ABSTRACT
It is absolutely essential that source strength can be uniquely defined. This
is because otherwise an accurate dose calculation cannot be made and
calculations for radiation shielding cannot be performed. In the early years
of the twentieth century only radium and radon were used for brachyther-
apy and dosimetry was essentially only milligram-hours (mgh) for radium
or millicuries-destroyed (mcd) for radon. These measurements units were
clearly inadequate.
