The Nature of Radioactivity
Radioactivity is the phenomenon of the spontaneous disintegration of unstable atomic
nuclei to atomic nuclei to form more energetically stable atomic nuclei.
The unstable, or radioactive, nuclei spontaneously decompose by emitting a small particle
that is very fast moving and therefore carries with it a great deal of energy.
Radioactive decay
Radioactive decay is the conversion of unstable nuclei into stable nuclei. In some types of
nuclear decomposition processes, atoms are converted from those of one element to those of
another as a consequence of this emission. Very heavy elements are particularly prone to this
type of decomposition, which occurs by the emission of a small particle. The product of a
radioactive decay process—called the daughter of the parent isotope.
The rate at which a radioactive element decays is expressed in terms of its half-life; i.e.,
the time required for one-half of any given quantity of the isotope to decay. Half-lives range from
more than 1024 years for some nuclei to less than 10−23 second.
Type of
An alpha ( ) particle is a radioactively emitted particle that has a charge of 2 and a mass number
of 4—i
A beta (
) particle is an electron. It is formed when a neutron splits
into a proton and an electron in the nucleus.
The Health Effects of Ionizing Radiation The α and β particles that are produced in the radioactive
decay of a nucleus are not in themselves harmful chemicals, since they are simply the nucleus of
a helium atom and an electron. However, they are ejected from the nucleus with an incredible
amount of energy of motion. When this energy is absorbed by the matter encountered by the
particle, it often ionizes atoms or molecules; for that reason, it is called ionizing radiation, or just
radiation. This radiation is potentially dangerous if we absorb it, since the molecular components
of our bodies can be ionized or otherwise damaged.
Although alpha and
particles are energetic, they cannot travel far
within
the human body, since they lose more and more of their energy—and consequently slow down—as they collide with more and more atoms.
Alpha particles can travel only a few thousandths of a centimeter
within the body, so they are not penetrating.
This is true because they are
relatively massive, and when they interact with matter they slow down, capture electrons from it, and are converted into harmless atoms of helium gas.
If an
particle is emitted outside the body, it will usually be absorbed in the
air or by the layer of dead skin, so it will do you no harm. However, inhaled
or ingested radioactive atoms can cause serious internal damage when they
emit
particles. The damage is particularly severe with
particles since
their energy is concentrated in a small area of absorption located within
about 0.05 mm of the point of emission. In their interaction with matter,
particles are highly damaging—the most highly damaging of all particles—
since they can knock atoms out of molecules or ions out of crystal sites. If the
molecules affected are DNA or its associated enzymes, cell death can result.
A more serious consequence for the individual can be the creation of mutations that could lead to cancer.
Beta particles move much faster than
particles since they are much
lighter and can travel about 1 m in air or about 3 cm in water or biological
tissue before losing their excess energy. Like particles, they can cause con-
siderable damage to cells if they are emitted from particles that have been
inhaled or ingested and the radioactive nucleus is consequently close to the
cell when it decays.
Gamma rays easily pass through concrete walls—and our skin. A few
centimeters
of
lead
are
required
to
shield
us
from
rays. Gamma particles are
the most penetrating and therefore the most damaging of the three, traveling a few dozen centimeters into our bodies or even right through them.
They are generally the most dangerous type of radioactivity, since they can
penetrate matter efficiently and do not have to be inhaled or ingested.
Although
they
can
pass
through
our
rays lose some of their energy
in the process, and cells can be damaged by this transferred energy, since it can
ionize molecules. Ionized DNA and protein molecules cannot carry out their
normal functions, potentially resulting in radiation sickness and cancer.
bodies,