[en] Measurements of k electron capture to positron emission ratios in the allowed decay of ⁹¹Mo, ¹²⁰Sb, ⁸⁹Zr and ¹⁴⁰Pr are reported. Discrepancies between experiment and theory are examined. (U.K.)

[en] Previous measurements by two authors of K-capture to positon emission ratios in the high-Z region are inconsistent. The nuclide ¹⁴⁰Pr was remeasured for the following reasons. Firstly, to remove the ambiguity in the above data and secondly, to reduce the uncertainty in the results by a careful choice of source material and detector system. An important advantage in the choice of ¹⁴⁰Pr is that the theoretical ratio is known with great accuracy (approximately 1%). The result obtained agrees with one of the authors and shows that the experimental and theoretical ratios differ by approximately 15%. (Auth.)

[en] The K-capture to positron emission ratio (Psub(K)/Psub(β sub(β⁺) for the decay of ⁹¹Mo to the ground state of ⁹¹Nb has been measured and found to be about 9% lower than the theoretical value. This tends to agree with a recent review which indicated that experimental (Psub(k)/Psub(β⁺) ratios disagree with theory, particularly for high-Z nuclei. (author)

[en] A 4π CaF₂(Eu) scintillation spectrometer is described which is suitable for measurements with electrons and X-rays. The detection efficiency for these radiations has been measured using ³²P and ¹⁰⁹Cd sources respectively. In addition, the resolution, linearity of response and total photon efficiency have been determined for this detector as functions of incident radiation energy. An insensitive region on the surfaces of CaF₂(Eu) crystals was determined to be (0.47+-0.10) mg/cm² thick using a collimated ²⁵²Cf α-source. A brief study of negaton and positon continuum spectra, obtained using ³²P and ¹²⁰Sb sources respectively, is also described together with the corresponding Fermi-Kurie plots. (Auth.)

[en] Recent measurements of K-electron capture to positron emission ratios in medium-Z isotopes have been shown to be systematically lower than theoretical predictions. However, the capture to positron ratio in ⁸⁹Zr yields a result greater than theory, confirming that the discrepancy between theory and experiment is not a simple one. (author)

No abstract available

No abstract available

[en] Recent review papers have indicated that experimental K-capture to positon emission ratios in allowed decays disagree with theory especially for high-Z nuclei. The experimental error has never been sufficiently small to verify this with certainty. The K-capture to positron emission ratio, Psub(K)/Psub(β⁺), in ¹²⁰Sb has been measured with an uncertainty of about 3% and found to lie about 16% lower than the most recent theoretical predictions. (Auth.)