The present disclosure describes a downhole tool that includes an electrically operated radiation generator that selectively outputs radiation to a surrounding environment based at least in part on supply of electrical power; a radiation detector that determines a first radiation metric based at least in part on first radiation measured when the electrically operated radiation generator is outputting radiation and that determines a second radiation metric based at least in part on second radiation measured when the electrically operated radiation generator is not outputting radiation; and a control system that determines whether the surrounding environment is properly shielded based at least in part on a relationship between the first radiation metric and the second radiation metric.