Detection of /sup 90/Sr//sup 90/Y with Cherenkov radiation

The highly radiotoxic /sup 90/Sr cannot be determined by /spl gamma/-spectrometry as /sup 90/Sr and its daughter /sup 90/Y are both pure /spl beta/-emitters. Cherenkov radiation of the relatively high energy /spl beta/-particles from /sup 90/Y (E/sub /spl beta///sup max/=2.27 MeV) allows for discrimination or at least for strong suppression of the lower energy /spl beta/-emitters. The contribution of both may then be determined from /sup 90/Y if their ratio is known. Measurements of efficiencies with a silica aerogel radiator (n=1.055), show a steep dependence on the /spl beta/ end-point energy above threshold (E/sub /spl beta///sup th/=1.09 MeV). Possible contributions from /spl beta/-emitters other than /sup 90/Y 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 /sup 90/Sr//sup 90/Y may be detected in a few hours of measurement of a thin sample (air filter or sediment).