As an aqueous chemical dosimeter for measuring ionizing radiation, the chemical 4,4' (5-chloro-2-thenilidene) bis [N,N-dimethylaniline], a derivative of the leuco triarylmethane compounds was used. This chemical dosimeter is an aqueous solution composed of 10(-4) M leuco compounds, 10(-4) M ferrous ammonium sulfate, 10(-4) M sodium chloride and 7 X 10(-3) M of hydrochloric acid. This solution is colourless but it becomes blue-green or bright blue after irradiation. The optical density of this solution at the main absorption peak of 635 millimicron increases linearly with the increasing x-ray dose of from 50R to 2,000 R and no dose-rate dependence is found from 13.5 R/min to 270 R/min of 60Co gamma-ray, 896 gram rads was the measured value of the integral absorbed dose per exposure in panoramic tomography (Orthopantomograph type OP-2).
