  A new measurement of the half-life of the positron emitter 10C has been made.
The 10C decay belongs to the set of superallowed 0+ -> 0+ beta-decays whose Ft
values offer stringent tests of the Conserved Vector Current (CVC) hypothesis
and which can be used in calculating |Vud|, the largest element of the
Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix of the Standard Model. The
experimental method used four plastic scintillator detectors in a 3-fold
coincidence mode in order to detect the unique 2x511keV+718keV gamma-ray decay
signature of 10C. The half-life values obtained from the data were strongly
dependent on the detector count rates, but a final value of 19.303 +/- 0.013 s
was determined by extrapolating the dependence to zero count rate. This study
highlights the significance of systematic errors due to high count rates in
precision half-life experiments and raises doubts about both the two previously
accepted values of the half-life of 10C.
