Specification of units for natural uranium and natural thorium. Statement of the national council on radiation protection and measurements (NCRP).

Abstract

Feeling that the use of the “special” curie for natural uranium and thorium has led to confusion, the NCRP recommends that this unit be replaced by units of mass. Previously stated values of the maximum permissible body burden (MPBB) and maximum permissible concentration in air and water (MPC) for uranium may be converted to mass units by multiplying them by 3 × 106 γg per “special” microcurie. Since the isotopic composition of natural thorium is not constant, the NCRP recommends that established MPBB and MPC values for each individual isotope be used instead of defining a limiting concentration for all natural thorium.