Neutrons are emitted only during an active fission process, such as that taking place in a nuclear reactor or at the actual moment of an atomic explosion. Neutron activation that is structurally significant takes many years, and is only a concern in materials that will be used to construct things like nuclear reactor vessels. This is in no way a concern when choosing structural material for a shelter.
It isn't hysteria, and GMO isn't 'evolution'. One of the biggest issues for preppers and survival is that GMO seeds will not reproduce in the same way if the seeds are saved and re-used. In fact, in many instances (maybe all?), it's illegal to save the seeds and re-use them! It's far better to track down heirloom seeds that are native to your area and/or compatible with your climate. A good place to start looking is