National Physical Laboratory

Fidelis Secondary Standard Radionuclide Calibrator

A wide variety of radionuclides are routinely used in Nuclear Medicine for diagnostic scans and cancer therapies. The internally administered dose needs to be accurately determined prior to administration to the patient and Radionuclide Calibrators are the most common instruments used for this purpose.

The NPL Radionuclide Calibrator (Fidelis)

The Fidelis Secondary Standard Radionuclide Calibrator comprises the NPL-designed ionisation chamber and a brand new electrometer and user interface unit from Southern Scientific.

Each ionisation chamber is built to the same specifications as the NPL Secondary Standard master ionisation chamber and is tested at NPL for a range of radionuclides before delivery to the customer. The extensive list of NPL calibration factors (for over 60 radionuclides) available with the calibrated instrument can then be used for accurate activity measurements, with full traceability to the UK National Standards maintained by NPL. Additionally, any new NPL calibration factors derived for emerging radioisotopes will be made available to the users of these systems.

The most recent list of available factors for the Fidelis Radionuclide Calibrator can be found here Adobe Acrobat PDF file

The Fidelis instrument is specified for use as a Secondary Standards Reference Calibrator and allows medical physicists to check the accuracy of other field Radionuclide Calibrators.

Its excellent stability, accuracy and traceability to NPL primary standards of activity for a wide variety of radionuclides makes the Fidelis Radionuclide Calibrator an ideal Secondary Standard system for other National Metrology Institutes.

This instrument is distributed in the UK by Southern Scientific Ltd and further details can be found on their website

Recommended half lives of radionuclides can be found here


For technical advice, please contact us at


Relevant publications and details of the NPL's Radionuclide Calibrator Users' Forum can be found here

Last Updated: 3 Mar 2014
Created: 16 Nov 2011


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