Spin and Hyperfine Structure of Arsenic-76

Abstract

Hyperfine structure in the $^{4}S_{\frac{3}{2}}$ ground state of the radioactive atom ${\mathrm{As}}^{76}$ has been investigated by the method of magnetic resonance in an atomic beam produced by microwave discharge dissociation of arsenic vapor. $\ensuremath{\Delta}F=0$ resonances were observed within both the $F=\frac{5}{2}$ and $F=\frac{7}{2}$ atomic levels at several values of magnetic field up to about 5 oe, indicating that the spin of the ${\mathrm{As}}^{76}$ nucleus is 2. An analysis of multiple quantum transition spectra within the same $F$ states gave a measurement for two of the hfs intervals: $\ensuremath{\Delta}{\ensuremath{\nu}}_{\frac{7}{2},\frac{5}{2}}=\ifmmode\pm\else\textpm\fi{}(117\ifmmode\pm\else\textpm\fi{}4)$ Mc/sec and $\ensuremath{\Delta}{\ensuremath{\nu}}_{\frac{5}{2},\frac{3}{2}}=\ifmmode\pm\else\textpm\fi{}(69\ifmmode\pm\else\textpm\fi{}16)$ Mc/sec, with the same sign for both. From the value of the hfs constant $A$, the magnitude of the magnetic field at the arsenic nucleus is (1.33\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}${10}^{5}$ oe in reasonable agreement with the variation in this field among similar atoms. The value of ${g}_{J}$ has been found to be 1.994\ifmmode\pm\else\textpm\fi{}0.003 for arsenic.