1. A method for analyzing material in a voxel of a target, the method comprising: illuminating the voxel of the target with a photon beam; measuring with at least one photon detector a first number of photons scattered from the voxel in a first energy range and in a first measurement direction; measuring with at least one photon detector a second number of photons scattered from the voxel in a second energy range and in a second measurement direction; determining in a processor a ratio of the first number of photons to the second number of photons; determining in a processor an average atomic number of the material in the voxel using the ratio; and based upon the average atomic number determined, taking an action chosen from the group consisting of: scanning the voxel at a higher resolution; performing a NRF scan of the voxel; scanning the voxel with another scanning method; displaying in an output device an image of at least a part of the target to an operator; and notifying the operator by means of an output device of a potential threat.