ISO/ASTM 51205 covers the preparation, testing and procedure for using the ceric-cerous sulfate dosimetry system to measure absorbed doses in water when exposed to ionizing radiation. The system consists of a dosimeter and appropriate analytical instrumentation. For simplicity, the system is referred to as the ceric-cerous system. It is classified as a reference standard dosimetry system. Ceric-cerous dosimeters are also used as transfer standard dosimeters or routine dosimeters. ISO/ASTM 51205 describes both the spectrophotometric and the potentiometric read-out procedures for the ceric-cerous systems.

The practice described applies only to gamma rays, X rays and high energy electrons and is applicable provided the following are satisfied:

the absorbed-dose range is between 5 times 10² and 5 times 10 ⁴ Gy;

the absorbed-dose rate is less than 10⁶ Gy/s;

for radionuclide gamma-ray sources, the initial photon energy is greater than 0,6 MeV;

for bremsstrahlung photons, the initial energy of the electrons used to produce the bremsstrahlung photons is equal to or greater than 2 MeV;

for electron beams, the initial electron energy is greater than 8 MeV.