# KE of electrons and X-ray Photon energy

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#1
Hi, according to my textbook (OCR A) when describing what happens with an X-ray tube, the 'energy output of X-rays is less than 1% of the kinetic energy of the incident electrons'.
I'm a bit confused on what they mean here??

To clarify, is it:
- the total X-ray photon energy is 1% of the total kinetic energy of all the electrons incident,
or - the total X-ray photon energy is 1% of the kinetic energy an individual electron incident
Last edited by Revran; 1 year ago
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1 year ago
#2
(Original post by Revran)
Hi, according to my textbook (OCR A) when describing what happens with an X-ray tube, the 'energy output of X-rays is less than 1% of the kinetic energy of the incident electrons'.
I'm a bit confused on what they mean here??

To clarify, is it:
- the total X-ray photon energy is 1% of the total kinetic energy of all the electrons incident,
or - the total X-ray photon energy is 1% of the kinetic energy an individual electron incident
Well I assume it means the energy of each photon is 1% of the incident electron. I don't know how an X-ray tube works but I imagine the incident electron interacts with some atom and that atom emits a photon, which seems to have 1% of the incident energy. I may be wrong though, I don't do ocr so I haven't seen this textbook
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#3
(Original post by DragonsOfAsshai)
Well I assume it means the energy of each photon is 1% of the incident electron. I don't know how an X-ray tube works but I imagine the incident electron interacts with some atom and that atom emits a photon, which seems to have 1% of the incident energy. I may be wrong though, I don't do ocr so I haven't seen this textbook
I see! that's what I thought before with the energies - the next section however talks about the conservation of energy and how the max K.E of an electron = max energy of an X-ray photon, which added to the confusion
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1 year ago
#4
(Original post by Revran)
I see! that's what I thought before with the energies - the next section however talks about the conservation of energy and how the max K.E of an electron = max energy of an X-ray photon, which added to the confusion
That's really weird, not sure what they're getting at tbh
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1 year ago
#5
Have a wee look at the physics section of this https://en.wikipedia.org/wiki/X-ray_tube and the second answer of this https://www.quora.com/Why-are-x-rays...with-the-metal to see how the energy of the x-rays relate to the kinetic energy of the incident electrons and also to energy conservation.
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#6
(Original post by Teenie2)
Have a wee look at the physics section of this https://en.wikipedia.org/wiki/X-ray_tube and the second answer of this https://www.quora.com/Why-are-x-rays...with-the-metal to see how the energy of the x-rays relate to the kinetic energy of the incident electrons and also to energy conservation.
Thanks! still a bit confused though haha since in the wiki section it said,
"Electrons from the cathode collide with the anode material, usually tungsten, molybdenum or copper, and accelerate other electrons, ions and nuclei within the anode material. About 1% of the energy generated is emitted/radiated".

so, does this mean that the total kinetic energies produced from the electrons will have 1% of its energy all transferred as X-ray photons?
(i am aware that one electron will release one X-ray photon as of eV = hf)
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1 year ago
#7
Most of the electrons are absorbed by the target and these electrons' kinetic energy are mostly converted into heat . Of the electrons fired at the target that do produce xrays, about 1% of their kinetic energy is converted into producing xrays. If you consider the size of an electron then relative to the size of the electron the target material is mostly "empty space" with some very small dense nucleii arrayed within it. When an electron is acted upon by the electric field of a dense positive nucleus, then the closer the electron's approach to the nucleus the larger the effect of the field on the electron and the larger the Bremsstrahlung radiation xray emitted. But remember that most of the target is "empty space" and so there are very few "near misses" in comparison to the number of electrons that are barely affected by the pull of the nucleus. So, most of the KE will be changed into heat and only a tiny amount will convert into Xrays.
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