The design of an array to record air showers of energy up to 1021 eV is described. Each recording station uses two scintillator tanks spaced 50 m apart and generates a master pulse if [Formula: see text] particles pass through each tank in coincidence, n can be preset in the range 1 to 10. Pulse heights from each scintillator and the time of arrival of the shower front (to ±50 ns) are recorded on tape. The stations are designed to run for at least one week between servicings. Details are given of the scintillators, the circuitry (operated entirely from storage batteries), and the coincidence techniques.
A pilot array has been operating since September 1966. Each station consists of two 6-ma liquid scintillators 2 m underground and separated by 50 m. The pilot array has three stations separated by 455, 595, and 630 m. A coincidence at one station triggers the nearby 64 scintillator and Geiger arrays. Construction of the first 25 stations of the main array began in January 1967. This array is made up of nine stations on a square grid of separation 400 m nesting within nine stations on a square grid of 800 m nesting within a square rid 3.2 x 6.4 km with a 1600-m spacing. scheduled to begin in May 1967.
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