Experiments on extensive cosmic ray air showers

Radiation from outer space falls continuously on the earth's atmosphere, and those particles which have energy greater than about 10 13eV produce the phenomenon called the extensive air shower. These showers are characterised by the production of thousands of secondary particles by the processes of cascade multiplication occurring in the atmosphere. As yet, there is no known high energy out off and primary cosmic rays with energy as high as 10 20ev (Linsley,1963) have been reported. Extensive air showers thus provide a means of investigating the interaction of particles with energies far greater than have yet been produced by laboratory accelerators. Cosmic rays have been studied by apparatus placed near or above the top of the atmosphere by balloons and rockets, but, because this apparatus is necessarily small, the 101 rate of events obtained means that this method can only be used to study primary rays below about 1014eV. For energies greater than this, only the extensive air shower can be used to investigate the prOperties of nuclear interactions. The low rate is not such a limiting factor because the lateral spread of the shower allows it to be detected at large distances from the axis. While the atmosphere has produced a magnification and made detection more simple, it has caused a loss of direct information about the primary interactions. This information now has to be deduced from the study of the particles which have resulted from many generations of cascade multiplication. The other main reasons for the study of extensive air showers are concerned with the source of the primaries and the prOperties of the space through-which they have travelled. It is expected that information on these matters could be obtained by the study of the energy spectrum of the primaries, the relative proportions of primaries of different mass numbers and any anisotrophy of the primary radiation