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The energy released in each decay can be enormous. This
decay process is utilized in atomic reactors and bombs.
When certain very heavy isotopes of uranium or plutonium
(or several other isotopes) decay, they may split apart. This
process is called fission. In fission, the entire nucleus splits
apart, causing two new atoms and releasing a very large
amount of energy. This process is not very predictable, for
the nucleus can split in many ways, yielding a wide variety
of new atoms and even some free neutrons. The free neu-
trons, when released, can be absorbed by other fuel atoms,
causing them, in turn, to fission -- leading to a continuous
or (if not controlled) explosive chain reaction. Due to the
wide range of new atoms produced in the fission process,
many of the daughter products are not stable and will, in
turn, decay themselves, leading to hazardous nuclear
waste and fallout.
In all of the above processes, another kind of radiation,
gamma, is almost always released. Unlike the particles pre-
viously mentioned, gamma radiation consists of tiny, dis-
crete bundles of energy called quanta. Light, X-rays and
gamma rays can all be described as quanta, the difference
being the total energy packed into each bundle.
In nuclear decay some energy in the unstable nucleus is
dissipated to its surroundings in the form of heat and radia-
tion in the instant that it decays. The nucleus may remain in
its unstable state for billions of years, and then suddenly
decay spontaneously. The time required for half of the at-
oms of a particular isotope to decay is called the half-life of
that isotope. For an isotope with a half-life of 1 year, the
pure isotope substance would be only 50% pure after one
year, half of the original atoms having decayed into some
other substance. After another year, 25% of the original
material would remain, and so on. Natural radioactive ma-
terials in our world are only those with very, very long half-
lives. Uranium-238, for example, has a half-life of 4 billion
years, and exists today only because not enough time has
elapsed since its creation for it to decay away to negligible
levels. It is thought that the universe was created from a
huge mass of subatomic particles and energy — the Big
Bang Theory.
Of the elements and their isotopes that constitute our
planet, the vast majority are quite stable, the result of bil-
lions of years of nuclear decay. The amount of radiation
