Jump to main content.

Ionizing & Non-Ionizing Radiation
Understanding Radiation:  

Beta Particles

Ionizing & Non-Ionizing Radiation

Beta particles are subatomic particles ejected from the nucleus of some radioactive atoms. They are equivalent to electrons. The difference is that beta particles originate in the nucleus and electrons originate outside the nucleus.

On this page:

The Basics

Beta Particles in the Environment

Health Effects

Protecting People from Beta Particles

The Basics

Who discovered beta particles?

Henri Becquerel is credited with the discovery of beta particles. In 1900, he showed that beta particles were identical to electrons, which had recently been discovered by Joseph John Thompson.

Top of page

What are the properties of beta particles?

Beta particles have an electrical charge of -1. Beta particles have a mass of 549 millionths of one atomic mass unit, or AMU, which is about 1/2000 of the mass of a proton or neutron. The speed of individual beta particles depends on how much energy they have, and varies over a wide range. It is their excess energy, in the form of speed, that causes harm to living cells. When transferred, this energy can break chemical bonds and form ions.

What conditions lead to beta particle emission?

Beta particle emission occurs when the ratio of neutrons to protons in the nucleus is too high. In this case, an excess neutron transforms into a proton and an electron. The proton stays in the nucleus and the electron is ejected energetically.

This process decreases the number of neutrons by one and increases the number of protons by one. Since the number of protons in the nucleus of an atom determines the element, the conversion of a neutron to a proton actually changes the radionuclide to a different element.

Often, gamma ray emission accompanies the emission of a beta particle. When the beta particle ejection doesn't rid the nucleus of the extra energy, the nucleus releases the remaining excess energy in the form of a gamma photon.

The decay of technetium-99, which has too many neutrons to be stable, is an example of beta decay. A neutron in the nucleus converts to a proton and a beta particle. The nucleus ejects the beta particle and some gamma radiation. The new atom retains the same mass number, but the number of protons increases to 44. The atom is now a ruthenium atom.

Other examples of beta emitters are phosphorous-32, tritium (H-3), carbon-14, strontium-90, and lead-210.

Top of page

Which radionuclides are beta emitters?

There are many beta emitters. You can find fact sheets for several of them at the Radionuclides page:

Top of page

Beta Particles in the Environment

How do we use beta emitters?

Beta emitters have many uses, especially in medical diagnosis, imaging, and treatment:

What happens to beta particles in the environment?

Beta particles travel several feet in open air and are easily stopped by solid materials. When a beta particle has lost its energy, it is like any other loose electron. Whether in the outdoor environment or in the body, these electrons are then picked up by a positive ion.

Top of page

How are people exposed to beta particles?

There are both natural and man-made beta emitting radionuclides. Potassium-40 and carbon-14 are weak beta emitters that are found naturally in our bodies. Some decay products of radon emit beta particles, but its alpha-emitting decay products pose a much greater health risk.

Beta emitters that eject energetic particles can pose a significant health concern. Their use requires special consideration of both benefits and potential, harmful effects.

At one time, strontium-90 was the major man-made beta emitter in the environment. Fallout from atmospheric nuclear testing from the 1950's to the early 1970's spread strontium-90 worldwide. However, most of the strontium-90 from these tests has now decayed away.

Testing also released large amounts of cesium-137 into the environment. Although, cesium-137 emits beta radiation, its gamma radiation is of greater concern. Some cesium-137 from fallout remains in the environment, but most of it has decayed as well.

Top of page

Does the way a person is exposed to beta particles matter?

Yes. Direct exposure to beta particles is a hazard, because emissions from strong sources can redden or even burn the skin. However, emissions from inhaled or ingested beta particle emitters are the greatest concern. Beta particles released directly to living tissue can cause damage at the molecular level, which can disrupt cell function. Because they are much smaller and have less charge than alpha particles, beta particles generally travel further into tissues. As a result, the cellular damage is more dispersed.

Top of page

Health Effects of Beta particles

How can beta particles affect people's health?

Beta radiation can cause both acute and chronic health effects. Acute exposures are uncommon. Contact with a strong beta source from an abandoned industrial instrument is the type of circumstance in which acute exposure could occur. Chronic effects are much more common.

Chronic effects result from fairly low-level exposures over a along period of time. They develop relatively slowly (5 to 30 years for example). The main chronic health effect from radiation is cancer. When taken internally beta emitters can cause tissue damage and increase the risk of cancer. The risk of cancer increases with increasing dose.

Some beta-emitters, such as carbon-14, distribute widely throughout the body. Others accumulate in specific organs and cause chronic exposures:

Top of page

Is there a medical test to determine exposure to beta particles?

There are tests which can detect the presence of beta-emitting radionuclides in the body, however, special equipment is required and testing is generally done by specialized laboratories and facilities, or such testing is associated with a specific medical procedure in a hospital.

Protecting People from Beta Particles

How do I know I'm near beta emitters and beta particles?

Three truncated pie segments spaced equally about a disc.You cannot tell if you are being exposed to beta radiation. You cannot see, or feel radiation hitting your body. Specialized equipment is required to determine if you are near a beta radiation source. However, you should be familiar with the radiation warning symbols such as the trefoil shown at right, which indicate that radioactivity is present.

You can protect yourself by avoiding devices with this symbol, and not entering areas where this symbol or others are posted.

What is the government doing to protect people from exposure to beta emitters and beta particles?

The U.S. Congress passes laws that authorize EPA and other federal agencies, to protect public health and the environment from radionuclides, including beta emitters. EPA has issued a variety of regulations that limit the release of radionuclides to the environment. You can learn about limits set for individual radionuclides by selecting beta emitters from the Radionuclides page.

Top of page

How do I protect myself and my family from beta particles?

While very unlikely, you or a member of your family may encounter an industrial instrument or device containing a radioactive source. Every year, hundreds of devices containing radiation sources are lost, stolen, or otherwise drop out of the system for tracking them. For example, a factory that has gone out of business may contain one or more such devices. As the building structure is being dismantled, these forgotten devices often are considered as scrap metal, or someone may think they have value and try to sell them.

You should avoid these devices. They may bear the radiation warning symbol, a trefoil, as shown above. They may also bear identifying information such as "Nuclear Regulatory Commission" or the name of a radionuclide. If you find a device you think may be radioactive, promptly call your state radiation control office or the hotline for reporting unwanted radioactive material:


This hotline is provided by the Conference of Radiation Control Program Directors (CRCPD).

Top of page


Local Navigation

Radiation Home

Jump to main content.