Airborne radioactivity monitors put up in a network as a warning system in case of nuclear accidents were used to gain insight in the temporal variations of 222Rn and its decay products. Average equilibrium equivalent decay product concentrations (EEDCs) over a period of five years for stations a,cross the country range from I to 3 Bq.m ". Hourly averaged concentrations show a diurnal variation at all stations. The amplitude of this variation is maximal in summer and minimal or nonexistent in winter. Superimposed is a seasonal variation with a maximum in late autumn and a minimum in spring, Wind velocity appears to be the major variable controlling the variation in EEDC in the outdoor environment of the Netherlands, Humidity seems to be correlated with the EEDC of 222Rn, probably because, due to plateout, a better equilibrium between 222Rn and its decay products is installed, Reduced EEDC during and shortly after rainfall seems to indicate a dilution of 222Rn in ground surface air due to enhanced vertical mixing below the rain cloud.

Radon and thoron progenies in Dutch dwellings cause ~400 cases of lung cancer per year. Some 30% of the risk is due to thoron progeny, which demonstrates that the influence of thoron progeny is much larger than previously anticipated. This was concluded from a national survey in 2500 Dutch dwellings, built since 1930. Radon concentrations (15.6 ± 0.3 Bq m-3 on average) are correlated to type of dwelling, year of construction, ventilation system, location (soil type) and smoking behaviour of inhabitants. The survey data support the establishment of a comparatively low national reference level for radon in dwellings in the Netherlands of 100 Bq m-3, in line with recommendations by WHO and ICRP. Some 24 thousand of the 6.2 million dwellings in the Netherlands (built since 1930) are expected to exceed this level. Around 80% of these are located in the relatively small group of naturally ventilated single-family houses in two designated geographical areas. Radon concentrations above 200 Bq m-3 are rare in the Netherlands and simple and inexpensive measures will be sufficient to reduce enhanced radon concentrations to values below the national reference level. Thoron progeny concentrations (0.64 Bq m-3, on average) show correlations with year of construction and smoking behaviour. In 75 additional dwellings, a pilot study was conducted to determine the relationship between the exhalation of thoron from walls and the concentration of thoron progeny in the room. Thoron exhalation values exceeding the median value of 2.2 × 10-2 Bq m-2 s-1 by a factor 10 or more were found frequently, but enhanced concentrations of thoron progeny were measured only occasionally. Under very unfavourable conditions, however, for instance if phosphogypsum is applied as finishing material on all walls and ceilings in the house, strongly elevated thoron progeny concentrations may occur. This survey yielded a maximum recording of 13.3 Bq m-3. There is no reason to expect that such levels are specific to the Netherlands, indicating that in other regions with low radon levels, thoron may be a more important contributor to the population dose as well.

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Automated monitors for the determination of airborne radioactivity are widely in use as early warning systems for nuclear emergencies; however, the data acquired for this purpose are seldom used for analyzing spatial and temporal variations of natural radioactivity (especially radon and short-lived decay products). This paper shows that a specific type of airborne gross alpha/beta activity monitor, applied in several European emergency networks, can be effectively used to study the transport of 222Rn progeny in the outdoor environment. Real-time recordings (10-min sampling time) can, independent of the actual equilibrium ratio, be converted to the equilibrium-equivalent decay-product concentration (EEDC) of 222Rn. Medium volume air sampling and a slow-moving tape air sampler yield a low detection limit of < or = 0.1 Bq m-3. This paper further describes all factors and processes contributing to the uncertainty in the data obtained in this way; the total error in single recordings is estimated at 20-25% (95% confidence interval). Data of 222Rn progeny obtained from the Dutch National Radioactivity Monitoring network agree with results of other radon surveys.