At the BEV two cylindrical cavity ionisation chambers have been establ
ished as primary standards to measure air kerma for Cs-137 gamma rays.
The design of both chambers is the same, the chambers only differ by
the specifications of the graphite they are made from. The main volume
of the cavity was determined by two independent methods, i.e. length
measurement of the diameter and of the depth of the cavity and also by
filling the cavity with water. The applied correction factors for air
density, recombination losses, humidity, stem scattering, wall attenu
ation, wall scattering, mean ori in of electrons, axial non-uniformity
and radial non-uniformity are described. The air kerma rates measured
by the two standards agree within 0.33%.