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Download BNMRfit istallation script Download BNMRfit Download BNMRminfit	Changing samples You must know the position number of the sample of interest before commencing a sample change. The order of samples should typically be noted in the bNQR logbook at the start of each beam period by whomever loads the ladder. 1. The samples are mounted on a "ladder," and as such are arranged vertically. A rod is attached to the top of the ladder and extends out of the cryostat; it is topped off by a black knob. The distance 'D' between the bottom of the upper portion of this knob and the topmost segment of the cryostat determines which sample is located in the path of the beam; see Fig. 6.1. 2. Ask the control room to place a beamstop (Faraday cup) upstream of the NQR cryostat before beginning the sample change. Sample changes should not be performed unless the temperature is at least ???K. 3. Carefully climb the stairs beside the cryostat so the rod and knob are within reach. 4. The ladder is secured in place (and makes thermal contact with the cryostat) by means of small wings attached to the sides of the ladder at the sample positions. Turn the black knob 1/4 turn counterclockwise (to the left looking down on the knob) to release the wings. 5. Adjust the height to the rod (up of down) such that the new D corresponds to the new sample position of choice (a measuring tape is required for this). 6. Turn the knob (i) clockwise [or (ii) counterclockwise] to reseat the wings and secure the ladder in the new position. If it is turned (i) the side of the sample facing the beam will be the same as before. If it is turned (ii) the side of the sample facing the beam will be the reversed from before. This is important because often the sample ladder is loaded in such a manner that at some positions the sample is different on each side, e.g., Au foil wrapped on sapphire; Au foil when facing one side, or sapphire when facing the back. (red tape / masking tape for this front/back choice???) 7. The sample has been changed, but may not be sufficiently aligned. Instructions for the alignement are given next. Figure 6.1: Schematic showing the distance between the top of the sample ladder and the mouth of the cryostat used to select whcich sample is placed in the path of the beam.
	Page last modified: 07/23/09 02:45 by Andrew MacFarlane.