In my mind there is no acceptable level-only minimum and maximum levels a human can tolerate .
You absorb radiation from being around other people, from eating foods, and from the ground. Sorry if that is unacceptable to you.
There is a minimum level?
Seeker, you really need to go get informed.
Radiation is all around you ALL THE TIME... its part of the world, and not only that, the UNIVERSE, we live in... Humans did not invent radioactivity, they did DISCOVER it, but it has existed since before the earth cooled and will exist long after its gone.
You are bombarded by radiation your entire life, and your body will be bombarded with it until it rots into dust. There is no such thing as a radiation free existence in nature.