Abstract
The radiation distribution in water around caesium-137 K-type sources has been measured and the experimental results used to provide data for an expression for dose calculations which may be conveniently applied in computer programs. The calculated absorbed dose rate obtained in this manner is estimated to be within 3% of the actual dose rate for any point in water up to 8 cm from the source. It is also suggested that the strength of a brachytherapy source be expressed in terms of an experimental exposure rate at some well-defined distance since this quantity may be determined more precisely and with less ambiguity than source activity.