The Response of Lithium Fluoride to Reactor Neutrons

A study has been made of the response of normal lithium fluoride and that depleted of ⁶Li when exposed to pure gamma rays and to the mixed neutron-plus-gamma fields of reactors. Results from a study of the glow curves of the two materials after gamma-ray exposure are similar. However, after reactor exposures in a known field of thermal neutrons and gamma rays, significant differences were found in the 200 and 275°C glow peaks for approximately the same integrated area under the curves. Presumably these are principally due to differences in the specific ionization of recoil electrons from gamma rays relative to that of the alpha particles and ³H recoils from the ⁶Li(n,α)³H reaction. By using thermal-neutron shields of ⁶Li or cadmium, the pure gamma dose can be obtained from the usual gamma-ray glow curves from either material. The response (integrated light output) of the depleted LiF per 10¹⁰ n/cm²(th) equals that caused by 0.7 rad of ⁶⁰Co gamma rays, while the corresponding response of the normal phosphor exceeds that from 200 rad of gamma rays. Having determined the response of these materials to thermal neutrons, and considering the relative independence of the response (per rad) upon gamma-ray energy, one may use the depleted phosphor to determine gamma-ray dose within a reactor environment and the normal material as an auxiliary thermal-neutron-plus-gamma-ray detector.