Study of optical absorbance and MR relaxation of Fricke xylenol orange gel dosimeters

Studies on the optical absorbance spectra of Fricke xylenol orange gel dosimeters were performed, in the wavelength range from 300 nm to 800 nm, in order to highlight some particular characteristics that can affect the achievable precision. The spectra are different mainly due to the different types of xylenol orange that was used and to a lower extent due to the different gelling agents (agarose or gelatine). The characteristic of variation of absorbance spectra versus dose, however, are similar in the various cases and can explain some peculiarities, as apparent effects of dose threshold. Changes of spectral shapes appear over the time after irradiation. Magnetic resonance measurements performed at various times after irradiation only reveal the slow changes due to the auto-oxidation effect, proving therefore that the modality of chelation of ferric ions by xylenol orange can affect the observed changes in the optical absorbance spectra.