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.
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.
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.
See fact sheets for individual
beta emitters at Radionuclides
Which radionuclides are beta emitters?
There are many beta emitters. You can find fact sheets
for several of them at the Radionuclides
page:
tritium
cobalt-60
strontium-90
technetium-99
iodine-129 and -131
cesium-137
Beta Particles in the Environment
How do we use beta emitters?
Beta emitters have many uses, especially in medical diagnosis,
imaging, and treatment:
Iodine-131
is used to treat thyroid disorders, such as cancer and
graves disease (a type of hyperthyroidism).
Phosphorus-32 is used in molecular biology and genetics
research.
Strontium-90
is used as a radioactive tracer in medical and agricultural
studies.
Tritium is
used for life science and drug metabolism studies to ensure
the safety of potential new drugs. It is also used for
luminous aircraft and commercial exit signs, for luminous
dials, gauges and wrist watches.
Carbon-14 is a very reliable tool in dating of organic
matter up to 30,000 years old.
Beta emitters are also used in a variety of industrial
instruments, such as industrial thickness gauges, using
their weak penetrating power to measure very thin materials.
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 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.
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.
See fact sheets for individual
beta emitters at Radionuclides
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?
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 Radura symbol, which indicates
that radioactivity is present. You can protect yourself
by avoiding devices with this symbol, and not entering areas
where the symbol is 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.
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 Radura
symbol, a trifoil as shown above. They may also bear identifying
information such as "Nuclear Regulatory Commission",
"Atomic Energy 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 :
1-800-999-7879
This hotline is provided by the Conference
of Radiation Control Program Directors (CRCPD).
Alpha Particles 
However,
you should be familiar with the Radura symbol, which indicates
that radioactivity is present. You can protect yourself
by avoiding devices with this symbol, and not entering areas
where the symbol is posted.