Evaluation of the 210Po method at the Midwest uranium deposit, northern Saskatchewan, Canada

Vertical profiles of 210Po in soils near the Midwest uranium deposit and an associated surficial radioactive sandstone boulder train in northern Saskatchewan show a high 210Po background in air-dried forest litter (24 pCi/g) and Ah horizon soil (11 pCi/g) relative to lower soil horizons (<1 pCi/g). These high levels mask the 210Po signal from the radioactive boulders in the near-surface soil horizons. Only in the Bf and C horizons can the existence of the radioactive boulders be inferred from 210Po determinations. For comparative purposes profiles for 226Ra, U, Ni, and other trace elements are also presented. Escape of most of the Rn from near surface soils into the atmosphere, homogenization and decay of Rn, and precipitation of decay products back onto surface soils satisfactorily explain the field observations discussed here. Compared to the highly anomalous 222Rn signal in soil gases over this boulder train the 210Po contrast is very weak and is of little use for prospecting for this type of boulder train. The relatively high 210Po background in surficial materials relative to lower soil horizons dictates that great care be taken with the 210Po method; the deepest possible horizons should be sampled. (orig.)