Patent ID: 7626169
Filing Date: 2009-12-01
Classification: G01J

Abstract:
1. An apparatus comprising: a source that emits radiation, the radiation traveling away from said source along a path of travel; a radiation detector disposed along said path of travel at a location spaced optically from said source; a detector calibration reference disposed along said path of travel at a location optically between said source and said detector, said detector calibration reference having mutually exclusive first and second portions that are offset in a direction transverse to said path of travel, said first portion being substantially opaque to radiation from said source, and said second portion being substantially transmissive to radiation from said source; and support structure supporting said detector calibration reference for movement relative to said path of travel in a manner so that said first and second portions become successively aligned with said path of travel; wherein said detector calibration reference includes a member made of a material that is opaque to radiation from said source, said second portion defining an opening through said member, and said first portion being a part of said member that is free of an opening through said member, said opening defined by said second portion having opposite side edges that each extend transversely to a direction of movement of said second portion; and wherein said member includes anti-reflection structure adjacent each said side edge, said anti-reflection structure including said member tapering in thickness toward each said side edge.