1. A method for analyzing the material in a voxel of a target, the method comprising: illuminating the voxel with a photon beam; measuring a first number of photons scattered from the voxel in a first energy range and in a first measurement direction; measuring a second number of photons scattered from the voxel in a second energy range and in a second measurement direction; determining a ratio of the first number of photons to the second number of photons; and determining an average atomic number of the material in the voxel using the ratio.