Spin Relaxation of Atomic Hydrogen in Fused Silica: Temperature Dependence

An unusual temperature dependence has been found for the spin-lattice relaxation time $T_1$ of the hydrogen atoms trapped in fused silica; $\frac{1}{T_1}$ is found to vary strongly with temperature in the range between 2 and 20°K and to approach proportionality to $T$ above 20°K. After removal of some of the hydrogen centers by thermal annealing, the relaxation is slower but has essentially the same temperature dependence. The data are interpreted in terms of a localized resonance mode of vibration having a large temperature-independent amplitude in the neighborhood of the hydrogen spin. The model proposed by Murphy fits the data accurately over four decades in $T_1$ with a characteristic frequency of 2.8 (${10}^{11}$) cps.