Neutrino's 70 years on

6 December 2000

Display high resolution version

On 4 December 1930, theorist Wolfgang Pauli wrote a famous letter in which he dared to hypothesise the existence of new particle - the particle now known as the neutrino. Pauli proposed the new particle to explain why energy seemed to go missing in the form of radioactivity known as beta-decay. The neutrino would took away energy but without being detected, as it has no electric charge and a very small mass. It was to be another 26 years before Fred Reines and Clyde Cowan claimed the first detection of Pauli's "undetectable" particle.

Nowadays, neutrinos are detected in many experiments throughout the world. In this image an electron-neutrino - the kind of neutrino that steals the energy in beta-decay - has been detected in the vast tank of water that forms the Super-Kamiokande experiment in Japan. Imagine looking down into the cylindrical tank, 42 m deep. The dots are phototubes on the curved walls, and the coloured blocks show where light has struck a tube. The ring of light has been produced by an electron moving through the water faster than light does, to produce Cherenkov radiation. You can find out more about this image, and a comparison with a muon-neutrino here.

Credit: Super-Kamiokande/Tomasz Barszczak