A long-term performance evaluation of the gamma-ray activity measurement laboratory in CPST, Lithuania

• Check sources and background measurements support quality control.
• Results obtained in 2001–2013 are presented.
• No traces of 137Cs peak at 661.7 keV were observed in the background spectra.
• Participation in proficiency-testing programmes is an endeavour of perfection.

The quality control procedures used for two HPGe detectors (a well-type and a GAMMA-X coaxial) are described. Since 2001, check sources containing 137Cs have been measured weekly for 7200s each, and the gamma-ray spectrometry system background was determined once per month for an acquisition time of 100,000 s. The laboratory participated in the international comparisons at environmental radioactivity level organized by the IAEA, Risø National Laboratory and NPL.