A magnetic semicircular focusing spectrometer with a radius of curvature of 13.6 cm has been constructed and adapted for the measurement of the $\beta$-ray spectra of emitters in gaseous phase.

The radioactive gases were produced by deuteron bombardment of gaseous samples in a cyclotron using special probes.

${\mathrm{A}}^{41}$ (109 min.) produced by the ${\mathrm{A}}^{40}\mathrm{}(d,p)\mathrm{}$ reaction showed a spectrum of maximum energy (1.245±0.005) Mev and an allowed spectrum shape down to at least 200 kev.

The half-life of ${\mathrm{O}}^{15}$, produced by the ${\mathrm{N}}^{14}\mathrm{}(d,p)\mathrm{}$ reaction, was determined to be (118.0±0.6) sec. The end point of its positrons was (1.638±0.005) Mev. The Fermi plot departed from linearity at 300 kev, but this effect may be of experimental origin.

• Received 21 November 1949

DOI:https://doi.org/10.1103/PhysRev.78.649