Glad you made this comment as I was thinking about this on the way home tonight. I didn't give it much thought this morning through my conjunctivitis infected eyes, but 8 MeV is associated with gamma. What was his photon source, a synchrotron?
A "linear accelerator" (Dark Moon, p. 540). No further information given. In the spectral classification based on wavelength/energy, 8 MeV is well into the gamma band. I.e., the sort of thing where you want to think about substantial thicknesses of steel and concrete to protect yourself while working around it. A 25-rad absorbed dose of this is what Romulus characterizes as, "relatively low levels of radiation," and which he insinuates is the lunar surface environment. Some devices classified as x-ray machines can generate energies above 100 keV, but those are for applications like looking for bombs in shipping containers.
I did a wee bit of poking around after he first mentioned the Groves thing to try to get a handle on the scale of the thing. The first strong hit I got was the Therac series. So, yes -- we are talking a machine capable of killing a human being in a matter of minutes under the right (wrong) conditions.
Its an order of magnitude problem again. If we assume film in a camera on the Moon is getting hit with this kind of insult, then you can wave your hands as hard as you like about the tenuous wisps of atmosphere up where the ISS orbits -- we're still talking LD50 well before the average astronaut stay there ends.
To go back to the naval cannon example our warrior liked, astronauts up there right now might be benefitting from the equivalent of a few sheets of cardboard. It makes no difference whether it is "a couple sheets" or "up to a dozen sheets" when you are facing a 16" shell.
And, yeah, I was seeing papers on "short liniacs" as the bleeding edge but it didn't quite intrigue me enough to face the paywalls.