The thing is that gamma radiation can be found from many different sources. They could've collected gamma radiation from the sky. Or from their own M-AM reactor!
So, is it that these special
photons must originate from a nuclear fission reactor/reaction? Are dilithium crystals picky about the source of the photon?
SPOCK: If memory serves, there was a dubious flirtation with nuclear fission reactors resulting in toxic side effects. By the beginning of the fusion era, these reactors had been replaced, but at this time, we may be able to find some.
KIRK: I thought you said they were toxic.
SPOCK: We could construct a device to collect their high-energy photons safely. These photons could then be injected into the dilithium chamber, causing crystalline restructure. ...Theoretically.