Abstract
Concentrations of 238U, 232Th and 40K contained in the front glass of CRTs (cathode ray tube) of three television sets are measured by γ-ray spectrometry on the assumption of radioactive equilibrium in uranium and thorium series. The concentrations of 238U and 232Th are also measured by neutron activation analysis. The obtained results by the two different methods agree well within experimental uncertainty, showing that the radioactive equilibrium is found to be established in the present samples, and that the concentrations of 238U and 232Th in the glass can be measured by the γ-ray spectrometry as well as by the neutron activation analysis. We also found that although the obtained concentrations of 238U (6.5－13.5 ppm in weight) and 232Th (8.4－15.1 ppm) vary considerably between these three kinds of CRTs, those of 40K (average:7.45±0.05 ppm) are almost equal for all samples. Moreover, the radiation dose rates are estimated for γ-rays from the CRT. At distances larger than 30 cm from the surface of the front glass, even the dose rate (5.65×10-3 μSv / h) for the CRT containing the highest concentration of 238U and 232Th is smaller than one-tenth of that (7×10-2 μSv / h) for background radiation, and that is practically negligible.
