The source strength of encapsulated 60Co gamma-ray brachytherapy sources for the high dose rate remote afterloader was measured by the newly developed sandwich method. The calibrated JAPM sub-standard dosemeter whose collecting size is 6 mm in diameter and 20 mm long was used with a digital voltmeter capable of four digits. A sandwich output measuring device made of lucite which has two build-up caps and a bar to fix a guide tube for source capsule was used to achieve a precise result at a short distance from the source. A space between two build-up caps is fixed at 16.0 cm to reduce an error due to geometrical setting up, in the just middle of which the source is transfered through a thin plastic guide tube from a source container. Correction factors were calculated for finite size of the ionization chamber and multi-cells source to regard them as a point detector and a point source. The output is given in the unit of R min-1 cm2 or Gy min-1cm2. The intercomparison of the source strength was also performed with 33 source capsules in 12 radiotherapy facilities.
