High-precision half-life measurements for the superallowed Fermi β+ emitter 14O

The half-life of the superallowed Fermi beta(+) emitter O-14 has been determined via simultaneous direct beta and gamma counting experiments at TRIUMF's Isotope Separator and Accelerator (ISAC) facility. A gamma-ray counting measurement was performed by detecting the 2312.6-keV gamma rays emitted from an excited state of the daughter N-14 following the implantation of samples at the center of the 8 pi gamma-ray spectrometer, a spherical array of 20 high-purity germanium (HPGe) detectors. A simultaneous beta counting experiment was performed using a fast plastic scintillator positioned behind the implantation site with a solid angle coverage of similar to 20%. The results, T-1/2(beta) = 70.610 +/- 0.030 s and T-1/2(gamma) = 70.632 +/- 0.094 s, form a consistent set and, together with eight previous measurements, establish a new average for the O-14 half-life of T-1/2 = 70.619 +/- 0.011 s with a reduced chi(2) of 0.99.