Radioactivity
How radiation travels
Radioactivity is energy and mass released by spontaneous changes in the nucleus of an atom.
Some atoms are stable. Others are unstable and 'decay', emitting radiation to achieve a stable state. The emissions from an unstable atom's nucleus, as it decays, can be in the form of alpha, beta or gamma radiation.
Alpha radiation is helium nuclei, while beta particles are electrons. Gamma radiation is similar to X-rays.
When an atom decays, it changes into another isotope, or form, of the same element or into a completely different element in a process called transmutation. Different isotopes of the same element differ in the number of neutrons in their nuclei.
Some elements reach stability via a series of steps through several isotopes, or 'daughter products'.
In the most extreme cases, such as that of uranium-238, it will finally become a stable isotope of lead, but its journey will take billions of years. Along the way, as its initial energy declines, it will transmute to elements, each more stable than the last: thorium, radium, radon, polonium and bismuth.
The discovery of radioactivity has delivered many benefits, but it must be handled with caution. A sheet of paper, or even the skin of our bodies, will stop alpha particles, while a thin sheet of perspex or glass will stop beta radiation. However, the energy of both can cause damage to cells if they enter the body through inhalation, swallowing or wounds. Thick barriers of lead, water and concrete are necessary to stop much more penetrating and damaging gamma radiation.