Capture of neutrons by cylindrical absorbing rods placed around a pile

The fraction T of neutrons escaping over the sides of a pile which will be captured by absorbing rods of radius R embedded in graphite and surrounding the sides of the pile in a single row with a regular spacing of 2a, and removed by a distance b from the edge of the pile, is given with the aid of a simple idealised model by:image Here image The values of image, based on simple diffusion theory, may be read off the graph of Fig. I. Numerical values of T for thorium metal are given in Fig. II, Fig. III, Fig. IV and Fig. V on the basis of the following assumptions: