I have a comment about the last two lines on page 72. It reads “The distinction between ‘natural’ and ‘man-made’ or ‘artificial’ radiation exposure has proven to be peculiar and unconstructive’ Is this true scientifically?
First, the terminology ‘natural’, ‘man-made’ or ‘artificial’ is vague in terms of science. These words are interpreted in the way stakeholders want.
Second, if uranium-bearing wastes from uranium fuel fabrication facilities are taken as an example, they are representative man-made substances and their uranium-235 is usually enriched. This means uranium-234 is also enriched. Its specific radioactivity is quite large and radon is one of its decay products. Radon causes serious radiological detriments in the distant future. Are the radon emanation coefficients of uranium-bearing wastes the same as those of natural soils and rocks which contain uranium? Definitely they are not. Typical emanation coefficients for rock and soil range from 0.05 to 0.7 according to UNSCEAR 2000 Report, but special types of soil are included. The word ’special’ means ‘non ubiquitous’. They are alum shale in northern Europe, diatomite in Denmark and agricultural soil in Hawaii all of which has very large emanation coefficients. This information is obtained from original paper referred to by Nazaroff’s “Soil as a source of indoor radon: generation, migration, and entry”(1988). Care must be taken if the word ‘natural’ is used to mean ‘ubiquitous’. In terms of ‘ubiquitous’, radon emanation coefficients should be take from Barretto’s Ph.D. thesis “Emanation characteristics of terrestrial and lunar materials and the 222Rn loss effect on the U-Pb system discordance (1973). According to this paper, radon emanation coefficients for ubiquitous soil and rock are not so large. On the other hand radon emanation coefficients for uranium-bearing wastes break into two types. One type is for uranium-bearing wastes which contain UO2 particles. Radon recoil range in UO2 is about 14nm. Although the particle size of UO2 ranges mainly below 1µm, radon will not be able to emanate so easily. The other type is for uranium-bearing wastes which contain once-dissolved uranium deposited on filter sludge or precipitation agents. The size of this type uranium is very small, maybe below several nanometers. Therefore most of radon emanates unless there are any obstacle in the radon’s travel direction. The radon emanation coefficients for the latter type uranium-bearing wastes are larger than those of ubiquitous soil and rock. The uranium-bearing wastes of the former type are usually easy to be decontaminated and so will be harmless. But the decontamination of those of the latter type is very difficult and so will become harmful in the distant future, especially if a large amount of them is buried in a shallow land.
The issue raised above also holds true for artificial substances like phosphorus fertilizer containing radium which once has gone through chemical dissolving process.
Would you please give the clear definition of terminologies and scientific explanation if you claim the last two lines on page 72.