A mass-spectrometer in which was used a new type of magnetic lens to focus ions from an extended source was already in existencewhen the research was begun, but no adequate source of positive ions had been devised. The research concerns itself with the investigationof three types of intense, directed-beam ion sources and with the application of the completed mass-spectrometer to the separation ofisotopes of potassium and lithium in quantity.
The ion-source finally used was adapted from a form designed by neglecting space charge and solving by a mechanical analogy theelectrostatic problem of focussing the ions from a large surface into a plane parallel beam. Revised to allow for space charge, this sourcegives 0.3 m.a. of potassium ions in a flat beam, which is 12% of the emission from 30 cm2.
Sources using a curved grid were set up and tested. A three-slit electrostatic lens was investigated mathematically and with themechanical analogy. The effect of thermal velocities of ions at the hot surface of the source was calculated and found to account for almostthe whole focal defect of the mass-spectrometer.
One-microgram samples of lithium isotopes were collected. Preliminary tests of radioactivity were hindered by contamination of thediscs on which the samples were collected, and an apparatus has been constructed by which these tests are being made without possibility ofcontamination.
