Ngineer said:
Can you please elaborate on that assumption? Do all gamma rays consist of just one photon?
Usually when discussing "gamma ray" interactions with atoms, the "gamma ray" consists of an individual photon per interaction.
Even when dealing with lower energy light rays, if the question went something like, "an excited electron spontaneously falls to an intermediate energy state before falling to the ground state," the implication here is that there are two photons produced, one for each interaction of the electron changing states. Each individual interaction (of a charged particle, like an electron bound to an atom) involves a corresponding, single photon. [Edit: I suppose there might be situations where an atom releases a pair of entangled photons, but still, this has implications that greatly differ from a single photon at twice the energy. See below.]
In this problem it reads, "a high energy gamma ray with wavelength 1 nm is absorbed by atom 'X'. Immediately following this interaction [...]" The implication here is that there is a single photon related interaction, implying a single gamma ray photon is absorbed by the atom (exciting something or other within the atom), before a subsequent reaction takes place involving the x-ray (also a single photon) and the ejected electron.
Particularly when talking about high energy gamma rays, you should at least be prepared, when in doubt, to make the assumption that a "gamma ray" means a single, high energy photon.
As a matter of fact, that's pretty much the crux of quantum principles: Things happen in individual chunks. An atom absorbing a single photon of energy
E might produce some interesting result (such as ejecting an electron and a lower energy photon). However, the interesting result would
not happen if instead the atom simultaneously absorbed two photons of energy
E/2, even though the total energy is the same. That's the fascinating result discovered by Albert Einstein in his 1905 paper on the photoelectric effect (one of a few of his groundbreaking papers published that year), which is also the origin of the
E = hf equation.*
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All that said, the million dollar question: should you talk to your professor about it? I don't know. I'll leave that up to you. The implication is pretty strong in this case that the question here is talking about a single photon. However, if the question was something like, "a light ray strikes a refractive material with an index of refraction of 1.2. What is the angle of refraction?" that would not necessarily imply a single photon (however in that case there's no implication of a single, atomic-level event). If you got dinged pretty bad and you want to argue the case that you misunderstood the problem's single photon implication, you might get some credit back. Maybe. But I wouldn't hold your breath. It's up to you and your professor.
*[Edit: Although back in 1905, they were not called "photons." That term didn't come into use until much later. If I remember correctly, Einstein called them "corpuscles" or some such. The discrete
packets of energy quality about them though was quite clear in his paper.]
