I've read from several sources that electromagnetic radiation begins to have an "ionizing" effect right around the time the frequency passes the uv spectrum and into x-ray/gamma ray spectrum. [1] [2] [3]
The reasoning given for this is that the higher frequency waves contain more energy, enough to tear apart molecular bonds.
When I compare this to sound waves it makes sense because high pitched sounds are more damaging to human ears than low pitched sounds are. [4]
However just because a high pitched sound may cause you to go deaf more easily, this doesn't mean my ears would enjoy standing 3 feet away from a 12,000-watt sub-woofer playing a low pitched sound.
In other words, I understand high-frequency waves contain more energy by nature, but if you ramp up the amplitude of the low-frequency waves they can start to do harm too.
So with electromagnetic radiation is there a point that I could say produce infrared waves that would also be ionizing? Or is there something that is inherently different about high-frequency em waves that cause the ionizing effect?
Answer
Background:
Einstein's photoelectric effect theory won him the Nobel prize, and it relates very closely to this. Although it's different from photoionisation, it relies on similar ideas.
His proposition: each atom will absorb the energy of one photon, and the energy of a photon is given by $$E=h\nu$$where $h$ is Plank's constant, a really, really tiny number ($6.62607004 × 10^{-34} m^2 kg / s$), and $\nu$ is frequency of the light. Higher intensity light, which is analogous to wave amplitude, contains more photons, but the energy of each photon is the same for a given frequency.
If I shine low-frequency high-intensity light on a surface, there's plenty of energy, but each atom, upon absorbing one photon, won't be able to lose an electron. However, if I shine high-frequency light, even if the intensity is low, each atom which absorbs a photon will be able to loose an electron, and we see ionization.
But when the intensity is high enough, even low frequencies will cause ionization.
This phenomenon, called multi-photon ionization, occurs when the atom absorbs more than one photon. It's usually pretty rare, because an atom frequently emits the other photons before it absorbs enough energy totally, but at very high enough intensities, it's appreciable.
Sound works differently in air: we generally don't say it's quantized in the same way, although if you examine it more minutely, you'll see that it can be quantized as phonons, which aren't evident in gases. But that's not relevant to your question, it's just something to keep in mind if you want to generalize a bit more by discussing sound in condensed matter.
Oddly enough, the parallel to sound and hearing loss is wrong! See this Biology SE question... high-frequency sounds are dangerous not particularly because they have more energy (which they do, see the equation for sound energy in a container), but because of the nature of the human ear and the alignment of hairs in it.
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