are gamma rays?
A gamma ray is a packet
of electromagnetic energy--a photon. Gamma photons are
the most energetic photons in the electromagnetic
spectrum. Gamma rays (gamma photons) are emitted from
the nucleus of some unstable (radioactive) atoms.
What are the properties
of gamma radiation?
Gamma radiation is very
radiation. Gamma photons have about 10,000 times
as much energy as the photons in the visible range of
the electromagnetic spectrum.
Gamma photons have no
mass and no electrical charge--they are pure
Because of their high
energy, gamma photons travel at the speed of light and
can cover hundreds to thousands of meters in air
before spending their energy. They can pass through
many kinds of materials, including human tissue. Very
dense materials, such as lead, are commonly used as
shielding to slow or stop gamma photons.
Their wave lengths are
so short that they must be measured in nanometers,
billionths of a meter. They range from 3/100ths to
3/1,000ths of a nanometer.
What is the difference
between gamma rays and x-rays?
Gamma rays and x-rays,
like visible, infrared, and ultraviolet light, are
part of the electromagnetic spectrum. While gamma rays
and x-rays pose the same hazard, they differ in their
origin. Gamma rays originate in the nucleus. X-rays
originate in the electron fields surrounding the
What conditions lead to
gamma ray emission?
emission occurs when the nucleus of a radioactive atom
has too much energy. It often follows the emission of
What happens during gamma
provides an example of radioactive decay by gamma
radiation. Scientists think that a neutron transforms
to a proton and a beta particle. The additional proton
changes the atom to barium-137. The nucleus ejects the
beta particle. However, the nucleus still has too much
energy and ejects a gamma photon (gamma radiation) to
become more stable.
How does gamma radiation
change in the environment?
Gamma rays exist only
as long as they have energy. Once their energy is
spent, whether in air or in solid materials, they
cease to exist. The same is true for x-rays.
How are people exposed to
Most people's primary
source of gamma exposure is naturally occurring
radionuclides, particularly potassium-40, which is
found in soil and water, as well as meats and
high-potassium foods such as bananas. Radium is also a
source of gamma exposure. However, the increasing use
of nuclear medicine (e.g., bone, thyroid, and lung
scans) contributes an increasing proportion of the
total for many people. Also, some man-made
radionuclides that have been released to the
environment emit gamma rays.
Most exposure to gamma
and x-rays is direct external exposure. Most gamma and
x-rays can easily travel several meters through air
and penetrate several centimeters in tissue. Some have
enough energy to pass through the body, exposing all
organs. X-ray exposure of the public is almost always
in the controlled environment of dental and medical
Although they are
generally classified as an external hazard, gamma
emitting radionuclides do not have to enter the body
to be a hazard. Gamma emitters can also be inhaled, or
ingested with water or food, and cause exposures to
organs inside the body. Depending on the radionuclide,
they may be retained in tissue, or cleared via the
urine or feces.
Does the way a person is
exposed to gamma or x-rays matter?
Both direct (external)
and internal exposure to gamma rays or X-rays are of
concern. Gamma rays can travel much farther than alpha
or beta particles and have enough energy to pass
entirely through the body, potentially exposing all
organs. A large protion gamma radiation largely
passes through the body without interacting with
tissue--the body is mostly empty space at the atomic
level and gamma rays are vanishingly small in size. By
contrast, alpha and beta particles inside the body
lose all their energy by colliding with tissue and
causing damage. X-rays behave in a similar way, but
have slightly lower energy.
Gamma rays do not
directly ionize atoms in tissue. Instead, they
transfer energy to atomic particles such as electrons
(which are essentially the same as beta particles).
These energized particles then interact with tissue to
form ions, in the same way radionuclide-emitted alpha
and beta particles would. However, because gamma rays
have more penetrating energy than alpha and beta
particles, the indirect ionizations they cause
generally occur farther into tissue (that is, farther
from the source of radiation).