National Physical Laboratory

Radioactive gas standards

Gas handling rigNPL gas-handling rig (left) with customer's
monitor attached

NPL provides a number of services giving traceability for measurements of radioactive gases both within the nuclear industry and for estimating doses to the general public.

Standardisation of gases

Sources of beta-emitting gaseous radionuclides (such as tritium and 85Kr in cylinders) can be calibrated using the NPL primary gas standard which consists of a set of length-compensated proportional counters with ancillary data acquisition, data processing and gas handling facilities. This system can be used to measure gases with activity concentrations in the approximate range 25 MBq m-3 to 27 GBq m-3 for radioactive gas in nitrogen. Higher activity concentrations for 85Kr from ampoules are possible by dilution. Accuracies of ± 3 % (k=2) are achievable. Various container types (e.g. cylinders and glass ampoules) can be accommodated.

Radon standards

The system for the provision of standards of 222Rn in gas is currently offline and UK needs for such standards are currently under review. Please contact us for an update if you are interested in standards for this radionuclide.

Calibration of monitors

Portable tritium-in-air and 85Kr monitors can be calibrated using gases standardised as above. The customer may require this for demonstration of response to activity as part of a calibration process or as part of a type testing procedure. The monitor to be exposed is either directly attached to a gas-handling rig incorporating the calibrated gas cylinder or is placed within a sealed enclosure attached to the rig. Use of the enclosure permits up to 6 monitors to be exposed simultaneously. Activity concentrations in the approximate range 5 MBq m-3 to 180 MBq m-3 are achievable for flow-through tritium-in-air monitors.

Download Tritium Monitor Calibration flyer Adobe Acrobat PDF file (PDF 2.97 MB)


Customer Service tel: +44 20 8943 8695

Last Updated: 3 Mar 2014
Created: 28 May 2009


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