Excerpt from Austrialina Radiation Protection and Nuclear Safety Aency. (2008). Safety Guide Radiation protection series No.15 Management of Naturally Occurring Radioactive Material (NORM)
Austrialina Radiation Protection and Nuclear Safety Aency. (2008). Safety Guide Radiation protection series No.15 Management of Naturally Occurring Radioactive Material (NORM) .
The decay chain starting with 222Rn can be conveniently grouped into two:
• The short-lived radon decay products 218Po, 214Pb, 214Bi and 214Po have a collective half-life of approximately 30 minutes, which means that they will grow in to a stream containing just 222Rn within 30 to 60 minutes; if separated from the 222Rn they will decay with a half-life of approximately 30 minutes.
• The longer-lived radon decay products consisting of 210Pb, 210Bi and 210Po. The 21 year half life of 210Pb means that while these grow in to radioactive equilibrium with the parent 222Rn slowly, they persist in equipment for significant periods.
As all the decay chain members below radon are solids, they will not indefinitely follow the fluid flow lines in the equipment. Instead they will tend to accumulate at points of impaction, such as control valves, orifice plates, pump suction strainers and pump impellers, and will also accumulate where flows are very low, such as in a storage vessel. There is also the possibility of a thermal precipitation effect in heat exchangers. These accumulation points can be thought of as being inefficient filters, which separate the radon from its decay products.