Typical inelastic (TAS) neutron experiment

Before coming to the instrument:

Know your system's lattice parameters and angles, and it's symmetry. Decide about the sample orientation - you get only one plane

Create hkl-intensity-list (reflection list). –> info about forbidden reflections and the (relative) intensities of the allowed. - Have it available for starting the experiment.

Mark the crystal direction on the sample holder

Mount the sample properly. Think about covering the glue or holder and about either fixing the sample by Al wire or mounting an Al foil bag around.

Mark the crystal direction outside on the cryostat

For magnets, sample mounting needs to be better than within 1°. Depending on the instrument, care that one crystal direction is parallel to the goniometer axis.

Start experiment. Experiment name, sample name, give sample metadata to system

Align the sample

• move instrument to elastic position
• calculate (hkl) of a strong allowed refelction in your scattering plane for your kf
• if there is no allowed reflection within the available q-range, think about removing the filter and orient at
• move stt/a4 to scattering angle
• rotate sample for 181° minimum (sometimes SE will hinder you, then take what you get)
• you should find at least one reflection, and the angles between refelctions should represent the symmetry of the crystal
• if there are more reflections than expected or the angles are wrong: filter forgotten? more than one grain? - think and decide
• if ok - move sth/a3 to maximum of the reflection. Take the one better suited for SE/other constraints
• go to maximum of the peak, define sth/a3 for the reflection [panda: setalign((h,k,l), nn)]
• gonio-scan in the related direction, go to max.
• check height
• repeat gonio-scan, until there is no relevant change
• check the lattice parameter. Care that horizontal focus is flat for this scan.
• adjust lattice parameter
• check gonio, height, lattice parameter iteratively up to no relevant changes occur. care about foci
• after last lattice parameter scan, define sth/a3
• claculate orthogonal reflection
• go there, you should find it immediately
• gonio-scan, lattice parameter iteratively (remember foci. height should be ok)
• adjust lattice patametr, fix gonios
• in case sth/a3 does not fit perfectly for both reflections, decide about a compromise depnding on you measureing goal
• check lattice parameters at the temperature you want to measure
• start first inelastic scans

Good luck!!!!

Background reduction

Background is a very important issue for PANDA. There are some (REAL) examples of how bad configuration can influence the measurement:

• Helium background