Development of hollow-cathode radiation sources. Part 1. Study of the effects of cones placed in the cavity on the emitted light intensity

Abstract

Aluminium cones were placed in a hollow cathode in order to examine the plasma, and bore holes were made along the cavity wall, as described previously. On the basis of the light intensity emitted through the bore holes, the effect of cones of different lenght on the optimum excitation position was studied. Increased surface area of the cones gave higher emitted light intensities. Cones of different materials (Fe, Cu and Al) and of different lenghts (0–10 and 0–25 mm) were placed in cavities of different materials (length 10 or 25 mm) and for analytical purposes the emitted light intensity parallel to the cavity was examined for the cones of different length and with pairs of cones and cavities of different materials. The increase in the intensities of the lines emitted by the cones does not appear to be caused by an increase in surface area, but by the fact that the tip of the cone is placed in the optimum excitaion position. With short cavities the optimum excitation position changes with the ratio of the internal diameter of the cavity to the length. When carrying out multi-element analyses, a 3 : 1 ratio of length to diameter is recommended, as the optimum excitation positions for the elements studied (Fe, Cu and Al) are all at the same height in the cavity.