Milkshakes and Gamma Rays

This object is among the most distant objects ever detected. Scientists can use gamma rays to determine the elements on other planets. When struck by cosmic rays, chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. These data can help scientists look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium.

The gamma-ray spectrometer on NASA's Mars Odyssey Orbiter detects and maps these signatures, such as this map below showing hydrogen concentrations of Martian surface soils. Gamma rays also stream from stars, supernovas, pulsars, and black hole accretion disks to wash our sky with gamma-ray light.

These gamma-ray streams were imaged using NASA's Fermi gamma-ray space telescope to map out the Milky Way galaxy by creating a full degree view of the galaxy from our perspective here on Earth. The composite image below of the Cas A supernova remnant shows the full spectrum in one image. Gamma rays from Fermi are shown in magenta; x-rays from the Chandra Observatory are blue and green. The visible light data captured by the Hubble space telescope are displayed in yellow.

Infrared data from the Spitzer space telescope are shown in red; and radio data from the Very Large Array are displayed in orange. The Earth's Radiation Budget. Retrieved [insert date - e. National Aeronautics and Space Administration. Tour of the Electromagnetic Spectrum. Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope.

Electromagnetic Spectrum Series Series Homepage. Neutron stars with a very high magnetic field magnetars , thought to produce astronomical soft gamma repeaters , are another relatively long-lived star-powered source of gamma radiation. More powerful gamma rays from very distant quasars and closer active galaxies are thought to have a gamma ray production source similar to a particle accelerator.

High energy electrons produced by the quasar, and subjected to inverse Compton scattering, synchrotron radiation , or bremsstrahlung, are the likely source of the gamma rays from those objects. It is thought that a supermassive black hole at the center of such galaxies provides the power source that intermittently destroys stars and focuses the resulting charged particles into beams that emerge from their rotational poles.

When those beams interact with gas, dust, and lower energy photons they produce X-rays and gamma rays. These sources are known to fluctuate with durations of a few weeks, suggesting their relatively small size less than a few light-weeks across.

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Such sources of gamma and X-rays are the most commonly visible high intensity sources outside our galaxy. They shine not in bursts see illustration , but relatively continuously when viewed with gamma ray telescopes.

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The power of a typical quasar is about 10 40 watts, a small fraction of which is gamma radiation. Much of the rest is emitted as electromagnetic waves of all frequencies, including radio waves. The most intense sources of gamma rays, are also the most intense sources of any type of electromagnetic radiation presently known. They are the "long duration burst" sources of gamma rays in astronomy "long" in this context, meaning a few tens of seconds , and they are rare compared with the sources discussed above.

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By contrast, "short" gamma-ray bursts of two seconds or less, which are not associated with supernovae, are thought to produce gamma rays during the collision of pairs of neutron stars, or a neutron star and a black hole. The so-called long-duration gamma-ray bursts produce a total energy output of about 10 44 joules as much energy as our Sun will produce in its entire life-time but in a period of only 20 to 40 seconds. The leading hypotheses for the mechanism of production of these highest-known intensity beams of radiation, are inverse Compton scattering and synchrotron radiation from high-energy charged particles.

These processes occur as relativistic charged particles leave the region of the event horizon of a newly formed black hole created during supernova explosion. The beam of particles moving at relativistic speeds are focused for a few tens of seconds by the magnetic field of the exploding hypernova. The fusion explosion of the hypernova drives the energetics of the process. If the narrowly directed beam happens to be pointed toward the Earth, it shines at gamma ray frequencies with such intensity, that it can be detected even at distances of up to 10 billion light years, which is close to the edge of the visible universe.

Due to their penetrating nature, gamma rays require large amounts of shielding mass to reduce them to levels which are not harmful to living cells, in contrast to alpha particles , which can be stopped by paper or skin, and beta particles , which can be shielded by thin aluminium.

Milkshakes and Gamma Rays by Scott Zimmerman

Gamma rays are best absorbed by materials with high atomic numbers and high density, which contribute to the total stopping power. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta emitting particles, but provide no protection from gamma radiation from external sources. The higher the energy of the gamma rays, the thicker the shielding made from the same shielding material is 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. Depleted uranium is used for shielding in portable gamma ray sources , but here the savings in weight over lead are larger, as portable sources' shape resembles a sphere to some extent, and the volume of a sphere is dependent on the cube of the radius; so a source with its radius cut in half will have its volume reduced by a factor of eight, which will more than compensate uranium's greater density as well as reducing bulk.

The loss of water or removal of a "hot" fuel assembly into the air would result in much higher radiation levels than when kept under water. When a gamma ray passes through matter, the probability for absorption is proportional to the thickness of the layer, the density of the material, and the absorption cross section of the material.

The total absorption shows an exponential decrease of intensity with distance from the incident surface:. As it passes through matter, gamma radiation ionizes via three processes: Additionally, gamma rays, particularly high energy ones, can interact with atomic nuclei resulting in ejection of particles in photodisintegration , or in some cases, even nuclear fission photofission. The highest-energy rays interact more readily with the background light photons and thus the density of the background light may be estimated by analyzing the incoming gamma ray spectra.

Gamma spectroscopy is the study of the energetic transitions in atomic nuclei, which are generally associated with the absorption or emission of gamma rays. As in optical spectroscopy see Franck—Condon effect the absorption of gamma rays by a nucleus is especially likely i. The immobilization of nuclei at both ends of a gamma resonance interaction is required so that no gamma energy is lost to the kinetic energy of recoiling nuclei at either the emitting or absorbing end of a gamma transition.

Such loss of energy causes gamma ray resonance absorption to fail. However, when emitted gamma rays carry essentially all of the energy of the atomic nuclear de-excitation that produces them, this energy is also sufficient to excite the same energy state in a second immobilized nucleus of the same type. Gamma rays provide information about some of the most energetic phenomena in the universe; however, they are largely absorbed by the Earth's atmosphere.

Instruments aboard high-altitude balloons and satellites missions, such as the Fermi Gamma-ray Space Telescope , provide our only view of the universe in gamma rays. Gamma-induced 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. Non-contact industrial sensors commonly use sources of gamma radiation in refining, mining, chemicals, food, soaps and detergents, and pulp and paper industries, for the measurement of levels, density, and thicknesses.

Typically, these use Co or Cs isotopes as the radiation source. These machines are advertised to be able to scan 30 containers per hour. Gamma radiation is often used to kill living organisms, in a process called irradiation. Applications of this include the sterilization of medical equipment as an alternative to autoclaves or chemical means , the removal of decay-causing bacteria from many foods and the prevention of the sprouting of fruit and vegetables to maintain freshness and flavor.

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.

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For example, in a PET scan a radiolabeled sugar called fludeoxyglucose emits positrons that are annihilated by electrons, producing pairs of gamma rays that highlight cancer as the cancer often has a higher metabolic rate than the surrounding tissues. The most common gamma emitter used in medical applications is the nuclear isomer technetiumm 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 for example, the spread of cancer to the bones via bone scan. Gamma rays cause damage at a cellular level and are penetrating, causing diffuse damage throughout the body. However, they are less ionising than alpha or beta particles, which are less penetrating.

Low levels of gamma rays cause a stochastic health risk, which for radiation dose assessment is defined as the probability of cancer induction and genetic damage. These effects are compared to the physical quantity absorbed dose measured by the unit gray Gy. When gamma radiation breaks DNA molecules, a cell may be able to repair the damaged genetic material, within limits.

However, a study of Rothkamm and Lobrich has shown that this repair process works well after high-dose exposure but is much slower than in the case of a low-dose exposure. The natural outdoor exposure in Great Britain ranges from 0. By comparison, the radiation dose from chest radiography about 0. An acute full-body equivalent single exposure dose of 1 Sv mSv causes slight blood changes, but 2. For low-dose exposure, for example among nuclear workers, who receive an average yearly radiation dose of 19 mSv, [ clarification needed ] the risk of dying from cancer excluding leukemia increases by 2 percent.

For a dose of mSv, the risk increase is 10 percent. By comparison, risk of dying from cancer was increased by 32 percent for the survivors of the atomic bombing of Hiroshima and Nagasaki. This has been replaced by kerma , now mainly used for instrument calibration purposes but not for received dose effect. The effect of gamma and other ionizing radiation on living tissue is more closely related to the amount of energy deposited in tissue rather than the ionisation of air, and replacement radiometric units and quantities for radiation protection have been defined and developed from onwards.

The conventional distinction between X-rays and gamma rays has changed over time. Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation gamma rays emitted by radioactive nuclei. However, since current artificial sources are now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs.

Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus. For example, modern high-energy X-rays produced by linear accelerators for megavoltage treatment in cancer often have higher energy 4 to 25 MeV than do most classical gamma rays produced by nuclear gamma decay.

One of the most common gamma ray emitting isotopes used in diagnostic nuclear medicine , technetiumm , produces gamma radiation of the same energy keV as that produced by diagnostic X-ray machines, but of significantly lower energy than therapeutic photons from linear particle accelerators. In the medical community today, the convention that radiation produced by nuclear decay is the only type referred to as "gamma" radiation is still respected. Due to this broad overlap in energy ranges, in physics the two types of electromagnetic radiation are now often defined by their origin: X-rays are emitted by electrons either in orbitals outside of the nucleus, or while being accelerated to produce bremsstrahlung -type radiation , [29] while gamma rays are emitted by the nucleus or by means of other particle decays or annihilation events.

There is no lower limit to the energy of photons produced by nuclear reactions, and thus ultraviolet or lower energy photons produced by these processes would also be defined as "gamma rays". However, in physics and astronomy, the converse convention that all gamma rays are considered to be of nuclear origin is frequently violated.

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In astronomy, higher energy gamma and X-rays are defined by energy, since the processes that produce them may be uncertain and photon energy, not origin, determines the required astronomical detectors needed. An example is "gamma rays" from lightning discharges at 10 to 20 MeV, and known to be produced by the bremsstrahlung mechanism.

Another example is gamma-ray bursts , now known to be produced from processes too powerful to involve simple collections of atoms undergoing radioactive decay. This is part and parcel of the general realization that many gamma rays produced in astronomical processes result not from radioactive decay or particle annihilation, but rather in non-radioactive processes similar to X-rays. A classic example is that of supernova SN A , which emits an "afterglow" of gamma-ray photons from the decay of newly made radioactive nickel and cobalt Most gamma rays in astronomy, however, arise by other mechanisms.

From Wikipedia, the free encyclopedia. This is the latest accepted revision , reviewed on 17 December This article is about the term's use in physics. For other uses, see Gamma ray disambiguation. Gamma rays are emitted during nuclear fission in nuclear explosions. Models of the nucleus. Nucleosynthesis and nuclear astrophysics. High energy nuclear physics. Villard "Sur le rayonnement du radium" , Comptes rendus , vol. Rutherford "The magnetic and electric deviation of the easily absorbed rays from radium" , Philosophical Magazine , Series 6, vol.

Gonoskov et al, Physical Review X , Phys.

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