[en] The method allows the isotope activities to be measured rapidly without the need to measure the transmutation curve from ⁹⁰Y. Chemical treatment of samples includes selective separation of Sr with Sr Resin. The yield is determined by gamma spectrometry by measuring the activity of ⁸⁵Sr added. The method was tested for Guardian and TriCarb instruments. The position of the measuring windows, basically determined by the maximum beta energies, depends on the quenching parameter of sample. The contributions from the blank, from the ⁸⁵Sr added, fine corrections of the detection efficiency and transformation factors of residual activities were also calculated in dependence on the quenching parameter. The measuring windows at higher energies are more robust with respect to other interfering radionuclides. Residual activities in the various measuring windows are compared statistically and the presence of interfering radionuclides can be indicated. Windows W1 through W4 were defined. The maximum beta energies for ⁹⁰Sr, ⁸⁹Sr, ²¹⁰Bi, and ⁹⁰Sr are 2283, 1491, 1161, and 546 keV, respectively. The W1 window corresponds to the window for ⁹⁰Y (from E(max) of ⁹⁰Y to E(max) of ⁸⁹Sr). The lower limit of W2 is determined by the maximum energy of ²¹0Bi. So the interval between E(max) of ⁸⁹Sr and ⁹⁰Sr is divided into 2 parts, the higher-lying part being more robust with respect to the presence of the probable interfering radionuclides. W3 is an auxiliary window, usable for the indication of interfering effects. W4 can be used for the indication and/or direct measurement of activities of freshly isolated ⁹⁰Sr, with a minor correction for increasing ⁹⁰Y activity. The lower limit of W4 is fixed and defines a window with relatively lower corrections for ⁸⁵Sr. Sample treatment consists of mineralization in a microwave oven, coprecipitation with hydrated Fe(OH)₃ and MnO₂, group isolation of Sr on a strongly basic annex in HCl, and isolation of Sr on a column packed with Sr Resin. The recovery of Sr lay within the range of 50%-90%. Typical detection limits for the TriCarb 3170 instrument were 10-40 mBq for ⁹⁰Y and 50-200 mBq for ⁸⁹Sr in sample (provided that ⁹⁰Y is absent). (P.A.)