Volume 13, Issue 9, 01 September 1942
Index of content:
13(1942); http://dx.doi.org/10.1063/1.1714907View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714908View Description Hide Description
This paper covers the general methods employed in mass spectrometry, machine design, and possible sources of error in relative‐abundance measurements which are inherently associated with instrument design. Also included are graphs for determining the critical constants of the usual types of instruments.
13(1942); http://dx.doi.org/10.1063/1.1714910View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714911View Description Hide Description
An adapter has been developed which allows a conventional electron microscope to be used interchangeably as an electron diffractioncamera or an electron microscope. The adapter comprises a unit which takes the place of the projection lens unit of the microscope, and includes a newly designed microscope projection lens, a specimen holder, and a focusing lens. To transform the instrument from a microscope to a diffractioncamera (or vice versa) it is necessary only to transfer the specimen from the regular object chamber to the adapter. Diffraction patterns may be obtained by either reflection or transmission. As a result of the excellent reproducibility of voltages and currents from the regulated power supplies used in the electron microscope, the diffractioncamera holds its calibration to within 0.1 percent over long periods. Using a calibration determined by measurements of gold patterns, lattice spacings of a number of common materials were determined and found to agree with x‐ray values to within 0.5 percent.
13(1942); http://dx.doi.org/10.1063/1.1714912View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714913View Description Hide Description
The variation of refractive power and spherical aberration with electrode voltages and field strengths is studied for two characteristic unipotential lenses, an immersion lens, and a magnetic lens. Conclusions are drawn herefrom regarding the variation, with lens strength and applied voltage, of the resolving power obtainable with the lens as an electron‐microscope objective. Scattered measurements by other authors agree satisfactorily with the results. The ``relativistic aberration'' of the electrostatic unipotential lenses, i.e., the effect on the image of fluctuations in the over‐all applied voltage, is calculated and shown to be of significance in the electrostaticelectron microscope. Furthermore, the axial chromatic aberrations are computed for the four systems and the question of upper limits of the last two aberrations is discussed.