XLVIII. Magnetic spectrometer of large solid angle

Summary An account is given of a magnetic spectrometer of large solid angle and good resolution which should find applications in the study of complex beta-ray spectra by the method of beta-gamma coincidences. The original apparatus, consisting of a segmented annular G.M. counter set round a radioactive source in a magnetic field is described, the method of use being to select from the output of the counter, large pulses which correspond to the simultaneous triggering of several sections by the passage of an electron tangentially to the annular counter. The performance of the instrument is discussed and modifications are described which rectify the defects in the earlier design and give a solid angle of 2·5 per cent of 4π with a resolution of 5 per cent. The geometry of this type of spectrometer is considered and the performance which might be obtained with good design is discussed. It is concluded that collecting angles up to the order of 50 per cent of 4φ are possible with good resolution.