Gamma ray

In nuclear physics gamma rays, often indicated with the corresponding lower case Greek letter γ, are the electromagnetic radiations produced by radioactive decay of atomic nuclei.

They are very high frequency radiations and they are among the most dangerous for man, as all ionizing radiations. The danger derives from the fact that they are high energy waves able to irreparably damage the molecules that make up the cells, leading them to develop genetic mutations or even death.

On Earth we can observe natural sources of gamma rays both in the decay of radionuclides and in the interactions of cosmic rays with the atmosphere; more rarely also lightning produces this radiation.

History and discovery

The first sources of gamma rays were observed in gamma decay, a process in which an excited nucleus decays emitting this radiation just after formation. The first to observe them was Paul Villard, French chemist and physicist, in 1900 while he was studying radiation emitted by radium. Ulrich Villard understood that this radiation was more penetrating than other observed in radium, such as beta rays (observed by Henri Becquerel in 1896) or alpha rays (observed by Ernest Rutherford in 1899). Villard however did not name this radiation by a different name.

Gamma radiation was recognized as a different fundamental radiation by Rutherford in 1903 and was so named with the third letter of the Greek alphabet, following alpha and beta. In addition to the greater penetrating ability of gamma rays, Rutherford also noted that they were not deflected by the magnetic field. Initially the gamma rays were thought to be particles (Rutherford himself thought they were very fast beta particles), but various observations, such as the reflection on the surface of a crystal (1914), showed that it was an electromagnetic radiation.

Rutherford and his collaborator Edward Andrade first measured the wavelength of gamma rays emitted by radium, obtaining values lower than those of beta rays, therefore a higher frequency. Gamma rays in nuclear decays are emitted as a single photon.

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