7) Mount the crystal on the diffractometer.
To mount your crystal, the goniometer must be in the right position. This was accomplished back on help stage 3 where you clicked the "\" button on the kappaCCD server computer.
Most goniometer heads used in small-molecule laboratories have a hole that the mounting pin sits inside. We do not use those - instead we use goniometer heads with a magnetic top and mounting pins fitted with a magnetic steel base. This makes mounting and retrieving crystals much faster and easier.
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The base fits snugly on the goniometer head and the strength of the magnet ensures that it will not move. Practice the action of mounting the pin - this should be automatic, requiring no thought.
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In this laboratory we always mount crystals with the goniometer head at an angle, as shown in the above pictures. This is to minimize the chances of growing frost on the pin, goniometer head and phi block, and to prevent pin shrinkage. To do otherwise CAN and WILL cause the crystal position to move, and this is NOT good. To have any confidence in your data, the crystal HAS to be centered and it has to REMAIN centered throughout. There are no exceptions here - do not try to invent any excuses, do it right the first time.
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