Method for non-intrusively identifying a contained material utilizing uncollided nuclear transmission measurements

A method for non-intrusively identifying a target material enclosed within a container, comprising the steps of:

• measuring a total path length for a beam of radiation transmitted through the container enclosing the target material, along a selected, essentially linear transmission path, such that the measured total path length is approximately equal to an unknown path length of the beam through the container plus an unknown path length of the beam through the enclosed target material, referred to as the total path length relationship;
• transmitting a first beam of mono-energetic gamma radiation having a first energy through the container and target material along the selected transmission path, and measuring a first count rate of uncollided, unscattered gamma radiation transmitted through the container and target material, with an on-axis detector aligned with the selected transmission path;
• transmitting a second beam of mono-energetic radiation having a second energy through the container and target material along the selected transmission path, and measuring a second count rate of uncollided, unscattered gamma radiation transmitted through the container and target material, with the on-axis detector aligned with the transmission path;
• applying an algorithm to determine an estimated first relative and an estimated second relative linear attenuation coefficient for the chemical agent exposed to the first and second gamma radiation energies respectively and calculating a ratio of the first estimated relative linear attenuation coefficient to the second estimated relative linear attenuation coefficient;
• and
• identifying the target material by comparing the calculated ratio with a known linear relative attenuation ratio unique to candidate target materials and thus, determining the candidate target material.