The radioactive decay of atomic nuclei produces electromagnetic radiation, of which gamma-ray decay (gamma radiation) is penetrating form. As it has the shortest wavelength electromagnetic waves, it imparts the highest photon energy. Gamma radiation was discovered in 1900 by Paul Villard, a French chemist and physicist while studying radium radiation. Also, Earnst Rutherford, in the same year, named another two types of decay radiation of less penetration which he called alpha and beta rays. He, in 1993, named gamma rays based on their ability of intense penetration of matter.
The energy range of gamma rays is a few keV (kilo electron volts) to around eight megaelectronvolts. The decaying radionuclides can be identified by using the energy spectrum of gamma rays. Some sources, such as Cygnus X-3 microquasar, can produce very-high-energy gamma rays of around 100-1000 teraelectronvolt (TeV). The natural source of gamma rays is radioactive decay and secondary radiation from atmospheric interactions with cosmic ray particles. Other natural sources are from terrestrial gamma-ray flashes. Fission in nuclear reactors, physics experiments such as neutron pion decay, and nuclear fusion are artificial ways to produce gamma rays.
Discovery of Gamma Decay
Gamma decay, a radioactive process, resulted in the discovery of the first gamma-ray. In its excited state, a nucleus emits the gamma-ray almost immediately when it is formed. The alpha particles, beta particles, and gamma rays are increasingly powerful as far as emission energy is concerned. The radiation process results in alpha decay, beta decay, and gamma decay only in the energy formation.
Gamma rays were initially thought of as fast beta particles, but the absence of magnetism proved that it is not so. However, it was confirmed that they are electromagnetic radiation when, in 1914, it was found that they get reflected from crystal surfaces. Gamma rays were found to be similar with X-rays when Rutherford and Edward Andrade measured its wavelength from radium (but with short wavelength and hence higher frequency)
Sources of Gamma Rays
The natural sources of gamma rays are radioisotopes such as Potassium-40 and secondary radiation from cosmic rays. Several astronomical processes produce very high-energy electrons resulting in gamma rays.
Gamma Radioactive Decay
Though all alpha, beta, and gamma particles are part of the radiation, their resultants differ considerably as alpha has a positive charge. The beta has a negative charge, and gamma rays are neutral. Thus gamma decay definition can be stated when a radioactive nucleus emits alpha and beta particles. The nucleus left in excited state decay to a lower energy state, releasing gamma rays.
The emission of gamma rays in the excited state is a very rapid process, and it takes on 10-12 seconds to emit gamma rays. The gamma decay process can also result in neutron capture, nuclear fission, or nuclear fusion. The formation of fluorescent gamma rays is also a subtype of radioactive gamma decay.
Any excited state emits gamma rays that may transfer energy mainly to the electrons in the K shell, resulting in the ejection of that electron from the atom, which is called the photoelectric effect. Most of the time, high-energy gamma rays scatter from the atomic electrons and transfer some of the energy to the scattered particles is called the Compton effect.
Application of Gamma Rays
Because of their properties, gamma rays are used in many fields with different applications. E.g., the medical applications of gamma rays are widely used in imaging techniques. Remember, gamma rays are more similar to X-rays. Applications such as positron emission tomography (PET) and very effective radiation therapies are used in detecting cancerous tumours. Positron emitting radioactive pharmaceuticals contributes to a particular physiological process like brain function. This is the reason why a short-lived positron is injected into the body.
They quickly combine with electrons and result in two 511-keV gamma rays that travel in opposite directions. This helps to form an image of the biological process under examination and highlights the location.
The radioactive traces of uranium and thorium can be searched with gamma-rays present on the Earth’s surface. They can trace the minerals containing these radioactive elements. Gamma rays can help other applications such as mineral exploration, geology, and environmental contamination identification. Orbiting satellites, telescopes, or high-altitude balloons can observe the Earth's strongly absorbing atmosphere for gamma rays.
Another established field of research is gamma-ray astronomy. There are many undiscovered gamma-ray sources, including powerful pulsars, quasars, and supernova remnants. Also, the gamma-ray burst has remained the most amazing unexplained astronomical phenomena to date (brief but intense emissions isotropically distributed in the sky).
Gamma Decay Definition in Particle Physics
Gamma rays are products of neutral systems which decay through electromagnetic interactions. In an electron-positron pairing, two gamma-ray photons are produced. Radioactivity is a neutral part of nature. Earth is said to have many stable elements with lower mass, like hydrogen, to highest like Pb or Bi. All elements with higher Z than Bi are radioactive. Some isotopes are long-lived. They can decay by more than one method.