[ Identification | Description | Input parameters | Links ]
MCViNE_SANS2D_ongrid_process 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. Union process. Part of the Union components: define this process, collect it into a material with Union_make_material (absorption is set there with my_absorption, the absorption inverse penetration depth at 2200 m/s), assign the material to Union_box/Union_cylinder/Union_sphere/Union_mesh geometries, and add a Union_master after them. Geometry, attenuation and multiple scattering are handled by Union_master; this component provides the MCViNE kernel: the scattering coefficient and the final-state sampling (weight). Orientation: this process is anisotropic; its frame (Q vectors, reciprocal vectors, atom positions) follows the ROTATED placement of this component. The kernel code is shared with the standalone component MCViNE_SANS2D_ongrid (mcvine-lib.c). Uses share/mcvine-lib.h/.c and share/mcvine-union-lib.h/.c; the process type MCViNE is declared in share/union-lib.h and registered with Union_master in share/mcvine-union-lib.h. Example: MCViNE_SANS2D_ongrid_process(S_QxQy="MCViNE/SANS2D_example.dat", scattering_coefficient=1)
| Name | Unit | Description | Default | |
| S_QxQy | str | 2D grid file (see description) | 0 | |
| scattering_coefficient | m^-1 | Scattering coefficient (inverse penetration depth for scattering) | 0 | |
| sigma_scat | barn | Alternative: scattering cross section per unit cell (used when Vc>0) | 0 | |
| Vc | AA^3 | Unit cell volume; when >0 the coefficient is sigma_scat/Vc | 0 | |
| packing_factor | 1 | Packing factor (scales the scattering coefficient) | 1 | |
| interact_fraction | 1 | Union: fraction of interactions forced to this process (-1: by cross section) | -1 | |
| init | string | Deprecated and unused, accepted like on the other Union components (see Union_init). | "" |
| AT ( | , | , | ) RELATIVE | |||
|---|---|---|---|---|---|---|
| ROTATED ( | , | , | ) RELATIVE |
MCViNE_SANS2D_ongrid_process.comp.
[ Identification | Description | Examples | Input parameters | Links ]
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