The most basic parameters of an X-ray tube are five: Tube voltage (adjustable), Tube current (adjustable), Focal Spot
Size (Focal Spot Size), X-ray beam angle (X-ray beam angle) and FOD (Focus to object distance). The following
paragraphs will examine the relationship between these five parameters and actual requirements.
1. Penetration, resolution and signal-to-noise ratio
Higher tube voltages can emit higher-energy X-ray photons that are able to penetrate thicker samples. So the
higher the tube voltage, the better the X-ray penetration.
The smaller the focal size of the X-ray source, the higher the resolution of the image and the clearer the picture.
The higher the tube current, the more X-ray photons will hit the sample per unit time (the brighter an electric lamp
can be compared to); The better the signal-to-noise ratio of the image, the shorter the exposure time required.
In summary, the sample thickness can be considered to adjust the upper voltage; Small focal size can be selected
for the fine structure of the sample; If you want to shorten the imaging time, you can try increasing the tube
current. But this is not always the case.
For the quality of the image (resolution and signal-to-noise ratio), we often need to choose a smaller focus size
and a higher tube current. However, if the tube voltage is also increased, the power focused on the focus (power =
tube current x tube voltage) will be enhanced, and concentrated on the focus of a small size, too high energy is
very easy to break the tube Target that produces X-rays (Target). This makes it difficult for us to guarantee the
image quality while taking into account the penetration required for thick sample imaging.
So in general:
Small focus - low power - low X-ray dose - dark image - need for integral calculation of the image - slow
processing speed - suitable for academic research and poor analytical use.
Large focus - high power - high X-ray dose - bright image - no need for image integration processing - fast
processing speed - suitable for online detection.
2. Magnification, field of view, X-ray camera layout size and imaging system volume
In most cases, we want a sample to be imaged in a single shot, so the size of the field of view of the imaging
system is better than or equal to the size of the sample, or the size of the area of interest.
Because the amplification of X-ray NDT/imaging systems follows the principle of similar triangles; Therefore, the
size of the field of view (often equal to the size of the sample, or the size of the area of interest) and the size of the
X-ray camera image layout determine the magnification of the entire imaging system.
