What is Ionizing Radiation?

Ionizing radiation is a type of energy released by radioactive atoms or produced by certain machines. The energy is in the form of electromagnetic waves (gamma or x-rays) or particles (alpha, beta, or neutrons). In general, human senses cannot detect ionizing radiation. Alpha particles are the heaviest and can be stopped by air, clothing, or the outer layer of our skin. Beta particles are much lighter than alpha particles and require more material to be stopped. Typically, neutrons, gamma, and x-rays require different thicknesses of specific shielding material (e.g., lead or concrete) to be blocked.

Ionizing radiation has many beneficial applications, including uses in medicine, industry, and research. From the CT scan to look for brain injury to the smoke detector in homes, radiation can be helpful. However, we can experience acute health effects if exposed to very high doses of ionizing radiation during a short period of time or chronic health effects if exposed to doses of ionizing radiation over the course of many years.

Where is ionizing radiation present?

Radiation is everywhere. Since the Earth was formed and life developed, all life on earth has been and is exposed to radiation. Radiation exposure comes from two sources: natural and human made.

Natural radiation comes from the soil, rocks, and the atmosphere as a result of radiation from outer space. Small amounts of radioactive material can be found in the ground, the air we breathe, the water we drink, and the food we eat.
Human-made radiation sources are those things that would not exist without people, such as some consumer products (e.g., tritium exit signs, welding rods containing thorium, smoke detectors) and medical devices like x-ray machines.

How much radiation am I exposed to?

On average in the United States (U.S.), we are exposed to 6.2 millisievert (mSv) per year. (Millisievert = unit of measure for radiation energy absorbed in humans)

We receive about half of that average from natural sources. For many people, the natural radiation dose is most of what we get in a year. Most of the natural radiation dose in the U.S. is from radon in the air.

Table 1. Average Yearly Radiation Doses for the U.S. Population

	Source	Average Yearly Dose (mSv)
Natural:	Radon inhalation, other inhalation, and ingestion	2.57	Sub-total
	Terrestrial	0.21	3.11
	Cosmic	0.33
Human-Made:	Medical	3.00	Sub-total
	Consumer products	0.13	3.14
	Occupational and others	0.008
	Total:	6.2
Source: NCRP Report No.160 - Ionizing Radiation Exposure of the Population of the United States (2009)

Note: Individual exposure will be different based on factors, such as lifestyle, geographic location, and whether you have had medical procedures that use radiation. You can calculate an estimate of your annual radiation dose using the U.S. Nuclear Regulatory Commission Personal Annual Radiation Dose Calculator: http://www.nrc.gov/about-nrc/radiation/around-us/calculator.html. External Link

What are the biological effects of radiation?

We tend to think of biological effects of radiation in terms of their effect on living cells. For low levels of radiation exposure, the biological effects, if any, are so small that they may not be detected. The human body can repair damage caused by radiation.

The following are three biological effects of radiation on living cells:

Cells will repair themselves with no residual damage.
Cells will die and be replaced by the body.
Cells will incorrectly repair themselves resulting in biophysical change.

Chronic Effects

Although radiation may cause cancer at high doses and high dose rates, currently there are no data to establish the occurrence of cancer when exposed to low doses or low dose rates (below 100 mSv). However, in an abundance of caution, the radiation protection community assumes that any amount of radiation exposure may pose some risk for causing cancer or a hereditary effect and assumes that the probability of these risks increases as exposure increases.

Low doses (<100 mSv) spread out over long periods of time might not have any observable effects. If an effect does occur, the most likely result of radiation exposure is cancer, and it will manifest 5–20 years after exposure.

High doses (500 mSv or greater) are associated with leukemia, multiple myeloma, breast, bladder, colon, liver, lung, esophagus, ovarian, and stomach cancers.

The relationship between cancer and radiation is complicated since radiation affects people in different ways and the cancer caused by radiation is indistinguishable from any other cancer. Associations between radiation exposure and cancer are mostly based on populations exposed to relatively high levels of ionizing radiation, such as Japanese atomic bomb survivors.

Acute Effects

High doses (500 mSv or greater) can kill so many cells that tissues and organs are damaged immediately. This can result in a rapid body response called Acute Radiation Syndrome, which can lead to severe illness or death. The outcome depends on many factors including the individual's health prior to the exposure and the quality and timeliness of medical care received following exposure.

Unfortunately, it is impossible to predict an exact radiation dose which would be considered fatal. It is believed that 50% of a population would die within 60 days after receiving a dose of 3,500 to 5,000 mSv to the whole body over a period ranging from a few seconds to a few hours.

How does the Department of Defense protect us from potential radiation health effects?

The Department of Defense (DoD) radiation protection community is specially trained to preserve the health and safety of people and the environment while allowing for beneficial and mission-critical uses of radiation.

Where can I get more information?

If you have any concerns about your health related to radiation exposure, you should speak with your healthcare provider. If indicated, your provider can refer you to a specialist for concerns related to radiation exposure.

Additional sources of information:

Ionizing Radiation