Production of ${\mathrm{Hg}}^{198}$ as a Possible Source of an Improved Wave-Length Standard

The green line 5461A from any of the even isotopes of mercury is superior, in many respects, to the red line 6438A of cadmium for a primary standard of wave-length. The mercury isotope of mass 198 was produced by utilizing the nuclear transformation ${}_{79}{}^{}{}_{}{}^{}\mathrm{Au}_{}^{197}{}_{}{}^{}+{}_0{}^{}{}_{}{}^{}n_{}^1{}_{}{}^{}\to {}_{80}{}^{}{}_{}{}^{}\mathrm{Hg}_{}^{198}{}_{}{}^{}+{}_{-1\mathrm{}}{}^{}{}_{}{}^{}\beta _{}^0{}_{}{}^{}$

One ounce of pure gold was sealed in a quartz tube and a section of 5-mm inside diameter quartz tube was sealed on the quartz-gold tube. The system was outgassed and 4-mm Hg pressure of spectroscopically pure argon was admitted and the tube was sealed. The gold was exposed to stray neutrons near the sixty-inch cyclotron for ten months. The gold was then heated and the mercury was condensed in the 5-mm quartz tube. The mercury vapor in the presence of argon gas was excited by means of a 100-megacycle oscillator and the spectrum was observed. The lines produced by the discharge were mercury lines, and the position of the lines of a Fabry-Perot etalon spectrogram agree with the position assigned by Schüler and Jones to the mercury isotope of mass 198. Larger quantities of gold exposed to known superior sources of neutrons will produce an adequate supply of the isotope for scientific purposes.