An investigation of extensive air showers in the range 10(^4) to 10(^6) particles

A small air shower array of radius 60 m is described which will bemused initially to study extensive air showers in the range 10(^4) to 10(^6) particles in size and to supplement existing research programmes into hadron and muon spectroscopy in the Cosmic Ray Laboratory of the University of Durham. There are fourteen plastic scintillator detecting elements, in the first stage of construction of the array, located in a hexagonal geometry around the Physics Department. An important feature of this array is in its data handling procedures in which the initial array data are assembled in analogue form, digitised and then transferred to an on-line I.B.M. 1130 computer disc for subsequent analysis. The array has been made as versatile as possible whilst retaining a measure of simplicity. It may be triggered in a variety of ways depending upon the mode chosen and upon the peripheral experiments and may also be added to with the minimum of electronic modification and delay. Because of the digitisation technique used one is able to provide instructions, when the data are being analysed, to compensate for any drift in the electronics automatically. A preliminary shower size spectrum, based on over 200 hours of operation, has yielded a spectrum in the range 8.10(^5) ≤ N ≤ 3.10(^6) with an integral exponent of Y(_I) = -2.6 ± 0.2.