Gamma rays are high-energy photons produced by a number of the most violent occasions within the universe.
Photons of sunshine are massless particles which can be basically packets of vitality. Because of a quantum-mechanical phenomenon referred to as wave-particle duality, particles can behave like waves, and photons are not any completely 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 probably 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 Space Agency describes how gamma-ray photons have energies in excess of 100,000 electronvolts (opens in new tab) (eV). We can 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 will 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 comparable to 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?
At 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).
However, when the French chemist Paul Villard started experimenting with the radioactive ingredient radium, which had been found two years prior by Marie and Pierre Curie, he observed 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 gentle, whereas alpha and beta particles are fabricated from matter.
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How to cease gamma rays
To block gamma rays requires a dense materials, and the thickness of that materials depends upon the substance. To scale back the power of incoming gamma rays by a billion, you want 13.8 toes (4.2 meters) of water, 6.6 toes (2 m) of concrete or 1.3 toes (0.39 m) of lead, in response to the radiation safety answer website StemRad.
This poses an issue for gamma-ray telescopes, comparable to NASA’s Fermi Space Telescope. Ordinary telescopes just like the Hubble Space Telescope use mirrors and lenses to gather and focus gentle, however gamma rays will merely move straight via an odd telescope. Instead, gamma-ray telescopes should make use of different means.
On the Fermi Space Telescope, a gamma-ray photon will move via a tool referred to 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 considered 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 course that the gamma-ray got here from in space, based mostly on the trajectory of the electron and the positron.
Finally, the electron after which positron have their energies measured by a calorimeter — a tool that measures the vitality of a particle by absorbing it — produced from cesium iodide, and subsequently the vitality of the gamma-ray will be decided.
Are gamma rays harmful?
Because of their excessive vitality, gamma rays are ionizing, that means they’ll dislodge electrons from atoms, in the end damaging dwelling cells and inflicting a hazard to well being. However, 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 may cause most cancers). In specific, one device utilized by docs is the ‘Gamma Knife‘, which is an ultra-precise type of surgical procedure through which a beam of gamma rays cuts away diseased mind cells and might 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 space. 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 ambiance is thinner or despatched into space.
The first gamma-ray space telescope was launched in 1961 on the NASA Explorer 11 satellite, 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 the years there have been many observatories, each on the bottom and in space, 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 Space 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 High-Energy Transient Explorer; HETE-1 had beforehand failed in orbit) that tracked down many GRBs between 2000 and 2008.
Currently, as of the tip of 2022, a number of satellites, observatories and telescopes proceed to conduct gamma-ray astronomy each on Earth and in space. NASA’s Swift satellite, launched in 2004, combines each X-ray and gamma-ray observations, as does Italy’s AGILE satellite launched in 2007. In 2002, the European Space Agency launched INTEGRAL, the International Gamma-Ray Astrophysics Laboratory.. The present most subtle gamma-ray space telescope is Fermi, which NASA launched in 2008.
Meanwhile, 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 (High Energy Stereoscopic System) in Namibia.
Gamma-ray bursts
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In 1963, the Soviet Union, the United Kingdom and the United States signed a nuclear take a look at ban treaty that prohibited the world’s superpowers from testing any nuclear gadgets within the ambiance or in space. However, the U.S. was suspicious that the Soviet Union would not adhere to the treaty, so that they launched the Vela collection of satellites to look at for any pulses of gamma-ray radiation that might be coming from secretive nuclear detonations. As it occurred, gamma rays had been detected, however from space: random blasts of highly effective gamma-ray vitality that appeared to be coming from throughout the Earth. But how far-off had been these gamma-ray bursts?
Related: Most powerful gamma-ray burst ever seen could help reveal how black holes are born
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 aircraft of the Milky Way. Instead, they had been unfold all around the sky, it may imply solely considered one of two issues. Either they had been very shut, inside our solar system, or they had been very far-off, past our galaxy. A particular debate was even convened in 1995, echoing the same ‘Great Debate‘ in 1920 between Harlow Shapley and Heber D. Curtis that mentioned the scale of our galaxy based mostly on the distribution of globular clusters.
In the 1995 debate, chaired by Martin Rees, astronomer Bohdan Paczynski of Princeton University argued that GRBs got here from very far-off, whereas Donald Lamb of the University 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.
Just two years later astronomers had their reply when the BeppoSAX satellite detected a gamma-ray burst that the William Herschel Telescope within the Canary Islands was capable of rapidly 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 gentle revealed it to have come from six billion light-years away. Bohdan Paczynski was proper!
There are two most important kinds of GRB. One sort is known as quick GRBs which final simply fractions of a second, whereas the opposite variety is called the lengthy GRBs, and might final many seconds as much as an hour. Short GRBS are emitted throughout the merger of two neutron stars, whereas lengthy GRBs are the loss of life cries of uncommon, massive stars.
Physicists Andrew MacFadyen and Stan Woosley of the University of California, Santa Cruz, developed a model to clarify how stars may explode and produce lengthy GRBs with out breaking the legal guidelines of physics. When an enormous star with 50–100 instances the mass of the sun reaches the tip of its life, the star begins to break down in on its core, and if the star is rotating quick sufficient, the vitality inside 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 referred to as synchrotron radiation, within the type of the gamma rays that we observe. Because the gamma rays are solely launched within the course of the jets, and never in all instructions without delay, the total vitality launched doesn’t contravene the legal guidelines of physics.
Additional assets
Learn extra about ionizing radiation with the United States Environment Protection Agency (EPA), and the American Cancer Society. Explore gamma rays in additional element in a tour of the electromagnetic spectrum with NASA Science.
Follow Keith Cooper on Twitter @21stCenturySETI. Follow us on Twitter @Spacedotcom and on Facebook.
Bibliography
Flash! The Hunt for the Biggest Explosions within the Universe by Govert Schilling (Cambridge University Press, 2002)
The Biggest Bangs: The Mystery of Gamma-Ray Bursts, The Most Violent Explosions within the Universe by Jonathan Katz (Oxford University Press, 2002)
