Super-allowed Fermi β decay: Half-lives of 14O and 38Km

The half-lives of the Fermi super-allowed β-ray transitions from ¹⁴O and ³⁸K^m have been measured by multiscaling γ rays (from ¹⁴O) or β rays (from ³⁸K^m) detected in a plastic scintillator. The activities were made via the reactions ¹²C(³He, n)¹⁴O at E_³He=2.9 MeV and ³⁵Cl(α, n) ³⁸K^m at E_α=8.0 MeV respectively. Results for the half-lives were as follows: ¹⁴0-70.613 +/- 0.025 sec, and ³⁸K^m-921.71+/-0.65 msec. Recommendations as to the "best" half-life values for the set of eight most accurately measured Fermi super-allowed transitions are presented and comments are made on the present status of knowledge of the nucleon's mean quark charge as extracted from such transitions following acceptance of Cabibbo universality and the gauge theories as exploited by Sirlin. The value recommended for the vector coupling coefficient effective for nucleon β decay (including the "inner" radiative correction) is g^R_βV=(1.412 48+/-0.000 44)×10^-49 erg cm³. NUCLEAR REACTIONS Radioactivity ¹⁴O, ³⁸K^m; measured T₁₂; deduced ft values; compared with systematics.