new_contents: #!/usr/bin/env python3
  
  import random
  
  import const
  from particle import Particle, propagate
  from detector import Detector
  from initial import Beam, Profile, Energy
  
  random.seed(91400)
  
  N = 1000
  
  beam = Beam(
      profile=Profile(
          centre=0,
          diameter=50,
          shape=const.UNIFORM,
      ),
      energy=Energy(
          mean=25,
          width=5,
          shape=const.GAUSSIAN
      ),
      divergence=30
  )
  
  detector = Detector(
      voxels=5,
      size=100
  )
  
  for _ in range(N):
      particle = Particle(beam)
      while particle.alive:
          particle = propagate(particle, detector)
          if detector.voxel(particle.position) is None:
              particle.alive = False
  
  detector.output()
  
subject: Add the 'shell' for the MC simulation.