The radiation exposure of the majority of persons professionally engaged in handling radiation sources and radioactive substances is less than about 1 rem per year, or less than one fifth of the maximum permissible dose allowed for radiation exposure of the gonads. A number of countries have reported that the genetic dose to the whole population arising from the dose received by occupationally exposed persons, who constitute only a small fraction of the total population, is about 0.1 - 0.2 mrem per year.