Calibration of Marinelli vessels for measurement of radioactive environmental samples

In order to measure low-activity radioactive environmental samples, both in liquid and solid phases, the use of Marinelli (reentrant) beakers is recommended. Standards were prepared by mixing of standardized radioactive solutions with CaCO3 of density 1.1 to 1.3 g cm−3, similar to densities of environmental samples. Measurements of calibrated Marinelli comparator standards on detector surface showed that the dependence of log Eff vs. log E is almost linear in the 120 keV to 1500 keV range. The data can be fitted more accurately by assuming a parabolic correlation (log Eff vs. log E). The validity of these standards was checked by determining the concentration of radio-europium, radio-cesium and 226Ra in three certified reference standard materials. The results obtained agreed well with the published certified data. The limit of detection for the determination of radio-cesium by γ-ray spectrometry under the prevailing experimental conditions is 0.1 Bq (2.7 pCi), for 0.5 kg of environmental samples.