In this blog post, we’ll explore everything from the differences between radiation, radioactive materials, and radioactivity to the units of radiation dose, its effects on the human body, and the basic information you need to know to properly understand radiation.
Although public concern about the dangers of radiation has risen significantly in the wake of past nuclear power plant accidents, few people have an accurate understanding of radiation. If we view radiation solely as a substance harmful to our bodies, it may actually be difficult to properly understand the relevant information. This is because radiation, when properly managed, can be put to good use in various fields such as medicine, industry, and research. Furthermore, information regarding radiation often circulates that mixes facts with exaggerations. Knowing the accurate facts helps us determine what is scientifically valid when encountering such information. Therefore, it is necessary to first understand the precise terminology and units related to radiation and to examine how radiation affects our bodies.
One reason the general public feels confused when encountering radiation is that there are many terms that seem similar. Radiation, radioactive elements, and radioactivity are related but do not mean the same thing. Radiation refers to particles or electromagnetic waves with enough energy to ionize matter; typical examples include particle radiation such as alpha and beta rays, and electromagnetic waves such as gamma rays and X-rays. Substances containing unstable atomic nuclei that emit such radiation while transforming into other nuclides are generally referred to as radioactive materials or radionuclides. For example, technetium-99m, used in medical nuclear medicine examinations, emits gamma rays while decaying into technetium-99. Radioactivity refers to the ability of a radioactive substance to emit radiation—that is, the rate of radioactive decay per unit time. Therefore, if we compare radiation to light, a radioactive substance can be likened to a light source, and radioactivity to a value indicating how intensely that source emits light. Meanwhile, although ultraviolet (UV) and visible light are also classified as electromagnetic waves in physics, it is necessary to distinguish them from ionizing radiation—the type typically discussed when explaining the effects of radiation on the human body or radiation protection. While some UV light possesses enough energy to ionize matter, visible light does not qualify as ionizing radiation.
Another important factor to keep in mind alongside terminology is units of measurement. Since units related to radiation represent different physical quantities, their respective meanings must be understood distinctly. First, the unit of radioactivity is the Bq (becquerel). The becquerel is a unit that indicates the rate of radioactive decay in a radioactive substance; if one decay occurs per second, this is 1 Bq. Therefore, if 10 decays occur per second, this amounts to 10 Bq. Although the becquerel is a unit that quantifies the radioactivity of a radioactive material, its value alone cannot determine how much radiation a person has actually been exposed to or the extent of the impact on the human body. This is because the actual radiation dose can vary depending on factors such as the type of radiation emitted by the radioactive material, its distance from the person, the duration of exposure, and whether the radioactive material has entered the body—even if the radioactive material has the same radioactivity. The unit of absorbed dose, which physically represents the energy received by the human body from radiation, is the Gy (gray). From the perspective of radiation protection, the effective dose—which takes into account the type of radiation and the sensitivity of body tissues—is the primary measure of the impact on the human body, and its unit is the Sv (sievert). Since the effective dose is a radiation protection indicator calculated by applying radiation weights and tissue weights to the degree of exposure of each tissue and organ, it does not simply refer to the amount of absorbed energy.
When radiation is directed at the body, it transfers energy to the tissues. If a very high dose is delivered in a short period of time, tissue reactions such as skin damage or burns may occur, and acute radiation syndrome may develop following very high whole-body exposure. However, when understanding the health effects of radiation, it is important to consider not only these acute effects but also the damage caused to cells and DNA. Ionizing radiation can damage DNA by ionizing molecules within cells or by generating reactive oxygen species; if cells fail to repair this damage properly, mutations and other changes may occur, potentially increasing the long-term risk of cancer. In particular, when radioactive material enters the body, internal exposure can occur due to the radiation emitted as the material decays. However, the risk of cancer from radiation exposure depends not only on the dose but also on the mode of exposure, the dose rate, the type of radiation, and the age and tissue of the exposed individual. Therefore, in the low-dose range, it is difficult to directly confirm whether individual exposures actually led to cancer; instead, the risk is estimated through epidemiological studies of various populations and research in radiation biology. International epidemiological studies have observed a relatively clear relationship between radiation exposure and an increased risk of cancer at doses exceeding 100 mSv, and there is a growing body of research suggesting that the risk of cancer may also increase at lower doses. However, there remains uncertainty regarding the precise quantification of risk at low doses.
To manage these radiation risks, radiation protection standards establish dose limits and aim to keep exposure as low as reasonably achievable. In South Korea’s radiation safety management, different standards are applied to the general public and radiation workers. The effective dose limit for the general public is, in principle, 1 mSv per year, while for radiation workers, the effective dose is managed so that it does not exceed 50 mSv in any single year and does not exceed 100 mSv over a five-year period. It is important to note that these dose limits are not simply the sum of all exposures—such as natural radiation or medical exposure during patient care—applied to the general public, but rather standards applied to planned exposure situations subject to radiation protection. Natural radiation originates not only from the earth and the atmosphere but also from radioactive materials present in food, water, and our own bodies. The level of exposure to natural radiation varies significantly depending on the region and an individual’s living environment; recent international assessments estimate the global average annual effective dose from natural radiation to be approximately 3.0 mSv. This figure differs from the 2.4 mSv estimate widely used in the past; however, it does not mean that the exposure levels of people worldwide have suddenly increased, but rather reflects improvements in assessment methods and data.
Since radiation is generally invisible to the naked eye and difficult to detect through smell or other senses under normal circumstances, it is not easy to intuitively assess its presence and risks. The Chernobyl and Fukushima nuclear accidents are prime examples demonstrating that radiation and radioactive materials can have a significant impact on society and the environment if not properly managed. However, this does not mean that all information regarding radiation should be viewed as a source of vague fear. Radiation is utilized in various fields, including medical diagnosis and treatment, non-destructive testing, sterilization and disinfection, as well as industry and research; it is a technology that can be put to good use provided it is properly managed and radiation protection measures are in place. The key is not to underestimate or exaggerate the risks of radiation, but to distinguish and understand concepts such as the types of radiation, radioactivity, exposure dose, exposure time and route, and dose rate. Since this information pertains to health, it is important to critically and proactively evaluate it based on scientific evidence and reliable data, rather than making judgments based solely on unverified rumors or isolated figures.
