Researched
Cosmic Rays Discovered (Hess)
On 7 August 1912 Victor Hess's balloon flight above 5,000 m showed that radiation grows with height: it comes from space. Cosmic rays became the first source of new particles.
Open in the interactive tree →Electroscopes lost their charge even when shielded, and physicists blamed radioactive rocks. In seven balloon flights in 1911 and 1912 Hess found that ionisation fell over the first kilometre, then rose to at least double the ground value at about 5 km, and a flight during a near-total solar eclipse showed that the Sun was not the source. Robert Millikan named the rays in the 1920s; the positron (1932), the muon (1936) and the pion (1947) were all first found in them, before big accelerators existed. Hess shared the 1936 Nobel Prize in Physics with Carl Anderson.
Prerequisites
- Balloon Flight1783Balloons carried his electroscopes to more than 5 km
- Radioactivity1896Radioactive rocks were the suspected cause of the ionisation Hess measured
Unlocks
- Antimatter1932Anderson found the positron in cosmic rays in 1932
- Radiocarbon Dating1949Cosmic rays make the carbon-14 that radiocarbon dating measures.
- Neutrino Oscillations1998Super-Kamiokande measured atmospheric neutrinos, which cosmic rays make in the air.
- IceCube & High-Energy Neutrinos2013IceCube searches for the sources of cosmic rays through the neutrinos they make
- Radiation and Life SupportopenGalactic cosmic rays are the main radiation hazard on long space trips