in [2].