Thoron and radon fluxes from the island of Hawaii

The accumulator method has been used to determine the flux of thoron and radon from 42 varied sites in Hawaii. This is the first part, aimed at measuring source terms, of a two-part study of the use of the decay product of thoron, Pb-212, as an atmospheric tracer. It was of particular interest to scientists at the baseline atmospheric sampling laboratory on Mauna Loa to know the origin of Pb-212 in their air samples. The observed average flux from lowland soils was 173 mBq m−2s−1 (4.7 pCi m−2s−1) on the wet eastern side of the island and 854 mBq m−2s−1 (23 pCi m−2s−1) on the west. Barren lava yielded 20 mBq m−2s−1, which is thought sufficient to contribute a significant amount of Pb-212 to the air stream after a path of a few miles over lava. A comparison of the radon flux measurements with a previous survey indicated that there are seasonal variations of radon and thoron fluxes.