As we discussed earlier this month, x-ray equipment is a good first step in screening mail — but it is only a first step. To understand why let’s look at how an x-ray works.
The technical definition for x-ray is “electromagnetic radiation of high energy and very short wavelength (between ultraviolet light and gamma rays) that is able to pass through many materials opaque to light.”
But what does that mean? Here is a simple way to think about it:
X-rays penetrate objects at different rates, for example, wood is penetrated more than lead. As the x-rays hit an object, the X-ray unit collects and analyzes the object’s density and absorption rate. It translates these results into different shades of grey. Low-density items like most powders appear light and shadowy, so difficult to see. For color displays, the color you see on the monitor is computer generated.