A technique is described by which concentrations of 222Rn in water as low as 10 pCi/l can be determined by a 40-min count of a 10-ml sample. Preparation time is about 1 min/sample, and no special equipment is required other than access to a commercial liquid scintillation system.

An estimate of the incremental population lung exposures (WLM) attributable to the domestic use of ground waters containing z2zRn is made for the vicinity of Houston, Texas. Because of the complexity of the water distribution system, extensive water sampling was required to characterize the concentration of radon in the water in various areas. Models describing the transfer of radon from water to indoor air and the resulting indoor concentrations were developed and experimentally tested. Census data on population and housing characteristics were folded into the final model used to compute an annual population exposure of 4000 WLM (approx. 40,000 rem) to the 1.6 million inhabitants of the study area. The resulting estimates are discussed in the context of similar exposures brought about by other technological activities.

A new category for human radiation exposure, technologically enhanced natural radiation (TENR), is proposed. The purpose of the new category is to permit clear distinction between truly natural human radiation exposure and exposure which occurs due to alteration of the natural sources by non-nuclear technology. Examples of TENR, such as radium emission from coal fired plants, radon in natural gas, radium in fertilizer, radon in water and enhanced cosmic ray exposure in high altitude aircraft are discussed. It is concluded that creation of theTENR category would be useful because (1) it would facilitate direct comparison of increments to the radiation environment due to nuclear and conventional activities, (2) it would direct research to TENR which would perhaps uncover significant human exposure and (3) it would permit regulatory authorities to control unambiguously TENR exposures without having to decide in each instance whether the exposure was natural or man-made.

Theoretical and experimental literature dealing with the release of radon from water to air is reviewed and synthesized. Primary emphasis is placed on releases from domestic water supplies to indoor air within the context of a general indoor radon problem. The widely used assumption of 1 pCi/L increment in indoor air per 10 000 pCi/L in the water supply is valid, but regional and individual variations are important.

A simple passive sampler for 222Rn with up to 24-hr integration times can be constructed by using a diffusion barrier to regulate the effective sampling rate of an ambient temperature activated carbon bed. The diffusion element serves to make sampler performance relatively independent of the properties of the type of carbon used. Satisfactory results are obtained if the total effective sample volume is kept well below the equivalent air volume of the activated carbon bed. The influence of various temperature and Rn profiles on the sampler's performance have been examined by experiment and by simulation. The amount of Rn adsorbed may be measured by gamma spectroscopy, by outgassing into an alpha scintillation flask, or by desorption into a liquid scintillator. In the latter case, a sensitivity of 0.2 pCi l-1 is obtainable for 24-hr exposures.