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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_AnySamp
*
* %I
* Written by: Henrich Frielinghaus
* Date: Sept 2004
* Origin: FZ-Juelich/FRJ-2/IFF/KWS-2
*
* Sample for Small Angle Neutron Scattering. To be customized.
*
* %D
* Sample for Small Angle Neutron Scattering.
* May be customized for Any Sample model.
* Copy this component and modify it to your needs.
* Just give shape of scattering function.
* Normalization of scattering will be done in INITIALIZE.
*
* Some remarks:
* Scattering function should be a defined the same way in INITIALIZE and TRACE sections
* There exist maybe better library functions for the integral.
*
* Here for comparison: Guinier.
* Transmitted paths set to 3% of all paths. In this simulation method paths are
* well distributed among transmission and scattering (equally in Q-space).
*
* Sample components leave the units of flux for the probability
* of the individual paths. That is more consitent than the
* Sans_spheres routine. Furthermore one can simulate the
* transmitted beam. This allows to determine the needed size of
* the beam stop. Only absorption has not been included yet to
* these sample-components. But thats really nothing.
*
* Example: SANS_AnySamp(transm=0.5, Rg=100, qmax=0.03, xwidth=0.01, yheight=0.01, zdepth=0.001)
*
* %P
*
* INPUT PARAMETERS
*
* transm: [1] coherent transmission of sample for the optical path "zdepth"
* Rg: [Angs] Radius of Gyration
* qmax: [AA-1] Maximum scattering vector
* xwidth: [m] horizontal dimension of sample, as a width
* yheight: [m] vertical dimension of sample, as a height
* zdepth: [m] thickness of sample
*
* %Link
* Sans_spheres component
*
* %E
*******************************************************************************/
DEFINE COMPONENT SANS_AnySamp
SETTING PARAMETERS (transm=0.5, Rg=100, qmax=0.03,
xwidth=0.01, yheight=0.01, zdepth=0.001)
/* Neutron parameters: (x,y,z,vx,vy,vz,t,sx,sy,sz,p) */
DECLARE
%{
double isq;
%}
INITIALIZE
%{
if (!xwidth || !yheight || !zdepth) {
exit(fprintf(stderr,"SANS_AnySamp: %s: sample has no volume (zero dimensions)\n", NAME_CURRENT_COMP));
}
int iqmax=30000,iq=iqmax; // number of intervals
double q,sq;
double a=Rg*Rg/3.0; // internal for function sq
isq = 0.0; // integral = 0
while (iq > 1) // start integrating with low intensities at large q
{ // MODIFIY HERE
q = (iq-0.5)*qmax/iqmax; // q always slightly larger than 0
sq = exp(-a*q*q); // define this function in INITIALIZE and TRACE part
sq*= q;
isq+= sq;
--iq;
}
isq*=qmax/iqmax;
%}
TRACE
%{
double a,q,qm,sq,q_v;
double transsim=0.03; // portion of paths for transmission
double transmr, t0, t1, v, l_full, l, dt, d_phi, theta;
double axis_x, axis_y, axis_z;
double arg, tmp_vx, tmp_vy, tmp_vz, vout_x, vout_y, vout_z;
char intersect=0;
transmr = transm; /* real transmission */
if (transmr<1e-10) transmr = 1e-10;
if (transmr>0.99 ) transmr = 0.99;
intersect = box_intersect(&t0, &t1, x, y, z, vx, vy, vz, xwidth, yheight, zdepth);
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 */
transmr = exp(log(transmr)*l_full/zdepth); /* real transmission */
dt = rand01()*(t1 - t0) + t0; /* Time of scattering */
PROP_DT(dt); /* Point of scattering */
l = v*dt; /* Penetration in sample */
qm = qmax; // adjust maximal q
if (qm > 2.0*v/K2V) qm = 2.0*v/K2V; // should not be totally wrong
q = sqrt(rand01())*qm; // otherwise normalization with isq is wrong
q_v = q*K2V; /* scattering possible ??? */
arg = q_v/(2.0*v);
if(rand01()>transsim)
{
a = Rg*Rg/3.0; // MODIFIY HERE
sq= exp(-a*q*q); // identical to INITIALIZE
p*= sq*(qmax*qmax*0.5)*(1.0-transmr)/(1.0-transsim)/isq;
theta = asin(arg); /* Bragg scattering law */
d_phi = 2*PI*rand01();
vec_prod(axis_x, axis_y, axis_z, vx, vy, vz, 0, 1, 0);
rotate(tmp_vx, tmp_vy, tmp_vz, vx, vy, vz, 2*theta, axis_x, axis_y, axis_z);
rotate(vout_x, vout_y, vout_z, tmp_vx, tmp_vy, tmp_vz, d_phi, vx, vy, vz);
vx = vout_x;
vy = vout_y;
vz = vout_z;
if(!box_intersect(&t0, &t1, x, y, z, vx, vy, vz, xwidth, yheight, zdepth)) fprintf(stderr, "SANS_AnySamp: FATAL ERROR: Did not hit box from inside.\n");
}
else
{
p*= transmr / transsim;
}
SCATTER;
}
%}
MCDISPLAY
%{
double radius = 0;
double h = 0;
{
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);
}
%}
END
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