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Q & A: Where do photons come from?

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Most recent answer: 03/02/2014
Q:
My question is about how photons are created I have read that photons are created by an electron orbiting an atom going to a lower energy level, and emitting a photon so as to conserve the energy, and the photon has a corresponding wavelength (or energy) as the distance between the two energy levels but in order to create a gamma ray photon, the electron would have to be at such a high orbit that the nucleus of the atom would be ionized, and the electron would be floating around unattached to the atom. furthermore in the beta decay process that creates a gamma ray, there doesn't appear to be any electron energy level switching going on...so what gives? is the process that creates lower energy photons (moving between energy levels) the same that creates high energy photons such as gamma rays, or is there two processes at work here?
- Travis Borstmayer (age 22)
Calgary, Alberta, Canada
A:

Hi Travis,

As you say, ordinary atomic transitions don't have nearly enough energy to create gamma ray photons. Gamma ray photons tend to be produced during nuclear decays, which can release a lot more energy than electronic transitions. (You can also get gamma ray-photons from some other high-energy processes, like lightning. See the wikipedia page for for more.)

In general, photons can come from a huge variety of sources. Photons are just an excitation of electric and magnetic fields, so all you need is a process to provide energy and a means of converting another form of energy into light. Here are some examples.

Any accelerating electric charge, such as electrons in a wire, radiates light waves.

Another source of photons is from various particle interactions; as particles are destroyed or created, photons can be released as by-products.

Even imploding bubbles in a liquid can create light (see sonoluminescence on wikipedia).

In addition, photons can be split into multiple lower-energy photons, and the energy of a photon can be increased by, for example, bouncing it off of a moving mirror. Light can also gain or lose energy by scattering off atoms or materials in a non-resonant way (think deflected, not absorbed or emitted).

Hope that helps,

David Schmid


(published on 03/02/2014)

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