Analysis of radioactivity in environmental samples and food


DTU Nutech issues certificates on radioactivity in environmental samples and food based on radiometric analyses.

DTU Nutech performs a range of analyses for certification purposes. Most of the work is related to export of foodstuff to countries outside the EU. The standard certificates concern gamma activity. Samples are analysed to certify a minimum activity of not higher than 5 Bq kg-1.
The radiation certificates is a day-to-day service.

The equipment used for the gamma-spectrometric analyses consists of germanium semiconductor detectors cooled in liquid nitrogen. The detectors are placed in lead shields of 10-cm thickness for the attenuation of the ambient gamma radiation. The detectors are connected to multichannel analysers where the gamma-ray spectra are accumulated. The spectra are processed using software developed at Risø.
The detectors have efficiencies in the range 25-40% relative to a 3"x3" NaI(TI) detector and their gamma-ray energy resolutions at 1.33 MeV range from 2.1 to 2.5 keV. For each spectrum 2000 channels are used at a gain of 0.7 keV per channel. Typical counting times for screening analyses of 1-litre samples placed in Marinelli beakers are 2000-3000 seconds.

Quality assurance
The systems are calibrated with standard radionuclide liquid solutions placed in geometries similar to those used for the samples. Quality assurance of the analytical results is achieved through regular participation in international intercalibration and intercomparison programs, which demonstrate that our analytical accuracy is better than 10%. This is documented through regular participations in the intercomparisons organised by the IAEA (International Atomic Energy Agency) laboratory in Monaco since 1970.

Gamma laboratory The picture shows three lead shields with gamma detectors inside. Below the detector containers with liquid nitrogen for cooling can be seen. The lead shields are use to reduce the signals from the natural backgound radiation in the detector systems.

The laboratory has been authorised by the Danish National Institute of Radiation Protection to issue certificates of radionuclide content in foodstuffs and other items to be exported from Denmark