General > General Technical Chat
Those damn 'X' Rays, from Tubes etc..
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pwlps:

--- Quote from: GlennSprigg on April 12, 2020, 11:30:34 am ---Ok... To be honest, I was not initially thinking about any real practical uses for this!  :)
I was simply wondering if say a 11/50kv differential across a pair of 'plates' outside of some SpaceCraft would start radiating uncontrolled X-Rays?? With or without a directly/indirectly radiant heated 'cathode'. I didn't think about Modulating anything for Communications etc!!   ;D

--- End quote ---

Without a heated cathode the current would be much smaller. Yet, as far as I understand X-rays were discovered by Roentgen without a heated cathode ?  I wonder how big was the intensity by today's standards.


--- Quote from: GlennSprigg on April 12, 2020, 11:30:34 am ---Mind you, since reading the interesting comments here, it opens a whole new ballpark. Thank you all !
Now I will have to read about the "ill-fated SSC synchrotron" etc...   8)

--- End quote ---

And here some refs on XFEL:
https://www.xfel.eu/facility/overview/facts_amp_figures/index_eng.html
https://photon-science.desy.de/sites/site_photonscience/content/e62/e189219/e187240/e208351/e187350/felbasics_eng.pdf


jmelson:

--- Quote from: pwlps on April 12, 2020, 03:44:58 pm ---Without a heated cathode the current would be much smaller. Yet, as far as I understand X-rays were discovered by Roentgen without a heated cathode ?  I wonder how big was the intensity by today's standards.

--- End quote ---
Roght, but I guess Roentgen's tubes had a little bit of gas in them, which ionized and provided electrons to get a discharge started.

Jon
jogri:

--- Quote from: coppercone2 on April 12, 2020, 03:13:43 pm ---would you say a tube being used this way for Xray generation is akin to a random noise source?

what does the profile look like (spectral density?)

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What do you mean with "random noise source"? An emitter that has the same intensity over a wide frequency/energy range? That's definitely not the case.

Here is the x-ray spectrum of a tungsten anode @110kV, that picture is from a PTB (national metrology institue of germany) news report (link: https://bit.ly/3c5Tykq). As you can see it really isn't linear as the spectrum accords to Plank's law. The higher the voltage the sharper the peak of the curve (the one that has its maxima at roughly 30kV, not the three smaller peaks) and vice versa. The peaks on the far right come from K-alpha/beta radiation, the ones in the middle from the L-radiation and the ones on the left from M-radiation.
pwlps:

--- Quote from: jogri on April 12, 2020, 04:18:17 pm ---
--- Quote from: coppercone2 on April 12, 2020, 03:13:43 pm ---would you say a tube being used this way for Xray generation is akin to a random noise source?

what does the profile look like (spectral density?)

--- End quote ---

What do you mean with "random noise source"? An emitter that has the same intensity over a wide frequency/energy range? That's definitely not the case.

Here is the x-ray spectrum of a tungsten anode @110kV, that picture is from a PTB (national metrology institue of germany) news report (link: https://bit.ly/3c5Tykq). As you can see it really isn't linear as the spectrum accords to Plank's law. The higher the voltage the sharper the peak of the curve (the one that has its maxima at roughly 30kV, not the three smaller peaks) and vice versa. The peaks on the far right come from K-alpha/beta radiation, the ones in the middle from the L-radiation and the ones on the left from M-radiation.

--- End quote ---

Actually it has nothing to do with the Planck law, for bremsstrahlung radiation profile see e.g.
https://en.wikipedia.org/wiki/Kramers%27_law

jogri:
Yeah, that sentence was rather misleading. What i meant was that the curve for the intensity of the x-ray emissions looks like a spectral radiance curve from a black body radiator (because most people have seen those and kinda know what they look like) but the way i said it makes it look like Planck's law applies to this situation, and that is most definitely not the case.

Props for pointing it out.
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