emission is usually found in association with Alpha and Beta emission. Gamma rays possess
no charge or mass; thus emission of Gamma rays by a nucleus does not result in a change in
chemical properties of the nucleus but merely in the loss of a certain amount of radiant
After Alpha and Beta radiation the new nucleus will have an excess
of energy and this is usually released by the emission of Gamma rays. Gamma rays are
electromagnetic radiation similar to radio waves, visible light, and X-rays, except that
they have a much higher frequency (or shorter wavelength).
Gamma rays are transmitted in small individual quantities of
energy known as Photons and in some ways they behave more like particles than waves. The
time delay between the decay and the gamma ray emission is so small, that for most
practical purposes they may be considered to occur simultaneously. A few cases are known
of pure Alpha and Beta emission. A number of pure Gamma emitting isotopes are also known.
Pure Gamma emission occurs when an isotope exists in two different
forms, called nuclear isomers, having identical atomic numbers and mass numbers, but
different in nuclear-energy content. The emission of Gamma rays accompanies the transition
of the higher-energy isomer to the lower-energy form. An example of isomerism is the
isotope Protactinium-234, which exists in two distinct energy states with the emission of
Gamma rays signalling the transition from one to the other.
Since Gamma radiation can penetrate very far into a material and
has the ability to disrupt chemical bonds, it is Gamma radiation that poses the most
danger when working with radioactive materials (sadly, it took scientists many years to
realise the perils of radioactivity....).
Gamma rays will penetrate to great depths in materials, and no
amount of absorber will completely stop all of the gamma radiation. What is usually done
in practice is to use sufficient thickness of an absorber to reduce the radiation level to
a more acceptable value.