He attributed this to a source of radiation entering the atmosphere from above, and in was awarded the Nobel prize for his discovery. For some time it was believed that the radiation was electromagnetic in nature hence the name cosmic "rays" , and some textbooks still incorrectly include cosmic rays as part of the electromagnetic spectrum.
However, during the 's it was found that cosmic rays must be electrically charged because they are affected by the Earth's magnetic field. From the s to the s, before man-made particle accelerators reached very high energies, cosmic rays served as a source of particles for high energy physics investigations, and led to the discovery of subatomic particles that included the positron and muon. Although these applications continue, since the dawn of the space age the main focus of cosmic ray research has been directed towards astrophysical investigations of where cosmic rays originate, how they get accelerated to such high velocities, what role they play in the dynamics of the Galaxy, and what their composition tells us about matter from outside the solar system.
To measure cosmic rays directly, before they have been slowed down and broken up by the atmosphere, research is carried out by instruments carried on spacecraft and high altitude balloons, using particle detectors similar to those used in nuclear and high energy physics experiments.
Cosmic Ray Energies and Acceleration: The energy of cosmic rays is usually measured in units of MeV, for mega-electron volts, or GeV, for giga-electron volts. One electron volt is the energy gained when an electron is accelerated through a potential difference of 1 volt. The number of cosmic rays with energies beyond 1 GeV decreases by about a factor of 50 for every factor of 10 increase in energy.
The highest energy cosmic rays measured to date have had more than 10 20 eV, equivalent to the kinetic energy of a baseball traveling at approximately mph! It is believed that most galactic cosmic rays derive their energy from supernova explosions, which occur approximately once every 50 years in our Galaxy. To maintain the observed intensity of cosmic rays over millions of years requires that a few percent of the more than 10 51 ergs released in a typical supernova explosion be converted to cosmic rays.
There is considerable evidence that cosmic rays are accelerated as the shock waves from these explosions travel through the surrounding interstellar gas. The various magnetic fields of the galaxy and universe deflect them, and put them on bendy paths.
There are a few huge projects underway to better understand where these cosmic rays come from. One involves a truly enormous block of ice at the South Pole. It is a 1-cubic kilometer about 1. These sensors are set up to detect when subatomic particles called neutrinos — which travel along with other subatomic particles in cosmic rays — crash into Earth. How it works is not so different from the cloud chamber experiment we showed you above. That means they travel through the universe in a relatively straight line, and we can trace them back to a source.
If I had a neutrino flashlight, that stream of neutrinos would go through the wall. But every once in a while a neutrino — perhaps every one in , — will hit an atom in the ice at the observatory and break the atom apart. Then something spectacular happens: The collision produces other subatomic particles, which are then propelled to a speed faster than the speed of light as they pass through the ice.
You might have heard that nothing can travel faster than light. The photons that make up light a subatomic particle in their own right actually slow down a bit when they enter a dense substance like ice.
But other subatomic particles, like muons and electrons, do not slow down. When particles are moving faster than light through a medium like ice, they glow. And the phenomenon is similar to that of a sonic boom. When you go faster than the speed of sound, you produce a blast of noise. When particles move faster than light, they leave wakes of an eerie blue light like a speedboat leaves wakes in the water. The neutrino is the tear-drop shape in gray.
The Pierre Auger Observatory , where Castellina works, uses an array of 1, tanks, each filled with 3, gallons of water. The tanks are spread across more than 1, square miles in Mendoza, Argentina.
The tanks work like the block of ice at the South Pole. But instead of using ice to record cosmic rays, they use water.
The tanks are completely pitch black inside. But when cosmic rays — more than just neutrinos — enter the tanks, they cause little bursts of light, via Cherenkov radiation, as they exceed the speed of light in water. If many of the tanks record a burst of cosmic rays at the same time, the scientists can then work backward and figure out the energy of the particle that hit at the top of the atmosphere.
They can also make a rough guess on where in the sky the particle was shot from. Like the tanks in South America, the array in Utah has a series of detectors spread out over an enormous area. The larger the area, the greater the chance to spot the most elusive and powerful cosmic rays. Measuring the half-life of each nuclei gives an estimate of how long the cosmic ray has been out there in space. In , a NASA spacecraft found most cosmic rays likely come from relatively nearby clusters of massive stars.
The agency's Advanced Composition Explorer ACE spacecraft detected cosmic rays with a radioactive form of iron known as iron Since this form of cosmic ray degrades over time, scientists estimate it must have originated no more than 3, light-years from Earth — the equivalent distance of the width of the local spiral arm in the Milky Way. It is expected to operate for three years, answering questions such as whether supernovas generate most cosmic ray particles, when cosmic ray particles originated, and if all the energy spectra seen for cosmic rays can be explained by a single mechanism.
CALET launched there in It has flown several times, including a record day flight over Antarctica between December and January Specifically, testing the emerging model of cosmic-ray origins in OB associations, as well as models for determining which particles will be accelerated," the SuperTIGER website said.
Citizen scientists can also participate in the search for cosmic rays by registering at the website crayfis. Researchers there are examining ultra-high energy cosmic rays using mobile phones. Earth's magnetic field and atmosphere shields the planet from However, for people outside the protection of Earth's magnetic field, space radiation becomes a serious hazard.
An instrument aboard the Curiosity Mars rover during its day cruise to Mars revealed that the radiation dose received by an astronaut on even the shortest Earth-Mars round trip would be about 0. This amount is like receiving a whole-body CT scan every five or six days.
A dose of 1 sievert is associated with a 5. The normal daily radiation dose received by the average person living on Earth is 10 microsieverts 0. The moon has no atmosphere and a very weak magnetic field. In August , Austrian physicist Victor Hess made a historic balloon flight that opened a new window on matter in the universe. As he ascended to metres, he measured the rate of ionisation in the atmosphere and found that it increased to some three times that at sea level.
He concluded that penetrating radiation was entering the atmosphere from above. He had discovered cosmic rays. When they arrive at Earth, they collide with the nuclei of atoms in the upper atmosphere, creating more particles, mainly pions. The charged pions can swiftly decay, emitting particles called muons.
Unlike pions, these do not interact strongly with matter, and can travel through the atmosphere to penetrate below ground. Studies of cosmic rays opened the door to a world of particles beyond the confines of the atom: the first particle of antimatter , the positron the antielectron was discovered in , the muon in , followed by the pion, the kaon and several more.
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