Title:

Proportional counter studies of orbital electron capture ratios

The first chapter of the thesis summarizes briefly the theoretical treatment of orbital electron capture. Particular attention is given to the theoreticallyobtained wave function ratios which are available for comparison with experimental values. It is pointed out that, when calculating values of atomic electron wave functions, it is customary not to consider the correlations which must exist among the atomic electrons, and that when such correlations are considered, the theoretical values for L/Kratios are increased over those obtained from the use of hydrogenlike functions. A comparison of theoretical and experimental values of L/Kratios is made and it is shown that further experimental work is required in all ranges of atomic number. In particular, the range of atomic number between 15 and 40 is shown to be suitable for investigation. The second chapter describes the characteristics required in the detection system and outlines the wallless counter technique used by the author. The experimental work is described in the next four chapters. Measurements of L/Kratios in the isotopes germanium71, krypton79, chlorine36 and argon37 are described, together with Incidental points of counter technique which were clarified in the course of the measurements. The values of 0.116 +/ 0.005, 0.108 +/ 0.005, 0.112 +/ 0.008 and 0.102 +/ 0.004, obtained for the L/Kratios in these isotopes, are greater than the respective theoretical values of 0.106, 0.101, 0.080 and 0.082 calculated from the ratios of wave functions prepared by Brysk and Rose. The difference between theory and experiment is most marked for isotopes of small atomic number. This is in accord with the predictions of Odiot and Daudel, who evaluated the effect of the electron correlations in light isotopes. Their value of 0.100 for the L/Kratio in argon37 is in good agreement with that obtained in the present work. Capture from the Mshell was detected in germanium71 and krypton79, the first direct observation of capture from this shell in isotopes with mass number less than 200. The values of the ratio of Mcapture to Lcapture in both isotopes was found to be 0.16 +/ 0.08, in reasonable agreement with the ratios of electron density given by Hartree wave functions. Indications that Mcapture occurred also in chlorine36 and argon37 were observed, but the evidence cannot be considered to be conclusive. The final chapter of the thesis summarizes the above results and, after comparison of the available theoretical and experimental values of L/Kratios, concludes that further theoretical work to evaluate the magnitude of the electron correlations as a function of atomic number is necessary. There are four appendices. The first contains analytical forms of the wave functions of an electron in the Coulomb field of a point charge, while the second gives some details about the counters used in the measurements. In the third, are some brief remarks about the new electronic units added in the course of the measurements. The fourth discusses measurements undertaken to establish the presence of a positron branch in the decay of chlorine36. It is shown that the observations are consistent with the existence of a weak branching, of intensity K/beta+ = 1500 +/ 300 500 relative the Xcapture component of the source.
