A collapsible cable management arm is foldable with a plurality of heat dissipation apertures. A control unit for controlling observation-condition setting devices, which include an electron-gun control unit, an irradiation-lens control unit, an objective-lens control unit, a magnifying-lens-system control unit, and a sample-stage control unit, is provided. The face seal assembly comprises three elements. The overflowbypass opening may be adjacent the top wall or bottom wall of the container. A sensing means is included in the apparatus for sensing an extraneous parameter that may influence the detection of the NQR signal from the item to be scanned. In order to reduce noise in the system, only one submixer is active at any time.