The spin and hyperfine structure separation $\Delta \nu$, of 10-min ${\mathrm{N}}^{13}$ have been measured by the atomic-beam magnetic-resonance technique. The atomic-beam machine was a modified focusing apparatus consisting of a six-pole A magnet, a Goodman-type C magnet, and an approximately uniform-gradient B magnet. This apparatus, which combines the high transmission of focusing machines and the smaller detector area of conventional machines, is described in detail. The ${\mathrm{N}}^{13}$, in the form of a gaseous molecule, was flushed continuously from the cyclotron target to the apparatus, where neutral atoms were produced in a microwave discharge in the neon carrier gas. The beam was detected on titanium foils heated to approximately 1025°C. The measurements were made in the ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ atomic ground state, but resonances were also observed in the ${}_{}{}^2{}_{}{}^{}P$ and ${}_{}{}^2{}_{}{}^{}D$ metastable doublets. The final results are $I=\frac{1}{2}$, as expected, and $\Delta \nu =33.347\mathrm{}\pm 0.020$ Mc/sec from a $\Delta F=1\mathrm{}$ measurement. Using the high-precision results on ${\mathrm{N}}^{14}$ and ${\mathrm{N}}^{15}$, we obtain an average value of $\left|{\mu }_I\right|$, which, corrected for shielding, is $\left|{\mu }_I\right|=0.32212\mathrm{} \mathrm{}\left(36\right)\mathrm{}$ nm. Assuming that the sign is negative (as in the case of ${\mathrm{N}}^{15}$), the sum of the magnetic moments of ${\mathrm{N}}^{13}$ and ${\mathrm{C}}^{13}$ is 0.380 nm, in agreement with the combined predictions of Kurath (for the ordinary part of the magnetic moment operator) and Sachs (for the mesonic current contributions). Further discussion of the result is given.

• Received 13 April 1964

DOI:https://doi.org/10.1103/PhysRev.136.B27