Half-Lives ofN12andB12

The half-lives of ${\mathrm{N}}^{12}$ and ${\mathrm{B}}^{12}$ have been measured with high precision because of recent interest in the spectrum shape of these two beta emitters. The ${\mathrm{N}}^{12}$ and ${\mathrm{B}}^{12}$ activities were made in the reactions ${\mathrm{B}}^{10}({\mathrm{He}}^3, n){\mathrm{N}}^{12}$ and ${\mathrm{B}}^{11}(d, p){\mathrm{B}}^{12}$ by bombarding boron targets with ${\mathrm{He}}^3$ ions and deuterons. The beam was obtained from the 3-MeV electrostatic accelerator at the Kellogg Radiation Laboratory, and was pulsed on for 20 msec and off for 180 msec. During the "beam-off" period, the counts from the ${\mathrm{N}}^{12}$ or ${\mathrm{B}}^{12}$ activity were recorded as a function of time using a 400-channel time interval analyzer. The measured values for the half-lives are $t_{\frac{1}{2}}\left({\mathrm{N}}^{12}\right)=10.95\mathrm{}\pm 0.05$ msec and $t_{\frac{1}{2}}\left({\mathrm{B}}^{12}\right)=20.3\mathrm{}\pm 0.1$ msec. Using these values, the $\mathrm{ft}$ values for the decays of ${\mathrm{N}}^{12}$ and ${\mathrm{B}}^{12}$ to the ground state of ${\mathrm{C}}^{12}$ are $ft\left({\mathrm{N}}^{12}\right)=(1.33\mathrm{}\pm 0.027)\times {10}^4$ and $ft\left({\mathrm{B}}^{12}\right)=(1.17\mathrm{}\pm 0.012)\times {10}^4$. The uncertainties quoted for the $\mathrm{ft}$ values include the uncertainties in the branching ratios and end-point energies for the two decays.