Detection of 90Sr/90Y with Cherenkov radiation

The highly radiotoxic ⁹⁰Sr cannot be determined by γ-spectrometry as ⁹⁰Sr and its daughter ⁹⁰Y are both pure β-emitters. Cherenkov radiation of the relatively high energy β-particles from ⁹⁰Y (E_β^max=2.27 MeV) allows for discrimination or at least for strong suppression of the lower energy β-emitters. The contribution of both may then be determined from ⁹⁰Y if their ratio is known. Measurements of efficiencies with a silica aerogel radiator (n=1.055), show a steep dependence on the β end-point energy above threshold (E_β^th=1.09 MeV). Possible contributions from β-emitters other than ⁹⁰Y in the sample may be detected by the shape of the pulse height spectrum. Using a multiwire proportional chamber in coincidence and plastic scintillation counters in anticoincidence reduces the background, so environmental activities down to about 1 Bq of ⁹⁰Sr/⁹⁰ Y may be detected in a few hours of measurement of a thin sample (air filter or sediment)