8MeV is the "intensity," but what was the duration?

I assume it's expected to be inferred from the given dosages: 25, 50, and 100 rem. Since all three exposures were using the 8 MeV x-ray emitter, we must assume dosage was varied by varying the exposure duration. In any case, his x-ray energy is three orders of magnitude higher than ambient cislunar. That alone invalidates the experiment.