An exhaustive answer is given above - I'll just add it.
There are several people at the entrance, they are not preoccupied with anything normal. How can they not stop you!
But I found that this can happen less often. To do this, I put the travel card in the inner pocket of my backpack. When I go into the hall, I open a compartment with a card and take it out without haste. The guards do not turn on so actively on the open backpack, and lately, I almost always pass without scanning.
No, it won't. Soft X-rays, which are used to shine through things in airports and the subway, not only do not leave induced radioactivity (that is, the formation of radioactive elements), but does not even light up photographic film. X-rays are harmful to living things that are exposed to them. Now, if you carry a hamster in this backpack, with which you ride the subway, then he has not long to live.
In order for your backpack to become radioactively dangerous, he needs to stay in the core of a nuclear reactor for a long time.