Gamma ray, also called gamma particle stream, is a ray released when the nuclear energy level transition is deenergized and is an electromagnetic wave having a wavelength shorter than 0.01 angstrom. Gamma rays have a strong penetrating power and can be used in the industry to detect flaws or to automatically control the flow line. Gamma rays have a lethal effect on cells and are medically used to treat tumors.
Gamma rays were first discovered by the French scientist P.V. Villard and were the third type of nuclear radiation discovered after α and β rays.
The new nuclei generated by radioactive nuclei after alpha decay and beta decay are often at high energy levels, and they must transition to low energy levels and radiate gamma photons. Nuclear decay and nuclear reactions can produce gamma rays. It is an electromagnetic wave with a wavelength shorter than 0.2 angstroms . The wavelength of γ-rays is shorter than X-rays, so γ-rays have a stronger penetration than X-rays.
Gamma photons are not charged, so their energy cannot be measured by the magnetic deflection method. Usually, the secondary effect caused by gamma photons is indirectly determined, for example, by measuring the photoelectron or the energy of positive and negative electron pairs. In addition, gamma spectrometers (using gamma rays to interact with matter) can be used to directly measure the energy of gamma photons.
A scintillation counter consisting of a fluorescent crystal, a photomultiplier tube and an electronic instrument is a common instrument for detecting the intensity of gamma rays.
The incident photon excites the atomic nucleus into an excited state, and then emits gamma photons when de-excited.
For a narrow beam of gamma rays (i.e., the gamma photons that pass through the absorption sheet consist of only non-interacting or uncollided photons), μ is recorded as the attenuation coefficient of the gamma ray across the absorption medium. It contains The gamma photons are truly absorbed by the medium and scattered off the two contributions of collimation. Some studies describe μ directly as the total absorption coefficient, μ corresponds to the macroscopic absorption cross section of the medium for γ-rays, and the dimension of μ is the reciprocal of the length. Obviously, μ value reflects the absorption ability of the medium for γ-rays.