Atomic number estimation of dual energy cargo radiographs using a semiempirical transparency model

TL;DR

This paper presents a new semiempirical method for estimating atomic numbers in dual energy cargo radiographs, improving material identification accuracy even with noisy data and shielding effects.

Contribution

It introduces a novel atomic number reconstruction technique based on minimizing chi-squared error with a semiempirical transparency model, adaptable to commercial systems.

Findings

Accurate atomic number predictions on simulated noisy images

Effective in the presence of shielding

Requires minimal calibration measurements

Abstract

Dual energy cargo inspection systems are sensitive to both the area density and the atomic number of an imaged container due to the $Z$ dependence of photon attenuation. The ability to identify cargo contents by their atomic number enables improved detection capabilities of illicit materials. This work introduces a novel method for atomic number reconstruction by minimizing the chi-squared error between measured transparency values and a semiempirical transparency model. This method is tested using two Geant4 Monte Carlo simulated radiographic phantoms, demonstrating the ability to obtain accurate material predictions on noisy input images, even in the presence of shielding. Furthermore, we provide a simple procedure for porting this method to a commercial system, requiring an approximate model of the scanner's beam spectra and detector response, along with only three calibration measurements.