Radiation as a health hazard has recently made its way into the news again, as it does from time to time. This undetectable (by human senses) energy form has held a special place in the human psyche as a uniquely sinister and stealthy hazard to human health, since the days of early experimentation with radioactive materials, the demonstration of the power of nuclear weapons, and the increasing use of nuclear power stations which brought people closer to sites using large radioactive sources.
Ionising radiation is frequently not well understood by the general public. The term encompasses a variety of energy forms emitted by different sources, which all have the property of being able to penetrate other substances and disrupt atomic structures, dislodging electrons or atomic nuclear particles, forming ions or isotopes, hence the term ionising radiation. Ionising radiation may be an electromagnetic wave with enough energy (the same as light, radio waves and microwaves) or an atomic particle like an electron or neutron. As long as the particle or wave is sufficiently energetic it can cause ionisation, regardless of the amount or intensity. In this way radiation is different to heat in the way it causes damage. Radiation can travel through a vacuum, and some forms can travel through other materials to differing degrees. This property is exploited in x-ray imaging, where bone absorbs the rays, casting a shadow on the film. Some forms of radiation can be stopped by a sheet of paper, others slowed by water or air, yet others need dense material such as concrete and lead to stop them.
In humans, ionisation confers the ability to damage molecules in the body directly, including cellular material, proteins and DNA, generating free radicals which are chemically reactive themselves and cause further damage to cellular material. This can result in radiation burns and radiation sickness in the short term and cancers in the long term.
Many forms of radiation occur naturally, and it is not possible to avoid all irradiation. UV light and cosmic rays from the sun are ever-present, and radiation is emitted from radioactive forms of naturally occurring minerals and rocks. Airline crews are relatively highly exposed to cosmic radiation because of high altitude flight. Background radiation from soil can vary widely depending on local geology. Radon gas is a decomposition product of uranium-containing soils which seeps out and can accumulate inside buildings which are well-sealed. Naturally occurring radioactive isotopes of substances ingested in food are present in the body and irradiate internally. Carbon-dating uses the decay of C-14 over long periods to estimate the age of biological specimens. X-rays and other diagnostic tests can expose an individual to radiation. Lastly, a variety of household items generate radiation in small amounts or contain radioactive material, including fluorescent bulbs, smoke detectors, luminous dials etc.
Radiation has many uses in modern life - in smoke detectors, ground surveys, industrial x-rays of critical components such as welds, as well as monitoring industrial processes through flow monitoring and thickness monitoring. Medical imaging and some procedures also involve radiation, and nuclear power plant workers obviously have the potential to be exposed. These workers are carefully monitored and their exposure limited by law, and they are required to undergo regular medical monitoring of their health.
