Gas Chromatography Detectors - Ionization Detectors > The Simple or Macro Argon Detector Sensor > Page 55
The cylindrical body can be made of stainless steel and the insulator made of PTFE or, for high temperature operation, a suitable ceramic. The very first argon detector sensors used a automobile sparking plug as the electrode, the ceramic seal being a very efficient insulator at very high temperatures.
Inside the main cavity of the sensor is a 90strontium source contained in silver foil. The surface layer on the foil that contained the radioactive material must be very thin or the b particles will not be able to leave the surface. This tenuous layer protecting the radioactive material is rather vulnerable to mechanical abrasion, which could result in radioactive contamination. The radioactive strength of the source is about 10 millicuries which for 90strontium could be considered a hot source. The source had to be inserted under properly protected conditions. The decay of 90strontium occurs in two stages, each stage emitting a b particle producing the stable atom of 90zirconium.
The electrons produced by the radioactive source were accelerated under a potential that ranged from 500 to 2000 volts depending on the dimensions of the sensor and the geometry of the electrodes. As an example, the main body had an I.D. of about 2 cm, a length of about 5 cm and a sparking plug was used as the electrode. This sensor geometry was shown to function well with an electrode potential of about 1200 volts.