Two papers have recently been published - Part 1 is on granite and radiation, and Part 2 is on granite and radon specifically. The papers are available for review in the RadonLeaders.org Radon Research section.
Below are my views on Part 1:
The paper is well written, and contributes to the literature; however, I have comments regarding the radiation paper, and maybe Joe A. can address them:
1) it appears the granite cores were measured without encapsulation, so a U-238 activity based on Pb-214 or Bi-214 fails to account for the loss of radon from the sample, which, based on literature and measurement values, is roughly 20% (range of 10-50%). Thus, the reported results are too low. In theory, one can compare the concentrations determined for Th-234 and Pa-234m (prior to Rn-222) to those determined for Pb-214 and Bi-214 (after Rn-222) to assess the radon emanation rate, however, in reality, the low efficiencies (63 keV of Th-234), low emission branches (Pa-234m), and interferences (92 keV of Th-234) make this comparison impossible for the poor statistics that exist at these concentrations. Did you account for gamma attenuation (self-absorption) by the stone matrix? If not, the results would be greater, by a factor based on the energy of the gamma rays used.
2) the maximum concentrations for U-238 and Th-232 that are provided in Table 1 are several times less than those I and others have measured in several granites. For our results, the doses would be significantly greater than those provided in the paper.
3) while I agree that dose determinations for direct contact with granite are very conservative, since gamma levels decrease with the square of the distance, a distance of 15 cm (6 inches) does not seem conservative. For 10 times closer, the gamma fluence is 100 times greater. I would like to know the estimated dose for 1 hr on contact, as I view this as much more realistic of someone sitting reading the newspaper, preparing or eating dinner, etc.
My opinions,
Mike Kitto
United States