From Wikipedia I read that non-ionizing radiation "does not carry enough energy per quantum (photon energy) to ionize atoms or molecules". https://en.wikipedia.org/wiki/Non-ionizing_radiation#Health_risks

From this I understand that a single photon from said non-ionizing radiation does not have enough energy to cause ionization (an electron to be removed from an atom). Isn't it possible for multiple photons (originating from the radiation source which does not have enough energy per single photon to ionize an atom with the energy of a single photon) to hit an atom (to be more specific to hit a single electron) in such short succession that the combined energy of all those photons causes ionization (when 'combined energy of photons' is greater than the ionization energy of said atom)?

According to this forum post, I quote:

Photons don't have amplitude. All photons of equal frequency have the same energy. Electromagnetic waves with different amplitudes basically consist of different numbers of photons, which is why their energies can depend on amplitude.

So if I understand correctly a wave with the same wavelength and different amplitude has more photons per second being emitted? If so, if we take for example a microwave and increase the amplitude infinitely the probability of enough photons origination from the microwave's radiation source hitting an electron enough times per second in order to ionize it would increase with the amplitude. Would it still (when the number of photons emitted per second increased toward infinity) not be possible for this radiation to cause ionization?

For a real world comparison: let's say the atom being hit with the radiation is a pinata and the photons of the radiation are children hitting the pinata. If a single child doesn't have enough force/energy to destroy the pinata in 1 hit, then the pinata could still be destroyed by a few of the children each hitting the pinata once. If increasing the amplitude translates to more children hitting the pinata in total, wouldn't increasing the amplitude of the microwave radiation result in a higher probability of ionization and eventually result in ionization from this microwave radiation?

I'm clearly misunderstanding some of the core concepts. What am I missing / what about my comparison is wrong?

  • $\begingroup$ @PM2Ring thanks for pointing it out. Should be fixed now $\endgroup$ Jan 20, 2020 at 6:55
  • $\begingroup$ That's a very interesting question! A very similar question appears in the discussion of the photoelectric effect: a beam of low frequency light doesn't have enough energy to create free electrons, regardless of intensity. This question illuminates one reason why quantum theory was necessary. $\endgroup$
    – dk2ax
    Jan 20, 2020 at 15:09

2 Answers 2


Isn't it possible for multiple photons ... to hit an atom

This is possible but has negligible probability. Furthermore, it would have to happen within an extremely brief time window, since after the first hit, the atom would deexcite.

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    $\begingroup$ If I uderstand correctly: So it is theoretically possible but very very unlikely for non-ionizing radiation to cause ionization even when the amplitude is very very high. Could you perhaps give an indication (or a way to estimate such a number) of how high the amplitude of such non-ionizing radiation would have to be in order to have any probability of causing ionization? Thank you! $\endgroup$ Jan 19, 2020 at 21:58
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    $\begingroup$ @Maarten-Monicaforpresident you should consider two numbers: the energy needed for ionization of an atom (typically ~6 volts), and the size of the atom (~2 Angstrom). If the electric field of the non-ionizing radiation reaches levels on the order of 6Volts/2Angstrom = 300 MegaVolts/Centimeter, then you have a decent probability of ionization. $\endgroup$
    – KF Gauss
    Jan 20, 2020 at 16:50

In the general environment of the Earth / where people live generally the density of photons is not high enough to have multiple photons interact with an atom or molecule near-simultaneously and cause an effect (i.e. ionization). However, there are some well known scientific techniques that do rely on multiple photon interactions for example: https://en.m.wikipedia.org/wiki/Two-photon_excitation_microscopy


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