1. A screening system to resolve an alarm detected in a cargo positioned within a scanning volume, wherein said screening system comprises a first muon detector, a second muon detector, a detector configured to detect muons, and, a processing unit, wherein said processing unit is configured to: receive a plurality of threat sensitivity vectors; record coordinates and directions of muons entering and leaving the scanning volume; record measurements of momentum of said muons; receive a two dimensional or three dimensional mass density map; use the two dimensional or three dimensional mass density map and the measurements of momentum of said muons to determine an expected energy loss of said muons as said muons traverse the scanned volume; use said an expected energy loss to determine an expected muon momentum at each point along its path; and use said expected muon momentum at each point along its path to reconstruct a 3D scattering density map.