Precise half-life measurement of the superallowed ${\beta }^{+}$ emitter ${}^{10}\mathrm{C}$

The half-life of ${}^{10}\mathrm{C}$ has been measured to be 19.310(4) s, a result with 0.02% precision, which is a factor of three improvement over the best previous result. Since ${}^{10}\mathrm{C}$ is the lightest superallowed $0^{+}\to 0^{+}$ ${\beta }^{+}$ emitter, its $\mathit{ft}$ value has the greatest weight in setting an upper limit on the possible presence of scalar currents.

Figure 1

Deposited energy versus position as recorded in the MARS focal plane from a 16-strip 300-μm-thick position sensitive detector. This result was obtained after the spectrometer had been tuned for a ${}^{10}\mathrm{C}$ radioactive beam. The dashed lines show the position that was selected for the extraction slits, 8-mm apart, which was used during the ${}^{10}\mathrm{C}$ half-life measurement. Thus, the extracted ${}^{10}\mathrm{C}$ beam was determined to have only a 0.3% contribution from ${}^8\mathrm{B}$, which has a 25-times shorter half-life.

Figure 2

Total time decay spectrum of ${}^{10}\mathrm{C}$.

Figure 3

Test for possible systematic bias in the ${}^{10}\mathrm{C}$ half-life measurement due to discriminator threshold or detector bias. The circles, squares and triangles represent discriminator settings of 150, 200, and 250 mV, respectively. The full symbols signify a detector bias of 2500 or 2550 V; the open ones signify 2600 or 2650 V; the open symbol with a diagonal line through it represents a bias of 2400 V. The shaded band gives one standard deviation around the average half-life. The quality of the fit to a single average value is given by ${\chi }^2/\mathrm{ndf}=38.6/27$.

Figure 4

Test for possible systematic errors in the measurement of the decay of ${}^{10}\mathrm{C}$ caused by undetected short-lived impurities or by rate-dependent counting losses. The abscissa represents the time period at the beginning of the counting cycle for which the data were omitted from the fit.