An automatic sample changer for α-, ß- and γ- active sources

Abstract

A sample changer with a turntable that accommodates twelve uncovered, solid sources for α- or soft ß-particle counting in a windowless gas-flow counter is described. The turntable movement was designed to position the sources accurately beneath the counter. A pneumatic jack unit raises the source and seals it to the counter so that entrapped air can be displaced by the counting gas during a flushing period that precedes the counting period. A second position is provided for a detector of a different type, an end-window ß-particle counter or a NaI(Tl) crystal, for example. An absorption curve can be obtained automatically with an end-window counter by placing the source on a shelf below the turntable and absorbers in the turntable. Sources can be counted for a selected time or until a selected number of counts accumulates, whichever occurs first. Timing is done by a tuning fork oscillator. The turntable position number, accumulated count, duration of count period and elapsed time from an arbitrary zero are recorded at the end of each count cycle by an electric typewriter and/or tape punch.