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At 7:31 in the following Youtube video (the link should start at 7:31, t=451):

There is an x-ray image being shown, of (I presume) part of the guts of an F-15.

How are these pictures taken? What machines are used, what are they called?

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  • $\begingroup$ Radiography is used in many different applications. One relevant example is shipping containers. So, radiography on a fighter really isn't that difficult. $\endgroup$
    – Jon Custer
    Oct 10, 2022 at 17:22
  • $\begingroup$ One reason to X ray a fighter aircraft is that a maintenance technician lost a tool. A screw driver or wrench being slammed around during a high G turn can do a lot of damage. Maintenance Technician have to account for every tool after working on a plane. If a tool is missing they do everything possible to find it. $\endgroup$
    – Jim
    Oct 11, 2022 at 14:21

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This is done by the NDI shop. Non Destructive Inspection.

NDI is responsible for ensuring the integrity of aircraft structures by utilizing multiple inspection methods such as eddy current, magnetic particle, radiographic and ultrasonic.

https://www.15wing.af.mil/News/Article-Display/Article/2919599/ndi-the-plane-docs/

Digital radiography

"The new digital X-ray system is really cool and fun to work with, providing a faster way to develop and read an image,"

https://www.tyndall.af.mil/News/Article/712369/x-ray-vision/

large-standoff/large-area thermography (LASLAT)

large-standoff/large-area thermography (LASLAT), an advanced thermal imaging tool that has expanded the capabilities of non-destructive inspection (NDI).

Thermographic inspection can use either a component’s inherit heat flow (passive thermography) or an induced heat flow (active thermography) to reveal component abnormalities.

https://www.compositesworld.com/news/ncms-report-demonstrates-thermography-innovations-for-enhanced-ndi-capabilities

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I know it's not what you directly asked, but a lot of medical imaging technologies scale up surprisingly well and find application in industrial settings. The synergy is quite a natural one - a boroscope inside a jet engine is basically a surgical tool in a different setting, after all!

I'm a medical physicist, and if you gave me a fighter jet and probably about $10m I could manufacture and build from scratch a multi-energy CT scanner to scan it with – and the system would have remarkably little major modifications to existing human (or veterinary) equipment. There are a number of industrial companies that offer such services – both X-rays, ultrasound and CT are routinely used in industry for non-destructive testing as it really lets you verify what welds are doing in the finished part. The main difference is that (for X-rays) the source and the detector are both portable, or (for CT) you tend to keep the beam and detector fixed and move the sample around in 3D slowly (if possible) rather than building a hangar-sized gantry (although large ones do exist). A cheap, portable X-ray machine you can buy on Alibaba looks like this: the X-rays come out of the top and you then put a film (yes, film!) plate some distance away that you then develop. The film doesn't have to be flat (though it usually is) and the X-rays come out in a cone (probably):

X-ray industrial source

One of the other "nice" things about imaging materials rather than people is that the radiation doses they can handle are far larger radiation dose and therefore imaging with other techniques than (living) biological systems could manage. Ignoring for the moment the fact that some highly bright national-level X-ray sources specifically support aerospace imaging, neutron imaging techniques come to mind: neutrons interact with matter differently and can provide information that is harder to obtain with X-rays.

Phoenix WI are a US-based neutron imaging organisation who have some beautiful images showing ceramic contamination within cooling channels in turbine blades via both X-rays and neutrons:

The manufacturing of jet engine turbine blades is one particular industrial niche for neutron radiography. Turbine blades are cast around ceramic molds which form cooling channels that prevent the blades from melting when exposed to the high temperatures of their operating environments. In manufacturing, fragments of ceramic can clog these cooling channels. A blade with clogged cooling channels could break or even melt while in operation, so such flaws must be rooted out with 100% certainty. The X-ray image (left) cannot clearly depict the cooling channels in a batch of blades; however, the channels show up much clearer in a neutron image of the same batch (right).

X-ray: X-ray images

Neutron: Neutron image

These differences can be made even more clear by using gadolinium as a contrast agent – something that I do routinely in patients, where Gd3+ ions chelated to various other compounds (such as DOTA) form the basis of most contrast agents in MRI because of their paramagnetic properties – by soaking the turbine blade in gadolinium-containing contrast, any (porous) ceramics left behind show up brightly:

Neutron adsorption

This sort of QA informs the manufacturer about how good their QA/QC processes are and how effectively made their turbine blades are. Making jet parts is difficult, they're often at the limit of the material's properties in basically every way at once and the consequences of an unplanned failure in a high-demand environment (e.g. at take-off) can be fatal. Modern radiographic imaging techniques have a lot to offer aviation beyond weld inspection – one of the reasons we've got so much better at building high-performance, fuel-efficient and complex aircraft is because we can prototype everything digitally, model what happens to it, manufacture it to micron tolerances, and then prove that what we have made is what we have modelled and everything ties up. Radiological techniques fill in the bit in between and tie the loop together between design and manufacture.

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