Sensitive and accurate methods for determination of low activity level of ⁹⁰Sr and ¹³⁷Cs in grass/vegetable samples

Sensitive, precise and accurate methods for determination of low activity level of ⁹⁰Sr and ¹³⁷Cs in grass/vegetable samples by a low background β-counter were developed. The method for ⁹⁰Sr determination was based on coprecipitation as carbonate, elimination of ²¹⁰Bi and iron with a Microthene-TOA column, separation of ⁹⁰Y with a Microthene-HDEHP column, and source preparation as Y₂(C₂O₄)₃. The method for ¹³⁷Cs determination was based on Cs adsorption on ammonium molybdophosphate and precipitation as Cs₃Bi₂I₉ for source preparation. The quality control tests indicated that the methods could provide accurate results. The method application showed that: (1) The mean yields of yttrium and cesium were 79 ± 6% and 84 ± 2%, respectively. (2) The activity concentrations of ⁹⁰Sr in 9 grass/vegetable samples were in the range of 0.04-1.8 Bq kg^-1, while that of ¹³⁷Cs in the range of 0.022-0.18 Bq kg^-1. And (3) the uptake rate of ⁹⁰Sr from soil to grass/vegetable was much higher than that of ¹³⁷Cs.