take-off angle

In the case of EDS analysis, "take-off angle" means that the angle at which characteristic X-rays emitted from the specimen are received with a detector placed above the specimen. This angle is defined by the angle of the line connecting the specimen center and the center of the detector against the normal plane to the optical axis. By setting this angle larger, signals cut by the specimen and specimen holder are reduced and the diffusion distance of the emitted X-rays in the specimen can be made shorter, thus the accuracy of quantitative analysis is improved. Previously, the take-off angle was set at 60°to 70°to reduce the above effects, which is called "High-Angle EDS" or "Top Take-off method." Recently, the take-off angle is however set at a low angle of ～20°by attaching the detector at the side of the objective polepiece because the detector is requested to place as near as possible to the specimen to increase the detection efficiency of the emitted X-rays or to increase the solid angle of the detector against the specimen, and the bore of the polepiece is requested to make small to obtain a high spatial resolution. This way of signal acquisition is called "Side Take-off method."