High-Precision Measurements of the Superallowed Beta+ Decays of 38Ca and 46V

As a part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, the decay of the superallowed 0? --> 0? beta emitters ??Ca and ??V has been studied in this dissertation. For ??Ca, the half-life, 443.88(36) ms, and superallowed branching ratio, 0.7738(41), have been measured. In our half-life experiment, pure sources of ??Ca were produced and the decay positrons detected in a high-efficiency 4[pi] proportional gas counter. Since the beta? decay of ??Ca feeds ??K^m, which is itself a superallowed beta? emitter, the data were analyzed as a linked parent-daughter decay. Our result for the half-life of ??Ca, with a precision of 0.08%, is a factor of five improvement on the best previous result. The branching-ratio of ??Ca depended on beta-delayed gamma-ray intensities being measured with a high-purity germanium detector calibrated for absolute efficiency to 0.2% precision. This branching-ratio result represents our first step in bringing the ft value for the superallowed ??Ca transition into the desired range of 0.1%. With our half-life and superallowed branching ratio results for ??Ca, we obtain the Ft to be 3072(17) s, in good agreement with the conserved vector current expectation. The half-life of ??V has been measured to be 422.66(6) ms, a factor of two more precise than the best previous measurement. Our present result determines the corresponding Ft value to be 3074.5(26) s, which is consistent with the average $Ft―$ value of 3072.08(79) s established from the 13 best-known superallowed transitions. This demonstrates that previously accepted half-lives of ??V were correct in their contribution to a precision test of the conserved vector current hypothesis.