original 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