[Radon levels in interiors in Valtellina, on the Angera hills and in the high valley of the Cervo river].
The results are reported of an investigation carried out from 1988 to 1990 in many houses in various sites in Lombardy and Piedmont. Measurements were actually carried out in Valtellina, in Angera--on the Lombard side of lake Maggiore--and in the high valley of the river Cervo, north of Biella. The patterns of radon immission in houses due to buildings materials and also to soil emissions are described. Average values of radon levels were obtained using track-etch detectors, whereas fluctuations were recorded daily with a unit capable of detecting alpha particles in real time. Some of the values obtained in 28 Valtellina towns were quite high--e.g., about 1,000 Bq/m3 in towns along the Insubrica fault. The area around Bormio and the Masino valley did not exhibit high radioactivity levels. A total number of nearly 100 houses were investigated in Angera; the highest radon concentrations were observed in cellars and especially in the areas where fractures are bigger and more diffuse. One particular house was accurately examined with real-time analysis of radon fluctuations. Four small towns in the pluton area were investigated in the valley of the river Cervo. In this instance, values were generally high (mean concentration: 842 Bq/m3); the highest concentrations were found in cellars and in ground-floor rooms.