Uranium

Radioactivity

Atoms are found in all matter. There are stable atoms, which remain the same forever, and unstable atoms, which spontaneously break down or 'decay' into new atoms. These unstable atoms are said to be 'radioactive', because they emit ionizing radiation from the nucleus as they decay. For a given element there are forms (isotopes) that are stable and isotopes that are radioactive.

Radioactive isotopes of elements such as uranium, radium, thorium, radon, americium and plutonium spontaneously break down. The energy that is released in the process is made up of small, invisible, fast-moving particles and high energy waves.  Other common elements with radioactive isotopes are carbon, hydrogen, and lead.

For some elements the radioactive isotopes (radioisotopes) are a small fraction of the naturally occuring element whereas for others, such as thorium, it is the major constituent.

Radioactivity is a random process that happens spontaneously as particular isotopes  decay. The radioactive isotopes continue to decay over time. The length of time that is taken for half of the nuclei in an isotope to decay is called its 'half-life'. A half-life can be very short (milliseconds to hours) or very long (hundreds of thousands of years).

Ionizing radiation also arises from nuclear fission. Nuclear fission releases very hazardous ionizing radiation and energy as the nucleus is split.

Radioactive isotopes are produced in nuclear weapons and in nuclear reactors.

Greater technical detail can be found on this topic by searching through the publications at http://www.ccsa.asn.au/nic/

In this section

• The Element
• Nuclear fission 
• Radioactivity 
• Ionizing radiation 
• Uranium Mining in South Australia