Radioactivity and gamma-dose rates observed at the Morungaba granites, Southeastern Brazil.

A ground gamma-ray survey was conducted over part of a large granitic body located near the city of Campinas, eastern São Paulo State, Brazil. The dominant rock types are K-feldspar porphyries-rich granites, porphyritic biotite and hornblend-bearing granites, fine to medium-grained monzogranites and medium to gross grained, biotite and muscovite-bearing monzogranites. The radioactive element distribution reflects local geology, in part re-worked by weathering, and the most radioactive rocks are the K-feldspar-rich granites. The rate of the absorbed dose by the air reflects the integrated effects of the radioactive elements distribution. Most of the observed values vary between 67 and 130 nGy h(-1) and with localised spots with the absorbed dose rate values up to 193 nGy h(-1) and low values of ∼25 nGy h(-1). The mean air absorbed dose rate for the studied area is 77 nGy h(-1).

Development and calibration of a portable radon sampling system for groundwater 222Rn activity concentration measurements.

The assembling of a system for field sampling and activity concentration measurement of radon dissolved in groundwater is described. Special attention is given in presenting the calibration procedure to obtain the radon activity concentration in groundwater from the raw counting rate registered in a portable scintillation detector and in establishing the precision of the activity concentration measurements. A field procedure was established and the system tested during one year of monthly observations of (222)Rn activity concentration in groundwater drawn from two wells drilled on metamorphic rocks exposed at Eastern São Paulo State, Brazil. The observed mean (222)Rn activity concentrations are 374Bq/dm(3) in one well and about 1275Bq/dm(3) in the other one. In both wells the (222)Rn activity concentrations showed a seasonal variation similar to variations previously reported in the literature for the same region.

Radium content in ground water from a granitic batholith of the metamorphic basement, eastern São Paulo State, Brazil.

The radon emanation method was applied to measure the activity of 226Ra, dissolved and associated with suspended solids, in the ground waters from two wells drilled in the Morungaba Batholith fractured granites, intruded in the metamorphic basement, eastern border of the Paraná basin in São Paulo State, Brazil. The water samples were collected from March 2003,to April 2004, with a time interval of about one month between sampling campaigns. The mean observed dissolved 226Ra activity concentrations in the two wells were 47.9 +/- 7.1 and 51.6 +/- 8.8 mBq/L. No systematic time dependence of the 226Ra activity concentration was clearly identified. The activity of 226Ra associated with suspended solids contained in 1L of ground water fell, during the sampling period, from 13 +/- 1 to 0.8 +/- 0.1 mBq in one well and from 4.9 +/- 0.3 to 0.6 +/- 0.1 mBq in the second well.