Direct and precise determination of environmental radionuclides in solid materials using a modified Marinelli beaker and a HPGe detector

A simple but precise detection method was studied for the determination of natural radionuclides using a conventional HPGe detector. A new aluminium b eaker instead of a plastic Marinelli beaker was constructed and examined to reach radioactive equilibrium conditions between radon and its daughter el ements without the escape of gaseous radon. Using this beaker fifteen natur al radionuclides from three natural decay series could be determined by dir ect gamma -ray measurement and sixteen radionuclides could be determined in directly after radioactive equilibrium had been reached. Analytical results from ground water were compared with those from conventional a spectroscop y and the results agreed well within 12% difference. Nitrogen gas purge was used to replace the surrounding air of the detector to obtain a stable bac kground and reducing the interference of radon daughter nuclides in the atm osphere. The use of nitrogen purging and the aluminium Marinelli beaker res ults in an approximately tenfold increase of sensitivity and a decrease of the detection limit of Ra-226 to about 0.74 Bq kg(-1) in soil samples.