The energy level at which radiation can be labelled as ionizing is about $10.00-33.85$ eV. This (the $33.85$ eV) is equivalent to $5.423368\cdot 10^{-18}$ Joules. In terms of joules this is a very low energy. How is this ionizing? Is this the energy of a single electron in the radiation, or then how many electrons are there?

  • 1
    $\begingroup$ Where did you get that data? It doesn't seem correct. And what type of radiation are you talking about? $\endgroup$
    – joseph h
    Apr 3, 2022 at 23:23
  • $\begingroup$ Yes, it isn’t many Joules. Which is why atomic physics tends towards using electron Volts. It takes 13.6 eV to remove the electron from a hydrogen atom. And an energetic, liberated electron can cause mor damage elsewhere, disrupting further bonds in biologically important molecules. $\endgroup$
    – Jon Custer
    Apr 4, 2022 at 0:32
  • $\begingroup$ @josephh " The energy of ionizing radiation starts between 10 electronvolts (eV) and 33 eV and extends further up" from wikipedia page on ionizing radiation. to convert from eV to Joules the conversion factor is 1.6022e-19. of course 33eV is the minimum energy of ionizing radiation. the one used in radiation treatment reaches MeV but even so like the 25MeV radiation is only equivalent to 4.005441412e-12 joules. $\endgroup$ Apr 8, 2022 at 23:40

1 Answer 1


Electron volt is a unit of energy per particle. You can think of it as temperature - about 10 thousands deg C per 1 eV.

Particles become harmful if their energy is above 5 eV or so, which is equivalent to ultraviolet light.

Also keep in mind avogadro number, 6e23, number of particles per mol - 18 grams of water. So when you consider energy per particle, multiply that by approximate number of particles involved.

Most chemical reactions only use several eV per reaction. So tens of eV is more than most chemical reactions can provide. So when you see 30 eV, you can think 'thats more energy than burning gasoline, per particle at least'.

Nuclear reactions may have energies of millions of eV per particle.

  • $\begingroup$ thanks for the clear answer, i had this thought too, yet this means it still dependent on the current number of electrons or in this case number of photons right? $\endgroup$ Apr 9, 2022 at 0:25
  • $\begingroup$ @MohamedAbdulraheem no, what you described is energy per 1 particle. You can get to total energy if you multiply by the nunber of particles $\endgroup$ Apr 9, 2022 at 4:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.