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During TEM operation, the sample is bombarded with high energy electrons. In certain modes of operation (e.g. low magnification, diffraction, grid travers, etc.) similarly high energy X-rays can be formed. When these create too large of an energy flux for a detector, the SiLi crystal and electronic components can be damaged. A common solution to protecting detectors in TEMs has been to use a shutter. This provides protection for the detector but requires an increased distance between the sample and detector to accommodate opening and closing of the shutter.
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The r-TEM has a specially designed, tungsten shutter mechanism (patent #US5,569,925) that opens when the detector is moved into the analyze position. When the detector is not in operation, the detector head retracts and, in the process, closes the shutter so it can absorb damaging high energy X-rays and electrons. It is important to note that retraction of the detector head occurs automatically in response to excessive flux incident on the crystal. The operator can also initiate motorized retraction or advance the detector with the dedicated hardware controller.
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| Since the shutter closes while moving to the retracted position, the detector can be positioned very close to the sample for the analyze mode. Creating this very compact specimen-to-crystal geometry gives the detector a large solid angle which translates into higher count rates and better performance. |
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