Rapid method for determination of ⁹⁰Sr in seawater by liquid scintillation counting with an extractive scintillator

A rapid determination method of ⁹⁰Sr is developed for the monitoring of seawater around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Three ideas of chemical separation and measurements to accelerate ⁹⁰Sr analysis are investigated. Strontium is co-precipitated in a two-step procedure with hydroxyapatite after the removal of magnesium phosphate in the presence of citric acid. The purification process of strontium is in combination with solid phase extraction disks. One or two sheets of Sr Rad disk and cyclic operations are examined to eliminate interfering substances and secure the exchange capacity. The suitable conditions of adsorption and stripping are determined with a ⁸⁵Sr tracer. Seawater samples up to 1L can be analyzed within 4h. Additionally, the appropriate pH conditions to extract strontium to the scintillator are studied, and the ⁹⁰Sr activity is assessed via liquid scintillation counting using an extractive scintillator based on the di-(2-etyl hexyl)-phosphoric acid (HDEHP) extraction method. The new scintillation counting method involves a small quenching effect and a low background compared to the conventional emulsion scintillator method. The minimum detectable activity (MDA) is 35mBq/L of ⁹⁰Sr in 180min of counting. The proposed method provides analytical results within a day after receipt of the samples.