Determination of Long-Life Radiocesiums Cs-134 and Cs-137 in Food by γ-Ray Spectrometry: Interlaboratory Study

Abstract

Abstract A gamma-ray spectrometric method for the determination of cesium-134 and cesium-137 in food was studied collaboratively in 13 laboratories, using 8 samples (including 4 blind duplicates) consisting of heather honey, milk, and mixed dried herbs. Low resolution, shielded Tl-activated Nal scintillation detectors were used to measure Cs-137 in the photon energy range 516 to 714 keV and Cs-134 in the range 716 to 880 keV. Results were generally acceptable and no outliers were identified for any sample results. The method worked well in the absence of “fresh” fission products. The method was less appropriate for radiocesium determinations where the activity concentration was <100 Bq/kg at a counting time of 900 s or where the Cs-137/Cs-134 activity-ratio was larger than 10. The accuracy of mean measurements of both isotopes (relative to reference measurements made in one laboratory using a high resolution GeLi detector) was in the range of 98 to 103%. For all samples analyzed, the repeatability relative standard deviation (RSDr) 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, whereas the reproducibility relative standard deviation (RSDR) values for these levels ranged from 10.7 to 14.9% for Cs-134 and from 4.1 to 7.4% for Cs-137.