private void followRay(
SimpleVector pos,
SimpleVector dir,
double energyEV,
FloatProcessor imp,
int scatterCount,
double totalDistance) {
if (energyEV <= 1 || scatterCount > 20000) {
System.out.println("energy low, times scattered: " + scatterCount);
return;
}
// follow ray until next interaction point
SimpleVector oldPos = pos.clone();
double dist = sampler.getDistanceUntilNextInteractionCm(material, energyEV);
pos.add(dir.multipliedBy(dist));
pathlengths.add(dist);
// draw the entire path
// imp.drawLine((int)(scale*oldPos.getElement(0)), (int)(scale*oldPos.getElement(1)),
// (int)(scale*pos.getElement(0)), (int)(scale*pos.getElement(1)));
// draw interaction points only
imp.drawDot((int) (scale * pos.getElement(0)), (int) (scale * pos.getElement(1)));
// choose compton or photoelectric effect
double photo =
material.getAttenuation(energyEV / 1000, AttenuationType.PHOTOELECTRIC_ABSORPTION);
double compton =
material.getAttenuation(energyEV / 1000, AttenuationType.INCOHERENT_ATTENUATION);
if (sampler.random() * (photo + compton) <= photo) {
// photoelectric absorption
energyEV = 0;
// System.out.println("absorbed after " + scatterCount + " collisions");
xs.add(pos.getElement(0));
ys.add(pos.getElement(1));
zs.add(pos.getElement(2));
return;
} else {
// compton scattering
energyEV = sampler.sampleComptonScattering(energyEV, dir);
// send new ray
followRay(pos, dir, energyEV, imp, scatterCount + 1, totalDistance + dist);
}
}
private void visualizeKleinNishina(double energyJoule) {
int gridWidth = 600;
int gridHeight = 500;
double maxAngle = 360;
Grid2D grid = new Grid2D(gridWidth, gridHeight);
FloatProcessor fp = new FloatProcessor(grid.getWidth(), grid.getHeight());
fp.setPixels(grid.getBuffer());
// find max value
double max = 0;
for (int i = 0; i < maxAngle; ++i) {
double value = XRayTracerSampling.comptonAngleProbability(energyJoule, Math.toRadians(i));
if (value > max) {
max = value;
}
}
fp.drawLine((int) 0, grid.getHeight() / 2, grid.getWidth(), grid.getHeight() / 2);
fp.drawLine(grid.getWidth() / 2, 0, grid.getWidth() / 2, grid.getHeight());
fp.drawOval((grid.getWidth() - grid.getHeight()) / 2, 0, grid.getHeight(), grid.getHeight());
double lastX = 0;
double lastY = 0;
// draw angle distribution
for (int i = 0; i < maxAngle; ++i) {
double value = XRayTracerSampling.comptonAngleProbability(energyJoule, Math.toRadians(i));
SimpleMatrix m = Rotations.createBasicZRotationMatrix(Math.toRadians(i));
SimpleVector v = new SimpleVector(((value / max) * ((double) grid.getHeight() / 2.d)), 0, 0);
SimpleVector r = SimpleOperators.multiply(m, v);
double x = grid.getWidth() / 2 + r.getElement(0);
double y = grid.getHeight() / 2 + r.getElement(1);
if (i > 0) fp.drawLine((int) lastX, (int) lastY, (int) x, (int) y);
lastX = x;
lastY = y;
}
grid.show(
"Normalized Klein-Nishina cross-section as a function of scatter angle ("
+ energyJoule / eV
+ "eV)");
grid = new Grid2D(gridWidth, gridHeight);
fp = new FloatProcessor(grid.getWidth(), grid.getHeight());
fp.setPixels(grid.getBuffer());
// draw histogram with rejection sampling of the klein-nishina
// distribution
int[] angles = new int[grid.getWidth()];
for (int i = 0; i < numSamples; ++i) {
double angle = Math.toDegrees(sampler.getComptonAngleTheta(energyJoule));
int pos = (int) (angle * grid.getWidth() / 360.d);
angles[pos] += 1;
}
double max2 = 0;
for (int i = 0; i < angles.length; ++i) {
if (angles[i] > max2) {
max2 = angles[i];
}
}
for (int i = 0; i < angles.length; ++i) {
double x = i;
double y = ((angles[i]) * (grid.getHeight() / (max2)));
fp.drawLine((int) x, (int) grid.getHeight(), (int) x, grid.getHeight() - (int) y);
}
// draw klein-nishina probability function
lastX = 0;
lastY = 0;
for (int i = 0; i < maxAngle; ++i) {
double value = XRayTracerSampling.comptonAngleProbability(energyJoule, Math.toRadians(i));
double x = (i * (grid.getWidth() / 360.f));
double y = grid.getHeight() - ((value) * (grid.getHeight() / (max)));
fp.drawLine((int) lastX, (int) lastY, (int) x, (int) y);
lastX = x;
lastY = y;
}
grid.show(
"Energy: " + energyJoule / eV + "eV; x-axis: angle[0-360]; y-axis: probability[0-max]");
}
