Radio-Frequency Orientation ofAs76

Abstract

Measurements are reported on the successful orientation of 26-hour ${\mathrm{As}}^{76}$ donors in a doped silicon crystal. A general discussion is given of the various methods of dynamic nuclear orientation and how they apply to ${\mathrm{As}}^{76}$. The use of radio-frequency orientation to determine the sign of the nuclear magnetic moment and the mixture of total angular momenta carried off by the electron-neutrino system is discussed. ${\mathrm{As}}^{76}$ has been oriented by both saturation of forbidden transitions and double resonance methods. The hyperfine splitting of ${\mathrm{As}}^{75}$ in the doped silicon crystal is +198.42±0.04 Mc/sec; the hyperfine splitting of ${\mathrm{As}}^{76}$ in the same crystal is -93.660±0.06 Mc/sec. The spin of ${\mathrm{As}}^{76}$ has been shown to be 2; its gyromagnetic ratio, -0.4514. The determination of the relative amounts of angular momenta carried off by the $2^{-}$→$2^{+}$, 2.41-Mev beta ray gives a result which is consistent with 5 parts $L=0, 2$ parts $L=1, \mathrm{and} 3$ parts $L=2\mathrm{}$. An unknown systematic error in these last measurements makes it difficult to say precisely what the mixture is. Unsuccessful attempts to produce orientation through the Overhauser and Abragam methods are summarized.