Gross Alpha
Gross Beta
Iodine-131
Iodine-129
Cesium-137
Cobalt-60
Strontium-90
Plutonium-238
Plutonium-239/240
Tritium
Americium-241
Particulate Matter
Ionizing Radiation
Technetium-99
Neptunium-237
Heavy Metals
Volatile Organics

What are beta particles?

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.  

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.

While beta particles are emitted by atoms that are radioactive, beta particles themselves are not radioactive. It is their 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. Scientists think that 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. Scientists think that 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-31, tritium (H-3), carbon-14, strontium-90, and lead-210.

Which radionuclides are beta emitters?

There are many beta emitters. 

  • tritium
  • cobalt-60
  • strontium-90
  • technetium-99
  • iodine-129 and -131
  • cesium-137

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.

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.

  • Key beta emitters used in medical imaging, diagnostic and treatment procedures are technetium-99m, phosphorus-32, and iodine-131. For example, people who have taken radioactive iodine will emit beta particles. They must follow strict procedures to protect family members from exposure.
  • Radioactive iodine may enter the environment during a nuclear reactor accident and find its way into the food chain. 
  • Industrial gauges and instruments containing concentrated beta-emitting radiation sources can be lost, stolen, or abandoned. If these instruments then enter the scrap metal market, or someone finds one, the sources they contain can expose people to beta emitters. 

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.

 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.

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:

  • Iodine-131 concentrates heavily in the thyroid gland. It increases the risk of thyroid cancer and other disorders. 
  • Strontium-90 accumulates in bone and teeth. 
What is gross beta radioactivity?

The gross beta radioactivity analyses is performed on the samples collected weekly.  It is simply a measurement of all beta activity present, regardless of specific radionuclide source.   Gross measurements are used as a method to screen samples for relative levels of radioactivity. 

Specific analyses of beta-emitting isotopes are  made at the end of each quarter when  samples are composited by location.