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Gamma rays (denoted as γ) are a form of electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions, such as electron-positron annihilation or radioactive decay. Gamma (uppercase &Gamma, lowercase γ Γάμμα is the third letter of the Greek alphabet. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Electron-positron annihilation occurs when an Electron and a Positron (the electron's anti-particle) collide Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Gamma rays are generally characterized as electromagnetic radiation having the highest frequency and energy, and also the shortest wavelength (below about 10 picometer), within the electromagnetic spectrum. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Gamma rays consist of high energy photons with energies above about 100 keV. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Gamma rays were discovered by Paul Villard, a French chemist and physicist, in 1900, while studying uranium. Paul Ulrich Villard (1860 &ndash 13 January 1934) was a French Chemist and Physicist, born in Saint-Germain-au-Mont-d'Or 28th of September 1860

Hard X-rays overlap the range of "long"-wavelength (lower energy) gamma rays. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. The distinction between the two terms, however, depends on the source of the radiation, not its wavelength; X-ray photons are generated by energetic electron processes, gamma rays by transitions within atomic nuclei.

Due to their high energy content, gamma rays can cause serious damage when absorbed by living cells.

## Properties

### Shielding

Artist's impression of an emission of a gamma ray (γ) from an atomic nucleus

Shielding gamma rays requires large amounts of mass. They are better absorbed by materials with high atomic numbers and high density. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton The higher the energy of the gamma rays, the thicker the shielding required. Materials for shielding gamma rays are typically measured by the thickness required to reduce the intensity of the gamma rays by one half (the half value layer or HVL). For example, gamma rays that require 1 cm (0. 4 inches) of lead to reduce their intensity by 50% will also have their intensity reduced in half by 6 cm (2½ inches) of concrete or 9 cm (3½ inches) of packed dirt. Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

### Matter interaction

The total absorption coefficient of aluminum (atomic number 13) for gamma rays, plotted versus gamma energy, and the contributions by the three effects. Over most of the energy region shown, the Compton effect dominates.
The total absorption coefficient of lead (atomic number 82) for gamma rays, plotted versus gamma energy, and the contributions by the three effects. Here, the photo effect dominates at low energy. Above 5 MeV, pair production starts to dominate

When a gamma ray passes through matter, the probability for absorption in a thin layer is proportional to the thickness of that layer. This leads to an exponential decrease of intensity with thickness. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value The exponential absorption holds only for a narrow beam of gamma rays. If a wide beam of gamma rays passes through a thick slab of concrete, the scattering from the sides reduces the absorption.

$I(d) = I_0 \cdot e ^{-\mu d}.$

Here, μ = nσ is the absorption coefficient, measured in cm−1, n the number of atoms per cm3 in the material, σ the absorption cross section in cm2 and d the thickness of material in cm. In nuclear and Particle physics, the concept of a cross section is used to express the likelihood of interaction between particles

In passing through matter, gamma radiation ionizes via three main processes: the photoelectric effect, Compton scattering, and pair production. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons The Compton shift formula Klein-Nishina formulaCompton used a combination of three fundamental formulas representing the various aspects of classical and modern physics combining See also Electron-positron annihilation Meitner–Hupfeld effect Pair instability supernova

• Photoelectric Effect: This describes the case in which a gamma photon interacts with and transfers its energy to an atomic electron, ejecting that electron from the atom. The kinetic energy of the resulting photoelectron is equal to the energy of the incident gamma photon minus the binding energy of the electron. The photoelectric effect is the dominant energy transfer mechanism for x-ray and gamma ray photons with energies below 50 keV (thousand electron volts), but it is much less important at higher energies.
• Compton Scattering: This is an interaction in which an incident gamma photon loses enough energy to an atomic electron to cause its ejection, with the remainder of the original photon's energy being emitted as a new, lower energy gamma photon with an emission direction different from that of the incident gamma photon. The probability of Compton scatter decreases with increasing photon energy. Compton scattering is thought to be the principal absorption mechanism for gamma rays in the intermediate energy range 100 keV to 10 MeV. Compton scattering is relatively independent of the atomic number of the absorbing material. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton
• Pair Production: By interaction with the electric field of a nucleus, the energy of the incident photon is converted into the mass of an electron-positron pair. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. Energy in excess of the equivalent rest mass of the two particles (1. 02 MeV) appears as the kinetic energy of the pair and the recoil nucleus. At the end of the positron's range, it combines with a free electron. In passing through matter Charged particles ionize and thus lose Energy in many steps until their energy is (almost zero The entire mass of these two particles is then converted into two gamma photons of at least 0. 51 MeV energy each (or higher according to the kinetic energy of the annihilated particles)

The secondary electrons (and/or positrons) produced in any of these three processes frequently have enough energy to produce much ionization themselves. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons

### Gamma production

Gamma rays are often produced alongside other forms of radiation such as alpha or beta. Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted When a nucleus emits an α or β particle, the daughter nucleus is sometimes left in an excited state. In Nuclear physics, a decay product, also known as a daughter product, daughter isotope or daughter nuclide, is a Nuclide It can then jump down to a lower level by emitting a gamma ray in much the same way that an atomic electron can jump to a lower level by emitting visible light or ultraviolet radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays

Decay scheme of 60Co

Gamma rays, x-rays, visible light, and radio waves are all forms of electromagnetic radiation. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. The only difference is the frequency and hence the energy of the photons. Frequency is a measure of the number of occurrences of a repeating event per unit Time. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Gamma rays are the most energetic. An example of gamma ray production follows.

First 60Co decays to excited 60Ni by beta decay:

${}^{60}\hbox{Co}\;\to\;^{60}\hbox{Ni*}\;+\;e^-\;+\;\overline{\nu}_e.$

Then the 60Ni drops down to the ground state (see nuclear shell model) by emitting two gamma rays in succession:

${}^{60}\hbox{Ni*}\;\to\;^{60}\hbox{Ni}\;+\;\gamma.$

Gamma rays of 1. Cobalt-60 (60Co is a Radioactive isotope of Cobalt, with a Half life of 5 Excitation is an elevation in energy level above an arbitrary baseline energy state Naturally occurring Nickel ( Ni) is composed of 5 stable Isotopes 58Ni 60Ni 61Ni 62Ni and 64Ni Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 In Nuclear physics, the nuclear shell model is a model of the Atomic nucleus which uses the Pauli principle to describe the structure 17 MeV and 1. 33 MeV are produced.

Another example is the alpha decay of 241Am to form 237Np; this alpha decay is accompanied by gamma emission. Americium ( Am) has no stable Isotopes A standard atomic mass cannot be given Neptunium ( Np) has no stable isotopes A standard atomic mass cannot be given Gamma (uppercase &Gamma, lowercase γ Γάμμα is the third letter of the Greek alphabet. In some cases, the gamma emission spectrum for a nucleus (daughter nucleus) is quite simple, (eg 60Co/60Ni) while in other cases, such as with (241Am/237Np and 192Ir/192Pt), the gamma emission spectrum is complex, revealing that a series of nuclear energy levels can exist. Iridium-192 (symbol Ir192 m) is an Isotope of Iridium. The "m" denotes that it is a Metastable isomer. The fact that an alpha spectrum can have a series of different peaks with different energies reinforces the idea that several nuclear energy levels are possible.

Image of entire sky in 100 MeV or greater gamma rays as seen by the EGRET instrument aboard the CGRO spacecraft. Bright spots within the galactic plane are pulsars while those above and below the plane are thought to be quasars. Pulsars are highly magnetized rotating Neutron stars that emit a beam of Electromagnetic radiation in the form of radio waves A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus.

Because a beta decay is accompanied by the emission of a neutrino which also carries energy away, the beta spectrum does not have sharp lines, but instead is a broad peak. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost Hence from beta decay alone it is not possible to probe the different energy levels found in the nucleus.

In optical spectroscopy, it is well known that an entity which emits light can also absorb light at the same wavelength (photon energy). In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. For instance, a sodium flame can emit yellow light as well as absorb the yellow light from a sodium vapor lamp. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 In the case of gamma rays, this can be seen in Mössbauer spectroscopy. Mössbauer spectroscopy (Mößbauer is a spectroscopic technique based on the Mössbauer effect. Here, a correction for the energy lost by the recoil of the nucleus is made and the exact conditions for gamma ray absorption through resonance can be attained.

This is similar to the Franck Condon effects seen in optical spectroscopy. The Franck - Condon principle is a rule in Spectroscopy and Quantum chemistry that explains the intensity of Vibronic transitions

## Uses

Gamma-ray Image of a truck taken with a VACIS (Vehicle and Container Imaging System)

Because the wavelength of gamma radiation is so short, a single incident photon can impart significant damage to a living cell. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Cargo scanning or non-intrusive inspection ( NII) refers to non-destructive methods of inspecting and identifying goods in transportation systems This property means that gamma radiation is often used to kill living organisms, in a process called irradiation. Irradiation is the process by which an item is exposed to Radiation. Applications of this include sterilizing medical equipment (as an alternative to autoclaves or chemical means), removing decay-causing bacteria from many foodstuffs or preventing fruit and vegetables from sprouting to maintain freshness and flavor. An autoclave is a pressurized device designed to heat aqueous solutions above their Boiling point at normal atmospheric pressure to achieve sterilization The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

Due to their tissue penetrating property, gamma rays/X-rays have a wide variety of medical uses such as in CT Scans and radiation therapy (see X-ray). Computed tomography (CT is a Medical imaging method employing Tomography. Radiation therapy (or radiotherapy) is the medical use of Ionizing radiation as part of Cancer treatment to control Malignant X-radiation (composed of X-rays) is a form of Electromagnetic radiation. However, as a form of ionizing radiation they have the ability to effect molecular changes, giving them the potential to cause cancer when DNA is affected. Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known The molecular changes can also be used to alter the properties of semi-precious stones, and is often used to change white topaz into blue topaz. A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash Topaz is a Silicate mineral of Aluminium and Fluorine with the Chemical formula Al 2 Si[[oxygen O]]4(

Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed on the growth in order to kill the cancerous cells. Gamma Knife® (or Leksell Gamma Knife®) is a device used to treat Brain tumors with a high dose of Radiation therapy in one day The beams are aimed from different angles to focus the radiation on the growth while minimizing damage to the surrounding tissues.

The Moon as seen in gamma rays by the Compton Gamma Ray Observatory. Surprisingly, the Moon is actually brighter than the Sun at gamma ray wavelengths.

Gamma rays are also used for diagnostic purposes in nuclear medicine. Nuclear medicine is a branch of Medicine and Medical imaging that uses the nuclear properties of matter in diagnosis and therapy Several gamma-emitting radioisotopes are used, one of which is technetium-99m. A radionuclide is an Atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created Technetium (tɛkˈniːʃɪəm is the lightest Chemical element with no Stable isotope. When 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. A gamma camera is a device used to image gamma radiation emitting radioisotopes a technique known as scintigraphy Such a technique can be employed to diagnose a wide range of conditions (e. g. spread of cancer to the bones).

Gamma ray detectors are also starting to be used in Pakistan as part of the Container Security Initiative (CSI). The Container Security Initiative ( CSI) was launched in 2002 by the U These US$5 million machines are advertised to scan 30 containers per hour. The United States dollar ( sign:$; code: USD) is the unit of Currency of the United States; it has also been The objective of this technique is to pre-screen merchant ship containers before they enter US ports.

## Health effects

Gamma rays are the most dangerous form of radiation emitted by a nuclear explosion because of the difficulty in shielding them. A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed Nuclear reaction. This is because gamma rays have the shortest wavelength of all waves in the electromagnetic spectrum, and therefore have the most ability to penetrate through any gap, even a subatomic one, in a what might otherwise be a shield.

Gamma-rays are not stopped by the skin. They can induce DNA alteration by interfering with the genetic material of the cell. DNA double-strand breaks are generally accepted to be the most biologically significant lesion by which ionizing radiation causes cancer and hereditary disease[1]. A study done on Russian nuclear workers exposed to external whole-body gamma radiation at high cumulative doses shows the link between radiation exposure and death from leukemia, lung, liver, skeletal and other solid cancers[2]. Leukemia or leukaemia (Greek leukos λευκός, "white" aima αίμα, "blood" is a Cancer of the Blood Alongside radiation, gamma-rays also produce thermal burn injuries and induce an immunosuppressive effect. Immunosuppression involves an act that reduces the activation or Efficacy of the Immune system. [3][4]

### Body response

After gamma-irradiation, and the breaking of DNA double-strands, a cell can repair the damaged genetic material to the limit of its capability. However, a study of Rothkamm and Lobrich has shown that the repairing process works well after high-dose exposure but is much slower in the case of a low-dose exposure. [1] This could mean that a chronic low-dose exposure cannot be fought by the body. The probability of detecting small alterations or of a detectable defect occurring is most likely small enough that the cell would replicate before initiating a full repair. Some cells can not detect their own genetic defects.

### Risk assessment

The natural outdoor exposure in Great Britain is in the range 20-40 nSv/h. The sievert (symbol Sv is the SI derived unit of dose equivalent. [5] Natural exposure to gamma rays is about 1 to 2 millisieverts per year, and the average total amount of radiation received in one year per inhabitant in the USA is 3. 6 mSv. [6]

By comparison, the radiation dose from chest radiography is a fraction of the annual naturally occurring background radiation dose,[7] and the dose from fluoroscopy of the stomach is, at most, 0. For medical radiography see Radiology Radiography is the use of X-rays to view unseen or hard-to-image objects Fluoroscopy is an imaging technique commonly used by Physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope 05 Sv on the skin of the back.

For acute full-body equivalent dose, 1 Sv causes slight blood changes, 2-5 Sv causes nausea, hair loss, hemorrhaging and will cause death in many cases. Bleeding, technically known as hemorrhaging / haemorrhaging (see American and British spelling differences) is the loss of Blood from More than 3 Sv will lead to death in less than two months in more than 80 percent of cases, and much over 4 Sv usually causes death (see Sievert). The sievert (symbol Sv is the SI derived unit of dose equivalent.

For low dose exposure, for example among nuclear workers, who receive an average radiation dose of 19 mSv, the risk of dying from cancer (excluding leukemia) increases by 2 percent. Leukemia or leukaemia (Greek leukos λευκός, "white" aima αίμα, "blood" is a Cancer of the Blood For a dose of 100 mSv, that risk increase is at 10 percent. By comparison, it was 32 percent for the Atom Bomb survivors. [8].