Fine, if we are going to scrutinise everything in a 'game' and wonder how it works according to real-world physics..
How does the plasma pistol/rifle work.
How does a pill cure radiation poisoning.
How do Mr Gutsy's/handy's float for hundreds of years without any visible gas tank. (let alone one that would contain enough fuel to last for centuries)
I think it's safe to say that there are a lot of things in this 'game' that when compared to physical reality are complete nonsense.
The problem with these arguments is that people seem to focus too much on comparison with reality, when of course its just a game, a game that is NOT based on our reality..
Thanks, Doom.
Plasma contained in a magnetic field then projected at the target. The better question is how that magnetic field sustains itself away from the weapon. Pre-War tech comes from a technological Golden Age based on "Science!" instead of science, so it is simply too advanced for us to comprehend.
To be fair, Rad Away is a fluid, and the in-game dialogue suggests that it "flushes out" the radioactive particles and probably kills cancerous cells/tumors. Rad-X is a pill that simply makes the body absorb less radiation, I imagine. Again, Golden Age Science! is at work here.
As valkebus says, Gutsies and Handies are nuclear powered, like nearly all devices in the Fallout universe. Remember, Science! The Pre-War world created nuclear fission batteries smaller than a man's fist. One of those could potentially power a robot, chainsaw, or ripper for centuries, if not thousands of years.