| 摘要 |
A collimator capable of being reduced in its external size without sacrificing an aperture is to be provided. To this end, the collimator comprises a pair of first plate members which defines a radiation passing aperture by a spacing between respective opposed end faces, a pair of second plate members which respectively overlap the first plate members at least partially so as to block any other radiation than the radiation passing through the aperture, a pair of third plate members which respectively overlap the second plate members at least partially so as to block any other radiation than the radiation passing through the aperture, an adjusting mechanism which adjusts the aperture by moving the pair of first plate members, and a follow-up mechanism which causes the pair of second plate members to move following the pair of first plate members with movement of the first plate members.
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