How can gamma rays affect a human body if they can move through atoms without colliding with them? I found this answer on this SE about why mirrors don't reflect gamma rays, and the answer says that it is because gamma rays are so, so small that they "see mostly empty space between the atoms of the solid.".
If that is true, so gamma rays can move through atoms without colliding with them, why can gamma rays affect people enough that they are said to be dangerous? If they are so small, that would mean it's very unlikely for a gamma ray to accidentally touch an atom, so it would be a very rare situation, which the body should be able to fix without problems due to it's unlikeliness, right?
 A: Based on your question: Yes, it is extremely unlikely that a gamma ray will hit an atom; however, Avogadro's number ($N_A$) is large: there are many atoms in your body, so it is likely it will interact.
Also: a single gamma interaction is not a problem, but for any appreciable source, there are many gamma rays. For instance, where I work we have a 20,000 Ci cobalt-60 source--that's $7.4\times 10^{14}$ decays per second, and there are about two gammas per decay (about 1.2 and 1.1 MeV, respectively).
Moreover, when a gamma ray interacts with tissue, by the photoelectric effect (low energy), then Compton scattering (at medium energy), and pair production (at high energy), the scattered electron interacts with many atoms before coming to rest.
The aforementioned source could dump several hundreds of Watts of power into your tissue, destroying most of your cells--the lethal exposure time is a few seconds. (Luckily, the shielding container is about 16 in feet diameter)
A: It's like this bro, if you look down a perfectly repeating crystal lattice at the top, you will see little holes depending on the packing structure, through which the gamma rays will just pass through the but if you align the nuclei, and have a long enough Crystal, and you turn it a very small degree the holes will close and one nucleus Center will be very close behind but just very small angle from being perfectly behind the one just before it. So if you have a really really long crystal, theoretically, gamma rays will be hitting the nuclei in that crystal lattice more frequently than if you just had it straight on, or something like this?
