Pulsed nuclear magnetic resonance of gamma-irradiated lithium hydride

Some of the effects of ⁶⁰Co gamma irradiation on lithium hydride are described. Volume increase and nuclear magnetic resonance data are given for samples irradiated from 40 to 395°C. Maximum swelling occurs between 160 and 200°C; negligible swelling occurs above 300°C. Motionally narrowed proton and ⁷Li nuclear magnetic resonance signals appear on irradiation and increase with increasing swelling. These decomposition products, which are trapped inside the LiH, can amount to more than one-tenth the total sample at doses of 50 Grad. At this point, 25 volume per cent swelling has occurred and the growth rate has subsided. The hydrogen nuclear magnetic resonance signal has been shown to come from H₂ molecules by observation of the ortho-para conversion on cooling. Hydrogen densities derived independently from the longitudinal relaxation time and the swelling data are in reasonable agreement. The corresponding gas pressures range from 750 to 5000 atm. The H₂ is thought to be in bubbles which cause the volume growth, and recent electron microscopy results support this view. The ⁷Li signal has a Knight shift, and the lithium is present as metal particles. Above 200°C, the H₂ and Li back-react rapidly. Above 300°C this reaction takes place as fast as the decomposition, which was caused by the irradiation.