External doses to humans from 137Cs in soil.

Calculations of absorbed doses in organs of the human body and the total effective dose due to Cs in soil as a source of external exposure are presented in this work. Calculations were done using the MCNP-4B software package. The assumption was made that photons with an energy of 662 keV are emitted in a cylindrical volumetric source in soil up to the depth of 20 cm. Depth distributions of Cs at 19 locations around Kragujevac (a city in central Serbia) were measured by a HPGe detector. An ORNL phantom of an adult human standing on the soil above the center of a cylindrical radioactive source was used to calculate the conversion coefficients, i.e., absorbed doses in an organ per unit specific activity. The conversion coefficients in organs are given as a function of the source depth in soil. The largest absorbed dose was found in skin. The annual effective dose in humans was estimated from these calculations and the measured activity depth profile of Cs in soil. The average effective dose was found to be 3.17 microSv y. This value was rather small in comparison with other sources of natural ionizing radiation. One may conclude that Cs was a negligible source of external exposure in the area around the city.