Gamma ray is a type of radiation from a nuclear reaction or a nuclide disintegration. Both gamma ray and X-ray are a photon. Gamma-ray usually has a energy unit of mega electron volt (MeV). X-ray are produced by interaction of an electron with matter. Gamma rays are generally characterized as electromagnetic radiation having the highest frequency and energy, and also the shortest wavelength, within the electromagnetic spectrum, i.e. high energy photons. Due to their high energy content, they can cause serious damage when absorbed by living cells.
Because the wavelength of gamma radiation is so short, a single incident photon can impart significant damage to a living cell. This property means that gamma radiation is often used to kill living organisms, in a process called irradiation. Applications of this include sterilising medical equipment (as an alternative to autoclaves or chemical means), removing decay-causing bacteria from many foodstuffs or preventing fruit and vegetables from sprouting to maintain freshness and flavour.
Due to their tissue penetrating property, gamma rays/X-rays have a wide variety of medical uses such as in CT Scans and radiation therapy (see X-ray). However, as a form of ionizing radiation they have the ability to effect molecular changes, giving them the potential to cause cancer when DNA is affected. The molecular changes can also be used to alter the properties of semi-precious stones, and is often used to change white topaz into blue topaz.
Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer. In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed on the growth in order to kill the cancerous cells. The beams are aimed from different angles to focus the radiation on the growth while minimizing damage to the surrounding tissues.
Gamma rays are also used for diagnostic purposes in nuclear medicine. Several gamma-emitting radioisotopes are used, one of which is technetium-99m. When administered to a patient, a gamma camera can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted. Such a technique can be employed to diagnose a wide range of conditions (e.g. spread of cancer to the bones.
Gamma ray detectors are also starting to be used in industry as part of the Container Security Initiative(CSI). These US$5 million machines are expected to scan 30 containers per hour. The objective of this technique is to pre-screen ship containers before they enter ports.
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