Effect of crossed electric and magnetic fields on the helium spectrum

Abstract

The authors describe a double canal-ray source, and discuss the general features of greatly improved analyses obtained through its use. A small canal-ray tube is placed along the axis of a hollow core of the magnet, the pole tip itself serving as the cathode with one small central perforation. A similar tube is symmetrically placed in the other core so that the double canal-ray tube provides opposing beams in the region between the pole faces. Here small field plates are set up to establish strong electric fields perpendicular to the canal rays. Light is taken out at right angles to both fields and analyzed by a six-prism glass spectrograph. Displacements and qualitative intensities are tabulated mainly for components of three line groups built round and including λλ 4922, 4472 and 4026 respectively. H = 25,800 oersteds while E = 10-131 kV/cm. Resolved components remain sharp at all field strengths. A few components correspond to Δm = ± 2; but there is no evidence for Δm = ± 3. Intensities of many components are critically dependent upon electric field strength, and in at least one notable case (2 3 P-5 3 G) displacements are similarly dependent. The latter is attributed to repulsion between levels of different m values which nevertheless are forced to cross over each other.