5. Quantities and Units

Radiological protection has the general aim of protecting humans and non-human species in the environment from harmful effects of exposure to ionizing radiation. This requires a quantitative description of the exposure to external radiation and radiation from radionuclides incorporated in the human body. Consistent use of terminology and units when discussing quantities of ionizing radiation is critical when health and safety decisions based on measurements are to be made. The scientists who analyze the data collected and communicate the results of radiation measurements to decisions makers need to take care to ensure the data are as accurate as possible. In high-stakes, time-critical environment following a nuclear power plant accident, however, lower levels of accuracy may have to be accepted. “Quantities” used for the quantitative description of physical phenomena or objects are generally called physical quantities. The value Q of a quantity is generally expressed as the product of a number { } Q and a unit [ ] Q (BIPM, 2016):