Gamma rays are high-energy photons produced by a few of the most violent occasions within the universe.
Photons of sunshine are massless particles which are basically packets of vitality. Due to a quantum-mechanical phenomenon often known as wave-particle duality, particles can behave like waves, and photons aren’t any totally different. Photons have wavelengths, and the amplitude of their wavelength determines the place they sit on the electromagnetic spectrum. Radio and microwave photons sit on the decrease vitality, longer wavelength finish of the spectrum, whereas within the shorter wavelength, higher-energy regime are photons of ultraviolet, X-rays and essentially the most energetic of all of them with the shortest wavelengths: gamma rays.
Gamma rays have wavelengths shorter than 10^11 meters and frequencies above 30 x 10^18 hertz. The European Area Company describes how gamma-ray photons have energies in excess of 100,000 electronvolts (opens in new tab) (eV). We are able to examine this to X-rays, which NASA describes as having energies between 100 eV and 100,000 eV (opens in new tab), and optical photons that we are able to see with our eyes, that are about 1 eV.
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On Earth, gamma rays are produced by radioactive decay, nuclear weapons and lightning, whereas in space they’re produced by violent, high-energy sources reminiscent of solar flares, quasars, black holes tearing stars apart, black-hole accretion disks, exploding stars and the sturdy gravitational environments of neutron stars.
How had been gamma rays found?
On the flip of the 20th century, two types of radiation emitted by decaying atoms had been identified, particularly alpha particles (that are helium nuclei) and beta particles (that are electrons and positrons).
Nevertheless, when the French chemist Paul Villard started experimenting with the radioactive factor radium, which had been found two years prior by Marie and Pierre Curie, he seen that the ionizing radiation produced by the decay of radium packed a more durable punch than both alpha or beta particles.
This radiation acquired its identify — gamma-rays — just because gamma is the third letter within the Greek alphabet after alpha and beta. Unbeknownst to Villard and his cohorts within the early 1900s, the important thing distinction between gamma rays and alpha/beta particles is that gamma rays are a type of mild, whereas alpha and beta particles are manufactured from matter.
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Easy methods to cease gamma rays
To dam gamma rays requires a dense materials, and the thickness of that materials relies on the substance. To scale back the power of incoming gamma rays by a billion, you want 13.8 ft (4.2 meters) of water, 6.6 ft (2 m) of concrete or 1.3 ft (0.39 m) of lead, in response to the radiation safety resolution website StemRad.
This poses an issue for gamma-ray telescopes, reminiscent of NASA’s Fermi Space Telescope. Abnormal telescopes just like the Hubble Space Telescope use mirrors and lenses to gather and focus mild, however gamma rays will merely move straight via an abnormal telescope. As an alternative, gamma-ray telescopes should make use of different means.
On the Fermi Area Telescope, a gamma-ray photon will move via a tool known as the Anti-coincidence Detector, which blocks cosmic rays which may give a false sign, according to NASA . The gamma-ray is then absorbed by certainly one of 16 sheets of tungsten, a fabric that’s dense sufficient to cease gamma rays.
By interacting with the tungsten, the gamma-ray is transformed into an electron and a positron (the antimatter or antiparticle counterpart of an electron), the paths of that are learn by a tracker, which is a module of silicon strips interweaved by tungsten foil that may decide the path that the gamma-ray got here from in area, primarily based on the trajectory of the electron and the positron.
Lastly, the electron after which positron have their energies measured by a calorimeter — a tool that measures the vitality of a particle by absorbing it — constructed from cesium iodide, and due to this fact the vitality of the gamma-ray will be decided.
Are gamma rays harmful?
Due to their excessive vitality, gamma rays are ionizing, which means they’ll dislodge electrons from atoms, finally damaging dwelling cells and inflicting a hazard to well being. Nevertheless, as with all radiation, it relies upon upon the dose that you simply obtain.
In small doses, very rigorously focused to restrict publicity, they can be utilized safely as a medical diagnostic device, and even to kill cancerous cells (ironic since publicity to radiation together with gamma rays could cause most cancers). Particularly, one device utilized by medical doctors is the ‘Gamma Knife‘, which is an ultra-precise type of surgical procedure wherein a beam of gamma rays cuts away diseased mind cells and may even penetrate deep into the mind with out damaging the outside lobes.
Gamma-ray astronomy
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Given their ionizing energy, it is lucky that Earth’s atmosphere is ready to block gamma rays from area. For astronomers, nonetheless, that is unlucky, as a result of it implies that to conduct gamma-ray astronomy observatories should both be constructed on mountaintops the place the environment is thinner or despatched into area.
The primary gamma-ray area telescope was launched in 1961 on the NASA Explorer 11 satellite tv for pc, however issues did not actually start to kick off till the late Sixties and early Seventies with a significant discovering, and it wasn’t even an astronomical telescope that made the invention.
Over time there have been many observatories, each on the bottom and in area, which have been designed to watch cosmic gamma-ray radiations. In 1990, NASA launched the Compton Gamma-Ray Observatory because the gamma-ray counterpart to the Hubble Area Telescope. The Compton Gamma-Ray Observatory explored the cosmos from 1991 till 2000. The aforementioned BeppoSAX was a joint Italian–Dutch mission that operated between 1996 and 2003, whereas NASA launched HETE-2 (the Excessive-Power Transient Explorer; HETE-1 had beforehand failed in orbit) that tracked down many GRBs between 2000 and 2008.
At the moment, as of the top of 2022, a number of satellites, observatories and telescopes proceed to conduct gamma-ray astronomy each on Earth and in area. NASA’s Swift satellite, launched in 2004, combines each X-ray and gamma-ray observations, as does Italy’s AGILE satellite tv for pc launched in 2007. In 2002, the European Area Company launched INTEGRAL, the Worldwide Gamma-Ray Astrophysics Laboratory.. The present most subtle gamma-ray area telescope is Fermi, which NASA launched in 2008.
In the meantime, on the bottom, there are a number of gamma-ray observatories together with VERITAS (Very Energetic Radiation Imaging Telescope Array System) on the Fred Lawrence Whipple Observatory in Arizona and HESS (Excessive Power Stereoscopic System) in Namibia.
Gamma-ray bursts
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In 1963, the Soviet Union, the UK and america signed a nuclear take a look at ban treaty that prohibited the world’s superpowers from testing any nuclear gadgets within the environment or in area. Nevertheless, the U.S. was suspicious that the Soviet Union would not adhere to the treaty, in order that they launched the Vela collection of satellites to look at for any pulses of gamma-ray radiation that may very well be coming from secretive nuclear detonations. Because it occurred, gamma rays had been detected, however from area: random blasts of highly effective gamma-ray vitality that gave the impression to be coming from throughout the Earth. However how distant had been these gamma-ray bursts?
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If these gamma-ray bursts, that are abbreviated to GRBs for brief, had been coming from our galaxy, then astronomers would detect them principally within the airplane of the Milky Way. As an alternative, they had been unfold everywhere in the sky, it might imply solely certainly one of two issues. Both they had been very shut, inside our solar system, or they had been very distant, past our galaxy. A particular debate was even convened in 1995, echoing an analogous ‘Great Debate‘ in 1920 between Harlow Shapley and Heber D. Curtis that mentioned the scale of our galaxy primarily based on the distribution of globular clusters.
Within the 1995 debate, chaired by Martin Rees, astronomer Bohdan Paczynski of Princeton College argued that GRBs got here from very distant, whereas Donald Lamb of the College of Chicago reasoned that GRBs should be from shut by as a result of the vitality required for them to be billions of light-years away would contravene the legal guidelines of physics.
Simply two years later astronomers had their reply when the BeppoSAX satellite tv for pc detected a gamma-ray burst that the William Herschel Telescope within the Canary Islands was in a position to shortly observe up on, within the course of detecting the faint afterglow of no matter explosion had created the GRB. Measuring the redshift of the afterglow’s mild revealed it to have come from six billion light-years away. Bohdan Paczynski was proper!
There are two fundamental varieties of GRB. One kind is named quick GRBs which final simply fractions of a second, whereas the opposite form is named the lengthy GRBs, and may final many seconds as much as an hour. Brief GRBS are emitted through the merger of two neutron stars, whereas lengthy GRBs are the dying cries of uncommon, massive stars.
Physicists Andrew MacFadyen and Stan Woosley of the College of California, Santa Cruz, developed a model to clarify how stars might explode and produce lengthy GRBs with out breaking the legal guidelines of physics. When an enormous star with 50–100 occasions the mass of the sun reaches the top of its life, the star begins to break down in on its core, and if the star is rotating quick sufficient, the vitality throughout the collapsing layers rebounds off the core and is blasted out in two jets that transfer at nearly the speed of light and blow the star aside. Charged particles inside these jets spiral round highly effective magnetic fields and produce one thing known as synchrotron radiation, within the type of the gamma rays that we observe. As a result of the gamma rays are solely launched within the path of the jets, and never in all instructions directly, the full vitality launched doesn’t contravene the legal guidelines of physics.
Further assets
Be taught extra about ionizing radiation with the United States Environment Protection Agency (EPA), and the American Cancer Society. Discover gamma rays in additional element in a tour of the electromagnetic spectrum with NASA Science.
Observe Keith Cooper on Twitter @21stCenturySETI. Observe us on Twitter @Spacedotcom and on Facebook.
Bibliography
Flash! The Hunt for the Greatest Explosions within the Universe by Govert Schilling (Cambridge College Press, 2002)
The Greatest Bangs: The Thriller of Gamma-Ray Bursts, The Most Violent Explosions within the Universe by Jonathan Katz (Oxford College Press, 2002)
