Comment by numpad0
14 days ago
Can't it be done with a DLP device? CRT was X-ray projection device with phosphor paint applied inside to convert the rays to visible light.
14 days ago
Can't it be done with a DLP device? CRT was X-ray projection device with phosphor paint applied inside to convert the rays to visible light.
CRTs were emitting an electron beam to draw images on a phosphorescent screen, not emitting X-rays: https://en.wikipedia.org/wiki/Cathode-ray_tube Blasting X-rays through a screen to the face of an observer would not have been a good idea…
X-rays are mentioned 28 times in the Wikipedia link about CRTs, https://en.wikipedia.org/wiki/Cathode-ray_tube
Although X-rays are not used to draw the image, they are generated as an unwanted side effect. The phosphorescent screen emits X-rays when struck by the electron beam. To protect the user, the glass must be a special kind of glass to absorb those X-rays, and the accelerator voltage has to be set not too high.
> X-rays are mentioned 28 times in the Wikipedia link about CRTs, https://en.wikipedia.org/wiki/Cathode-ray_tube
CTRL-F for "X-ray" gives me 1 result, "-ray" gives me 13 results ;)
Absolutely agree that X-Rays are generated in the phosphorent screen, but they are not emitted by the CRT.
> […] and the accelerator voltage has to be set not too high.
Yes, with electrons only so high that they reach the screen, which is low enough to only generate very minor secondary X-rays in the screen, which is then nicely shielded. If the phosphorous screen would be blasted with X-rays, the shielding of the screen would need to be much thicker and expensive.
(I’m working with shielded microCT machines, so speaking with a bit of experience)
Interestingly, a lot of folks used to repeat the x-ray thing, that's where the term "eyeball cancer machine" came from.
Well... Technically we spent a lot of time looking down the barrel of a particle accelerator...
2 replies →
Ask the Therac-25 patients if the difference between electron beans and X-rays is important
The difference is important in the case of a CRT screen, and less important in the case of cancer treatment with Therac-25.
CRTs produce a (low-intensity) electron beam that has just high enough energy for exciting the phosphorous screen.
Therac-25 was able to produce both a high-intensity electron beam or an X-ray beam, depending on the therapy need.