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.