[ Identification | Description | Input parameters | Output parameters | Links ]
Monochromator_pol
ComponentBased on Monochromator_flat. Flat, infinitely thin mosaic crystal, useful as a monochromator or analyzer. For an unrotated monochromator component, the crystal surface lies in the Y-Z plane (ie. parallel to the beam). The mosaic and d-spread distributions are both Gaussian. Neutrons are just reflected (billard ball like). No correction is done for mosaicity of reflecting crystal. The crystal is assumed to be a ferromagnet with spin pointing up eta-tilde = (0, 1, 0) (along y-axis), so that the magnetic field is pointing opposite (0, -|B|, 0). The polarisation is done by defining the reflectivity for spin up (Rup) and spin down (Rdown) (which can be negative, see now!) and based on this the nuclear and magnetic structure factors are calculated: FM = sign(Rup)*sqrt(|Rup|) + sign(Rdown)*sqrt(|Rdown|) FN = sign(Rup)*sqrt(|Rup|) - sign(Rdown)*sqrt(|Rdown|) and the physics is calculated as Pol in = (sx_in, sy_in, sz_in) Reflectivity R0 = FN*FN + 2*FN*FM*sy_in + FM*FM (= |Rup| + |Rdown| (for sy_in=0)) Pol out: sx = (FN*FN - FM*FM)*sx_in/R0; sy = ((FN*FN - FM*FM)*sy_in + 2*FN*FM + FM*FM*sy_in)/R0; sz = (FN*FN - FM*FM)*sz_in/R0; These equations are taken from: Lovesey: "Theory of neutron scattering from condensed matter, Volume 2", Eq. 10.96 and Eq. 10.110 This component works with gravity (uses PROP_X0). Example: Monochromator_pol(zw=0.2, yh=0.2, mosaic=30.0, dspread=0.0025, Rup=1.0, Rdown=0.0, Q=1.8734)
Name | Unit | Description | Default |
---|---|---|---|
zw | m | Width of crystal | |
yh | m | Height of crystal | |
mosaic | arc minutes | Mosaicity (FWHM) | 30.0 |
dspread | 1 | Relative d-spread (FWHM) | 0 |
Q | AA-1 | Magnitude of scattering vector | 1.8734 |
DM | Angstrom | monochromator d-spacing instead of Q = 2*pi/DM | 0 |
pThreshold | - | if probability>pThreshold then accept and weight else random | 0 |
Rup | 1 | Reflectivity of neutrons with polarization up | 1 |
Rdown | 1 | Reflectivity of neutrons with polarization down | 1 |
debug | - | if debug > 0 print out some info about the calculations | 0 |
Name | Unit | Description | Default |
---|---|---|---|
mos_rms | |||
d_rms | |||
mono_Q | |||
FN | |||
FM |
Monochromator_pol.comp
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[ Identification | Description | Input parameters | Output parameters | Links ]
Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Mon Feb 7 13:18:37 2011