Alpha Recoil and Radon Emanation

The a-particle is the most massive of all radioactive decay products (not including, of course, daughter products and fission products). As an nf-decay occurs, a daughter element is produced along with the or-paiticle. This process occurs with conservation of momentum. Therefore, the newly produced daughter element recoils in the opposite direction from that in which the o -particle was emitted. This recoil is similar to that of a gun (and the person holding it) as a bullet is fired. The distance of the 

Actinides and Their Daughter and Fission Products Chap. 13 

Rn dose of nonsmoking individuals with lung cancer is difficult to estimate because people move from house to house and place to place over their lifetimes thus levels of exposure that may be considered dangerous are not well established. For these and other reasons, indoor Rn remains a contentious issue in scientific and regulatory circles (cf. Hopke 1987 Nazaroff and Nero 1988). 

A soil with 5 pCi/g of Ra, has an emanation coefficient of 0.20, an average porosity of 0.3, and a solid density of 2.7 g/cm. Therefore, the bulk density is about 1.9 g/cm. Calculate the average Rn concentration in the soil gas, assuming secular equilibrium. 

If secular equilibrium is attained, then 1 gram of soil, along with its entrained air, also contains 5 pCi of Rn, 1.0 pCi (20%) of which escapes to the soil gas. With a porosity of 0.3, 1 gram of soil contains 0.16 cm of air. The Rn concentration in soil gas is thus 6.3 pCi/cm, or 6300 pCi/Lof soil gas. Compared to the U.S. EPA s recommended maximum level of 4 fCi/L of Rn in indoor air, this is a huge Rn concentration  

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