NMR and electron microscopy studies on irradiated lithium hydride

Abstract Gamma-irradiated lithium hydride has been studied with pulsed NMR and electron microscopy. Cubic voids were seen in the micrographs, and were shown to be hydrogen gas bubbles. Formation of these bubbles caused LiH to swell as much as 25 volume per cent on irradiation. The average bubble size seems to be mainly a function of the irradiation temperature; the average size ranges from 80–1500 A for irradiation temperatures between 120 and 265°C. Hydrogen gas in the bubbles gives rise to a motionally-narrowed NMR signal. The longitudinal relaxation time T 1 , appears to be a function only of the gas density, as is expected for gases. The transverse relaxation time T 2 m is strongly affected by wall interactions and, therefore, decreases markedly with decreasing bubble size.