Measurements of ionization rates at increasing heights above the ground during the decade from 1900 to 1910 showed a decrease that could be explained as due to absorption of the ionizing radiation by the intervening air.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.
Composed primarily of high-energy protons and atomic nuclei, they are of mysterious origin.
Data from the Fermi space telescope (2013) high-energy particles with intrinsic mass are known as "cosmic" rays, while photons, which are quanta of electromagnetic radiation (and so have no intrinsic mass) are known by their common names, such as "gamma rays" or "X-rays", depending on their energy.
The kinetic mass-energy of massive particles can increase drastically due to relativistic effects.
Through this process, the particles can acquire tremendously high energies, significantly higher than those of even the highest-energy photons detected to date (whose energy depends solely on frequency and not on speed, as photons always travel at the same speed).
The Oh-My-God particle, the highest-energy fermionic cosmic ray detected to date, had an energy of about times more energetic than the highest-energy detected cosmic photons. hydrogen nuclei; 9% are alpha particles, identical to helium nuclei, and 1% are the nuclei of heavier elements, called HZE ions.
Of primary cosmic rays, which originate outside of Earth's atmosphere, about 99% are the nuclei (stripped of their electron shells) of well-known atoms, and about 1% are solitary electrons (similar to beta particles). A very small fraction are stable particles of antimatter, such as positrons or antiprotons.
The precise nature of this remaining fraction is an area of active research.
An active search from Earth orbit for anti-alpha particles has failed to detect them.
Cosmic rays attract great interest practically, due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, and scientifically, because the energies of the most energetic ultra-high-energy cosmic rays (UHECRs) have been observed to approach 3 × 10 the highest-energy ultra-high-energy cosmic rays have energies comparable to the kinetic energy of a 90-kilometre-per-hour (56 mph) baseball.