Detection of /sup 90/Sr with aerogel Cherenkov detector with low background

/sup 90/Sr is a highly radiotoxic fission product which may pollute the environment following an accident in a nuclear power plant. It is a pure /spl beta/ emitter and thus difficult to detect by standard methods. Recent progress in silica aerogel production as well as the new large multichannel photomultiplier tubes offer possibilities for detection of /sup 90/Sr, based on Cherenkov radiation of /spl beta/ particles emitted by its daughter /sup 90/Y. An appropriate choice of the aerogel refractive index (produced in the range between 1.005 to 1.06) determines the threshold for Cherenkov radiation and thus separates between higher and lower energy /spl beta/ particles. Also multichannel PMT´s permit the counting of the Cherenkov photon yield, offering additional discrimination. An additional multiwire proportional chamber operating in a coincidence with the photon detector hits was used to lower the background and for timing. A prototype apparatus was constructed for detection of the relatively high energy /spl beta/ particles emitted by /sup 90/Y (E/sub max/ = 2.27 MeV). The efficiency of the prototype detector and the photon yield as a function of the /spl beta/ spectrum end-point energy is presented, as well as results of investigations of various backgrounds and the lower limit of activity required for quick and accurate measurements of samples extracted from animal bone, air filters or sediments.