Gamma rays or gamma radiation is a stream of high-energy electromagnetic radiation given off by an atomic nucleus undergoing radioactive decay.
Definition of Gamma Rays
Gamma rays are ionizing in nature, which means that they can release electrons from atoms. Gamma rays are biologically dangerous and can cause animal cells to decay. Usually, gamma rays have frequencies above 10 exahertz and energies over 100 keV, and wavelengths less than 10 picometers.
Detecting gamma rays are not as easy as detecting the other types of ray such as x-ray or light. A mirror cannot reflect it because of its high density, which allows it to pass through such devices undetected. The detection of gamma rays requires a special kind of detector, called a gamma rays telescope, which uses the Compton Scattering process to detect gamma rays.
Discovery of Gamma Rays
Gamma radiation or gamma-ray is an extremely high-frequency radioactive radiation consisting of high-energy photons. It was first discovered by a French chemist and physicist, Paul Villard, in 1900. It was named gamma-ray by Ernest Rutherford in 1903.
British physicist Ernest Rutherford coined the term gamma-ray in 1903 following early studies of the emissions of radioactive nuclei. Just as atoms have discrete energy levels associated with different configurations of the orbiting electrons, atomic nuclei have energy level structures determined by the configurations of the protons and neutrons that constitute the nuclei.
While energy differences between atomic energy levels are typically in the 1- to 10-eV range, energy differences in nuclei usually fall in the 1-keV (thousand electron volts) to 10-MeV (million electron volts) range.
When a nucleus makes a transition from a high-energy level to a lower energy level, a photon is emitted to carry off the excess energy; nuclear energy-level differences correspond to photon wavelengths in the gamma-ray region.
Mechanism of Gamma Radiation Production
The Gamma rays are produced in number of ways:
- Thermal radiation: Only an extremely hot medium (T = 108 K) is likely to produce gamma radiation. Such media are extremely rare, and this process is not fundamental to the production of this radiation.
- Inverse Compton effect: During a collision with low energy photon, a relativistic electron can transfer a significant part of its energy to it. The photon can then have an energy of 100 MeV.
- The Synchrotron radiation: A relativistic electron spiraling through the force lines of a magnetic field radiates electromagnetic energy. Thus, energy electrons 3 × 108 MeV in a magnetic field of 3 × 10−6 Gauss will create gamma radiation. But, by radiating, the electrons lose energy: their lives are therefore limited.
- Bremsstrahlung or braking radiation: An electron passing near a nucleus is influenced by its Colombian field. The deceleration of the electron is accompanied by a loss of energy in the form of gamma radiation when the electron has a relativistic speed.
- Production of meson π 0: A meson can be produced during reactions of several types:
- Collision between two protons or a proton and alpha (helium nucleus).
- Collision between a proton and an antiproton; if the antimatter exists in the Universe, observing the gamma radiation produced is a method for detecting it. The meson (π0) then disintegrates into two photons.
- Nucleus de-excitation: Like an atom or a molecule, a nucleus has energy levels whose transitions between the least excited levels give gamma radiation. Such nucleus de-excitation may occur either during the interaction of a nucleus with neutrinos or during specific thermonuclear reactions.
Uses of Gamma Radiation
Though gamma rays are bio-hazardous in nature, they can be controlled and used for various important purposes:
- It is used in the treatment of cancer without surgery. The cancerous tumor is subjected to gamma radiation, which kills its DNA.
- It is used to sterilize surgical instruments.
- It is also used in the food industry to kill harmful bacteria.
- Gamma radiation has the ability to change the properties of specific semi-precious stones. It is often used to change white topaz into blue topaz.
Properties of Gamma Rays
The waves from the high-frequency end of the electromagnetic spectrum which do not have any mass are called gamma rays. They have the greatest power of penetration.
They are the least ionizing but most penetrating, and it is extremely difficult to stop them from entering the body. These rays carry a huge amount of energy and can even travel through thin lead and thick concrete.
Applications of Gamma Rays
There are some applications of gamma rays:
1. Medical Physics Applications
The major application of radiation in medicine is radiotherapy and treatment by ionizing radiation. A few months after the discovery of X-rays, over a century, it has become clear that biological action radiation could be used to treat cancers.
Cancers cells divided more quickly are more sensitive than normal cells to ionizing radiation. By sending these cells a certain dose of radiation, it is possible to kill them and eliminate the tumor. Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer since the rays also kill cancer cells.
In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed to the growth in order to kill the cancerous cells. The beams are aimed from different angles to concentrate the radiation on the growth while minimizing damage to surrounding tissues.
Gamma rays are also used for diagnostic purposes in nuclear medicine in imaging techniques. A number of different gamma-emitting radioisotopes are used. For example, in a PET scan, a radiolabeled sugar called fluorodeoxyglucose emits positrons annihilated by electrons, producing pairs of gamma rays that highlight cancer as cancer often has a higher metabolic rate than cancer in the surrounding tissues.
The most common gamma emitter used in medical applications is the nuclear isomer technetium-99m which emits gamma rays in the same energy range as diagnostic X-rays.
When this radionuclide tracer is administered to a patient, a gamma camera can be used to form an image of the radioisotope’s distribution by detecting the gamma radiation emitted (see also SPECT). Depending on which molecule has been labeled with the tracer, such techniques can be employed to diagnose a wide range of conditions.
2. Sterilization of Objects by Gamma Radiation
Irradiation of surgical and food material: Irradiation is a privileged means to destroy micro-organisms (fungi, bacteria, viruses…). As a result, many applications of radiation exist for the sterilization of objects.
For example, most medical-surgical equipment (disposable syringes, etc.) is today radio-sterilized by specialized industrialists. Similarly, the treatment by irradiating food ingredients allows improving food hygiene: sterilization of spices and eliminating salmonella from shrimp and frog legs.
This technic is also known as food ionization. Irradiation of art objects: Treatment with gamma rays helps eliminate larvae, insects, or bacteria inside objects to protect them from degradation.
This technic is used in the treatment of conservation and restoration of art objects, ethnology, and archaeology. It is applicable to different types of materials: wood, stone, leather, etc.
3. Industrial Applications
Elaboration of materials: Irradiation causes, under certain conditions, chemical reactions that allow the development of more resistant materials, more lightweight, capable of superior performance.