NRE VI, International Symposium, June 5-9, 1995, Montreal, ENVIRONMENT INTERNATIONAL, Vol. 22, Suppl. 1, pp. S3-S8,1996
NATURAL RADIOACTIVITY MAPPING OF GREEK SURFACE SOILS
A total of 1440 samples of soil, collected across Greece from the 1
cm surface layer, were analysed for natural radioactivity (Ra-226,
Th-232 & K-40). The samples were air-dried and then hermetically
sealed in 0.282 L plastic boxes covered with a film of epoxy resin to
ensure that no gases escape from them. Secular equilibrium of Ra-226
and Th-232 with their decay products was obtained before the samples
were analysed using high resolution Ge gamma-ray detectors. A
Unix-based in-house built complex Data Base/Geographical Information
System (DBGIS) was used to analyze the data and present them in map
form. The analysis of a second 1 cm thick sample, collected at several
sites at a depth of 10 cm, led to the statistically justified
conclusion that the natural radioactivity content of the surface and
of 10 cm deep soil layers do not significantly differ. According to
these results the natural radioactivity content of Greek surface soils
is rather low (mean ± standard deviation in Bq/kg):
Ra-226(U-238): 25 ± 19 Ra-228(Th-232): 21 ± 16 K-40: 355 ± 220
and entails a gamma-ray dose rate outdoors equal to 40 nGy/h. A
statistical analysis showed that only 90 samples, collected at 67
locations, have Ra-226 content exceeding their mean value by more than
1.65 std. dev. The Ra-226/Th-232 and Ra-226/K-40 concentration ratios
were equal to (mean value ± % std. dev.) 1.10 ± 44% and 0.06 ± 56%,
respectively.