Category: Health Effects

15 Jun 2021

The Truth About Background Radiation

Background radiation is all around us, and always has been. That idea can be a frightening concept at face value, but the truth is background radiation is natural, normal, and expected.

Most natural background sources of radiation fall into one of three categories:

Cosmic Radiation

Think of this as steady waves of external radiation being sent from the sun and stars in space to Earth. This type of radiation occurs naturally and introduces extremely low levels of radiation to the average person. The amount (or dose) of cosmic radiation one receives can depend on weather and atmospheric conditions, the Earth’s magnetic field, and differences in elevation. For example, people who live at higher altitudes like Denver, Colorado are exposed to slightly more cosmic radiation than people who live in lower altitudes, such as New Orleans, Louisiana or Miami, Florida. Furthermore, the farther north or south one is from the equator results in a higher dose of cosmic radiation due to the way the Earth’s magnetic field deflects cosmic radiation toward the North and South poles.

silver airplane flying above orange clouds

Air travel can also expose individuals to low levels of cosmic radiation. The received dose is similarly dependent on altitude, latitude, and the duration of the flight. A coast-to-coast flight in the United States would expose an individual to approximately 3.5 mrem. For comparison, a typical medical procedure involving radiation, such as a chest X-ray, exposes an individual to 10 mrem, and the average American receives a total radiation dose of 540 mrem each year.

In general, a person’s average dose from cosmic radiation in the United States is small, making up only 6% of their total annual dose.

Terrestrial Radiation

Terrestrial radiation is the portion of natural background radiation that is emitted by naturally occurring radioactive materials on earth, and it is responsible for approximately 3% of the average person’s annual received dose. The physical earth, including soil and sedimentary and igneous rock, contains common elements like uranium, thorium, and radium. These naturally occurring radioactive materials, which have existed as part of the earth’s crust since the earth was formed, are released into the water, vegetation, and the atmosphere as they breakdown at different rates. People are largely exposed to the resulting emitted radiation through their skin.


diagram of radon gas infiltrating a house

Perhaps the most significant form of terrestrial radiation is that which is inhaled. When the naturally occurring radioactive element uranium (found in the earth’s crust, underwater caves, and seawater) decays it can change into a scentless, invisible gas called radon. All the air we breathe contains trace amounts of radon, and it is responsible for the largest portion of background radiation dose that the average American receives in a year. Outdoors, this radioactive gas disperses rapidly and does not pose any health risk to human beings. A build-up of radon gas indoors, however, can potentially increase the risk of lung cancer over time, which is why it is important to test homes and workplaces for radon on a regular basis. Smoking, especially near or inside the home, can amplify the risk of cancer when coupled with radon exposure.

The average person can expect to receive 42% of their annual radiation dose from radon.

Internal Radiation

Background radiation can also be received through ingestion. Some common foods contain small amounts of radioactive elements that do not pose a radiation risk to the person ingesting them. The most common example is the banana. This delicious, nutritious fruit contains naturally high levels of potassium which helps muscles contract, keeps your heartbeat regular, and offsets the harmful effects of sodium on blood pressure. A tiny portion of potassium is also naturally radioactive. A single banana emits 0.01 mrem, which is received internally by the person eating it. According to the EPA, a person would have to eat 100 bananas to receive the same amount of radiation exposure naturally received each day from the environment. (It should be noted that this naturally occurring radiation is not the same thing as food irradiation, which is a process used by humans to kill bacteria, molds, and pests to prevent foodborne illnesses and spoilage.) Overall, the levels of natural radionuclides found in our food and water are low and considered safe for human consumption by regulatory bodies.

Most surprisingly for some is the fact that other humans are also a source of exposure to one another. From birth, people have internal radiation in the form of radioactive potassium-40, lead-210, and carbon-14. These elements reside in our blood and bones. As previously noted, humans also ingest traces of naturally occurring radioactive material found in our food and water. When our bodies metabolize the non-radioactive and radioactive forms of potassium and other elements, they then contain small amounts of radiation which can act as exposures to others.

Man-Made Radiation Exposure

A more familiar source of radiation exposure to many is man-made radiation, such as procedures using X-Rays and radiation therapy to treat cancer. According to the Health Physics Society, approximately 42% of annual dose comes from man-made radiation. This percentage includes medical procedures, household products like smoke detectors, and small quantities of normal discharges from nuclear and coal power plants.

Learn more about the health effects of man-made ionizing radiation in our blog post here.


Natural background radiation has always been a part of life on earth, and it always will be. It is important to understand that this is not something to be feared. Low levels of ionizing radiation from naturally occurring sources such as space, the ground beneath our feet, and even some of the food we eat are not dangerous and do not pose a direct health risk to ourselves or our loved ones.

For more information, visit the Health Physics Society webpage,, or the International Atomic Energy Agency.

Note: Visit our regulatory page to learn how Versant Physics’ board-certified Internal Dose Specialists, Medical Physicists, and Health Physicists, can assist with your radiation safety program needs.

Additional Sources:

NCRP Report 160

NCRP Report 184

20 May 2021
Smiling pregnant worker

Occupational Radiation Exposure & Pregnancy

Employees who become pregnant and work with radiation or radioactive materials during their pregnancy are often concerned about the safety of doing so, as well as the potential effects of radiation to their unborn child. Occupationally exposed workers are not required to declare a pregnancy to their employer. However, if they decide to declare there are dose limits that should be observed and additional protective measures that can be taken to protect both mom and baby.

Declaring a Pregnancy

In the United States, pregnant employees who work with or around radiation have the option of declaring their pregnancy. This declaration is voluntary and informs the worker’s employer in writing of their pregnancy as well as the estimated date of conception. This information is confidential and shared only with the employer and radiation safety officer, however, it is valuable for reducing exposure and allowing for close monitoring of both the employee and the baby throughout the pregnancy.

pregnant woman at a consultation

The NRC and States require licensees and registrants (i.e., the facility the employee works at) to make efforts to limit the declared pregnant worker’s received dose. This can mean that some normal job functions may not be permitted if doing those jobs would result in the fetus/embryo receiving more than 500 mrem. Employees also have the option to discuss with their employer or radiation safety officer about potential changes to their job status prior to declaring a pregnancy if they so choose. The option to revoke a declaration of pregnancy even if the worker is still pregnant is also available at any time throughout the pregnancy.

When an employee declares a pregnancy, they should sit down with their radiation safety officer for a one-on-one counseling session. This is a great opportunity to ask questions and address any monitoring or safety concerns that may arise. They are then issued a fetal dosimeter in addition to their regular monitoring device, which is worn at the hip or waist level. For procedures where a lead apron is worn, the dosimeter should be worn beneath it while the regular dosimeter is worn on the outside at the neck or collar. The fetal dosimeter is monitored monthly by the radiation safety officer to ensure that the regulatory fetal dose limits are not exceeded.

According to regulations, the lower dose limit for the embryo or fetus remains in effect until the worker withdraws the declaration in writing or is no longer pregnant. If it is not withdrawn, the original declaration expires after one year.

If an employee chooses not to declare their pregnancy, the employee and her baby are restricted to the standard occupational dose limits that apply to all occupationally exposed workers. The annual total effective dose equivalent (TEDE) for the whole body is 5,000 mrem. (10 CFR Part 20.)

Occupational Exposure

In most cases, the ways in which a pregnant woman may be occupationally exposed to radiation within regulatory limits are not likely to cause adverse health effects for the developing fetus.  However, most regulations are guided by the principle that any level of radiation can potentially result in negative biological effects and that the likelihood of such effects increases as the dose received increases.

The NRC requires licensees to “limit exposure to the embryo/fetus of an occupationally exposed individual to 500 mrem (5 mSv) or less during pregnancy for a declared pregnant worker who is exposed to radiation from licensed radioactive materials including radionuclides.” (10 CFR 20.1208) This lower dose limit is “based on a consideration of greater sensitivity to radiation of the embryo/fetus and the involuntary nature of the exposure.”  

Pregnant nurse on the phone with ipad

To break this down further, the regulations state that the radiation dose from occupational exposure should be limited to 500 mrem for the duration of the pregnancy and no more than 50 mrem per month. At this level, (1/10 the dose that a regular occupationally exposed worker may safely receive in a year) the risk of negative health effects is low. Pregnant workers can speak directly with their radiation safety officer or on-site medical or health physicist to determine the safest dose limits for their individual needs, which may depend on their exposure history and the types of jobs they perform on a regular basis.

Undergoing Medical Procedures While Pregnant

Occupational limits for declared pregnant workers do not apply to individuals who undergo diagnostic or therapeutic procedures, such as X-rays, fluoroscopy, or radiation therapy.

According to Robert Brent, MD, Ph.D. for, diagnostic procedures of different parts of the body, such as the head, teeth, legs, or arms do not directly expose the fetus. Modern medical imaging procedures focus the X-ray beam only on the body part of interest, and the amount of radiation that could reach the embryo or fetus during these diagnostic procedures is small and unlikely to increase the risk of miscarriage or birth defects. Most procedures expose the developing fetus or embryo to less than 50 mSv, if at all. At this level of exposure, there is no cause for concern.

Regardless of pregnancy status, the ALARA principle should be implemented by the individual’s care team to guide decisions made about treatment and diagnostic procedures. A radiation safety officer or medical physicist can also help provide options to minimize dose. It should also be noted that those with fetal dosimeters should not wear their dosimeter during an X-ray or nuclear medicine procedure.


Ultimately, the decision to declare a pregnancy is that of the individual worker. Under the current safety guidelines, the risk for adverse health effects to an embryo or fetus posed by occupational exposure or medical procedures is low. However, employees should take advantage of the resources available such as the NRC regulations, literature provided by the Health Physics Society, and the expertise of their radiation safety officer and on-site medical or health physicist.


Visit our website to learn more about Versant Physics regulatory services, including radiation safety officer support, personnel dosimetry, and more.

21 Apr 2021

Deterministic vs. Stochastic Effects

Ionizing radiation is useful for diagnosing and treating a range of health conditions–broken bones, heart problems, and cancer, for example.  Medical imaging with x-rays, diagnostic radiopharmaceuticals, and radiation therapy are often life-saving procedures.

However, the accidental or misuse of medical radiation can sometimes cause unforeseen and unfortunate consequences.  Radiation protection guidelines and policies help to ensure the safe use of radiation in the medical setting for both patients and staff.

Health effects of ionizing radiation are usually classified into two categories: deterministic and stochastic.

Deterministic Effects

According to the International Atomic Energy Agency (IAEA), a health effect that requires a specific level of exposure to ionizing radiation before it can occur is called a deterministic effect. The severity of a deterministic effect increases as the dose of exposure increases and considers a minimum threshold, below which no detectable clinical effects occur. This type of effect is predictable and reproducible.  For example, localized doses to certain parts of the body at increasing levels will result in the same biological effects.

Deterministic effects are caused by severe cell damage or death. Individuals who experience the physical effects of this cell death do so when it is large enough to cause significant tissue or organ impairment.

Deterministic effects are short-term, adverse tissue reactions resulting from a dose that is significantly high enough to damage living tissues.  The severity of a deterministic effect increases with radiation dose above a threshold, below which the detectable tissue reactions are not observed. 

Deterministic effects are usually predictable and reproducible.  For example, localized doses to certain parts of the body at increasing levels will result in well-understood biological effects.

how to understand and communicate radiation risk diagram
Figure 1 Radiation – Deterministic and Stochastic Effects – Image Wisely, March 2017 “How to Understand and Communicate Radiation Risk”

Some examples of deterministic effects include:

  • Radiation-induced skin burns
  • Acute radiation syndrome
  • Radiation sickness
  • Cataracts
  • Sterility
  • Tumor Necrosis

Stochastic Effects

Stochastic effects are probabilistic effects that occur by chance.  An extremely rare stochastic effect is development of cancer in an irradiated organ or tissue.  The probability of occurrence is typically proportional to the dose received.  Stochastic effects after exposure to radiation occur many years later (the latent period).  The severity is independent of the dose originally received.

Since many agents in the environment are also known carcinogens, and since many cancers occur spontaneously, it is not possible in most cases to directly link radiation exposure to an observed cancer.  If a population group receives a dose of ionizing radiation at one time, it is therefore not possible to predict who in that group will develop cancer, if any, or to tell if the people who do develop cancer did so as a result of the dose of ionizing radiation or some other lifestyle factor, such as smoking.   

Examples of stochastic effects include:

  • Cancer
  • Heritable or genetic changes

Dose Limits and Radiation Protection

In our day-to-day lives, we are exposed to both background and manmade sources of radiation.  Everyone receives radiation exposure from natural cosmic and solar rays, and radionuclides in soil.  The benefits of diagnostic and therapeutic medical radiation far exceed the risks.  Fortunately, the health risks associated with natural background levels are small, and by regulations, we are protected from man-made radiation. 

The National Council on Radiation Protection and Measurements (NCRP) recommends dose limits for managing exposures to ionizing radiation and protecting humans from adverse effects.  Their purpose is to prevent acute and chronic radiation-induced tissue reactions (deterministic effects) and to reduce the probability of cancer (stochastic effect) while maintaining the benefits to people and society from activities that generate radiation exposures (NCRP Report No. 180, 2018).

Type of limitRadiation workerPublic
Stochastic limits Effective dose, whole body (mSv/year) 501
Deterministic limits Tissue absorbed dose (mGy/year)
Lens of the eye5015
Extremities (hands and feet)500

Figure 2.  Values from NCRP Report No. 180, Management of Exposure to Ionizing Radiation:  Radiation Protection Guidance for the United States (2018).

The concept of dose limits also takes into account the ideas that any use of radiation should do more good than harm, and that permissible exposure should be maintained “as low as reasonably achievable” (ALARA).   In line with this philosophy, medical professionals strive to minimize medical radiation exposures to patients without compromising imaging quality and therapy effectiveness. 


Adverse health effects can occur after exposure to ionizing radiation.  For radiation protection, scientific advisory organizations have recommended dose limits to prevent deterministic effects and reduce the probability of stochastic effects in radiation workers, medical professionals, patients, and other members of the general public. 

Versant Physics is a full-service medical physics and radiation safety consulting company based in Kalamazoo, MI. Contact us for all of your regulatory, radiation safety, and personnel dosimetry needs.



Happy Holidays!

10% off

Our gift to you this holiday season. Enjoy 10% off our entire catalog of online courses, including MRSO, Fluoroscopy, Medical X-ray, and DOT Training.



Permit Profile

Each permit has a dedicated profile of information that includes authorized personnel, radioactive material, machines, and devices. Permit conditions, completed audits, and forms are also found on this profile.

Authorized Condition Database

Create and view authorized conditions included on permits. Previously created authorized conditions are listed with their code, category, and description.

Permit Enforcement

Information specified on a permit not only serves as a record of that permit, but also controls what can be added to other modules. The location, owner and type of radioactive materials, machines, and equipment can be enforced by permits.

Permit Audits

Perform permit audits, mail the results to relevant personnel, and track responses to non-compliances.