Dense lithium fluoride for gamma-ray-free neutron shielding

Abstract

A simple method of processing powdered LiF into dense and strong LiF, suitable for self-supporting neutron shielding, was developed. The processing was carried out in two stages. In the first stage, chemically pure LiF powder was slip-cast and sintered for periods of from 1 to 5 hours at temperatures ranging from 500° to 840°C, in order to establish the best conditions for making dense and volume-stable LiF aggregate. Aggregates were prepared with densities in the range 52 to 92% of theoretical, depending on sintering temperature and time. Maximum density was achieved by sintering at 700°C for 3 hours. In the second stage, dense and stabilized LiF aggregate was graded, pressed into shapes at 4000, 6000 and 8000 psi, and heated at 600° and 800°C to find the best conditions for making dense compacts. LiF compacts, as large as 8 3 4 by 4 1 2 by 3 in., with densities in the range 78 to 85% of theoretical, were prepared. Maximum density and good mechanical strength were attained when the graded aggregate was pressed into shapes at a pressure of 8000 psi and the shapes were heated for five hours at 800°C. The material can be cut and machined to close, dimensional tolerances.