The Diffusion of Imprisoned Resonance Radiation in Mercury Vapor

The rate of diffusion of imprisoned resonance radiation in mercury vapor.—The imprisonment of resonance radiation in mercury vapor was studied by measuring the rate at which resonance radiation emerged from one face of a slab of vapor after the exciting light, incident upon the other face, was cut off. The radiation was found to fall off exponentially, and the exponential constant of decay was measured for vapor densities ranging from 0.77×${10}^{15}$ atoms per cc to 29×${10}^{15}$ atoms per cc, corresponding to temperatures ranging from 60°C to 130°C. Slabs of two different thicknesses were studied, one 1.95 cm, and the other 1.30 cm. It was found that for vapor densities lower than about 4×${10}^{15}$ atoms per cc, the exponential constant varied approximately inversely as the square of the thickness of the slab, in qualitative agreement with the theory of the diffusion of imprisoned radiation as worked out by Milne.