Snyder Head Directory README.   September 30, 2005
This directory contains two subdirectories, Analytical and Voxel.
Both contain MCNP input decks with different representations of the
Snyder Head model.
The Analytical directory contains the analytical form, with 
  curved surfaces representing the boundaries between bone,skin and tissue.
The Voxel directory contains two input decks with the same geomtery
  represented as small voxels, either 1.6 or 0.8 cm along an edge.
  Materials within a voxel are homogeneous.

More about this input deck geometry, neutron source, and kerma calculations,
as well as a discussion about the comparison between analytical and voxel
models can be found in:
Goorley T, Kiger WS III, Zamenhof RG. Reference Dosimetry Calculations 
for Neutron Capture Therapy with Comparison of Analytical and Voxel Models. 
Med. Phys. 29 (2) 2002. pp. 145-156.