HIGHLY EFFICIENT SPECTROMETER OF DELAYED COINCIDENCES FOR MEASURING POSITRONIUM LIFETIME

We have designed and built an automated spectrometer of delayed coinci dences to study a new phenomenon, namely monofrequent oscillations in the angular distribution of gamma-quanta due to 3 gamma-decay of posit ronium in a weak magnetic field. The spectrometer detection unit consi sts of three NaI(Tl) scintillation detectors 100 mm long and 150 mm in diameter. The time resolution of the facility is 7 nsec. A magnetic f ield is generated by permanent samarium-cobalt magnets. A powdered tar get that generates positronium is placed in a vacuum-tight flask with a positron source made from Na-22. Experimental results are given and a data-processing technique which compensates for the differential non linearity of the time-to-analog converter is proposed.