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Beta radiation
. A beta particle consists of an electron emitted from
an atom. Beta particles penetrate matter less deeply than gamma
or X-rays, but they are biologically significant because they can be
more effective than gamma radiation at disrupting cellular material.
Alpha radiation
. An alpha particle consists of two protons and two
neutrons, the same as the nucleus of a helium atom. It generally
can travel no more than 1 to 3 inches in air before stopping, and
can be stopped by a piece of paper.
When an atom emits an alpha or beta particle or a gamma ray, it
becomes a different type of atom. Radioactive substances may go
through several stages of decay before they change into a stable, or
non-radioactive, form.
An element may have several forms, or isotopes. A radioactive
form of an element is called a radioisotope or radionuclide. Each
radionuclide has a half-life, which is the time required for half of a
quantity of the material to decay.
Electron
Proton
Neutron
A hydrogen atom has one electron
and one proton. The most common
isotope has no neutrons and is stable.
Tritium is a radioactive isotope of
hydrogen. It has two neutrons in
its nucleus.
The following chart shows the complete decay chain for Uranium
238, which ends with a stable isotope of lead. Notice that the half-
life of the radionuclides in the chain range from 164 microseconds
to 4.5 billion years.