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]"); }