ISO 18589-5:2019 describes the principles for the measurement of the activity of ⁹⁰Sr in equilibrium with ⁹⁰Y and ⁸⁹Sr, pure beta emitting radionuclides, in soil samples. Different chemical separation methods are presented to produce strontium and yttrium sources, the activity of which is determined using proportional counters (PC) or liquid scintillation counters (LSC). ⁹⁰Sr can be obtained from the test samples when the equilibrium between ⁹⁰Sr and ⁹⁰Y is reached or through direct ⁹⁰Y measurement. The selection of the measuring method depends on the origin of the contamination, the characteristics of the soil to be analysed, the required accuracy of measurement and the resources of the available laboratories.

These methods are used for soil monitoring following discharges, whether past or present, accidental or routine, liquid or gaseous. It also covers the monitoring of contamination caused by global nuclear fallout.

In case of recent fallout immediately following a nuclear accident, the contribution of ⁸⁹Sr to the total amount of strontium activity will not be negligible. This standard provides the measurement method to determine the activity of ⁹⁰Sr in presence of ⁸⁹Sr.

The test methods described in this document can also be used to measure the radionuclides in sludge, sediment, construction material and products by following proper sampling procedure.

Using samples sizes of 20 g and counting times of 1 000 min, detection limits of (0,1 to 0,5) Bq°kg^-1 can be achievable for ⁹⁰Sr using conventional and commercially available proportional counter or liquid scintillation counter when the presence of ⁸⁹Sr can be neglected. If ⁸⁹Sr is present in the test sample, detection limits of (1 to 2) Bq°kg^-1 can be obtained for both ⁹⁰Sr and ⁸⁹Sr using the same sample size, counting time and proportional counter or liquid scintillation counter as in the previous situation.