Gamma rays are the highest energy and shortest wavelength electromagnetic radiation, with a wavelength of less than 1 picometer. They are generated in energetic events and can penetrate through thick shields. Gamma rays are ionizing radiation and can strip electrons from atoms, causing disruptions. Gamma ray bursts are the most energetic activity in the universe and can be explained by collapsars or degenerate binary stars. Gamma rays are also used in medicine for gamma-knife surgery to kill cancer cells.
Gamma rays are the form of electromagnetic radiation with the highest energy and the shortest wavelength. They are defined as waves with a period (wavelength) of less than 1 picometer, which is 0.001 nanometers. By comparison, the diameter of a hydrogen atom is 50 picometers. Therefore the wavelength of gamma radiation is by definition subatomic. Their energy is of the order of 1.25 MeV (megaelectron volt) or higher. Gamma rays are generated in highly energetic events such as supernovae, in and around bodies of exotic matter such as neutron stars, pulsars and black holes, or less spectacularly when radioactive nuclei break apart in the interstellar medium.
The wavelength of gamma rays can go down to 10-15 or 0.000001 nanometers, around the classical radius of an electron. As the wavelength decreases, the corresponding energy increases. Because of their enormous energy, gamma rays are extremely difficult to stop. To shield something from gamma rays requires thick (1m+) shields of substances with the highest possible atomic number. Lead is a popular substance. Gamma rays are known to travel through 3 meters of concrete. Because of their high energy and penetrating ability, gamma rays are extremely dangerous from a biological point of view: they can kill living cells on contact. The most dangerous initial effect of a nuclear explosion is the gamma ray burst.
Gamma rays were first observed by Paul Ulrich Villard in 1900, while he was studying the radioactivity of uranium. At first, gamma rays were suspected to be particles, like their radiative cousins, alpha particles and beta particles, but passing them through a crystal showed that they were indeed electromagnetic waves. Like alpha and beta particles, gamma rays are ionizing radiation, although (unlike beta particles) they are not themselves charged. The ionizing radiation is powerful enough to strip electrons from the atoms it strikes, giving them a charge and causing disruptions to the resident material.
One of the most surprising phenomena involving gamma rays is the gamma ray burst (GRB). These are huge gamma ray bursts that occur in deep space. They are the most energetic activity in the universe since the Big Bang. (More energetic than supernovae.) In 10 seconds, a large gamma-ray burst releases more energy than the Sun releases during its 10 billion-year life. Several have been constructed to explain the various types of gamma-ray bursts. The prevailing theory is that of a collapsar. A collapsar is a special supermassive star that ejects high-energy relativistic jets from its poles as it undergoes its final collapse. We look at these as GRBs. A different kind of GRB is probably explained by degenerate binary stars. Extremely dense neutron stars occasionally collide, releasing huge amounts of gamma rays in the fusion process.
Gamma rays are also used medicinally to kill malignant cells, such as cancer cells. This procedure is called gamma-knife surgery.
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