Chemical dosimeters are best qualified for the measurement of high, kGy-range, doses, utilising the chemical reactions induced by ionising radiation within the medium. The radiolysis of water develops radicals which irreversibly oxidate the metal ions of the solution. FRICKE-Dosimetry uses ferrous sulphate where Fe2+ is translated to Fe3+. The mechanism of this dosimeter lies in the proportionality between the applied energy dose and the concentration of produced Fe3+.
To determine the dose, the concentration of Fe3+ must be quantified. For this, the optical density E (extinction) of the original and the irradiated dosimeter solutions are measured with a spectral photometer and compared. Iron(III)ions show an absorption maximum at 304 nm. The absolute value of the extinction around this wavelength is directly proportional to the absorbed dose.
FRICKE-Dosimetry is applicable in the dose range between 5 Gy and 0.4 kGy. For higher doses, the system goes into saturation. With a modification of the solution it is possible to shift this measuring range to higher doses. I.e., the raise of the Fe2+-concentration effects that the saturation starts not until 1.5 kGy. The addition of Cu2+ (ferrous sulphate-copper sulphate-dosimeter) enables the measurement of doses of at least 25 kGy.