Mass Spectrum Analysis 1. The Mass Spectrograph. 2. The Existence of Isobars of Adjacent Elements

Abstract

(1) The simultaneous fulfillment of the conditions for high resolving power, sensitivity and dispersion have been obtained in an instrument for the investigation of isotopes. Important features of the design are the linearity of the mass scale over a broad region of the recording plate, the elimination of the troublesome effects of surface charges on the electric deflection plates, and the use of relatively wide collimating slits at small separation. The ions diverging from the second collimating slit $S_2$ are deflected through $\frac{\pi }{\sqrt{2}}$ radians, using the radial field method of electrostatic focusing introduced by Hughes and Rojansky, which produces an energy spectrum in front of the third slit $S_3$. Beams of ions of all $\frac{m}{e}$ values comprising up to 3 percent of this energy spectrum, traversing $S_3$, are further deflected through a mean angle of $\frac{\pi }{3}$ radians by a magnetic field which focuses the ions and produces a mass spectrum on the recording plate. The mean dispersion is 5 mm for one percent mass difference, the mean radius in the electric and magnetic fields is 25.4 cm, and a resolving power $\frac{M}{\Delta M}$ of $\mathrm{ca}$. 10,000 is attained in routine work. Over 140 mm on the plate, the maximum divergences from linearity are ±1/7000. (2) Mattauch and Sitte have suggested that isobars differing by one unit in atomic number are unstable or do not exist at all. To test for the existence of isobars of this class, singly and in some cases doubly ionized germanium, cadmium, indium, tin, tellurium, mercury, lead and bismuth were examined, using hydrogen free ion sources. Definite proof was obtained for the existence of three isobaric pairs ${\mathrm{Cd}}^{113}$ ${\mathrm{In}}^{113}$, ${\mathrm{In}}^{115}$ ${\mathrm{Sn}}^{115}$ and ${\mathrm{Sb}}^{123}$ ${\mathrm{Te}}^{123}$, which apparently are stable. The isotopes ${\mathrm{Cd}}^{115}$, ${\mathrm{Sn}}^{121}$, ${\mathrm{Hg}}^{197}$, ${\mathrm{Pb}}^{209}$, which have been reported as members of isobaric pairs, cannot be present to greater than 1/8, 1/60, 1/2, 1/10, respectively, of the amounts published by Aston. The existence of ${\mathrm{Pb}}^{205}$ is also doubtful. In accordance with Beck's suggestion, developed by Bethe, and by Yukawa and Sakata, both members of these isobaric pairs could be stable for a neutrino mass $m_n>0\mathrm{}$. This hypothesis would necessitate modifications in the theory of the emission of $\beta$-rays. Alternatively, a difference in the nuclear spins of the members of the isobaric pairs might result in a condition of effective stability for these nuclei.