Developed Method for Better Detection of Radionuclides in Plants by Gamma Spectrometry

Ahmed El-Sharkawy, Hanan Al-Ghamdi, Hekmat El-Begawy

As a result of a previous fail in the International Atomic Energy Agency intercomparison (IAEA-TEL-2012-03) for the determination of the activity concentration of 137Cs in hay sample, the major source of error in determining the photopeak efficiency of the 661.6 keV gamma energy line of the 137Cs was due to the difficulties to reproduce the same matrix and elemental composition of the certified reference calibration materials as that of the hay sample. New approach was developed through the digestion of the ashed plant sample and delivers a clear small volume sample solution into the standard counting container for gamma measurements. The activity of the target radionuclide was determined by comparison with an acidified deionized solution spiked with known amounts of the typical radionuclide and 133Ba as a yield tracer in identical conditions. Method validation was established by analyzing replicates of the IAEA-TEL-2012 hay sample and the IAEA-372 grass sample for 137Cs.  The validation was established using several parameters; accuracy, precision and bias in order to ensure that it fits for the purpose. Trueness was evaluated in terms of relative bias, and no significant deviations from the true values due to samples densities and/or matrix-variation effect were found. The closeness of the determined 137Cs activities to the target values was evaluated in terms of accuracy, and was found to have an average of 0.98. The precision of the method is found to be fairly good, with uncertainties less than 7%. It can be concluded that the method is capable of providing high accuracy and precision measurements of 137Cs in plant samples. Also, it may be recommended that better detection limits for 226Ra and 228Ra activities in environmental plant samples can be achieved with this method using bulk plant samples.