Inter comparison exercise on the determination of radionuclide in sediment

Full text: For the quality assurance of gamma spectrometric measurements, inter comparison exercises are essential and Environmental Studies Section, Bhabha Atomic Research Centre, carries out such exercises periodically among the Environmental Survey Laboratories in India.This paper reports the results of such an inter comparison exercise conducted for the determination of radionuclide in a sediment sample, in the year 2009. Homogenized sediment sample containing 137Cs, 60Co and natural radionuclide was prepared and sent to seven laboratories. The participants were requested to determine the activity levels of 137Cs, 60Co and 40K using energies 1460.73 for 40K, 661.66 for 137Cs and 1173.24 keV and 1332.46 keV for 60Co. The target value and its standard deviation were calculated by taking mean of the reported values of laboratories with the omission of data of large deviation. The reported results were evaluated against the acceptance criteria for trueness and precision as per IAEA methodology and assigned the status Acceptable (A), Warning (W) or Not acceptable (N). In addition, z score, u score and relative bias were also calculated. The results of the three laboratories were Acceptable for all the three radionuclide 137Cs, 60Co and 40K. In the case of one laboratory the results were Acceptable for 137Cs and 40K but Warning status was given for 60Co. For another laboratory the results of 137Cs and 60Co were Acceptable and the status of result of 40K was Warning. The result of 40K was Acceptable and the result of 137Cs and 60Co was Not acceptable in the case of another laboratory. In another case, the results of all the three radionuclide were Not acceptable. From z score analysis, it is observed that the performance of six laboratories were satisfactory for the results of 40K and five laboratories were satisfactory for the results of 137Cs and 60Co. The results were intimated to each laboratory and necessary measures were taken to improve the performance of laboratories