A Search for Element 87 by Analysis of Positive Rays

Abstract

The methods used in previous attempts to discover eka-caesium are briefly examined and their limitations pointed out. Estimates are given for the sensitivity of detection and identification of element 87 by atomic weight determinations, radioactive means, physiological effects, x-ray and optical spectrum analysis. Predictions of spectral values by Moseley's Law and an empirical relation give: $V_i=4.05\mathrm{}\pm 0.05$ volts, $7{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}=21340\mathrm{}\pm 200$ ${\mathrm{cm}}^{-1\mathrm{}}$, $7{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}=19670\mathrm{}\pm 200$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\Delta \nu$ separately determined 1675±50 ${\mathrm{cm}}^{-1\mathrm{}}$, principal series resonance lines 8720±200A and 7600±200A. The large uncertainty is due to uncertainty in the iso-electronic Ra II spectrum. No absorption lines were found in the sun's spot spectrum, although possible, as element 87 should be less highly ionized than Cs. A tungsten filament heated to 1200°-1300°K converts into ions all caesium atoms which strike the tungsten surface and ekacaesium should behave the same way. By this means, first investigated by Langmuir and Kingdon, and Ives, an intense homogeneous source of positive ions is secured. This positive ion source was incorporated into a tube similar to Dempster's mass spectrograph in method of focussing and ray analysis, and positive ions were looked for of mass number 223 or 224. Chemical separation of caesium and any admixed ekacaesium was made from pollucite and lepidolite ores from Oxford Country, Maine. Eka-caesium was not existent to an extent greater than 3.5×${10}^{-7\mathrm{}}$ part of the caesium from pollucite or greater than 7.3×${10}^{-6\mathrm{}}$ part of the caesium from lepidolite.