Why X-rays Cannot be produced from lighter atoms?

X-ray photons are produced when electrons in the outermost shells of an atom drop to the inner shells. (Hydrogen atoms do not emit X-rays, because the electron energy levels are too closely spaced together to permit the emission of high-frequency radiation.)

Why heavy atoms are required for emission of X-ray?

It is large compared with other atomic emissions because it is produced when an inner-shell vacancy is filled, and inner-shell electrons are tightly bound. Characteristic x ray energies become progressively larger for heavier elements because their energy increases approximately as Z2.

Why X-rays Cannot produce pair production?

The photon must have higher energy than the sum of the rest mass energies of an electron and positron (2 ⋅ 511 keV = 1.022 MeV, resulting in a photon-wavelength of 1.2132 picometer) for the production to occur. (Thus, pair production does not occur in medical X-ray imaging because these X-rays only contain ~150 keV.)

What causes pair production?

For pair production to occur, the electromagnetic energy, in a discrete quantity called a photon, must be at least equivalent to the mass of two electrons. The positron that is formed quickly disappears by reconversion into photons in the process of annihilation with another electron in matter.

Why are 2 gamma rays produced in annihilation?

VII POSITRON ANNIHILATION. (17.26) The electron has much more momentum than the positron, and momentum balance causes the two gamma rays, to make a slight angle with respect to each other as they depart in opposite directions.

What is pair production in xray?

Pair production occurs when an electron and positron are created with the annihilation of the x-ray photon. Photodisintegration (PD) is the process by which the x-ray photon is captured by the nucleus of the atom with the ejection of a particle from the nucleus when all the energy of the x-ray is given to the nucleus.

Why does pair annihilation produce two photons?

Annihilation occurs when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy. Two photons are produced in the process (as a single photon only would take away momentum which isn’t allowed, as no outside forces act).