| 摘要 |
The apparatus comprises a rotatably mounted slotted disk (14) wherein the slot (22) is continuously varying in width around the circumference of the disk. The disk incorporates an elongated magnet (16) which causes it to rotate in relation to an external magnetic field. The slotted disk is placed in a fluid filled chamber. A first and second aperture are located on the top and bottom elements of the chamber defining an emission passage. The apertures have a rectangular length approximately the maximum width of the slot. A source detector is provided below the chamber proximal an emission source, and a second source detector is provided above the chamber. The source detectors provide a response to the intensity of emission incident upon them. As the disk rotates the continuously variable width of the slot linearly attenuates the source intensity relative to the second source detector.
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