An automated krypton-85 γ-ray stack monitor

A Ge(Li) γ-ray detector was used in conjunction with a 6-l pressurized (60 psia) well spectroscopy gas cell to selectively detect 85_Kr stack emissions. This system was calibrated so as to relate the 514-keV γ-ray counting rate to 85_Kr concentration. Counting rate, or concentration, was continuously recorded with a count-rate meter/strip-chart recorder combination and was also time averaged over 15-min intervals using a programmable multichannel analyzer system with cassette readout. Being completely automated, this γ-analysis system required little more than liquid nitrogen service and data record retrieval throughout a 4-month-long sampling period. The sensitivity of this γ-ray analytical system was such as to achieve a minimum detectable 85_Kr stack concentration of 2 μCi/m³ for 15-min counting intervals.