• 24 NOV 15

    The Science Behind X-ray Inspection of Food

    Last week’s blog focused on how to make the right product inspection choice to ensure food safety. Now let’s take a closer look at x-ray inspection.

    X-ray inspection is all about differences in absorption. The amount of x-ray energy absorbed during an x-ray beam’s passage through a product is affected by the product’s thickness, density and atomic mass number. Measurement of the differences in x-ray beam absorption between a product and a contaminant is the basis of x-ray inspection.

    Chemical Composition – Atomic Mass Number is Key

    Cast your mind back to your school days and you may remember learning about the periodic table in chemistry. The table shows all the chemical elements arranged in order of increasing atomic mass.

    Food products typically contain compounds made from chemical elements with atomic mass numbers of 16 (oxygen) and under. The absorption of x-rays by food products containing low-mass elements is proportional to their density and thickness. In other words, the thicker or denser the product, the more x-rays it absorbs.

    A potential contaminant is detectable by an x-ray system if it has a high atomic mass, a feature that’s generally related to the contaminant’s density. Some contaminants, such as mineral stone or glass, often contain trace levels of some very high atomic mass elements.

    Contamination Detection – it’s All About DensityContam-Table

    Since food products typically contain low atomic mass elements and have low density, while some contaminants contain high atomic mass elements and generally have a higher density, it’s convenient to use density as the benchmark for contaminant detection.

    In general, contamination detection is only possible on contaminants that are denser than the food product in which they are embedded. This explains why low-density contaminants such as insects, wood, hair and polypropylene, are typically not detectable by x-ray inspection.

    Denser items absorb more x-ray energy and are detectable. Moving further up the table, the densities increase. Items higher up the table absorb more x-ray energy and are more easily detected. This also means that smaller particles of these items can be detected.

    For more information on x-ray inspection, click to read our X-ray Inspection Guide ‘Building an Effective Programme’.

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