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 neutrons, 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 previously mentioned,
gamma radiation consists of tiny discrete 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 radiation 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 atoms 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 materials In our world
are only those with very, very long half-lives. Uranium-238, for
example, has a half-life of 4 1/2 billion years, and exists today only
because not enough time has elapsed since its creation for it to
decay away to negligible levels.
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