We cannot see ultraviolet light but it can have hazardous effects on the human body. Ultraviolet light in sunlight can cause the skin to tan or burn. Fluorescent substances are used in energy-efficient lamps - they absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light.
Changes in atoms and their nuclei can cause electromagnetic waves to be generated or absorbed. Gamma rays are produced by changes in the nucleus of an atom. They are a form of nuclear radiation. High energy waves such as X-rays and gamma rays are transmitted through body tissues with very little absorption. This makes them ideal for internal imaging. X-rays are absorbed by dense structures like bones, which is why X-ray photos are used to help identify broken bones.
Ultraviolet waves, X-rays and gamma rays are types of ionising radiation. They can add or remove electrons from molecules, producing electrically charged ions. Ionisation can have hazardous effects on the body:
Radiation dose is a measure of the risk of harm caused by exposing the body to ionising radiation. Radiation dose is measured in Sieverts (Sv). As radiation dose figures are generally small, they are usually given in millisieverts (mSv):
1000 mSv = 1 Sv
Background radiation is all around us, all the time. Sources include:
The level of background radiation and dose are affected by factors such as the jobs that people do and the places where people live.
The yearly limit for the radiation dose to the whole body of a worker is 20 mSv. Give this value in Sv.
20 mSv = 20 ÷ 1000 = 0.02 Sv