One century ago, in experiments that began in 1909 and ran until 1911, Theodor Wulf attempted to measure the background radiation at different altitudes, scaling mountains and towers from the Netherlands to Switzerland. In 1912, Victor Hess went 5,200 metres up in a balloon, taking measurements of the background radiation. The major result of these efforts was the realisation that with increasing altitude comes an increase in radiation, rather than a decrease as would be assumed were all the radiation from the Earth. The result was a noble prize for Hess for the discovery of cosmic rays, awarded 1936.
Further investigations into the nature of the particle radiation coming from above continued. In 1930, Pierre Auger discovered particle showers – high energy particles impacting on atmospheric particles, creating new particles at lower energies that then go on impacting to create even lower energy particles until the energy falls off enough for the impacts not to create more particles. In 1956, Frederick Reines & Clyde Cowan discover the neutrino, a ghostly particle that interacts very weakly with other particles, and get a Noble prize for it in 1995. In 1987 sees neutrinos from Supernova SN 1987A being detected, 1998 sees ‘oscillations’ of cosmic neutrinos (where neutrinos interfere with each other and disguise their type, or ‘flavour’) and 2002 sees Raymond Davis and Masatoshi Koshiba receiving the Noble Prize for detecting neutrinos from the Sun and SN 1987A. 1989 sees the detection of the first extraterrestrial source of gamma rays, highly energetic photons.
The 10th-17th of October 2009, however, sees the first European week of astroparticle physics. Paris will be honouring pioneers of the discipline by sticking cosmic ray detectors onto their highest tower, Montparnasse Tower, and firing a laser beam at the Paris Observatory every time one is detected during the night. It will also be open to the public for them to meet scientists and view animations. Public openings of laboratories will occur in the Czech Republic, The Netherlands, Poland and Romania, meanwhile in Rome on the 27th of October, a new exhibition, the first on Astroparticle Physics, will be opened – “Astri e particelle. Le parole dell’ Universo”.
Astroparticle physics, as well as looking at cosmic ray, neutrino and high energy photon astronomy also aims to answer questions relating to possible particle origins of Dark Matter and Gravity. Futher information on the week can be found here, pictures can be found here and an appropriate twitter feed can be seen here.