Exercise 8: Finite beam divergence

Object: Randomly generate initial particle angles to create a beam dispersion.

Similar to Exercise 7, but randomly vary the initial gamma angle by 2 milliradians (from 0 to 2 milliradians) using a uniform distribution. Again, the sampling should be done in 'gukine.f'.  Note, if you are using polar coordinates (p,phi) for the random sampling variables, you need to sample p2, not p, and if you are using (theta,phi), you need to sample cos(theta), not theta.

Similar to Exercise 7, it is a good idea to histogram the initial angular distribution to verify the shape and distribution of your beam dispersion.

Then change to a Gaussian distribution, with sigma=2 milliradian. You can use a 2D fit or a fit to a BANX/BANY to verify you have the right shape.

The effect should be similar to the finite beam spot of Exercise 7, of course, because the photons are spread out by the time they hit the cylinder.

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