1. A second stage screening system to resolve a threat alarm detected in a cargo by a first stage screening system, wherein said first stage screening system generates threat sensitivity vectors, said second stage system comprising: a first muon detector set placed above the cargo to generate first muon information comprising a first coordinate and an angle of incidence of incoming muons; a second muon detector set placed below the cargo to generate second muon information comprising an actual coordinate and an actual angle of exit of the incoming muons; a detector to measure a momentum of said incoming muons; and, a processing unit, wherein said processing unit: receives threat sensitivity vectors determined from the first stage; operates a positioning system that positions a high-Z threat within the cargo relative to said first and second muon detectors; and, employs said first and second muon information and threat sensitivity vectors to confirm a presence of high-Z materials.