The lifetimes of the first excited states of ${\mathrm{C}}^{15}$ and ${\mathrm{B}}^{10}$ have been measured using a pulsed Van de Graaff beam, with a slanted-target technique to reduce the duration of beam pulses on the target. The mean lives of these levels are (3.73±0.23) nsec for ${\mathrm{C}}^{15}$, and (1.04±0.02) nsec for ${\mathrm{B}}^{10}$. This result for ${\mathrm{C}}^{15}$, together with recent gamma angular distribution and stripping measurements, confirms the spin and parity of the first excited state of ${\mathrm{C}}^{15}$ as $\frac{5}{2}+$.

• Received 19 January 1962

DOI:https://doi.org/10.1103/PhysRev.126.1811