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ucph>Tommy: Created page with "You should now perform the virtual experiment. The idea is to perform a scan in reciprocal space with a constant energy transfer, \(\hbar\omega= 2.0\) meV. You should move the..."

2019-07-14T21:44:23Z

Created page with "You should now perform the virtual experiment. The idea is to perform a scan in reciprocal space with a constant energy transfer, \(\hbar\omega= 2.0\) meV. You should move the..."

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You should now perform the virtual experiment. The idea is to perform a scan in reciprocal space with a constant energy transfer, \(\hbar\omega= 2.0\) meV. You should move the spectrometer along a line in reciprocal space through the (200) position, intersecting the phonon branch twice.

However, before you can perform the scan, you should calculate the setting of the spectrometer. First, construct the scattering triangle, given by the known wave vectors \({\bf k}_{\rm i}\), \({\bf k}_{\rm f}\), and \({\bf q}\) and use it to calculate the scattering angles, TT and OM. Use \(E_f=5.0\) meV, \(\hbar\omega = 2.0\) meV, and \({\bf q}=\boldsymbol\tau=(2,0,0)\). (Scattering angles should in general be calculated with a precision of \(0.01^\circ\).)

Convince yourself that by rotating the sample (by \(\Delta\)OM), you will make a close-to-transverse constant-\(E_{\rm i}\) scan in reciprocal space, without changing the angles of the scattering triangle.

{{hidden begin|toggle=right|title=Hint|titlestyle=background:#ccccff}}
The scattering triangle, and hence \({\bf q}\), is fixed in the laboratory coordinate system, but you need to describe \({\bf q}\) in the coordinate system of the sample.
{{hidden end}}

Calculate how \((h,k,l)\) and \(\Delta\)OM corresponds to one another.

{{hidden begin|toggle=right|title=Hint|titlestyle=background:#ccccff}}
You need only go to first order in \(\Delta\)OM.
{{hidden end}}

Perform the virtual close-to-transversal scan. Perform the scan also in the opposite orientation, changing the sign of both OM and TT (the "+-+" configuration).

For the best of the two configurations found above, perform scans for a few other energy transfers, ''e.g.'' \(\hbar\omega = 1.0\) meV and 3.0 meV.

Fit the processed data and use the fitting results to calculate the measured velocity of sound in Pb.

Simulation Project tripleaxis: A full virtual experiment - Revision history

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ucph>Tommy: Created page with "You should now perform the virtual experiment. The idea is to perform a scan in reciprocal space with a constant energy transfer, \(\hbar\omega= 2.0\) meV. You should move the..."