Measurements of indoor radon concentrations and assessment of radiation exposure

In the past decade many international studies have established that the radioactive gas radon is responsible to a large extent for the radiation dose absorbed by the population. Consequently the Swiss Federal Health Office started and sponsored a research program called RAPROS (Radon Programm Schweiz, 1987–1991) to assess the relevant aspects of radon exposure in Switzerland.The average indoor radon concentration in Swiss living rooms is about 60–70 Bq m⁻³, this corresponds to an annual dose of about 2.2 mSv, but values largely exceeding 1000 Bq m⁻³ were also found. Often very strong temporal fluctuations of indoor radon concentrations were measured.The ground directly underneath buildings is the main radon source of indoor radon. The material properties that influence the radon production and transport in soils are: radium content, emanating coefficient and soil gas permeability; among them only the last one can vary over many orders of magnitude. The permeability is consequently the decisive factor that enables radon transport in the subsurface. To characterize the radon potential of soils a radon availability index (rav) was introduced.Our investigations have also shown that in karst systems the radon concentration in the air is often increased to 10–100 times higher than in buildings. This radon-charged air is able to travel over considerable distances through faults and cavities in the underground and reach living rooms built over karstified areas.     

A kinematics-uplift model for the HimalayanTibetan region

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Rapid laboratory analysis by neutron activation: experience in bauxite exploration

The efficiency of neutron activation as an analytical technique has been evaluated for exploration of lateritic and karstic bauxites in Sierra Leone, Guinea, Australia (Gove), Philippines and Jamaica. The 10-g bauxite samples are prepared in the field and sent to a central laboratory. With the “Automatic Bauxite Analyzer” — equipped with an isotopic neutron source — a single Al and Si determination can be made in 5 minutes. For calibration, standards are required which are similar in composition to the samples to be analyzed. Using sample pairs and averaging the results of three subsequent determinations an accuracy of ±2% Al₂ O₃ and about ±0.6% SiO₂ can be obtained. Time requirements, accuracy and cost of this technique are compared with wet chemistry and X-ray fluorescence. For an exploration programme incorporating for example 15,000 drill core samples, a 50% reduction in expenditure for analytic determinations can be achieved by applying neutron activation instead of X-ray fluorescence alone.     

Heat-generating radioelements in granitic magmas

Spatial variation trends of the radioelements U, Th and K in granitic units show distinct regularities: zonation patterns of U and Th (at fairly constant K contents) are common in individual granitic bodies. It is shown that radioelement abundance and distribution result from a combined migration-diffusion process in the fluid phase during and after solidification of the granite magma. The process is mainly governed by pressure and temperature gradients as well as by chemical potentials. Model calculations yield numerical values for the intrinsic diffusion coefficient (≈ 10⁻⁴ cm²/s) and migration velocity (0.2–2 cm/s) which are in agreement with laboratory experiments on comparable systems. The process distributing the radioelements is of limited duration; it is also clearly related to the cooling history of the granite. Analogies to the overall distribution of crustal radioactivity are discussed.