A portable time of flight mass spectrometer using plasma desorption sample ionization. The sample is deposited onto a sample surface by condensing a sample gas stream onto the surface. While the instrument is evacuated, the sample surface is cooled and a sample gas stream is injected into the instrument near the sample surface causing a portion of the gas stream to condense on the sample surface and the remainder to be removed by the evacuation pump. A mass spectrometer having a linear geometry is disclosed. A reflective geometry is also disclosed wherein the flight path length is maximized by placing the fission source between the sample surface and a single detector. A collector surface for receiving start signal-generating fission fragments is sized to insure equal collection of start signal fragments and sample ionizing fragments. An area on the sample surface which is occluded by the fission source is compensated for by appropriate sizing of the fission source and the collector surface.
David T. Young;Jill T. Marshall;Emile A. Schweikert;Melvin A. Park