Improvement and Application of a High-Intensity Magnetic-Lens Type of Mass-Spectrometer

Citation

West, Samuel Stewart (1934) Improvement and Application of a High-Intensity Magnetic-Lens Type of Mass-Spectrometer. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5HXP-8063. https://resolver.caltech.edu/CaltechTHESIS:08262019-151405915

Abstract

A mass-spectrometer in which was used a new type of magnetic lens to focus ions from an extended source was already in existence when the research was begun, but no adequate source of positive ions had been devised. The research concerns itself with the investigation of three types of intense, directed-beam ion sources and with the application of the completed mass-spectrometer to the separation of isotopes 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 the electrostatic problem of focussing the ions from a large surface into a plane parallel beam. Revised to allow for space charge, this source gives 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 the mechanical analogy. The effect of thermal velocities of ions at the hot surface of the source was calculated and found to account for almost the whole focal defect of the mass-spectrometer.

One-microgram samples of lithium isotopes were collected. Preliminary tests of radioactivity were hindered by contamination of the discs on which the samples were collected, and an apparatus has been constructed by which these tests are being made without possibility of contamination.

Thesis Files