Direct observation of individual cosmic ray showers

A simple method is described, based on Cerenkov light measurements, for the accurate determination of arrival detection, estimation of primary energy, and direct observation of cascade development in individual showers. The method does not depend on the usual approach to shower analysis and does not require an accurate center of symmetry to be determined from ground level data. It is considered that measurements of the kind described, employing the improved equipment at locations having long periods of clear sky conditions, may substantially help in attempts to measure the atomic mass number of primary cosmic rays. Measurements were made during about 100 hours of clear sky moonless night time during the winter of 1975-76, using an array of Cerenkov light detectors spread over an area of 1 km2 in Yorkshire. The likely origin in the atmosphere of the light observed was assessed by computer simulations using an air shower model incorporating contemporary hadron physics. (U.K.)