Gamma Rays - Electromagnetic Spectrum

Definition

Gamma rays are commonly known as gamma radiation. They belong to the electromagnetic spectrum and arise from the radioactive decay of the atomic nuclei. They have the shortest wavelength making them impart the highest photon energy. Paul Villard was a French scientist who discovered gamma rays in 1900 while studying radiation emitted by radium.

On Earth, gamma rays are present due to radioactive decay or from the atmospheric interactions with cosmic ray particles. Other sources like terrestrial gamma-ray flashes also produce gamma rays from electron action upon the nucleus. Artificial sources of gamma rays include fission from nuclear reactors or high fission experiments like nuclear fission or neutral pion decay. They have photon energy above 100 keV.

Gamma rays are biologically hazardous due to their ionizing property. They can damage bone marrow and internal organs because of their high penetration power. They require shielding from dense materials like concrete and lead. Gamma rays cannot be reflected off a mirror, and their wavelengths are so small that they will pass between atoms in a detector.

Sources

The following is the list of sources that produce gamma rays-

1) Radioactive decay (gamma decay) – It is a type of nucleus decay. In this, no particles are ejected from the nucleus              when gamma rays undergo gamma decay. Instead, high-energy electromagnetic radiation – gamma-ray photons – is              released.
2) Terrestrial thunderstorms – It is a burst of gamma rays produced on Earth. They are caused by the intense electric              fields produced above or inside thunderstorms.
3) Solar flares – It is a burst of radiation from the Sun to release magnetic energy. Gamma rays are released when solar            flares are caught in the Earth’s magnetic field.
4) Pulsars and magnetars – They are a type of neutron stars that eject gamma rays upon fission.
5) Cosmic rays - They are produced when particles propel out of the expanding cloud of gases and magnetic fields. They        eject gamma rays upon collision.
6) Quasars and active galaxies – They are the centers of active galaxies, the most luminous and powerful sources of                 gamma-ray radiation.
7) Gamma-ray bursts – It is the most energetic and luminous electromagnetic event since the Big Bang. They can release      more energy in 10 seconds than the Sun emits in its entire 10-billion year lifetime.

Properties

1) Gamma rays are not deflected by magnetic and electric fields. This shows that they do not possess any charge. Therefore, the charge on gamma particles is zero.
2) Gamma rays belong to the region near X-rays. They both possess similar properties, but their wavelength is smaller than that of X-rays.
3) The rest mass of the photon is zero. However, the momentum is not zero. It can be explained with the help of Einstein’s energy formula as-

E = pc
where E = energy of the photon
p = momentum of the photon
c = speed of light

The momentum of photon in terms of wavelength is given by the following derivation-
p = mc
The energy (E) of a photon is given as E = mc2,
E = hν (frequency,ν=c/λ)
Therefore,
E = hc/λ
hc/λ=mc2
m =h/λc
from p = mc and m = h/ λc, we get

E = photon energy
h= Planck’s constant(6.62607015×10−34 Js)
λ = wavelength of light
Photon momentum is a comparatively small value to measure. For example, an electron with the same momentum has a 1460 m/s velocity, which is non-relativistic.

4) Gamma rays travel with the speed of light.
5) They have enormous penetrating power and can pass through heavy metals like iron and lead if ejected with great force.
6) They produce fluorescence in will mites.
7) They affect photographic plates more than beta particles.
8) Gamma rays can knock electrons from the surface where they may fall.
9) They can produce nuclear reactions.
10) They have small ionizing power but are dangerous.

Applications

1) Gamma rays are used to alter the properties of precious gems and stones, like topaz, quartz, etc.
2) It is used in various non-contact industrial sensors in various industries like mining, refining, food, soaps, detergents,            chemicals, pulp, and paper.
3) It is used to measure water levels or any other fluid levels in oil industries.
4) They are used as scanners to scan industrial boxes and containers before importing goods from other countries.
5) It is used to kill living organisms. This process is called irradiation.
6) Gamma rays are used to treat cancer and kill cancerous cells despite their cancer-causing properties. Therefore, they are        widely used in gamma-knife surgery.
7) They are also used in imaging techniques in nuclear medicine for diagnostic purposes.
8) The most common gamma emitter, nuclear isomer technetium-99m, emits the same energy as X-rays and is widely used      in medical applications.