Radon emanation from coals: effects of moisture and particle size.

The emanation of 222Rn from several coal samples (including lignites) was measured as a function of particle size and water content. From 10 to 0.85 mm, particle diameter had no measurable effect on 222Rn emanation. However, the fraction of 222Rn emanated did have a linear dependence on water content, the upper limit observed being equal to the weight fraction of water in the coal. Coals and lignites having typical concentrations of 238U emanate no more 222Rn than do comparable masses of typical soils. Our results appear to have implications for the spatial relationship between the 226Ra atoms and the pores in the coals on the scale of the 222Rn recoil range (0.05 micron).