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/*******************************************************************************
*
* McStas, neutron ray-tracing package
* Copyright 1997-2003, All rights reserved
* Risoe National Laboratory, Roskilde, Denmark
* Institut Laue Langevin, Grenoble, France
*
* Component: Sans_spheres
*
* %I
* Written by: P. Willendrup, K. Lefmann, L. Arleth
* Date: 19.12.2003
* Origin: Risoe
* Modified by: KL, 7 June 2005
*
* Sample for Small Angle Neutron Scattering - hard spheres in thin solution, mono disperse.
*
* %D
* Sample for use in a SANS instrument, models hard, mono disperse spheres in thin solution.
* The shape of the sample may be a filled box with dimensions
* xwidth, yheight, zdepth, a cylinder with dimensions radius and yheight,
* a filled sphere with radius.
*
* Example: Sans_spheres(R = 100, Phi = 1e-3, Delta_rho = 0.6, sigma_abs = 50, xwidth=0.01, yheight=0.01, zdepth=0.005)
*
* %P
*
* INPUT PARAMETERS
*
* R: [AA] Radius of scattering hard spheres
* Phi: [1] Particle volume fraction
* Delta_rho: [fm/AA^3] Excess scattering length density
* sigma_abs: [m^-1] Absorption cross section density at 2200 m/s
* radius: [m] Outer radius of sample in (x,z) plane for cylinder/sphere
* xwidth: [m] horiz. dimension of sample, as a width
* yheight: [m] vert . dimension of sample, as a height for cylinder/box
* zdepth: [m] depth of sample
* target_index: [1] Relative index of component to focus at, e.g. next is +1
* focus_xw: [m] horiz. dimension of a rectangular area
* focus_yh: [m] vert. dimension of a rectangular area
* focus_aw: [deg] horiz. angular dimension of a rectangular area
* focus_ah: [deg] vert. angular dimension of a rectangular area
* focus_r: [m] Detector (disk-shaped) radius
*
* Optional parameters:
* target_x: [m]
* target_y: [m] position of target to focus at
* target_z: [m]
*
* Variables calculated in the component
*
* my_s: Attenuation factor due to scattering [m^-1]
* my_a: Attenuation factor due to absorbtion [m^-1]
*
* %Link
* The test/example instrument <a href="../examples/SANS.instr">SANS.instr</a>.
%L
* Some alternative implementations exist as contributed components.
* %E
*******************************************************************************/
DEFINE COMPONENT Sans_spheres
SETTING PARAMETERS (R=100, Phi=1e-3, Delta_rho=0.6, sigma_abs=0.05,
xwidth=0, yheight=0, zdepth=0, radius=0,
target_x = 0, target_y = 0, target_z = 6, int target_index=0,
focus_xw=0, focus_yh=0, focus_aw=0, focus_ah=0, focus_r=0)
/* Neutron parameters: (x,y,z,vx,vy,vz,t,sx,sy,sz,p) */
DECLARE
%{
double my_s_pre;
double my_a_v;
double shape;
%}
INITIALIZE
%{
shape=-1; /* -1:no shape, 0:cyl, 1:box, 2:sphere */
if (xwidth && yheight && zdepth) shape=1; /* box */
else if (radius > 0 && yheight) shape=0; /* cylinder */
else if (radius > 0 && !yheight) shape=2; /* sphere */
if (shape < 0)
exit(fprintf(stderr,"Sans_spheres: %s: sample has invalid dimensions.\n"
"ERROR Please check parameter values.\n", NAME_CURRENT_COMP));
/* now compute target coords if a component index is supplied */
if (!target_index && !target_x && !target_y && !target_z) target_index=1;
if (target_index)
{
Coords ToTarget;
ToTarget = coords_sub(POS_A_COMP_INDEX(INDEX_CURRENT_COMP+target_index),POS_A_CURRENT_COMP);
ToTarget = rot_apply(ROT_A_CURRENT_COMP, ToTarget);
coords_get(ToTarget, &target_x, &target_y, &target_z);
}
if (!(target_x || target_y || target_z)) {
printf("Sans_spheres: %s: The target is not defined. Using direct beam (Z-axis).\n",
NAME_CURRENT_COMP);
target_z=1;
}
my_a_v = sigma_abs*2200*100; /* Is not yet divided by v. 100: Convert barns -> fm^2 */
my_s_pre = Phi * 4*PI*R*R*R/3 * Delta_rho*Delta_rho;
%}
TRACE
%{
double t0, t1, v, l_full, l, l_1, dt, d_phi, theta, my_s;
double aim_x=0, aim_y=0, aim_z=1, axis_x, axis_y, axis_z;
double arg, tmp_vx, tmp_vy, tmp_vz, vout_x, vout_y, vout_z;
double f, solid_angle, vx_i, vy_i, vz_i, qx, qy, qz,q;
char intersect=0;
/* Intersection neutron trajectory / sample (sample surface) */
if (shape == 0)
intersect = cylinder_intersect(&t0, &t1, x, y, z, vx, vy, vz, radius, yheight);
else if (shape == 1)
intersect = box_intersect(&t0, &t1, x, y, z, vx, vy, vz, xwidth, yheight, zdepth);
else if (shape == 2)
intersect = sphere_intersect(&t0, &t1, x, y, z, vx, vy, vz, radius);
if(intersect)
{
if(t0 < 0)
ABSORB;
/* Neutron enters at t=t0. */
v = sqrt(vx*vx + vy*vy + vz*vz);
l_full = v * (t1 - t0); /* Length of full path through sample */
dt = rand01()*(t1 - t0) + t0; /* Time of scattering */
PROP_DT(dt); /* Point of scattering */
l = v*(dt-t0); /* Penetration in sample */
vx_i=vx;
vy_i=vy;
vz_i=vz;
if ((target_x || target_y || target_z)) {
aim_x = target_x-x; /* Vector pointing at target (anal./det.) */
aim_y = target_y-y;
aim_z = target_z-z;
}
if(focus_aw && focus_ah) {
randvec_target_rect_angular(&vx, &vy, &vz, &solid_angle,
aim_x, aim_y, aim_z, focus_aw, focus_ah, ROT_A_CURRENT_COMP);
} else if(focus_xw && focus_yh) {
randvec_target_rect(&vx, &vy, &vz, &solid_angle,
aim_x, aim_y, aim_z, focus_xw, focus_yh, ROT_A_CURRENT_COMP);
} else {
randvec_target_circle(&vx, &vy, &vz, &solid_angle, aim_x, aim_y, aim_z, focus_r);
}
NORM(vx, vy, vz);
vx *= v;
vy *= v;
vz *= v;
qx = V2K*(vx_i-vx);
qy = V2K*(vy_i-vy);
qz = V2K*(vz_i-vz);
q = sqrt(qx*qx+qy*qy+qz*qz);
f = 3 * (sin(q*R) - q*R*cos(q*R))/(q*R*q*R*q*R);
l_1 = v*t1;
double pmul=l_full*solid_angle/(4*PI)*my_s_pre*f*f*exp(-my_a_v*(l+l_1)/v);
p = p * pmul;
SCATTER;
}
%}
MCDISPLAY
%{
if (shape == 0) { /* cylinder */
circle("xz", 0, yheight/2.0, 0, radius);
circle("xz", 0, -yheight/2.0, 0, radius);
line(-radius, -yheight/2.0, 0, -radius, +yheight/2.0, 0);
line(+radius, -yheight/2.0, 0, +radius, +yheight/2.0, 0);
line(0, -yheight/2.0, -radius, 0, +yheight/2.0, -radius);
line(0, -yheight/2.0, +radius, 0, +yheight/2.0, +radius);
}
else if (shape == 1) { /* box */
double xmin = -0.5*xwidth;
double xmax = 0.5*xwidth;
double ymin = -0.5*yheight;
double ymax = 0.5*yheight;
double zmin = -0.5*zdepth;
double zmax = 0.5*zdepth;
multiline(5, xmin, ymin, zmin,
xmax, ymin, zmin,
xmax, ymax, zmin,
xmin, ymax, zmin,
xmin, ymin, zmin);
multiline(5, xmin, ymin, zmax,
xmax, ymin, zmax,
xmax, ymax, zmax,
xmin, ymax, zmax,
xmin, ymin, zmax);
line(xmin, ymin, zmin, xmin, ymin, zmax);
line(xmax, ymin, zmin, xmax, ymin, zmax);
line(xmin, ymax, zmin, xmin, ymax, zmax);
line(xmax, ymax, zmin, xmax, ymax, zmax);
}
else if (shape == 2) { /* sphere */
circle("xy", 0, 0.0, 0, radius);
circle("xz", 0, 0.0, 0, radius);
circle("yz", 0, 0.0, 0, radius);
}
%}
END
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