Is it possible to have a multi-cellular complex organism capable of emitting ionizing radiation and I am not talking about banana I meant intelligent lifeforms that can develop tools also on top of that these species must consume radioactive substances in large quantity without suffering from any side effects and I am not talking about gorilla... and what kind of traits should my species have so that they cannot be harmed by their craving for exotic foods?
Radioactive isotopes generally have the same chemistry as the non-radioactive ones, so all the usual biological processes should be able to work in a world where only radioactive isotopes are available, at least briefly.
To be able to survive with all that internal radiation, start with deinococcus radiodurans — it's only a bacterium, but it has the ability to repair its DNA. That same mechanism could probably work in the cells of a larger creature. You'd also want a fairly fast metabolism to deal with things like replacing all the iron in the blood faster than it turns into cobalt.
So far, this is just a creature that can survive a high radiation environment, but it could easily evolve to depend on the radiation - for example it might require a highly efficient cooling system to handle the heat of radioactive decay, but the same system would cause hypothermia if that heat source was no longer available.