Background radiation occurs naturally in our environment and is all around us. Most background radiation is released by:
- Radioactive substances in soil and rocks.
- Cosmic rays from outer space.
Some background radiation come from man-made sources and waste products. Industry and hospitals both contribute to background radiation levels, but this is only a small percentage of the total background radiation.
Radioisotopes are used as tracers in industry and hospitals. In idustry, tracers are used to:
- Track the dispersal of waste.
- Find leaks and blockages in underground pipes.
- Find the routes of underground pipes.
A radioactive material that emits gamma rays is put into the pipes. (Gamma is used because it can penetrate through the soil to the surface.) The progress of the material is then tracked by a detector above ground. If there is a:
- Leak - the radioactive material will escape and be detected at the surface.
- Blockage - the radioactive material will stop flowing so it can't be detected after this point.
Most smoke detectors contain Americium-241, an alpha emitter. Emitted particles cause air particles to ionise, and the ions formed are attracted to the oppositely charged electrodes. This results in a flow of electric current. This is what happens when the smoke enters the space between the two electrodes:
1. The alpha particles are absorbed by the smoke particles.
2. Less ionisation takes place.
3. A smaller current than normal now flows. and the alarm sounds.
A small amount of carbon in our atmosphere and the bodies old plants and animals is radioactive Carbon-14.
Measurements from radioactive carbon can be used to date old, once-living materials, such as wood.
The activity of radioactive carbon can be used to find the approximate age of a once-living material. The amount of radioactive Caron-14 in the atmosphere has remained unchanged for thousands of years. A dead object doesn't exchange gases with the air as living matter does. As the Carbon-14 in the dead object decays, it is not replaced so the radioactivity of the sample decreases.
So, the dead object will have a different radioactivity to living matter. The ratio of these two activities can be used to find a fairly accurate approximate age for the objects within known limits (approximately 50 years).