Correct. That's the insidious thing. Without a device to detect its energy, it's entirely possible not to know radiation is present until it's already begun affecting the body. Many of the scientists who discovered these elements later succumbed to radiation poisoning without understanding what caused it.

[It seems so naive now. But a lot of the prewar world strikes him as naive.]

Where I come from, it's a constant concern. People have developed preventative medications and treatments to help the effects of radiation, and there are devices to filter it out of our water supply. But without such things here, it's better we simply avoid having any exposure, regardless of the source.

[This place is fairly nice. He'd rather it not turn into a second wasteland, with pre-dead residents this time.]