Abstract
The half-life of 14 O, a superallowed Fermi β + emitter, has been determined via simultaneous γ and β counting experiments at TRIUMF’s Isotope Separator and Accelerator facility. Following the implantation of 14 O samples at the center of the 8 π spectrometer, a γ counting measurement was performed by detecting the 2313 keV γ -rays emitted from the first excited state of the daughter 14 N using 20 high-purity germanium (HPGe) detectors. A simultaneous β counting experiment was performed using a fast plastic scintillator positioned directly behind the implantation site. The results, T ½ ( γ ) = 70:632 ± 0:094 s and T ½ ( β ) = 70:610 ± 0:030 s, are consistent with one another and, together with eight previous measurements, establish a new average for the 14 O half-life of T ½ = 70:619 ± 0:011 s with a reduced χ 2 of 0.99.
Highlights
High-precision measurements of the β decay f t values for superallowed Fermi β transitions between nuclear analog states of spin Jπ = 0+ and isospin T = 1 provide demanding, and fundamental, tests of the properties of the electroweak interaction by directly probing the weak vector current [1]
A weighted average of the eight previous precision measurements of the 14O half-life [3,4,5,6,7,8,9,10] yields 70.620(12) s, a result that is precise to ±0.019%, but there is cause to question the accuracy of this average T1/2 value
The 8π γ-ray spectrometer, a spherically symmetric array of 20 high-purity germanium (HPGe) detectors, and the Zero-Degree Scintillator (ZDS), a fast plastic scintillating detector positioned at zero degrees relative to the beam axis and directly behind the thin aluminized mylar tape on which the beam was implanted, were used to collect data
Summary
High-precision measurements of the β decay f t values for superallowed Fermi β transitions between nuclear analog states of spin Jπ = 0+ and isospin T = 1 provide demanding, and fundamental, tests of the properties of the electroweak interaction by directly probing the weak vector current [1] Measurements of these f t values have been used to validate the conserved vector current (CVC) hypothesis to better than 2 parts in 104, provide the most precise determination of Vud, by far the most precisely measured element of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix [2], and are used to constrain the presence of induced or fundamental scalar currents in β decay. The same systematic effect appears to be present in previous half-life determinations for 10C where the f t value for this decay could potentially be modified by up to 0.6σ These would have direct implications on the overall value deduced for Vud, the test of CKM unitarity, and the present constraint on the existence of a fundamental or induced scalar interaction in the minimal electroweak Standard Model. It is this half-life discrepancy that has motivated the simultaneous high-precision β and γ counting 14O half-life measurements reported here
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