BETA BRANCHING RATIO AND CONVERSION COEFFICIENTS IN 137CS DECAY

The decay of137Cs has been reinvestigated using several precision counting methods. The emission rate of β-particles plus internal conversion electrons was measured by the 4 π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. The K-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. The K/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. The γ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of the β-decay to the ground state of137Ba could be determined to (5.4±0.3)% of the137Cs decays, the K-conversion coefficient to 0.0916±0.0004, and the K/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the137Cs decays and the K X-ray emission intensity is (8.13±0.10)% of the emitted γ-rays. All errors are discussed in detail. © 1969 Springer-Verlag.