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Scientists believe that the universe was created from a huge mass
of sub-atomic 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 billions of years of
nuclear decay. The amount of radiation given off from natural
radioactive minerals in the earth's crust is a major constituent of
background radiation. For the most part, its quite low, due to the
long time required for the remaining radioisotopes to decay. In
atomic reactions (either natural or forced by man) the decay
process is sped up by the effect of neutrons given off in the fission
process interacting with more unstable isotopes to cause
immediate decay. While this allows the energy of the isotope to be
harvested in a conveniently short time, the unstable decay
products produced generally have short half-lives, on the order of
seconds to centuries, and are very radioactive. As a result of this
process, considerable larger quantities of short half-live (high
decay rate) isotopes, such as Iodine-125, Iodine-131, and
Cesium-137, become a part of the world we live in. This is the
basis for the controversy and concerns on the subject of nuclear
power generation, waste disposal, and nuclear weapons.
Interaction of Radiation with Matter
The particles and photons that result from nuclear decay carry
most of the energy released from the original unstable nucleus.
The value of this energy is expressed in electron Volts, or eV. The
energy of beta and alpha rays is invested in the particles' speed. A
typical beta particle from Cesium-137 has an energy of about
500,000 eV, and a speed that approaches that of light. Beta
energies can cover a wide range, and many radioisotopes are
known to emit betas at energies in excess of 10 million eV. The
penetration range of typical beta particles is only a few millimeters
in human skin.
Alpha particles have even shorter penetration ranges than beta
particles. Typical alpha energies are on the order of 5 million eV,
with ranges so short that they are ext remely difficult to measure.
Alphas are stopped by a thin sheet of paper, and in air only travel
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