An apparatus is for moving a sample holder on a platform from a loading position where the sample holder can be removed from the platform to a locked position where the sample holder is securely held. The sample holder is configured to rest on wheels within a recessed portion on the platform. The apparatus is configured such that: (i) movement of the platform from the loading position to the locked position causes a vertical clamp to lower down on top of the sample holder, and a horizontal clamp to be pressed to an outer periphery of the sample holder; and (ii) movement of the platform from the locked position to the loading position causes the vertical clamp to rise above the sample holder, and the horizontal clamp to be moved away from the outer periphery of the sample holder.