Early stages in the development of a UK primary standard for positron emitters in gas

A UK primary standard and monitor calibration service for positron emitting radionuclides in gases are needed by users of cyclotron facilities to enable them to calibrate radioactivity-in-air monitors and thus ensure the accuracy and traceability of measurements of any airborne radioactivity releases arising from the production of these radionuclides. A system of gas flow proportional counters, already established at the National Physical Laboratory (NPL) for the standardization of β⁻-emitting gases, was used as the basis of the primary standard. This paper focuses on initial problems encountered in the use of the system for measuring positron emitters.