PURPOSE:To lower the noise level by applying a voltage to a grid and inserting a resonance circuit. CONSTITUTION:Secondary electrons emitted from a sample 5 upon collision of primary electrons are subjected to energy variation by an AC perturbation voltage applied between the sample 5 and the earth and pass through first and second grids 1, 2 to arrive at a collector 3. The collector 3 is applied with the block voltage of a resonance circuit 8 and a higher voltage arrives at the collector 3 but a lower voltage is bounced off the surface of the collector 3. In other words, the electrons are subjected to energy antalysis on that plane and since the resolution DELTAE is constant, the waveform is sharpened on the high energy side. The grids 1, 2 are connected respectively, with LC resonance circuits 6, 7 having high voltage Q to provide high impedances against signal current thus preventing the S/N ration from lowering. Furthermore, the S/N ratio can be prevented from lowering on the high energy side by applying a negative voltage of substantially same level as the collector 3 on the grid 2 through a variable resistor 10 and a bias resistor 11.
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