Fig. 4.

Measurement of phosphorus and nitrogen distributions (atoms/nm²) in thymocyte nucleus as function of electron dose. Each data point was calculated from a series of four images with intensities I^unfilt (unfiltered), I^zero (zero-loss), I^pre (pre-edge), and I^post (post-edge), for P and N, respectively. Even for doses exceeding 10⁷ e^–/nm², which are typically required for elemental tomography, no significant loss of P and N was observed. It was not feasible to obtain useful compositional maps below a dose of 10⁵ e^–/nm² because the signal-to-noise ratio was too low.