Determination of long-life radiocesiums Cs-134 and Cs-137 in food by gamma-ray spectrometry: summary of collaborative study

A collaborative study was conducted to validate a ray spectrometric method for determining cesium-134 and cesium-137 in foods. The Cs-134 and Cs-137 contents are measured with a low-resolution, shielded TI-activated NaI scintillation detector connected to a multichannel gamma-ray spectrometer. Thirteen laboratories participated in the study. Participants received 8 samples of heather honey, milk, and mixed dried herbs, including 4 blind duplicates. The accuracy of mean measurements of both isotopes was in the range of 98 to 103%, compared with reference measurements made in one laboratory using a high-resolution GeLi detector. Repeatability relative standard deviation (RSD(r)) values varied from 4.3 to 11.7% for 2 Cs-134 levels ranging from 121 to 337 Bq/kg and from 2.0 to 7.3% for 4 Cs-137 levels ranging from 210 to 1130 Bq/kg. Reproducibility relative standard deviation (RSD(R)) values ranged from 10.7 to 14.9% for Cs-134 and from 4.1 to 7.4% for Cs-137. No outliers were identified, and the method worked well in the absence of "fresh" fission products. However, the method was less appropriate for radiocesium determinations for activity concentration 100 Bq/kg at a counting time of 900 s or when Cs-137/Cs-134 activity ratio was larger than 10. The gamma-ray method for determining Cs-134 and Cs-137 in foods has been adopted first action by AOAC INTERNATIONAL