Enhanced sensitivity of chemical dosimeters using liquid-core optical waveguides

The spectrophotometric sensitivity of chromophoric chemical dosimeters can be enhanced by increasing the optical path length through the light absorbing medium. This approach is used with optical waveguide (OWG) dosimeters, consisting of liquid-phase light-propagating media filling the core of a long, thin flexible polymer tubing. The liquid phase consists of dimethyl sulfoxide, N, N,-dimethylformamide, or triethyl phosphate solutions of hexa (hydroxyethyl) pararosaniline cyanide, a wellknown radiochromic dye precursor, which on irradiation converts from the leucoform into a brightly colored dye chromophore. The experimental design is described, as well as the influences of some experimental parameters: length of the OWG, curvature of the waveguide loops, cross section of the liquid light-guiding core, the temperature and the solvent. It was shown that concentrations of the radiation-generated dye as low as 5 × 10⁻⁸ mol dm⁻³ (corresponding to absorbed doses of about 10 mGy) can be measured on a standard spectrophotometer using a 100 cm long waveguide. It was also shown that sensitivity (optical absorbance increase per unit length per unit dose) was the same whether the light passed on a straight path or through a multiply looped waveguide as long as 150 cm. It is suggested that such long OWG assemblies can be used for enhancing the response of chemical dosimeters for medical and radiation protection applications, as well as in analytical chemistry and for chemical kinetics studies.