The Distribution of Indoor Radon Concentrations in a Large Population of Homes

One of the least understood qualities of radon and its associated risk is the relationship between its concentration at the source and the statistical distribution of concentrations found in indoor environments. In this presentation I will clarify several of the important factors and provide a simple statistical model for discussing and communicating distribution qualities of our primary source of ionizing radiation. A few of these are as follows: (1) Radium, like most other minerals in the earth’s crust, has an overall log-normal distribution in concentration; (2) The factors which affect the concentration of indoor radon do so in a multiplicative fashion; (3) The measured data sets of indoor radon concentrations follow a log-normal distribution which is characterized by a skewed distribution with a long tail to hazardous levels; (4) A fundamental comparison property for such a distribution is the geometric ratio of levels and not the arithmetic difference; and (5) The response of the soil gases to the building stock and ventilation parameters thereof provide an additional factor of approximately 2. These facts provide critical information for developing health strategies for states, communities and individual homeowners.