Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
143. Measurement of radiation exposure levels using fluorescent substances
The extent of radiation exposure determines its impact on health. There are various measuring devices to detect levels of radiation and radioactivity.
The previous article explained that substances that illuminate by absorbing energy from other light sources—similar to luminous alarm clock dials—are called fluorescent substances. We also reported that fluorescent substances are used in many measuring devices for air radiation dose rates (scintillation detectors).
Actually, this fluorescence is used in the badge type of personal radiation dosimeters (also known as “glass badges”). People wear these around their necks to measure the level of external radiation exposure.
These glass badges have glass films containing silver, which changes its nature when exposed to radiation. When a glass badge is exposed to radiation for three months, the amount of altered silver increases in response to the cumulative level of radiation exposure.
Upon exposure to radiation, the silver transforms into a fluorescent substance that emits orange light when exposed to ultraviolet light. By observing the intensity of the orange light emitted by the badges under ultraviolet light, we can estimate the total level of external radiation exposure in 3 months.
144. Measurement of radiation by number of electrons
The extent of radiation exposure determines its impact on health. There are various measuring devices to detect the level of radiation and radioactivity.
As radiation rays pass through substances in their way, they also collide against them. Sometimes, electrons are ejected from those substances. This phenomenon is called ionization. The measuring device that detects the amount of emitted electrons is called a Geiger-M?ller tube, more commonly known as a Geiger counter.
When radiation passes the device, which is filled with stable gas, the radiation rays collide against the substances composing the gases. As a result, electrons are ejected—In other words, ionization occurs in the device. The measuring device incorporates a positive and negative electrode in it, and the emitted electrons (which are negatively charged) will flow toward the positive electrode. The level of radiation is estimated by measuring the number of electrons pulled toward this electrode.
Geiger counters are usually used to detect radioactive substances attached to the surfaces of clothes or people’s bodies.
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on 8th and 15th October 2017 was reproduced for MRIC Global under the author's permission.