The beta decay of ${\mathrm{F}}^{17}$ and ${\mathrm{C}}^{11}$ has been investigated with a magnetic lens spectrometer. The positron spectrum of ${\mathrm{F}}^{17}$ consists of one component of maximum energy 1.748±0.006 Mev. The ground-state transition, comparative half-life $ft=2420\mathrm{}$ sec, has the allowed shape down to 570 kev. Beta-ray branching to the first excited state of ${\mathrm{O}}^{17}$ at 874 kev, if present, has a relative intensity of less than one percent, corresponding to a comparative half-life $\mathrm{ft}\gtrsim 2\times {10}^4$ sec. The positron spectrum of ${\mathrm{C}}^{11}$ consists of one component of maximum energy 968±8 kev. The ground-state transition, comparative half-life $ft=4170\mathrm{}$ seconds, has the allowed shape down to 255 kev.

• Received 1 February 1954

DOI:https://doi.org/10.1103/PhysRev.95.765