Radiation Safety Exploration Using Radio-photoluminescence Dosimeter for Crookes Tubes in Junior and Senior High School in Japan

Background: Crookes tube is utilized in junior high and high schools in Japan to study the character of electrons and current, and not for radiological education. There is no official guideline or regulation for these radiation source to the public. Therefore, most teachers have no information about the leakage of X-rays from Crookes tube. The peak energy of X-rays is approximately 20 keV, and it is impossible to measure using conventional survey meters. Materials and Methods: Each leakage dose of low energy X-rays from 38 Crookes tube in the education field, such as junior and senior high schools in Japan, was explored by the teachers in the school using radio-photoluminescence (RPL) dosimeters. Before and after the measurements, the dosimeters were sent by postal mails. Results and Discussion: At the exploration in this study, it was estimated that the 70 ㎛ dose equivalent, H_p(0.07) of X-rays from 31 Crookes tubes were smaller than 100 µSv in 10 minutes, at the distance of 1 m, where the Crookes tube was usually observed. However, the highest dose was estimated as 0.69 mSv by an equipment with the full power. Furthermore, one Crookes tube exhibited 0.62 mSv with minimum output power of the induction coil. This relatively large dose was reduced by the shorter distance of discharge electrodes of the induction coil. Conclusion: The leakage dose of low energy X-rays from 38 Crookes tube was explored using RPL dosimeters. It was estimated that the H_p(0.07) of X-rays from 31 Crookes tubes were smaller than 100 µSv in 10 minutes at the distance of 1 m, while some equipment radiated a higher dose. With this study, the provisional guideline for the safety operation of Crookes tube is established.