Is this sci-fi premise as absurd as it sounds?

[Eli]

I'm writing a sci-fi story, and while sci-fi isn't necessarily scientifically sound all the time, I'd like to make it close enough so that smart people don't laugh at me for my foolishness.

One of the characters in my story is almost entirely cyborg, except for his central nervous system. The way I wanted to go with this was, because almost none of him is organic, he's practically immune to radiation poisoning. But considering he still has an organic brain and spinal cord, obviously that's not true. My question is, to what extent is this idea flawed? Like, is he LESS vulnerable to the radiation because fewer parts of his body can be damaged? Or does he have just as much a chance of dying (or getting sick) from it as anyone else? Can he stay in a radioactive facility (think Chernobyl) for longer periods of time than a normal person? How can I come off as intelligent as possible without admitting that science fiction is already ridiculous by nature?

 

[vulcan]

He could have some sort of shielding surrounding his brain and spinal column which keeps out the radiation....

 

[LeEeGant]

There's a number of stories which use cyborgs.

So, first thing: the skin and bones actually can take a lot of radiation before the internal structures are affected. They act as a shield to keep the radiation away from the more important parts. If a body is being built to house a brain (and the main nervous system), it would be built to withstand even more radiation than a normal body. It's heavier, so it also need a good power pack to go with it. Since the power pack would probably be nuclear powered (an ounce of uranium or some such, which would keep it going for about 160 or so years), there is probably heavy shielding in place already, so Chernobyl would be very easy to go through, for weeks if not months.

Look up radiation shielding, to get an idea of how good some materials are at absorbing radiation, especially graphite (which is based on carbon).