riginal nuclei; the loss is expressed as energy.
By the 1930's, physicists had concluded that this was the process which
powered the sun and stars; but the nuclear fusion process remained only
of theoretical interest until it was discovered that an atomic fission
bomb might be used as a "trigger" to produce, within one- or
two-millionths of a second, the intense pressure and temperature
necessary to set off the fusion reaction.

Fusion permits the design of weapons of almost limitless power, using
materials that are far less costly.

Note 3: Radioactivity

Most familiar natural elements like hydrogen, oxygen, gold, and lead
are stable, and enduring unless acted upon by outside forces. But
almost all elements can exist in unstable forms. The nuclei of these
unstable "isotopes," as they are called, are "uncomfortable" with the
particular mixture of nuclear particles comprising them, and they
decrease this internal stress through the process of radioactive decay.

The three basic modes of radioactive decay are the emission of alpha,
beta and gamma radiation:

Alpha--Unstable nuclei frequently emit alpha particles, actually helium
nuclei consisting of two protons and two neutrons. By far the most
massive of the decay particles, it is also the slowest, rarely
exceeding one-tenth the velocity of light. As a result, its
penetrating power is weak, and it can usually be stopped by a piece of
paper. But if alpha emitters like plutonium are incorporated in the
body, they pose a serious cancer threat.

Beta--Another form of radioactive decay is the emission of a beta
particle, or electron. The beta particle has only about one
seven-thousandth the mass of the alpha particle, but its velocity is
very much greater, as much as eight-tenths the velocity of light. As a
result, beta particles can penetrate far more deeply into bodily tissue
and external doses of beta radiation represent a significantly greater
threat than the slower, heavier alpha particles. Beta-emitting
isotopes are as harmful as alpha emitters if taken up by the body.

Gamma--In some decay processes, the emission is a photon having no mass
at all and traveling at the speed of light. Radio waves, visible
light, radiant heat, and X-rays are all photons, differing only in the
energy level each carries. The gamma ray is similar to the X-ray
photon, but far more penetrating (it can traverse several inches of
concrete). It is capable of doing great dam