[ Identification | Description | Input parameters | Output parameters | Links ]

The PerfectCrystal Component

Based on a perfect crystal component by: Miguel A. Gonzalez, A. Dianoux June 2013 (ILL) Changelog: Version 1.1 - BUGFIX: correct neutron energy shift in Doppler mode - added option 'debyescherrer' to select analyzer geometry - added option 'facette' to approximate analyzer sphere by small, flat crystals Version 1.0 - inital release



Perfect crystal component, primarily for use as monochromator and analyzer in
backscattering spectrometers. Reflection from a single Bragg reflex of a flat or
spherical surface is simulated using a Darwin, Ewald or Gaussian profile. Doppler
movement of the monochromator is supported as well.

Orientation of the crystal surface is *different* from other monochromator components!
Gravitational energy shift for tall analyzers should work in principle, but it not tested yet.
See the parameter description on how to define the geometry and properties.

[1] Website for Backscattering Spectroscopy: http://www.ill.eu/sites/BS-review/index.htm

IN16B (ILL) Si111 large angle analyzers (approximate dimensions):
PerfectCrystal(radius=2, lambda=6.2708, sigma=0.24e-3,
               ttmin=40, ttmax=165, phimin=-45, phimax=+45, centerfocus=1)

IN16B (ILL) Si111 Doppler monochromator:
PerfectCrystal(radius=2.165, lambda=6.2708, sigma=0.24e-3,
               width = 0.500, height = 0.250, centerfocus=0,
               speed = 4.7, amplitude = 0.075, exclusive=1)

WARNING: This is a contributed Component.

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
ttmin NAN
ttmax deg analyzer coverage angle in horizontal xz-plane between -180 and 180 NAN
tt0 only if centerfocus==1 [deg] angular center position in the horizontal plane NAN
ttwidth deg horizontal coverage as center and full width NAN
width m absolute width NAN
phimin NAN
phimax -180 and 180 if debyescherrer==1 [deg] vertical analyzer coverage between -90 and 90 NAN
phi0 only if centerfocus==1 [deg] angular vertical position NAN
phiwidth deg vertical coverage as center and full width NAN
height only if debyescherrer==0 [m] absolute height NAN
debyescherrer -180...180 (0/1) bend analyzer following a Debye-Scherrer ring along scattering angle tt (twotheta) (phi = 0
facette m width of square crystal facettes arranged on the spherical surface (set 0 to disable). Default: 0 Warning: Facettation will fail at the poles along +-y axis. 0
facette_xi deg random misalignemt of each facette. Default: 0 0
centerfocus 0/1 Component origin is the center of the analyzer sphere if 1, if set to 0 the origin is on the analyzer surface. Default: 0 0
radius m Radius of curvature, set to 0 for a flat surface. Default: 0 0
tau sometimes also called Q... [A^-1] Scattering vector of the reflex NAN
lambda A Alternatively to tau: backscattered wavelength NAN
R0 1.0
dtauovertau 1 Plateau width of the Ewald/Darwin curve (see NAN
dtauovertau_ext randomized for each trajectory, full width [] Relative variation of tau 0
ewald Ewald [0/1] Use Ewald curve if 1, Darwin curve if 0. Default: 1 1
sigma The width will be transformed and the Gaussian is actually calculated in k-space. [meV] Width of the Gaussian reflectivity curve in meV (corresponding to the energy resolution). NAN
ismirror 0/1 Simply reflect all neutrons if 1. Good for debugging/visualization. Default: 0 0
speed m/s Maximum Doppler speed. The actual monochromator velocity is randomized between -speed and +speed. Default: 0 0
amplitude m Amplitude of the Doppler movement. Default: 0 0
smartphase 0/1 Optimize Doppler phase for better MC efficiency if set to 1. *WARNING:* Experimental option! Always compare to a simulation without smartphase. Better do not use smartwidth with Ewald/Darwin curves due to their endless tails. Default: 0 0
smartwidth meV Half width of the possible energy reflection window for smartphase. Default: 5*sigma OR 10*2*dtauovertau*E0 NAN
exclusive 0/1 If set to 1, absorb all neutrons that missed the monochromator/analyzer surface. Default: 0 0
transmit 0...1 Monte-Carlo probability of transmitting an event through the monochromator/analyzer surface. (Events with R=1.0 for DarwinE/Ewald curves are always reflected!). Default: 0 0
verbose 0


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Wed Nov 23 21:27:24 2022