Well, to be fair they were trying to build a microwave emitter as far as I know, and it was supposedly a directed beam, not an expanding sphere. Microwaves: EM radiation, not radioactive decay radiation. The beam wouldn't decay in strength as a result of expanding to uselessness, but rather as a result of interference. Standing behind a wall, for instance, would shield you because microwaves are not very good penetrators. I also seem to see about 5 different methods of emitting harmful rays that the news are claiming they used, so they could actually have been wanting to use radioactive decay as the source. Or x-rays, or microwaves, or something else. In one article they even said "they could not obtain a radiation source" and "using x-rays" in the same article.....you don't need a radiation source to make an x-ray emitter...