Victor Franz Hess
Born: 24 June 1883, Peggau, Austria
Died: 17 December 1964, Mount Verno, NY, USA
Affiliation at the time of the award: Innsbruck University, Innsbruck, Austria
Prize motivation: "for his discovery of cosmic radiation"
Field: astrophysics, cosmic radiation
Prize share: 1/2
When radiation and atoms interact, charged atoms, ions, are often produced. In 1912 Victor Hess measured atmospheric ionization as function of altitude using balloons. Surprisingly, he found that ionization first decreased, but then increased again at higher altitudes. He concluded that the upper atmosphere is ionized by radiation from space. He proved that this radiation is not solar through experiments performed at night and during eclipses: cosmic rays had been discovered.