Natural radiation in Poland and its disturbance in an urban environment

Natural gamma radiation was investigated in both a rural and an urban environment in a two-part program. In the first part, outdoor doses were monitored for 2 yr at 300 locations throughout the country, mainly rural regions. The second series of measurements was performed in and around a medium-sized town. For 1 yr, the dose rates were measured in the open air and inside residential buildings. Surveys were carried out by means of TL dosimetric cards that were evaluated automatically and by a pressure ionization chamber. We found that in Poland the natural radionuclides from the upper layer of the earth produce outdoor dose rates ranging from 1.5 to 9 mu rad hr-1 absorbed in air and the terrestrial radiation contributes 20-70% of the total outdoor radiation. Significant variations were observed during different seasons of year. The population-weighted outdoor average found for the whole country amounted to 3.73 mu rad hr-1, i.e. 20% lower than the estimated world average. The natural outdoor radiation field is significantly altered in towns because of different ground beddings. Low-activity coverings made of asphalt or concrete reduce the dose rates above them by about 15%, while those made of certain kinds of stone increase the dose rates by 50-100%. Dose rates inside buildings are higher than those outdoors by 20-80%, depending on the building material.