1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
/*******************************************************************************
*
* McStas, neutron ray-tracing package
* Copyright 1997-2003, All rights reserved
* Risoe National Laboratory, Roskilde, Denmark
* Institut Laue Langevin, Grenoble, France
*
* Component: SANS_Guinier
*
* %I
* Written by: Henrich Frielinghaus
* Date: Sept 2004
* Origin: FZ-Juelich/FRJ-2/IFF/KWS-2
*
* Sample for Small Angle Neutron Scattering: Guinier model
*
* %D
* Sample that scatters with a Guinier shape. This is just an example where analytically
* an integral exists. The neutron paths are proportional to the intensity
* (low intensity > few paths).
*
* Guinier function (Rg)
* a = Rg*Rg/3
* propability_unscaled = q * exp(-a*q*q)
* integral_prop_unscal = 1/(2*a) * (1 - exp(-a*q*q))
* propability_scaled = 2*a * q*exp(-a*q*q) / (1 - exp(-a*q*q))
* integral_prop_scaled = (1 - exp(-a*q*q)) / (1 - exp(-a*qmax*qmax))
*
* In this simulation method many paths occur for high propability.
* For simulation of low intensities see SANS_AnySamp.
*
* 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_Guinier(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] horiz. dimension of sample, as a width
* yheight: [m] vert.. dimension of sample, as a height
* zdepth: [m] thickness of sample
*
* %Link
* Sans_spheres component
*
* %E
*******************************************************************************/
DEFINE COMPONENT SANS_Guinier
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
%{
%}
INITIALIZE
%{
if (!xwidth || !yheight || !zdepth) {
exit(fprintf(stderr,"SANS_Guinier: %s: sample has no volume (zero dimensions)\n", NAME_CURRENT_COMP));
}
%}
TRACE
%{
double a,qm,q,q_v;
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>1e0 ) transmr = 1e0;
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 */
a = Rg*Rg/3.0;
qm= qmax;
if (qm<1.0/Rg) qm = 1.0/Rg;
if (qm>sqrt(log(1e6)/a)) qm = sqrt(log(1e6)/a);
q = sqrt(-log(1.0-rand01()*(1.0-exp(-a*qm*qm)))/a);
q_v = q*K2V; /* scattering possible ??? */
arg = q_v/(2.0*v);
if(arg<1.0 && rand01()>transmr)
{
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_Guinier: FATAL ERROR: Did not hit box from inside.\n");
}
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
|
