Key facts
- Ionizing radiation is a type of energy given off by certain atoms in the form of electromagnetic waves or particles.
- People are exposed to natural sources of ionizing radiation, including what is found in soil, water and plants, and to other man-made sources such as X-ray machines and medical devices.
- Ionizing radiation has many useful applications, including its uses in fields such as medicine, industry, agriculture, and research.
- As the use of ionizing radiation increases, the potential for health risks increases if it is not used or contained properly.
- Severe health effects such as skin burning or acute radiation syndrome can occur when radiation doses exceed very high levels.
- Exposure to low doses of ionizing radiation can increase the risk of long-term effects, such as cancer.
What is ionizing radiation?
Ionizing radiation is a type of energy given off by certain atoms and transmitted in the form of electromagnetic waves (gamma rays or x-rays) or in the form of particles (beta or alpha neutrons). The spontaneous disintegration of atoms is called “radioactivity,” and the excess energy released is a form of ionizing radiation. Unstable elements that decay and emit ionizing radiation are called radionuclides.
The unique properties of all radionuclides are determined by the type of radiation they emit, the energy of that radiation, and its half-life.
Activity, which is used as a measure of the amount of radionuclides present, is measured in a unit called the becquerel (Bq), and one becquerel is equivalent to one decay process per second. The half-life is the time required for the activity of radionuclides to decline due to radioactive decay to half their initial value. The half-life of a radioactive element is the time it takes for half of its atoms to disintegrate. Half-lives range from just a fraction of a second to millions of years (for example, the half-life of iodine-131 is 8 days while the half-life of carbon-14 is 5730 years).
Radiation sources
People are exposed to natural sources of radiation as well as man-made sources on a daily basis. Natural radiation comes from many sources, including more than 60 naturally occurring radioactive substances found in soil, water and air. Radon is a natural gas that comes from rocks and soil, and is the main source of natural radiation. Every day, people are exposed to radionuclides through inhalation and ingestion from the air, food and water.
People are also exposed to natural radiation from cosmic rays, especially at high altitudes. On average, 80% of the background radiation dose that humans receive annually comes from naturally occurring terrestrial and cosmic rays. Exposure levels to background radiation vary geographically due to geological differences. Exposure in certain regions can be more than 200 times higher than the global average.
Radiation exposure also comes from man-made sources ranging from nuclear power generation to medical uses of radiation for diagnostic or treatment purposes. Today, medical devices, including X-ray machines and CT scanners, are the most common man-made sources of ionizing radiation.
Exposure to ionizing radiation
People can be exposed to ionizing radiation under different circumstances, at home or in public places (general exposure), at their workplace (occupational exposure), or in a medical setting (medical exposure).
Radiation exposure may occur through internal or external pathways.
Internal exposure to ionizing radiation occurs when radionuclides are inhaled, ingested, or otherwise enter the bloodstream (for example, by injection or through wounds). Internal exposure stops when the radionuclides are eliminated from the body, either spontaneously (through waste, for example) or as a result of treatment.
External exposure may occur when airborne radioactive materials (such as dust, liquid, or aerosol) deposit on skin or clothing. This type of radioactive material can often be removed from the body by washing it. Exposure to ionizing radiation can also occur as a result of radiation from an external source, such as exposure to medical radiation from X-rays. External radiation stops when the radiation source is removed or when the person leaves the radiation field.
For radiation protection purposes, exposure to ionizing radiation can be classified into three exposure situations: planned, existing and emergency. Planned exposures result from the intentional introduction and operation of radiation sources for specific purposes, such as in the medical use of radiation to diagnose or treat patients, or the use of radiation in industry or research. Existing exposure occurs when radiation is already present and a decision has to be made about controlling it - for example, exposure to radon in homes or workplaces or exposure to natural background radiation from the environment. Emergency exposures result from unexpected events that require an immediate response, such as nuclear accidents or malicious acts.
Medical use of radiation accounts for 98% of the contributing factors to population dose from all anthropogenic sources, and represents 20% of total population exposure. Annually worldwide, more than 4,200 million diagnostic radiological examinations are performed, 40 million nuclear medical procedures are performed, and 8.5 million radiotherapy treatments are given.
Health effects of ionizing radiation
The type of damage that radiation causes to tissues and/or organs of the human body depends on the radiation dose to which it is exposed, or on the absorbed dose, which is measured in a unit called the gray (Gy). The damage likely to result from the absorbed dose depends on the type of radiation and the sensitivity of different tissues or organs.
Effective dose is used to measure ionizing radiation in terms of its potential to cause harm. The sievert (Sv) is a unit for measuring effective dose that takes into account the type of radiation and the degree of sensitivity of tissues and organs. It is a way to measure ionizing radiation in terms of its potential to cause harm. In addition to the amount of radiation (dose), an important parameter is the dose transmission rate (dose rate), which is expressed in microsieverts/hour (μSv/hour) or millisieverts/year (mSv/year).
If radiation exceeds certain limits, it can impair the functions of tissues and/or organs and lead to severe effects such as skin redness, hair loss, radiation burns, or acute radiation syndrome. The higher the dose quantity and the higher the dose rate, the more severe the effects become. For example, the threshold dose for acute radiation syndrome is about 1 Sv (1,000 mSv).
If the radiation dose is low and/or received over a long period of time (low dose rate), the risk is much lower because the damage is more likely to be repaired. There is still a risk of long-term effects such as eye blockage or cancer, but they may appear years or even decades later. Effects of this type will not always occur, but the probability of them occurring is proportional to the radiation dose. This risk is higher for children and adolescents because they are more sensitive to radiation exposure compared to adults.
Epidemiological studies in populations exposed to radiation, such as atomic bomb survivors or patients treated with radiation, have shown a significant increase in cancer risk in people exposed to doses higher than 100 mSv. More recently, some epidemiological studies in individuals who experienced medical exposure during childhood (pediatric CT) have indicated that the risk of cancer may be increased even at low doses (between 50-100 mSv).
Exposure to ionizing radiation in the prenatal stage may lead to brain damage in fetuses after exposure to an acute dose exceeding 100 mSv in the period between the eighth and fifteenth weeks of pregnancy, and 200 mSv in the period between the sixteenth and twenty-fifth week of pregnancy. Before week 8 or after week 25 of pregnancy, human studies have not shown a risk of radiation on fetal brain development. Epidemiological studies indicate that the risk of cancer following fetal exposure to radiation does not differ from the risks resulting from exposure to radiation in early childhood.