Cosmic rays are extremely high-energy radiation, mainly originating outside the Solar System. Cosmic rays are composed primarily of high-energy protons and atomic nuclei. They are of mysterious origin. They were given the name "rays" in the mistaken belief that they were a form of electromagnetic radiation. However, cosmic rays are fermions rather than photons. Due to relativistic effects, cosmic rays have a very high mass and reach energies of up to 1014 eV.
In 1909 Theodor Wulf developed an electrometer, a device to measure the rate of ion production inside a hermetically sealed container. Wulf used it to find higher levels of radiation at the top of the Eiffel Tower than at its base. However, his paper was not widely accepted. In 1911, Domenico Pacini wanted to determine if ionizing radiation came from the Earth or from other sources. He measured simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface. His measurements suggested that there was a source other than just the Earth.
In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5300 meters in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level. Hess eliminated 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. He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913–1914, Werner Kolhörster confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km. Hess received the Nobel Prize in Physics in 1936 for his discovery.
Cosmic rays react with Nitrogen and Oxygen in the Earth's atmosphere that among other things results in Ozone depletion. Cosmic rays also react with Carbon to form Carbon-14. Until the time of nuclear testing, the amount of 14C has been relatively constant, which is the basis for carbon-dating of materials.
Cosmic rays can interfere with electronic devices and make space travel more dangerous as they are a form of radiation.
- Sharma (2008). Atomic And Nuclear Physics. Pearson Education India. ISBN 978-81-317-1924-4.
- D. Pacini (1912). "La radiazione penetrante alla superficie ed in seno alle acque". Il Nuovo Cimento, Series VI 3: 93–100. doi:10.1007/BF02957440.
- Nobel Prize in Physics 1936 – Presentation Speech. Nobelprize.org (1936-12-10). Retrieved on Sept 4, 2016.
- V.F. Hess (1936). The Nobel Prize in Physics 1936. The Nobel Foundation. Retrieved on Sept 4, 2016.