The Design of a Portable Instrument for the Detection of Atmospheric Pentaborane and Other Toxic Gases

A direct reading, automatic, and temperature insensitive instrument has been developed for the detection and recording of pentaborane in air down to and below 0.1 parts per million (ppm) sensitivity using the flame-emission principle. Toxic levels of many other volatile materials may also be detected with appropriate modification. A small hydrogen flame takes on a typical greenish cast in the presence of boranes, the radiation intensity being proportional to the pentaborane concentration. A multiplier phototube with an appropriate interference filter detects this energy and the amplified current at the multiplier anode is applied to a dc differential amplifying stage using field-effect transistors. A panel meter is applied to this circuit, and recorder and control outputs are provided. The hand-carried instrument can operate for an eight-hour period using a self-contained hydrogen supply and rechargeable silver-zinc batteries. An automatic battery charge and cutoff circuit is built into the device.