Radiation is energy traveling through space or matter, often in the form of waves or particles. This energy is released by a source and can interact with the surrounding environment, including living tissues. Radiation is a fundamental property of the universe, existing long before humans. However, human activities in medicine, industry, and power generation have added to the overall exposure. Understanding the topic requires looking at where this energy comes from, both naturally (Earth and space) and from human-created devices and practices.
Sources Originating from Nature
The largest source of radiation exposure for the average person comes from the natural environment, existing independently of human actions. This unavoidable background radiation is categorized into three main types: cosmic, terrestrial, and internal. These sources have been present since the formation of the planet, contributing a constant baseline exposure.
Cosmic Radiation
Cosmic radiation originates from the sun and deep space, consisting of high-energy protons and other particles that constantly bombard the Earth’s atmosphere. The atmosphere and the planet’s magnetic field act as natural shields, reducing the amount of radiation that reaches the ground. Exposure to cosmic rays increases significantly with altitude because there is less atmospheric shielding. People living in mountainous areas or frequent airline passengers receive a higher dose from this source than those at sea level.
Terrestrial Radiation
Terrestrial radiation comes from naturally occurring radioactive materials found in the Earth’s crust, such as uranium, thorium, and potassium-40. These elements are present in varying concentrations in soil, rocks, and water across the globe. A significant contributor is radon gas, a decay product of uranium found in soil. Radon seeps up from the ground and can accumulate in poorly ventilated indoor spaces, often becoming the largest source of natural background exposure for many people.
Internal Radiation
Internal radiation is caused by radioactive isotopes naturally present inside the human body. The most notable example is Potassium-40, a radioisotope essential for cell function. This isotope, along with others like Carbon-14, is incorporated into the body through daily food and water consumption. The amount of internal radiation exposure is relatively consistent among people, unlike the variable doses from cosmic and terrestrial sources.
Sources Generated by Human Activity
Human activities have introduced additional sources of radiation exposure that supplement the natural background. These man-made sources are primarily linked to medical applications, industrial processes, and consumer products. Unlike natural sources, the dose received from these is largely controllable through regulation and personal choice.
Medical Applications
Medical and dental procedures represent the largest contribution to man-made radiation exposure for the general public. Diagnostic tools like X-rays and Computed Tomography (CT) scans use radiation to create images of the body’s interior. CT scans deliver a higher dose than a standard chest X-ray because they take multiple images to create a detailed cross-sectional view. Nuclear medicine procedures also contribute, involving the ingestion or injection of radioactive substances, such as Iodine-131, to diagnose or treat diseases.
Industrial and Consumer Sources
Industrial and power generation activities involve the use of radioactive materials and devices. Nuclear power plants release small, controlled amounts of radioactive material into the environment during normal operation. Industrial processes utilize radiation sources for non-destructive testing, such as gamma radiography to check the integrity of welds, or gauging devices to measure material thickness.
Consumer products also contain minor amounts of radioactive material. Examples include ionization-type smoke detectors, which use a small amount of Americium-241. Older luminous watch dials used radioactive elements like tritium, though modern versions use safer alternatives. Security scanners at airports also emit radiation, but the dose from these devices is very small.
Measuring and Contextualizing Total Exposure
To compare the different origins of radiation, scientists use the Sievert (Sv) or its smaller form, the millisievert (mSv). This unit represents the effective dose and accounts for the potential health risk, allowing for a standardized comparison across different radiation types and affected organs. The average annual effective dose combines all sources of exposure, both natural and man-made.
The total average annual dose varies globally, but for a typical person, exposure is usually split between natural and man-made sources. In many developed nations, the overall dose is roughly 50% natural background and 50% man-made, though this ratio shifts based on individual medical history. Radon gas is the dominant element within the natural background, often accounting for half of the total natural dose.
Comparing doses helps put exposure into perspective. For instance, a single chest X-ray may deliver a dose equivalent to a few days of natural background radiation. The dose from a long-haul airplane flight, which increases cosmic ray exposure, might be comparable to a few dental X-rays. Modern medical technology has become a comparable source of total exposure for the general population.