| 摘要 |
An apertured ring made of a metal having a lower atomic number for use in instruments for measuring the thickness of layers by means of back-scattered radio active radiation, comprises on its upper side a bearing surface for the object to be measured, a small recess in relation to the height of said ring for the unhindered passage of radiation, said recess leading into the bearing surface, and a recess in the form of a circular cone which extends from the lower side of the apertured ring and leads into the first small recess in the vicinity of its upper end. The small recess is provided in a jewel for fine mechanics which has a low atomic number and is held adhesively in a bore on the upper side of the ring.
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