Chemistry Reference
In-Depth Information
Radioactive Radiation
The
radiation
emitted when radioisotopes decay may be of one or more
of three different types: alpha and beta radiation, which are streams of
energetic particles, and gamma rays.
Alpha radiation
is a stream of
bundled, positively charged particles known collectively as
alpha particles
;
each alpha particle has a mass and charge equal in magnitude to two
protons together with two neutrons. Alpha radiation travels very short dis-
tances (only a few centimeters) in air, as the particles lose their energy as
soon as they collide with anything; they are therefore easily shielded by a
sheet of paper or by human skin (see Fig. 9).
Beta radiation
is a stream of negatively charged particles, known
as
beta particles
, which have the same mass and electric charge as the
electrons. Beta radiation travels in the air longer distances than alpha
FIGURE 9
Penetrating radiation.
Ionizing radiation (see Fig. 8) has sufficient
energy to penetrate and interact with some types of matter and is therefore also
known as “penetrating radiation.” Gamma and X-rays, for example, travel many
meters in air and readily penetrate thick layers of many materials, such as rock
and metal. By extension, the term “penetrating radiation” is also used to refer
to streams of energetic particles that penetrate and interact with matter. Streams
of alpha particles emitted from some atomic nuclei undergoing radioactive
decay, for example, known as “alpha radiation,” have a very short range of pen-
etration; alpha radiation travels only a few centimeters in air, but does not pen-
etrate human skin or clothing. Streams of beta particles, which may travel several
meters in air, are known as “beta radiation;” beta radiation penetrates human
skin, other animal and vegetable tissues, and thin metal sheets, but not thick
metal plates. Neutron beams, streams of uncharged nuclear particles, are the
most penetrating form of particles. Neutrons (which can be generated with
special equipment) penetrate very thick layers of most materials.
