Cosmic radiation
ALTERNATIVE NAME/S: Cosmic rays
DETAILS: In the early 1900s, scientists noted that there was more radiation at the surface of the earth than terrestrial sources produced. In 1912, Victor Hess* took a radiation counter up in a balloon and confirmed that "extra" radiation was coming in from outside our atmosphere.
Cosmic radiation is primarily made up of protons, but also includes atomic nuclei, antiprotons, electrons and positrons. We do not yet know where cosmic radiation comes from or how it is accelerated or propagated through space. Some feel that most cosmic radiation was formed at the beginning of the universe.
Supernovae are also generally considered to be an important source. As it travels, cosmic radiation undergoes a number of changes because it interacts with matter, magnetic fields, and other radiation. If we can discover the history of cosmic radiation, it can provide information about events and processes in distant parts of space, including things that happened in the cosmic past.
Interaction with the rest of the universe means that cosmic radiation does not always follow straight paths, so identifying its source is difficult. We cannot simply look back along the direction that cosmic radiation was following when it arrived at Earth. However, the higher the energy in the cosmic radiation, the less it interacts with anything else, so the higher energy cosmic radiation may eventually offer an opportunity to find out where it comes from.
ONELINER: Cosmic radiation
OTHER CONNECTIONS: None
History
After the discovery of radioactivity by Henri Becquerel in 1896, it was generally believed that atmospheric electricity, ionization of the air, was caused only by radiation from radioactive elements in the ground or the radioactive gases or isotopes of radon they produce.[20] Measurements of increasing ionization rates at increasing heights above the ground during the decade from 1900 to 1910 could be explained as due to absorption of the ionizing radiation by the intervening air.[21]
Discovery
Pacini makes a measurement in 1910.
In 1909, Theodor Wulf developed an electrometer, a device to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the Eiffel Tower than at its base.[22] However, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911, Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 metres from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth.[23]
In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers[3] to an altitude of 5,300 metres in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level.[3] Hess ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes.[3] He concluded that "The results of the observations seem most likely to be explained by the assumption that radiation of very high penetrating power enters from above into our atmosphere."[24] In 1913–1914, Werner Kolhörster confirmed Victor Hess's earlier results by measuring the increased ionization enthalpy rate at an altitude of 9 km.[25][26]
Hess received the Nobel Prize in Physics in 1936 for his discovery.[27][28]
BIBLIOGRAPHY: "Victor F. Hess – Biography." Nobel e-Museum. http://www.nobel.se/physics/laureates/1936/hess-bio.html Accessed April 3, 2004.
"Figures in Radiation History: Victor F. Hess." Office of Radiation, Chemical & Biological Safety, Michigan State University. http://www.orcbs.msu.edu/radiation/radhistory/victorhess.html Accessed April 3, 2004
"Cosmic Ray Research." New Mexico State University. http://www.ece.nmsu.edu/pal/cosmicrays.html Accessed April 3, 2004.
"Cosmic Rays." Astrophysics Research Group, University of Leeds. http://ast.leeds.ac.uk Accessed April 3, 2004. Click on link "ultra high energy cosmic rays" on home page, and then on link "Cosmic Rays" on the next page to access the Cosmic Rays table of contents.
AUDIO/VISUAL:
On various pages, there are diagrams of the path of cosmic rays, how they are detected, etc., and some photographs. Astrophysics Research Group, University of Leeds. http://ast.leeds.ac.uk/haverah/origin.shtml Accessed April 3, 2004.