b. Natural radioactivity, in which the nuclear disintegration is spontaneous, is
exhibited in certain naturally occurring elements, such as radium. Artificial radioactivity
is brought about by bombarding the atomic nucleus with various subatomic particles.
Alpha and beta particles, protons (nucleus of the hydrogen atom), neutrons, and
deuterons (nucleus of deuterium, or heavy hydrogen, atom) are most commonly used.
However, the relatively small size of the atomic nucleus makes bombardment extremely
difficult. To produce artificial radioactivity, the bombarding subatomic particle must
deliver a direct hit to the atomic nucleus. With the proper bombardment technique, any
stable atom or element can be made radioactive.
c. The radiation emitted with atomic nuclei disintegration may be in the form of
corpuscular radiation or electromagnetic waves. The corpuscular radiations are the
alpha and beta particles. The electromagnetic radiations include gamma radiation and
x-radiation. Gamma radiation is emitted directly from the nucleus while x-radiation is
produced by radiative and collisional interactions of electrons outside the nucleus.
(1) Alpha particle. The alpha particle is a stable combination of two protons
element emits an alpha particle during nuclear disintegration, the particle is traveling at
speeds of 9,000 to 20,000 miles per second, but it is slowed down rapidly in its passage
(a) Eventually, the alpha particle, which has a positive charge of +2,
passes through matter causing many ion pairs by attracting the outer orbital electrons.
The alpha particle becomes a stable helium atom when it has annexed two electrons.
The Z number and A number of the nucleus of the element that gives up the alpha
particle are reduced by 2 and 4, respectively.
(b) An alpha particle also has an extremely high ionizing ability. It may
cause some skin damage, but its greatest danger lies in its penetrating abilities.
(2) Beta particle. A beta particle is an extremely high-speed electron
(negative beta, -01℮) or positron (positive beta, +01e) which is ejected from the nucleus
of a disintegrating atom. Electrons emitted from the nucleus probably result from
spontaneous conversion of a neutron into a proton and an atomic nucleus ordinarily
does not contain free electrons. Except for its speed and origin, the electron is identical
to the electrons that orbit about the nucleus of atoms. As a result of the neutron split
which ejects an electron and retains a proton, the Z number of the element is increased
by an addition of one, but its A number remains the same.
(a) In relation to the alpha particle, the beta particle has a smaller mass
and travels at a much higher speed, almost as fast as light. Because of this, the beta
particle exerts less force for a shorter period on the atoms of material through which it
passes. Thus, its ionizing ability per unit path length is less than that of an alpha
particle, though its range is greater.