final double r =
random.nextGaussian() * GAUSSIAN_TO_FWHM * diameter / 2.0;
final double th = 2.0 * Math.PI * random.nextDouble();
initialPos[0] += r * Math.cos(th);
initialPos[1] += r * Math.sin(th);
return new Electron(initialPos, getTheta(), getPhi(), getBeamEnergy());
}