It's actually pretty normal for most food to get irradiated if it's going into a warehouse. It's good at killing bacteria. That's the only reasonable reason I can think of why the shrimp has this kind of contamination.

But like normally it's a sealed source of radioactive material that's just in the same room or maybe an x-ray gun or something. The crates of food often aren't even opened since radiation will punch straight through cardboard or wood or whatever. I have no idea what was going on for cesium-137 to end up in the shrimp. Or why cesium 137 was used in the first place because I've only ever heard of cobalt-60 being used for this

(I do chemical stuff in warehouses)