The BIPM maintains primary standards for the determination of the quantity air kerma in x-radiation with generating potentials in the range from 10 kV to 250 kV. Three free-air ionization chamber standards cover this range:
one low-energy standard operating from 10 kV to 50 kV,
another from 25kV to 35 kV for mammography beams, and
the medium-energy standard from 100 kV to 250 kV.
For these standards, key comparisons with those of the national metrology institutes (NMIs) are made at a series of reference radiation qualities covering diagnostic and therapy radiation beams.
The results of all key comparisons are maintained in the BIPM key comparison database (KCDB) and some examples are illustrated in this poster.