10 Basic Principles of X-Ray Inspection
1. Safety Operating X-Ray Cabinet Systems
Safety is our first priority when building our cabinets. For this reason, our systems exceed domestic and international safety standards. In the USA the Food and Drug Administration regulates all cabinet x-ray systems. Their norms require a series of features to be present in the system, including redundant interlocks, warning lights, and maximum radiation allowed. On that note, the FDA specifies “radiation emitted from the cabinet x-ray system shall not exceed an exposure of 0.5 milliRoentgen in one hour at any point five centimeters outside the external surface” [21 CFR 1020.40(c)(1)(i)]. That means that operators can safely work on the x-ray inspection system in a full time capacity with no danger to their health.
T0 keep x-ray radiation inside the cabinet, the TruView systems are built with a proprietary “sandwich” of steel-lead-steel that eliminates random radiation leaks while allowing for feature upgrades. Having the walls built in this fashion allows for lower weight with not compromise in shielding – with the added benefit of having cabinets Made in USA!
2. Size and Weight of X-Ray Inspection Systems
The size of the x-ray cabinet is a direct function to the maximum sample size that can be inspected and the amount of manipulation that can be achieved. As seen in our product line, the smallest cabinet (TruView Prime) also has the smallest viewable area, 12”x12”. Conversely, the larger cabinet of the TruView Elite can inspect larger samples (34”). The weight of the x-ray cabinet is also a function of the size of the cabinet. Larger cabinets often weight more than smaller cabinets. Another important parameter that determines the weight of a cabinet is the maximum power of the x-ray source. More powerful x-ray sources need more shielding material – lead and steel – to keep radiation inside the cabinet. As a result, systems with very powerful x-ray sources tend to be very heavy.
3. X-Ray Image
The x-ray source produces x-ray radiation (photons) that travels thru the sample and cast a shadow onto the x-ray sensor. This shadow is a direct result of the shielding properties of the sample. For example, a heavy sample will block most of the radiation going thru it. As a result, in that path to the x-ray sensor only a few photons will arrive. This lack of radiation creates a dark spot in the x-ray sensor. Conversely, lighter areas of the sample will allow most of the radiation to go thru, thus shining the x-ray sensor. Differences in the density of the sample allow the x-ray inspection to be a powerful tool in internal analysis of samples.
Magnification (M) is a geometric relationship between the distance between the sample and the x-ray sensor (D1) and between the sample and the x-ray source (D2). As seen in the following animation, the closer the sample is to the source, the higher is the magnification (zoom in). The amount of magnification in a x-ray inspection system can be calculated as:
M = 1+D1/D2
*Click on image to see animation
Resolution is the measure of the smallest feature that an x-ray system can identify. Often given in micrometers or line pairs per millimeter, it is a measure of image quality.
6. Field of View
The field of view of an x-ray system is directly correlated to the size of the x-ray sensor. Flat panel detectors found in modern x-ray inspection systems have allowed to large fields of view. TruView systems have a standard 3”x4” megapixel flat panel that produces high quality images.
7. X-Ray Inspection Area
Sometimes these two parameters, x-ray inspection area and viewable area have very different meanings. X-ray inspection area is the total size of the x-ray chamber. In other words, the size of the largest object that can be placed inside the x-ray machine. Viewable area, on the other hand, accounts for the maximum area of the object that can be seen in the x-ray machine. As an example the x-ray inspection area of the TruView Prime is 24”x24”. However, it has a viewable area of 12”x12” to account for the movement of the XY table that locates the sample inside the cabinet.
8. Power of X-Ray Tube
The power of the x-ray tube is composed of two parameters: voltage (rated in kilovolts, or kV) and current (rated in milliamperes, or mA). The voltage determines the maximum energy of the x-ray photon produced by the source. Higher energies have more penetrating power, so x-ray sources with higher kV can penetrate denser materials. The proper determination of how many kV you need for your application is critical: price goes up fast with kVs! The current of the source is a measure of how many x-ray photons are being produced in a certain amount of time. As a result, increasing the current of the x-ray source produces a brighter image – at the same penetration level.
9. X-Ray Sensor
The x-ray sensor, or x-ray camera, is a critical component of every x-ray inspection system. Modern x-ray inspection systems like the TruView x-ray use flat panel sensors that are very sensitive and produce incredible pictures. Image intensifiers have been made obsolete apart a small niche of applications – a niche that is being taken over by ever better flat panels.
10. Sample Positioning
Modern x-ray inspection systems have migrated to semi or fully automated manipulation of samples inside the cabinet. The TruView Prime is an example of a semi-automated system, while the TruView Number Series and TruView Elite are examples of fully automated x-ray systems. With these systems the user can safely manipulate the sample inside the machine without a direct contact with the sample. Multiple degrees of freedom are available to allow the user to image the sample.