Sources of radiation, a reference for radiologic technologists

Man with sources of radiation


Since the beginning of life on Earth, radiation has been a constant environmental factor affecting all living organisms. However, the general public is often not fully informed about the different sources of radiation that exist around us, encompassing both naturally occurring and artificially created types. It is estimated that approximately 50 percent of the radiation to which humans are exposed comes from natural sources such as cosmic rays, radon gas, and terrestrial radiation. The other 50 percent results from man-made sources, including medical procedures, industrial applications, and nuclear power production. This article delves into the wide range of radiation sources, highlighting their roles and impacts on our daily lives.

A worker manages a plutonium button. Historically, plutonium was viewed as a rare, primarily man-made element. In contemporary practices, remnants from its initial manufacturing processes, as well as plutonium reclaimed from dismantled nuclear arsenals, undergo a sophisticated reprocessing. This repurposing transforms these materials into high-quality plutonium metal, underscoring its sustained importance and utility in various applications.

Radiation surrounds us in various forms and emanates from multiple sources. It exists naturally and has been a part of the Earth’s environment since its formation. Natural radiation comes from the sun, pervades the atmosphere, and is embedded in the earth’s crust. Moreover, with the progression of technological advancements, numerous artificial or man-made sources of radiation have been developed. These include medical imaging devices, industrial equipment, and nuclear facilities. Interestingly, despite the proliferation of these man-made sources, natural sources of radiation still account for the majority of human exposure, typically four to five times that of artificial radiation.

Sources of Radiation
Sources of Radiation

Sources of Radiation Exposure

According to information from the Nuclear Regulatory Commission (NRC), there are several common sources of routine radiation exposure. These sources encompass a wide range of natural and man-made environments. Below is a list detailing these prevalent sources:

    • Possessing porcelain crowns or false teeth, which contribute approximately 0.07 mrem to your annual radiation exposure.
    • Use gas lantern mantles when camping (0.003 mrem)
    • Wear a luminous wristwatch (LCD) (0.006 mrem)
    • Use luggage inspection at airports (using typical x-ray machine) (0.002 mrem)
    • Watch TV (<1 mrem)
    • Use a video display terminal (<1 mrem)
    • Have a smoke detector (0.008 mrem)
    • Wear a plutonium-powered cardiac pacemaker (100 mrem)
    • Have had diagnostic x-rays (e.g., upper and lower gastrointestinal, chest) (40 mrem)**
    • Have had nuclear medical procedures (e.g., thyroid scans) (14 mrem average)
    • Live within 50 miles of a nuclear power plant (pressurized water reactor) (0.0009 mrem)
    • Live in a stone, brick, or concrete building (7 mrem)
    • Travel by jet plane (1 mrem for each 1,000 miles)
    • Live within 50 miles of a coal-fired electrical utility plant (0.03 mrem)
    • The NRC website has an interactive personal annual radiation dose calculator to estimate your personal dose.

Learn more about your radiation exposure

Terrestrial Radiation

Terrestrial radiation forms a significant part of natural background radiation, emanating from radioactive materials naturally present in the earth such as uranium, thorium, and radon. Key elements of concern in terrestrial radiation include common elements with radioactive isotopes in low abundance, such as potassium and carbon, as well as long-lived radioactive elements like uranium and thorium and their decay products, including radium and radon, which are intensely radioactive despite their low concentrations. Over time, the activity of these sources has been decreasing due to radioactive decay since the Earth’s formation. Notably, the activity of uranium-238 today is only about half of what it was originally, attributable to its 4.5 billion-year half-life. The implications of this gradual decline are minimal on human timescales, given the vast disparity between the half-life duration of these elements and the relatively short span of human history.

Terrestrial Radiation

Cosmic Radiation

Cosmic radiation constitutes a significant portion of natural background radiation originating from outer space. This radiation is comprised of penetrating ionizing radiation, which includes both particulate and electromagnetic elements. Cosmic rays, which are high-energy particles primarily originating from beyond the Solar System, have the potential to create showers of secondary particles as they interact with the Earth’s atmosphere. These secondary particles can sometimes penetrate down to the Earth’s surface. The sun and other stars continuously emit cosmic radiation towards Earth, similar to an unending drizzle of rain.

The intensity of cosmic radiation varies based on several factors including elevation, atmospheric conditions, and the protective influence of the Earth’s magnetic field. The amount of cosmic radiation increases significantly at higher altitudes, such as those experienced during commercial flights. At these altitudes, cosmic radiation can be substantially more intense compared to ground level, although it remains relatively low in terms of overall risk. For instance, it would require approximately 100 one-way flights between Toronto and Vancouver to match the radiation exposure obtained from other natural background sources in one year. This illustrates the relatively minor but notable impact of cosmic radiation on everyday life.

cosmic radiation

Lithium, beryllium, and boron are not only relatively abundant in the universe but also frequently found in increased quantities within particle showers produced by cosmic rays. Additionally, cosmic rays are responsible for the formation of both cosmogenic stable isotopes and radioisotopes, such as carbon-14, which are generated when cosmic rays interact with the Earth’s atmosphere. Another significant component of galactic cosmic rays (GCRs) are the HZE ions. These are high-energy nuclei with an electric charge greater than +2, which encompasses all elements heavier than hydrogen (which has a +1 charge) and helium (which has a +2 charge). HZE ions are characterized by their nuclei, which are devoid of orbiting electrons, thus their net charge equals the atomic number of the nucleus. This property makes HZE ions particularly noteworthy in the study of cosmic radiation.

A solar proton event (or proton storm) occurs when protons emitted by the Sun become accelerated to very high

Energetic proton events occur primarily near the Sun during solar flares or in interplanetary space due to the shocks associated with coronal mass ejections. In addition to protons, these cosmic phenomena can involve other nuclear particles, such as helium ions and HZE ions, leading to what are sometimes referred to as solar particle events. Scientifically, there is no substantial evidence to suggest that these energetic proton events pose any harm to human health at ground level, especially within the latitudinal bands where the majority of the Earth’s population lives. The Earth’s magnetic field plays a critical role in shielding the planet from the potentially radioactive effects of these high-energy particles, effectively preventing them from reaching the Earth’s surface.

However, increased radiation levels have been recorded on high-altitude commercial transpolar aircraft flights during such cosmic events. To mitigate these risks, there is an established warning system in place that alerts pilots to such events, allowing them to reduce their cruising altitudes to safer levels, thus limiting the exposure to enhanced radiation.

Aircraft flights that operate away from polar regions generally experience minimal impact from solar proton events. However, significant proton radiation exposure can occur for astronauts operating beyond the protective shield of the Earth’s magnetosphere, such as those in transit to or stationed on the Moon. Nonetheless, the risks of proton radiation for astronauts can be significantly reduced if they remain within low Earth orbit and confine themselves to the most heavily shielded sections of their spacecraft. It is noteworthy that proton radiation levels in low Earth orbit vary with the orbital inclination: the closer a spacecraft gets to the polar regions, the higher the exposure to energetic proton radiation becomes.


Actinides are a group of naturally occurring radioactive metals, including well-known elements such as uranium and plutonium. Positioned on the periodic table, the actinides encompass the 15 metallic chemical elements with atomic numbers from 89 to 103, stretching from actinium to lawrencium. All actinides are inherently radioactive, emitting energy through radioactive decay processes. Among them, thorium and uranium stand out as the most prevalent radioactive elements found on Earth, present since the planet’s formation. These elements, particularly uranium, thorium, and plutonium, are crucial in various applications such as nuclear reactors and nuclear weaponry. The majority of actinides beyond these are not found naturally but are synthesized in laboratories.

Actinides share typical metallic characteristics; they are soft, possess a silvery appearance but tarnish when exposed to air, and are both dense and malleable. Some actinides are so soft they can be sliced with a knife. Within the actinide series, there are two overlapping groups: the transuranium elements, which are those beyond uranium in the periodic table, and the transplutonium elements, which are those beyond plutonium. These subgroups share similar properties and collectively enhance our understanding of chemical and nuclear science.

Actinides are not only fundamental to advanced scientific applications but also have practical uses in everyday life. For example, they are employed in common household items such as smoke detectors and gas mantles. Beyond these uses, actinides play a crucial role as fuel in nuclear reactors and as key components in nuclear weapons, demonstrating their critical importance in both energy production and national defense strategies.

periodic table
The Periodic Table highlighting Actinides in the bottom row, including thorium and uranium, the two most prevalent radioactive elements on Earth.

In the realm of nuclear power, uranium-235 is recognized as a crucial isotope due to its use in thermal reactors, which are the most common type of nuclear reactor. Other actinide isotopes such as thorium-232 and uranium-233 also hold promise for future applications in nuclear energy, thanks to their potential utility in different reactor designs.

Plutonium-238 is another significant radioactive isotope within the actinide series, possessing a half-life of 87.7 years. Its primary utility stems from being a potent alpha emitter that releases minimal amounts of other types of radiation, which are generally more penetrating and pose greater safety hazards. Due to these characteristics, plutonium-238 is extensively used in radioisotope thermoelectric generators (RTGs) and radioisotope heater units (RHUs), which are critical for supplying heat and electricity in spacecraft and other remote applications where traditional power sources are unfeasible.

Plutonium, a key member of the actinide series, is predominantly used in nuclear weapons and as fuel in nuclear reactors due to its high fissionable properties. Beyond terrestrial applications, Plutonium-238 has found utility in space exploration, powering thermopiles and water distillation systems aboard some satellites and space stations. This isotope’s ability to release steady amounts of heat over extended periods without the need for recharging makes it particularly valuable in such challenging environments. Additionally, Plutonium-238 is notable for its use in medical technology; it serves as a long-lasting energy source in cardiac pacemakers. This application is especially beneficial because Plutonium-238 can power these devices for durations approximately five times longer than conventional batteries, significantly enhancing the quality of life for patients by reducing the frequency of surgical battery replacements.

plutonium pellet
plutonium pellet

A pellet of Plutonium-238, destined for use in a thermoelectric generator on a space mission, emits a visible glow due to its own thermal energy. This pellet, capable of producing 62 watts of heat, glows because of the intense heat generated through its radioactive decay, primarily via alpha particle emission.

On September 11, 1957, a significant incident occurred at the Rocky Flats Plant, a nuclear weapons production facility located near Denver, Colorado. A fire broke out in one of the gloveboxes used to handle radioactive materials, specifically metallic plutonium, which is known for its pyrophoric properties and potential to ignite spontaneously under certain conditions. The fire started when the combustible rubber gloves and plexiglass windows within the glovebox caught alight, possibly triggered by the plutonium’s reaction with air at room temperature. This accident led to extensive contamination of Building 771 and resulted in the release of plutonium particles into the atmosphere, posing significant health and environmental risks.


Radon is the primary source of public exposure to naturally occurring ionizing radiation and often represents the most significant portion of an individual’s background radiation dose. The concentration of radon can vary greatly depending on geographic location. This radioactive gas originates from natural sources and can accumulate in buildings, particularly in enclosed areas such as basements and attics, as well as in some spring waters and hot springs. There is substantial epidemiological evidence linking high concentrations of radon with an increased risk of lung cancer. Consequently, radon is recognized globally as a major indoor air quality contaminant. The United States Environmental Protection Agency ranks radon as the second leading cause of lung cancer in the U.S., following cigarette smoking.

Radon is a chemical element designated by the symbol Rn and atomic number 86. It is a radioactive noble gas that is colorless, odorless, and tasteless, forming naturally as a secondary decay product of uranium or thorium. As one of the densest gases under normal conditions, radon remains gaseous, making it difficult to detect without specialized equipment. The radioactivity of radon presents significant health hazards, contributing to its classification as a major indoor air pollutant. Due to its high radioactivity, conducting chemical studies on radon is challenging, resulting in only a few known compounds of the element.

radon atom
Illustration of a Radon Atom. Known for being one of the densest gases under standard conditions, radon significantly contributes to environmental background radiation levels.
radon map

Map of radon concentration.

Radon in Homes

The issue of high radon levels accumulating in homes came to public attention quite unexpectedly in 1984. The discovery was made when an engineer working at a nuclear power plant was found to be contaminated by radioactive substances, which, surprisingly, were traced back to his own home rather than the plant. This incident led to the realization that radon gas from the soil is the primary source of indoor radon problems. Radon can infiltrate homes through various pathways including from the ground, through well water, and, in less common cases, from certain building materials that emit radon. This awareness has since heightened the focus on radon mitigation and safety measures in residential settings.

While building materials can emit radon, they seldom are the sole contributors to radon issues within homes. To identify and address potential radon problems, testing is readily available and strongly recommended by the Environmental Protection Agency (EPA). There are various testing methods, with short-term testing options ranging from a few days to several months, allowing homeowners to quickly assess radon levels and take necessary actions if elevated levels are detected.

The most prevalent radon testing devices currently available include charcoal canisters, electret ion detectors, and alpha track detectors. For accurate short-term radon testing, it is advised to conduct these tests in the lowest living area of the home, such as a basement, where radon levels tend to be highest. To ensure reliable results, keep all doors and windows closed during the test, which is best performed during the cooler months of the year when homes are typically less ventilated and radon accumulation can be more accurately assessed.

Long-term testing is recognized as the most accurate method for detecting radon levels within a home. This type of testing can extend up to a full year, providing a comprehensive assessment of the average radon concentration over time. Alpha track detectors and electret ion detectors are commonly used for long-term radon testing. When selecting a test kit, it is crucial to choose one from a company that is “qualified.” Detailed information on identifying a “qualified” radon service professional can be found on the EPA’s website at Additionally, many state radon offices provide a list of radon measurement companies that comply with state-specific requirements. It’s noteworthy that nearly one out of every 15 homes in the U.S. is estimated to have elevated radon levels, underscoring the importance of regular and accurate radon testing.

The EPA outlines specific steps for testing radon levels effectively in your home:

  • Step 1: Conduct a short-term radon test. If the result indicates 4 pCi/L or higher, it is recommended to proceed with a follow-up test to confirm the findings.
  • Step 2: Follow up with either a long-term test for a more comprehensive analysis or a second short-term test to verify the initial results.

For more detailed information on radon testing, visit

radon in home

Diagram illustrating potential radon entry points in a typical home.


    1. Cracks in solid floors
    2. Construction joints
    3. Cracks in walls
    4. Gaps in suspended floors
    5. Gaps around service pipes
    6. Cavities inside walls
    7. The water supply.

Naturally Occurring Food Radiation


Bananas are known to contain radioactive isotopes of potassium.

It is a lesser-known fact that nearly all foods naturally contain small amounts of radioactivity, even without any exposure to man-made sources. Among these, bananas are notably radioactive, primarily because of the radioactive isotope potassium-40 (40K) they contain. Collectively, all food sources contribute to approximately 40 millirems of radiation per person each year, which accounts for more than 10% of the average total radiation dose from both natural and man-made sources combined. To put this into perspective, there is a measurement known as the banana equivalent dose, which estimates the amount of radiation exposure from consuming just one banana.

Radiation leaks from nuclear plants are often quantified in extremely small units, such as the picocurie, which is a trillionth of a curie. To make sense of these measurements in a more understandable way, comparisons are sometimes made to the banana equivalent dose—an informal measurement that equates radiation exposure to the amount received by eating a single banana. For example, the cumulative dose from eating one banana each day over the course of a year (365 bananas in total) amounts to about 3.6 millirems (or 36 microsieverts). This comparison helps provide a clearer, more relatable understanding of the actual risks associated with radiation exposure from nuclear plant incidents.

In addition to bananas, other potassium-rich foods also contain the radioactive isotope potassium-40 (40K). These include potatoes, kidney beans, sunflower seeds, and various nuts. Notably, Brazil nuts not only contain high levels of 40K but also radium, with radioactivity levels reaching up to 444 Bq/kg (12 nCi/kg) — nearly five times that of bananas. However, there’s no need to eliminate these foods from your diet. Health experts, including those at the EPA, explain that the levels of potassium—and by extension, 40K—in the human body are regulated by homeostasis. This means any excess potassium absorbed from food is promptly balanced by the body’s natural elimination processes.

Nuclear Fallout

Nuclear fallout, often referred to as simply fallout or historically as “Black Rain,” is the residual radioactive material that is propelled into the upper atmosphere after a nuclear explosion or a nuclear reaction that occurs in an unshielded facility. The term “fallout” comes from how this material “falls out” of the sky once the explosion and the subsequent shock wave have dissipated. This fallout typically includes the radioactive dust and ash produced when a nuclear weapon explodes, though similar materials can also be released from a compromised nuclear power plant.

This radioactive dust consists of materials that were either directly vaporized by the nuclear explosion or those that were irradiated by the exposure. It represents a highly dangerous form of radioactive contamination that poses significant health risks.

fallout map
Per capita thyroid doses in the continental United States from Iodine-131 resulting from all routes of exposure from all atmospheric nuclear tests conducted at the Nevada Test Site.

Following an air burst during a nuclear explosion, several phenomena occur. Fission products, un-fissioned nuclear material, and residues from the weapon that were vaporized by the intense heat of the fireball quickly condense into a fine suspension of tiny particles, ranging from 10 nanometers to 20 micrometers in diameter. These particles can be rapidly carried into the stratosphere, especially if the yield of the explosion exceeds 10 kilotons. Once in the stratosphere, the particles spread globally and pose a persistent environmental hazard.

The radiobiological risk associated with worldwide fallout is primarily a long-term concern. This risk stems from the potential for long-lived radioisotopes, such as strontium-90 and caesium-137, to accumulate in the human body through the consumption of contaminated food. The health implications of these isotopes are profound as they can integrate into bone and muscle tissue, leading to various radiation-induced conditions. While the global fallout presents a significant long-term threat, it is the local fallout—material that falls to the ground within a few hours of an explosion—that often requires more immediate attention due to its higher initial radiation levels and direct impact on the surrounding area.

In the event of a nuclear explosion that occurs at or near the surface of the land or water, the intense heat generated by the blast vaporizes significant amounts of earth or water. This vaporized material is then drawn up into the resulting radioactive cloud. As it ascends, it mixes and condenses with fission products and other radioactive contaminants that have been activated by neutrons. This process imbues the vaporized earth or water with radioactivity.

When the radioactive cloud eventually settles back to the ground, it contaminates large expanses of land and bodies of water. This widespread contamination introduces radiation into ecosystems and drinking water supplies, which can lead to profound and lasting biological effects. The resultant radiation exposure can cause genetic mutations and other severe health impacts across a wide range of animal and human populations, thereby altering the affected ecosystems for generations.

A nuclear explosion at the surface generates a significant amount of particulate matter, ranging from ultrafine particles less than 100 nanometers in diameter to larger fragments several millimeters across. This mix includes extremely fine particles that contribute to global fallout. In the dynamics of a surface burst, the larger particles typically spill out from the stem of the mushroom cloud and cascade downward in a downdraft even as the main cloud continues to rise. This process causes fallout to begin settling near the blast site within an hour of the explosion.

Local fallout, which consists of over half of the total debris from the bomb, tends to land on the ground within approximately 24 hours of the explosion. The deposition rates of these particles are influenced by the chemical properties of the elements involved; less volatile elements tend to settle to the ground first. This immediate deposition of radioactive material poses a severe hazard to the environment and public health in the vicinity of the explosion site.

Severe local fallout contamination from a high-yield surface detonation can extend well beyond the immediate area affected by the blast and thermal radiation, impacting regions far from the explosion site. The distribution and extent of fallout are heavily influenced by the prevailing weather conditions at the time of the detonation and subsequently. For instance, strong winds can carry the fallout over a greater distance, speeding its travel across a wider area. However, while the fallout may cover a larger area due to strong winds, it also tends to be more diluted or spread out as it descends. This dynamic can affect the severity and concentration of contamination across different regions, impacting cleanup efforts and long-term environmental consequences.

The distribution of fallout is significantly influenced by wind conditions. Specifically, the width of the fallout pattern at any given dose rate tends to be narrower in areas where higher winds increase the downwind distance of the fallout’s travel. Despite this variation in distribution, the total amount of radioactive material deposited by a specific time remains constant, regardless of the wind patterns. Consequently, the overall casualty figures from fallout are generally not affected by changes in wind speed or direction. However, weather conditions such as thunderstorms can alter the dynamics of fallout deposition. Thunderstorms can cause radioactive material to precipitate more quickly than it would under dry conditions, particularly through processes known as “washout” (where the mushroom cloud is beneath the thunderstorm) and “rainout” (where the mushroom cloud is mixed with the thunderstorm). This accelerated deposition can lead to localized areas of increased radioactivity.

Remaining in areas contaminated by radioactive materials leads to direct external radiation exposure and presents potential internal hazards due to the inhalation and ingestion of radioactive contaminants. One notable radioisotope is iodine-131, which, despite its relatively short half-life, poses significant health risks as it tends to accumulate in the thyroid gland.

According to a 1992 report from the National Cancer Institute, approximately 150 million curies of radioactive iodine were released into the atmosphere during the nuclear testing conducted in Nevada from the early 1950s to the early 1960s. This release had widespread effects, including significant contamination of the nation’s milk supply. Fallout particles, including iodine-131, settled on grazing fields where dairy cows feed. These contaminants were then transferred into the milk produced by these cows, posing a health risk to consumers. In response to such risks, modern safety protocols include the regular collection and testing of pasteurized milk samples at dairy plants for signs of radioactivity, ensuring the safety and health of the public.


Internal exposure to radioactive iodine-131 through ingestion.

Human Bodies

Several essential elements that constitute the human body, particularly potassium and carbon, contain radioactive isotopes that contribute to our natural background radiation exposure. As a result, all individuals inherently possess internal radiation, primarily from radioactive potassium-40 and carbon-14, which have been present within their bodies since before birth. Consequently, every person inherently emits a small amount of radiation, thereby exposing those around them. However, the variation in radiation dose from one person to another due to these isotopes is relatively minor compared to the fluctuations associated with cosmic and terrestrial radiation sources.

vitruvian man

Vitruvian Man by Leonardo Da Vinci. Even all human bodies normally contain some traces of radioactive isotopes.

Depleted Uranium

Depleted uranium (DU) is a form of uranium that has a reduced concentration of the fissile isotope U-235 compared to natural uranium. This material is notable for its extremely high density, measuring 19.1 g/cm3, which is 68.4% denser than lead. This unique property makes depleted uranium valuable for a variety of applications. In the civilian sector, DU is commonly used as counterweights in aircraft, providing necessary balance due to its weight. It is also employed in radiation shielding for medical radiation therapy and industrial radiography equipment, where its density helps effectively block harmful radiation. Additionally, depleted uranium is utilized in containers designed for the safe transportation of radioactive materials, leveraging its protective qualities against radiation.

Military applications of depleted uranium include its use in defensive armor plating and armor-piercing projectiles. The majority of depleted uranium is derived as a byproduct from the process of enriching uranium, which is primarily done for creating fuel for nuclear reactors and for the production of nuclear weapons. The incorporation of depleted uranium in military munitions has sparked significant controversy, largely due to concerns over the potential long-term health effects associated with its use. Uranium is a toxic metal, and exposure to it can adversely impact the normal functioning of vital organs and systems, including the kidneys, brain, liver, and heart, among others. These health risks have fueled ongoing debates regarding the safety and ethical implications of using depleted uranium in warfare.

Depleted uranium exhibits only weak radioactivity, primarily due to the exceptionally long half-lives of its isotopes; uranium-238 has a half-life of about 4.468 billion years, and uranium-235 has a half-life of approximately 700 million years. Additionally, the biological half-life of uranium—the average time it takes for the human body to eliminate half of the amount ingested or inhaled—is relatively short, about 15 days. This means that uranium tends to be cleared from the body relatively quickly, though its weak radioactivity and chemical toxicity still pose health concerns.

The primary radiation hazard associated with depleted uranium comes from its emission of alpha particles. These particles have very limited penetration abilities—they do not travel far through air and cannot penetrate clothing. Therefore, the main risk associated with depleted uranium is internal exposure, which can occur through inhalation, ingestion, or contamination via shrapnel wounds. While there are concerns about the radiation risk, available evidence indicates that the chemical toxicity of depleted uranium poses a greater health threat than its radiological aspects. This chemical hazard is significant and warrants careful handling and precautions to avoid internal exposure.

depleted uranium shells

Gunner’s mates inspect linked belts of Mark 149 Mod 2 20mm ammunition before loading it into the magazine of a Mark 16 Phalanx close-in weapons system aboard the battleship USS MISSOURI.

Other Man Made Sources

Other Man-Made Sources

While medical procedures are recognized as the primary man-made source of radiation exposure for the public, various consumer products and materials also contain trace amounts of radioactive substances. These include construction materials used in building homes and roads, as well as combustible fuels like gas and coal that release radiation during combustion. Additionally, everyday devices such as x-ray security systems, televisions, and fluorescent lamp starters incorporate radioactive elements that contribute to overall exposure. Common household items such as smoke detectors, which utilize americium, luminous watches, and even tobacco smoke, are further sources of low-level radiation. Certain ceramics also contain radioactive materials, adding to the diverse array of man-made sources that contribute to environmental radiation.

radiation in smoke
radiation in smoke

“Smoking Club” – An illustration included in Frederick William Fairholt’s Tobacco, its history and associations. Tobacco smoke is known to contain radioactive elements.

Cobalt is a significant component in steel alloys, enhancing their properties for various applications. A notable radioactive isotope of cobalt, Cobalt-60 (60Co), is extensively used in medical and industrial settings, particularly for the sterilization of equipment and supplies. However, the management of Cobalt-60, especially its disposal, poses challenges. Improper disposal of 60Co in scrap metal has led to unintentional radioactivity in numerous iron-based products. This contamination occurs when scrap metal containing residual 60Co is recycled and reused in the production of new iron and steel products, underscoring the importance of rigorous controls and monitoring in the handling of radioactive materials.

petco radioactive bowl

In August 2012, Petco issued a recall for several models of steel pet food bowls following an alert from US Customs and Border Protection, which discovered that the bowls were emitting low levels of radiation. Further investigations revealed that the source of this radiation was Cobalt-60 (60Co), a radioactive isotope that had inadvertently contaminated the steel used to manufacture the bowls. This incident highlights the critical need for careful monitoring and regulation of recycled materials in the manufacturing process to prevent radioactive contamination in consumer products. More information on this recall can be found on Petco’s official website:

In January 2012, an alarming discovery was made when Metal Boutique tissue boxes manufactured in India and distributed to Bed, Bath & Beyond stores across 20 states were found to contain radioactive Cobalt-60 (60Co). This incident highlighted the risks associated with inadequate monitoring of imported goods. A similar case occurred in May 2013 when a batch of metal-studded belts sold by the online retailer Asos tested positive for 60Co and had to be confiscated. These belts were subsequently held in a U.S. radioactive storage facility to prevent public exposure. Such events underscore the importance of rigorous testing and regulation of imported products to ensure they meet safety standards. More information about the tissue box recall can be found here: To learn more about orphaned sources of radiation, visit: Read more about orphaned sources of radiation.

Radiation From Medical Procedures

The overwhelming majority of man-made radiation exposure encountered by the general population originates from medical procedures. The table provided below compares various types of man-made radiation exposure against radiation-based medical procedures, organizing them by the level of exposure measured in Sieverts (Sv). Additionally, it includes a column that approximates how long it would take for an individual to receive the equivalent dose of radiation from natural environmental sources. This comparison aims to offer some perspective on the radiation doses associated with medical imaging and treatments, particularly for patients concerned about the risks of radiation.

The radiation dose values listed are based on typical effective doses for each type of scan. However, it’s important to note that actual radiation doses can vary widely depending on factors such as the medical facility’s protocols, the specific equipment used, the patient’s size, and other clinical considerations. Subsequent chapters will discuss strategies to minimize radiation exposure. As healthcare providers, there is a fundamental responsibility to ensure that radiation levels are kept as low as reasonably achievable to protect patient health.


Type of Radiation Exposure Approximate
Dose in mSv
Approximate Equivalent
Time Period of Natural
Background Radiation
Airport Security X-ray scanner 0.0001 Less then 1 hour
7 hour airplane flight 0.003 A few days
Chest X-ray 0.1 1 week
Mammogram 0.4 2 months
Chest CT 7 2.3 years
Flouroscopy BE 8 2.7 years
CT Heart Angiography 16 5.3 years
Whole body PET scan 14 4.6 years
Flouroscopy KUB 15 5 years
CT Whole body 22.5 7.5 years
Nuclear Medicine
Cardiac Stress Thalium
40.7 13.6 years
Transjugular Intrahepatic
Shunt Placement
70 23.3 years

Sources of radiation exposure along with typical doses and compared to the time it would take to receive a similar dose from natural background radiation. (adapted from Mettler, Jr. FA, Huda W, Yoshizumi TT, and Mahesh M. (July 2008) Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog, Radiology, 248(1): 254-26)

relative rad doses
relative rad doses




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1. What are the primary sources of natural background radiation?

Natural background radiation primarily comes from three sources: cosmic radiation from space, terrestrial radiation from radioactive materials in the earth, and internal radiation from radioactive isotopes naturally present in the human body. These sources contribute to the constant low-level radiation exposure that all living organisms experience.

2. How does cosmic radiation contribute to our overall radiation exposure?

Cosmic radiation originates from outer space and the sun, and it contributes to our overall radiation exposure by penetrating the Earth’s atmosphere. The intensity of cosmic radiation increases with altitude and latitude, meaning people who live at higher altitudes or fly frequently are exposed to higher levels of cosmic radiation.

3. What are some common sources of man-made radiation?

Common sources of man-made radiation include medical imaging procedures (such as X-rays, CT scans, and nuclear medicine), radiation therapy for cancer treatment, industrial applications (such as radiography and nuclear power plants), and consumer products (such as smoke detectors and certain types of luminous watches). These sources contribute to additional radiation exposure beyond natural background levels.

4. How do medical imaging procedures contribute to radiation exposure?

Medical imaging procedures contribute to radiation exposure through the use of X-rays, CT scans, and nuclear medicine. These procedures involve the use of ionizing radiation to create images of the body’s internal structures, which helps in diagnosis and treatment planning. While beneficial, it’s important to minimize exposure by using the lowest effective dose and adhering to safety protocols.

5. What measures can be taken to minimize radiation exposure from natural and man-made sources?

To minimize radiation exposure, several measures can be taken:

  • Following the ALARA (As Low As Reasonably Achievable) principle in medical imaging and radiation therapy.
  • Using protective shielding and personal protective equipment (PPE) when working with radiation sources.
  • Limiting time spent near radiation sources and increasing distance from them.
  • Regularly maintaining and calibrating radiation equipment to ensure it operates correctly and safely.
  • Staying informed about radiation safety practices and adhering to regulatory guidelines and recommendations.

These measures help reduce unnecessary exposure and protect both patients and professionals from the potential harmful effects of radiation.