Choice of sites and method of measurement for survey of external dose rate of natural background radiation in China

The principles of choice of sites for survey of external dose rate of natural background radiation in China are as follows: (a) Every surveyed district was determined on the basis of a county. (b) About 15 to 30 survey sites of outdoors, indoors and roads were chosen randomly in each district to be surveyed. (c) The distribution of sites should be as uniform as possible. And the factors concerning distribution of population, roadway and geology in the surveyed district were also considered. In order to meet different requirements and situations, ionization chambers, scintillation radiometers, spectrometers and altimeters were used in the survey of external dose rates. The height for measurement was standardized to be 1 +- 0.3 m above the ground. Each outdoor site should be 50 m or more apart from buildings and 20 m apart from highways. Five points were measured for each outdoor site with an area of 10 x 10 m2, while four corners and the centre of a room were measured for each indoor site. The survey points in the rooms were 30 cm away from walls. At each road site five points at a distance of about 10 m from the centre of the road were measured