A Microprocessor Controlled on-Line Monitor with Computed Trip Points for Long Lived Alpha Emitters in Aerosols

A four-channel microprocessor-controlled alpha-particle monitor with trip levels computed from background and source activity levels has been designed and constructed. This instrument, intended for monitoring uranium and transuranic particles contained in aerosols, uses virtual impactors to collect the particles and to provide background separation. Alpha spectrometry is subsequently used to separate the desired isotopes. The microprocessor performs trip point calculations, controls 12 four-decade counters and 12 fourdecade liquid crystal displays. It also monitors trip input information from flow and pressure monitors, a key pad for operator input, and controls a small printer used for report generation. This article covers the hardware and software techniques used to implement the device and the theoretical aspects of calculating the sliding scale trip point.