I was watching a program on the History Channel about some ways the earth might end. The last installment I watched examined the possibility that a gamma ray burst from the nearby merger of two black holes might end life on our planet. Certainly a direct hit by such a burst would be a bad day for life here. But one of the claims made on this installment I was very skeptical about. In it it was claimed that the gamma ray burst would cause all canned food to become radioactive. When I heard that, I said, "What!?"

As far as I know the only way to cause an element that is not radioactive to become so is for its nucleus to gain one or more neutrons or protons, and since gamma radiation is high-energy photons, which have neutral charge, I don't see how that could happen, unless those photons were capable of knocking subatomic particles off of the nuclei of the atoms of the food in the cans.

That's the question: can gamma radiation transmute elements into a radioactive form, and if so, how?

• No time to write a real answer. The search term is "photo-activation" and it is very much a thing at high gamma-intensity facilities (bremsstrahlung sources and to a lesser extent in the beam bends for CEBAF or high current, recirculating free electron lasers). – dmckee --- ex-moderator kitten Nov 2 '16 at 20:00
• @dmckee, thanks for the info. I did some reading and came across a process referred to as photodisintegration whereby a high-energy photon strikes a nucleus with an energy > 2MeV for light nuclei like deuterium or 10MeV for heavier elements. There was also an event around the year 774 AD suspected to be a gamma ray burst that produced high amounts of C-14. So it seems a GRB could cause food to become radioactive. The question then becomes, would that increased radioactivity be lethal? Considering the isotopes are those of the lighter element (N, C, O, H), I think not. – BillDOe Nov 3 '16 at 18:35

• The thing they do at sites with very high gamma intensities is design the area to use only those elements that don't off any strong activation reactions. I'm no expert but I believe that mostly involves selecting materials with low $Z$ elements. – dmckee --- ex-moderator kitten Nov 3 '16 at 1:04