[ Identification | Description | Input parameters | Links ]
MCViNE_SANS2D_ongrid ComponentQx, Qy are sampled uniformly over the grid range; the neutron gets v_perp -= Q*K2V and vz = sqrt(vi^2 - vx^2 - vy^2) (elastic). The weight is the bilinearly interpolated S(Qx,Qy) (no solid-angle Jacobian, as in mcvine.acc; use scattering_coefficient to set the absolute scale). File layout: first numeric row Qx values (nx, ascending), second row Qy values (ny), then ny rows of nx values (row index = Qy), i.e. the (y,x) image layout used by mcvine.acc. Transport (same as MCViNE HomogeneousNeutronScatterer): on the first passage the neutron is forced to scatter at a uniformly chosen depth, weighted by path length, attenuation exp(-(mu+sigma)x) and the scattering coefficient; on exit it is attenuated by exp(-(mu+sigma)L_out). With order>1 further scatterings are sampled analogically (truncated exponential). With p_transmit>0 that fraction of events is kept as the attenuated direct beam. mu(v) = absorption_coefficient*2200/v. Events for which the kernel cannot scatter (kinematically forbidden) are absorbed. Geometry: box (xwidth,yheight,zdepth), cylinder (radius,yheight), hollow cylinder (+thickness) or sphere (radius only). All vectors (Q, targets, reciprocal vectors, atom positions) are in the component's local frame. Uses the shared runtime share/mcvine-lib.h/.c. Example: MCViNE_SANS2D_ongrid(S_QxQy="MCViNE/SANS2D_example.dat", scattering_coefficient=1, xwidth=0.01, yheight=0.01, zdepth=0.001)
| Name | Unit | Description | Default | |
| S_QxQy | str | 2D grid file (see description) | 0 | |
| absorption_coefficient | m^-1 | Absorption coefficient at 2200 m/s (MCViNE convention; scales as 1/v) | 0 | |
| scattering_coefficient | m^-1 | Scattering coefficient | 0 | |
| sigma_abs | barn | Alternative: absorption cross section per unit cell at 2200 m/s (used when Vc>0) | 0 | |
| sigma_scat | barn | Alternative: scattering cross section per unit cell (used when Vc>0) | 0 | |
| Vc | AA^3 | Unit cell volume; when >0, coefficients are computed from sigma_abs, sigma_scat | 0 | |
| radius | m | Outer radius of a cylinder (with yheight) or of a sphere (yheight=0) | 0 | |
| xwidth | m | Width of a box sample | 0 | |
| yheight | m | Height of a box or cylinder sample | 0 | |
| zdepth | m | Depth of a box sample | 0 | |
| thickness | m | Wall thickness of a hollow cylinder (0: filled) | 0 | |
| pack | 1 | Packing factor (scales absorption and scattering coefficients) | 1 | |
| p_transmit | 1 | Monte Carlo fraction of events kept as unscattered transmitted beam (0: always scatter) | 0 | |
| order | 1 | Maximum number of scattering events per neutron (1: single scattering) | 1 |
| AT ( | , | , | ) RELATIVE | |||
|---|---|---|---|---|---|---|
| ROTATED ( | , | , | ) RELATIVE |
MCViNE_SANS2D_ongrid.comp.
[ Identification | Description | Examples | Input parameters | Links ]
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