The photon shutter, when open, allows radiation to reach the downstream experimental stations. The First Optics Enclosure (FOE) components are still illuminated when the photon shutter is closed, however.

The integral photon shutter is derived from the standard APS P9-50 design, modified to accommodate vertical and horizontal x-ray beam excursions encountered when using upstream focusing mirrors. Modifications implemented consists of a larger input aperture, 31.4 x 26.5 mm^2 (v x h), larger shutter blocks, 72.0 x 60.0 mm^2 (v x h), actuators with appropriate stroke length, and an additional stainless steel exit mask to prevent radiation leakage around the shutter assemblies. The exit aperture size is 31.0 x 27.0 mm^2 (v x h).

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