published_or_final_version / Physics / Master / Master of Philosophy

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The frequency variation of various nuclear interactions under lead has been studied by comparing the number of different kinds of stars produced in Ilford G5 emulsion exposed directly to the air, and under 15.1cm and 10.lcm of lead. From these observations the attenuation lengths in lead are found to be: 320 +/- 12g. per cm^2 for all stars; 274 +/- 27g. per cm^2 for stars with charged primaries; 200 +/- 35g. per cm^2 for stars with uncharged primaries, excluding simple evaporation stars. The size-frequency distribution of stars and its relation to the composition of the emulsion is discussed.

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Previous work on the muon component of extensive air showers is described and reviewed with particular reference to the muon heights of origin with respect to the main cascade. Thu mechanical and operating details of a specialist experiment to determine the heights of origin of muons are described together with the results from detailed computer simulations which are tailored to resemble the characteristics of the equipment. The raw experimental data are examined in detail as a precursor to interpreting the data from the equipment. The final results from the experiment are given in detail and their relevance to air shower cascade development discussed. Suggestions are made for future work in this and related fields.

This thesis is concerned with the measurement of the longitudinal cascade development of large cosmic-ray showers from observations of atmospheric Cerenkov radiation. The purpose of the measurements is to obtain information on the mass composition of the primary cosmic rays and on the gross features of the high-energy hadronic interactions. The characteristics of the Cerenkov light signal which are strongly coupled to the longitudinal shower development are described with reference to computer simulation results. An experiment designed to measure these characteristics was deployed in Dugway, Utah, U.S.A. between October 1977 and March 1980. Measurements were made in showers of primary energy 10(^15) – 10(^18) eV. Existing data analysis techniques have been refined and new procedures developed in order to optimise the reduction of the digital data. A detailed analysis is given of two aspects of the time structure of the Cerenkov light signal in showers of mean primary energy ~ 2 x 10(^17) eV. The measurements are interpreted in terms of the mean depth of electron cascade maximum and the fluctuations occurring between showers. The many results on the cascade development currently available from the Dugway data are summarised. Interpretation of the results is found to be possible in the framework of scaling-based models of the high energy hadronic interactions which incorporate an enhancement of the central-region multiplicity. This allows certain inferences to be made concerning the primary mass composition. Specifically, primaries of energy ~ 10(^16) eV appear to be predominantly heavy nuclei, and the mass composition becomes lighter with increasing primary energy until at least ~ 2 x 10(^17) eV. While no other single experiment has yet been in a position to corroborate these results, broad consistency is found between the Dugway results and the combined results from a number of other experiments.