Analysis of uncertainties and detection limits for the double measurement method of 90Sr and 89Sr

The determination process of the 90Sr and 89Sr contents in a sample, although it involves their radiochemical isolation, results always in a complex measurement process due to the interferences among their respective beta emissions and also among those of the daughter of 90Sr, 90Y, a beta emitter as well.In this paper, the process consisting in a double measurement method after the Sr radiochemical isolation is analyzed, developing the formulae to obtain activity concentrations, uncertainties and detection limits. A study of the trend of uncertainties and detection limits as function of the time in which the first measurement since the isolation is done, the delay between the two measurements and the activity concentration of each strontium isotope in the sample is carried out as well.Results show that with a very precise determination of the times involved in the whole process (isolation, measurement and duration of measurements) this method permits a reliable assessment of both strontium radioisotopes. The quicker the first measurement since the isolation is done and the longer the delay between measurements is chosen, the lower are the detection limits and the uncertainties of the activities obtained.

► The double measurement method for 90Sr and 89Sr determination is analysed.
► Uncertainties and detection limits are determined and their dependences studied.
► Proposals for the optimization of the method are given.