Everybody knows X-ray devices from hospitals but only some people are aware of the fact that X-ray can be used also in industry. During production processes there are frequent situations in which a check of the inner components is needed after the product´s encasement. For this purpose the X-ray device is perfect.
It is well known that X-rays can pass through objects. This phenomenon was described not only by famous Wilhelm Conrad Roentgen but also by many other world-known inventors including Nikola Tesla, Heinrich Hertz, Thomas Alva Edison or Hermann von Helmholtz. They all significantly contributed to gaining the knowledge of X-ray use. The most important role was accredited to Mr. Roentgen for his systematic study of all the facts known about X-rays and summarizing all his findings in a scientific study in 1985. In some countries (e.g. in the Czech Republic) the X-rays are named after him and known as “Rentgenové záření” (Roentgen radiation). But some languages (including English) prefer the term “X-ray radiation”. The history of Roentgen radiation development is quite complex. If you are interested we can publish more detailed articles on history of this important invention.
Let’s have a look at the basic characteristics of the radiation: the X-ray radiation is an ionizing high-energy photon radiation with the wavelength range from 10-12m to 10-8m. The main advantage of X-rays in practice (next to its use for tumour irradiation) is the ability to pass through objects. The X-ray permeability is based primarily on the energy of radiation. The higher the energy is, the better it passes through various materials. Simply we can say that with an equal amount of energy the photon becomes more compact and passes through materials easily, without colliding with other atoms. Because the atomic-level interactions follow probability rules, a high number of atoms and photons always causes a high number of interactions. For this reason the radiation permeability is highly influenced by radiation intensity.
The absorption of radiation intensity is the main feature observed when using X-ray radiation (as far as scanning is concerned). A big advantage is that each material has a different level of absorption. The level of radiation absorption is dependent on two factors: the atomic density and the thickness of the material. The whole X-ray imaging system is based on a hypothesis that if there is a homogeneous X-ray beam which passes through an object of inhomogeneous material or thickness, the output intensity of the radiation beam will be homogeneous. This hypothesis is demonstrated well in the following picture:
Obr. 1. : Schematic description of radiation absorption
The image depicts the principle of X-ray absorption process using a photographic film. Thin material has almost no effect on the radiation absorption and the film is exposed maximally (white upper segment). The thicker the material is, the more radiation is absorbed (two middle segments). The lowest segment shows no film exposition due to the absorption of all the radiation by the material. Also modern devices work on similar principle these days with the only exception of the photographic film being replaced by CCD and CMOS sensors.
From the point of view of defectoscopy, the Figure1 shows how potential void or bubble in the material is displayed. The radiation passes through the void with almost no radiation absorption, thus on the outcome image such defect is visible thanks to the increased radiation intensity. The brighter spot on the image is apparent and the defect can be further analysed.
These days X-ray defectoscopy plays an important role in many fields. It is used especially in foundry industry and casting of plastics as it enables the precise control of the casting for any defects like voids or bubbles. But X-ray defectoscopy can be used in other fields, expanding especially in electronics where it is used mainly in the soldering process of BGA components. During the soldering process of BGA packaging the defect in form of bridges between solder balls might occur and thus the mounting to a printed circuit is not correct. Thanks to X-ray, quick and easy check of BGA components and its proper soldering can be verified.
More articles about X-ray defectoscopy and its use in various areas will be published soon.