XCVII. The ratio of K-capture to positron emission in fluorine 18

Abstract

The existence of electron capture in the decay of ¹⁸F has been revealed by the detection of K-radiations of oxygen in a proportional tube spectrometer containing a gaseous BF, source. The K/β⁺ ratio determined from the number of counts in the observed K-peak and the total number in the positron spectrum is 0·030, with an estimated accuracy of 6%. A scintillation spectrometer investigation showed the absence of any gamma rays with intensity greater than 0·5% of the positrons, suggesting that both K-capture and beta decay are ground state to ground state transitions. A comparison between theoretical and measured values of the K/β⁺ ratio gives, for the ratio of the axial vector and tensor coupling constants, C_A/C_T=(0·4±2)%.