Plutonium was first produced by Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan and Arthur C. Wohl by bombarding an
isotope
of
uranium
, uranium-238, with
deuterons
that had been accelerated in a device called a
cyclotron
. This created
neptunium
-238 and two free
neutrons
. Neptunium-238 has a
half-life
of 2.1 days and decays into plutonium-238 through
beta decay
. Although they conducted their work at the
University of California
in 1941, their discovery was not revealed to the rest of the scientific community until 1946 because of wartime security concerns.
Plutonium's most stable
isotope
, plutonium-244, has a
half-life
of about 82,000,000 years. It decays into
uranium
-240 through
alpha decay
. Plutonium-244 will also decay through spontaneous fission.
Only two of plutonium's isotopes, plutonium-238 and plutonium-239, have found uses outside of basic research. Plutonium-238 is used in radioisotope thermoelectric generators to provide electricity for space probes that venture too far from the sun to use solar power, such as the
Cassini
and
Galileo
probes. Plutonium-239 will undergo a fission chain reaction if enough of it is concentrated in one place, so it is used at the heart of modern day nuclear weapons and in some nuclear reactors.