Technological developments for strontium-90 determination using AMS

Accelerator mass spectrometry (AMS) is one of method used for ⁹⁰Sr determination. It would enable rapid ⁹⁰Sr measurements from environmental samples such as water, soil, and milk. However, routine analysis of ⁹⁰Sr using AMS has not yet been achieved because of difficulties associated with isobaric separation and production of intense negative ion beams characterized by currents from hundreds of nanoamperes to several microamperes. We have developed a rapid procedure for preparing samples with optimum compositions for use with AMS, which enables production of intense Sr beam currents from an ion source. Samples of SrF₂ were prepared from a standard Sr solution and agricultural soil. The time required to prepare a SrF₂ sample from a soil sample was 10 h. Negative ⁸⁸SrF₃⁻ ions were successfully extracted at 500 nA from mixed samples of SrF₂ and PbF₂. In the present work, negative ions of ⁹⁰Zr, included as an impurity, were accelerated with a tandem accelerator operated at a terminal voltage of 5 MV. Ions characterized by a charge state of 6+ were channeled into a gas counter. An atomic ratio of ⁹⁰Zr/⁸⁸Sr of 3 × 10⁻⁸ was estimated for the soil sample. No signal was detected from the assay of PbF₂, which was pressed in an aluminum cathode, for a mass number of 90. PbF₂ revealed good performance in the production of negative SrF₃⁻ molecular ion beams and detection of ⁹⁰Sr with a gas counter.