I am not an expert in backscatter x-ray physics, but I am knowledgeable scientist in the business of evaluating the scientific literature of a number of subjects related to, but not directly in this field, and this article has alarm bells going off right from the start:

1. Authors: One emeritus, one not associated with an academic or recognized lab. The first author published years ago in MRI but is not now an active researcher in backscatter x-ray physics.

2. Image source: Published public images.

3. Method: monte carlo simulation with no direct measurement of exposure, no actual testing of subjects with simulated explosives or contraband, no new data other than simulation output, i.e. GIGO;

4. References: Literature references on the model, a couple of very old books, a recent letter to the editor by the lead author. No auto-cites of relevant papers describing basic research by either author.

This is an incredibly weak paper by someone who ran a series of simulations. While I think the debate over safety and efficacy of these devices is important, this paper is not the one to trot out to prove your case. This is a perfect example of what science is not.