Estimation of Mass Thickness of Biological Samples from their Electron Micrographs

Abstract

DURING the past several years a number of investigations^1–13 have been made to compute the mass thickness of biological samples, from the contrast in their electron microscope images. The basis of all these measurements is the well-established relation: where I_t/I₀ is the image contrast of an elemental object area of mass thickness ρt and S is the scattering cross-section per gm. of the object. By using carbonaceous samples, for example, spheres of polystyrene latex, of known diameter and density and measuring their image contrast, several authors^3,12 have estimated the value of S under various operating conditions of the electron microscope. From these results, curve 1 in Fig. 1 has been plotted, showing the variation of S with the angular aperture α, for 50-kV. energy electron beam. A few values of S for (i) carbon film calculated from the experimental data of Lippert¹⁴ and (ii) ‘Formvar’ film (from data of Bahr⁵) have also been plotted in Fig. 1.