Part 2: Use of X-ray Inspection Systems in the Food Industry

Why are X-ray systems used for contaminant detection in food?

Product inspection has become an indispensable element of responsible food production, an inherent part of any HACCP concept, and an absolute prerequisite of successful IFS certification. Any contamination of food with impurities of any kind may have most serious consequences for a company, because under the product liability law every food producer is liable for contaminations of his products in case a consumer should be harmed by such contaminations. Systems for contaminant inspection are used to prevent such problems. Metal detectors are most useful for the detection of magnetic and non-magnetic metals, but they reach their limits for example in the inspection of aluminium-coated packing materials.

Contaminations with glass, ceramics, stones, and similar materials also constitute a serious problem. X-ray detection systems for food are therefore used for such applications. Sesotec RAYCON systems furthermore offer additional advantages compared to conventional metal detectors (and other X-ray systems available on the market). For example, RAYCON allows the parallel inspection of two different products. Incorrectly placed or overlapping products also are no problem at all. And apart from contaminations, other product defects such as missing product components also can be detected.

How does an X-ray system work?

The X-rays for "radiographing" are generated by an electric X-ray tube.  A line-shaped detector that measures the arriving radiation is positioned above the conveyor belt (see picture on the right). X-rays have a very high energy and are thus able to penetrate solid bodies. Depending on the density of the inspected object the X-rays, when passing through the product, are attenuated to a higher (high density) or lower (low density) degree. The detector converts the remaining radiation into an electrical signal, and differences in the density of the inspected object can thus be represented in an image. The higher the density of a material, the darker its representation on the X-ray image, and vice versa. The image processing software detects the contrast differences in the image, highlights the contaminants or the missing products, and outputs a corresponding signal.

Some examples of radiographs taken of inspected food products:

What types of contaminants can be detected in food by X-ray systems?

Basically X-ray systems can detect any contaminants whose density essentially differs from the density of the product to be inspected. Usually this applies to metals such as steel and stainless steel, but also to glass, sandstone, quartz, shale, and many others. Sesotec RAYCON systems also detect contaminants that contain higher-value elements such as PVC, PTFE, raw bones, and salt lumps. Another special feature of X-ray systems is that apart from contaminations they also are able to detect other product defects. Missing products in packings, unwanted air bubbles, overweight or underweight, broken products, shape deviations, and even incorrect positions of individual components can be detected to some extent. This not only guarantees product purity, but also further improves the quality of the end product.

Application examples for Sesotec RAYCON systems:

  • Confectionery and cereals industry
  • Meat and sausage products
  • Dairy products
  • Canning industry
  • Bakery products
  • Baby food

However, even X-ray technology is not able to detect all types of contaminants. For example, it is not possible to detect thin foils, insects or molluscs, hair, wood, fibres, textiles, and plastics consisting only of hydrocarbons (PP, PA, PC, etc.).

Are X-rays dangerous for food products or for operators?

X-rays are classified as ionising radiation, which in case of improper use may be dangerous for persons and for their surroundings. The risk potential, however, depends on the energy and on the dosage of radiation. Since the production and processing of food of course is a highly sensitive field, the European Union has passed a specific directive 1999/2+3EG concerning the use of inspection systems on X-ray basis to guarantee 100 % safety of the inspected products:

"Food may be inspected with X-rays if the absorbed dose [...] with a maximum radiation energy of 10 MeV does not exceed 0.5 Gy."

Sesotec RAYCON X-ray systems have been designed to operate far below these permitted statutory limits. For comparison:

The maximum permissible X-ray voltage for the inspection of food is 10 MeV (mega electron volt)=10,000 keV (kilo electron volt)
Sesotec RAYCON systems operate with max. 80 keV (125 times less than permitted)

With additional safety aspects we furthermore guarantee the absolutely safe use of our X-ray systems in the inspection of products in the food sector:

  • We only use low-energy, soft X-rays
  • X-ray voltage and current are individually adapted for every product
  • The X-ray tube is hermetically shielded
  • All the radiation protection covers are monitored by safety switches
  • X-rays can only be turned on if the system functions perfectly


For operators of X-ray systems it furthermore is important that the maximum permissible X-radiation outside the system is 0.5 μSv/h.
Sesotec RAYCON systems here cause radiation values of less than 0.2 μSv/h.

The operation of Sesotec systems therefore is absolutely safe.

Here you can find all parts of our guidelines on contaminant detection in the food industry

Part 1: Basics of Metal Detection in the Food Industry
Part 2: Use of X-ray Inspection Systems in the Food Industry
Part 3: Determining Critical Control Points in Food Production Processes
Part 4: Testing of Contaminant Detector Performance According to BRC Standards