My textbook states that: Henry Moseley found using x-rays that the atomic number of each element has a characteristic positive charge.

I don't know much about x-rays and can't find an answer online or elsewhere. How does this technique work ?

My thoughts are that maybe all protons emit x-ray photons at the same frequency and rate. If this is true then some kind of x-ray detector could be used to detect the energy at that x-ray frequency that a nucleus emits. The number of protons could then be calculated. I could be way off here.

Can someone explain how x-rays can be used to count the number of protons in a nucleus?

  • 2
    $\begingroup$ See Wikipedia article Moseley's law $\endgroup$
    – MaxW
    Commented Nov 28, 2020 at 19:34

1 Answer 1


X-rays are not emitted by protons. They are emitted by atomic electrons when they fall down from an upper orbit (or level) to another one near the nucleus. Of course the electrons have first to be excited (= sent to this highly excited level). But whatever the way of exciting the electron, the energy of the transition corresponding to the return to the lowest level is proportional to the number of protons in the nucleus. If you are able to measure the energy of the emitted X-ray produced during this transition (or fall), you can calculate the number of protons of the nucleus. I am sorry. I have used a rather simple language. Pure theorists will prefer using a better vocabulary, which may not have been understood by Kantura. I may be wrong.


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