High-precision measurements of the superallowed beta+ decays of Calcium-38 and Vanadium-46

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 38Ca and 46V has been studied in this dissertation.;For 38Ca, 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 38Ca were produced and the decay positrons detected in a high-efficiency 4π proportional gas counter. Since the β + decay of 38Ca feeds 38K m, which is itself a superallowed β+ emitter, the data were analyzed as a linked parent-daughter decay. Our result for the half-life of 38Ca, with a precision of 0.08%, is a factor of five improvement on the best previous result. The branching-ratio of 38Ca depended on β-delayed γ-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 38Ca transition into the desired range of 0.1%. With our half-life and superallowed branching ratio results for 38Ca, we obtain the Ft to be 3072(17) s, in good agreement with the conserved vector current expectation.;The half-life of 46V 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 F¯t¯ value of 3072.08(79) s established from the 13 best-known superallowed transitions. This demonstrates that previously accepted half-lives of 46V were correct in their contribution to a precision test of the conserved vector current hypothesis.