[Murphy] Why does GURPS measure radiation sources in Rads anyway?

[Anthony]

Originally Posted by callen

This really isn't true, though.

It's true for the radiation that's a threat beyond ingestion or skin contact range. GURPS basically normalizes against gamma rays.

[callen]

Originally Posted by Anthony

It's true for the radiation that's a threat beyond ingestion or skin contact range. GURPS basically normalizes against gamma rays.

You have to make some assumptions for this statement to be true. Those assumptions are pretty dependent upon what type of game you're playing. The most common and biggest radiation threats in the game I'm running are neutrons and alpha radiation from fusion and hydrogen plasma in solar winds. None of these are contact-only nor ingestion threats. They're long-range threats.

Chris

[Fred Brackin]

Originally Posted by Lord Carnifex

More seriously, I think this is legacy from 3e, .

Oh no. This is a legacy from 1e. Specifically Space 1e where the first treament of the subject appeared.

On another point, Gurps radiation rules do use gamma radiation as the default. This was established during the playtest for the 4e version of Bio-tech where some types of radiation therapy (like bracytherapy) produce no effective rad dose.

Different pentration for different types of radiation is also discussed on B.436.

It's even whole body gamma rather than sharply directional beams of limited aperture. This normall gets glossed over for the sake of playability though.

So the "standard" for Gurps is the gamma radiation flash from a nuclear weapon used in outer space which probably should effect a mouse and an elephant to a very similar degree.

[Ulzgoroth]

Originally Posted by callen

You have to make some assumptions for this statement to be true. Those assumptions are pretty dependent upon what type of game you're playing. The most common and biggest radiation threats in the game I'm running are neutrons and alpha radiation from fusion and hydrogen plasma in solar winds. None of these are contact-only nor ingestion threats. They're long-range threats.

Chris

Alpha radiation is generally harmless if it comes from outside your body, due to extremely limited penetration.

[callen]

Originally Posted by Ulzgoroth

Alpha radiation is generally harmless if it comes from outside your body, due to extremely limited penetration.

I believe you are referring to alpha particles coming from typical fission reactions. In that case even a few centimeters of air and things like clothing will do a lot. Right? But what happens when the particles are moving at much higher speeds? They penetrate further, especially when there's no air.

Chris

[Anthony]

Originally Posted by callen

Right? But what happens when the particles are moving at much higher speeds?

In the hundreds of MeV they're dangerous penetrating radiation, but you don't get that from fusion, you only get it from various sorts of electromagnetic acceleration, and that mostly produces high energy protons, not alphas.

[callen]

Originally Posted by Anthony

In the hundreds of MeV they're dangerous penetrating radiation, but you don't get that from fusion, you only get it from various sorts of electromagnetic acceleration, and that mostly produces high energy protons, not alphas.

Ah, yes, you're right. The alpha particles in both cases are quite comparable. I had forgotten. Still, aren't the 17.6-MeV neutrons a threat? And aren't the protons and electrons in space a problem (from CME, etc.)?

Chris

[Lord Carnifex]

Originally Posted by callen

Ah, yes, you're right. The alpha particles in both cases are quite comparable. I had forgotten. Still, aren't the 17.6-MeV neutrons a threat? And aren't the protons and electrons in space a problem (from CME, etc.)?

I'm guessing that GURPS assumes that anyone in space exposed to ambient background radiation is either in a suit or a spaceship designed to shield the occupant from this sort of thing. As a GM, I'd probably rule that any character who had any sort of vacuum tolerance also would be appropriately shielded. Anyone in space without a suit, spaceship, or innate vacuum support is probably in enough trouble without worrying about radiation exposure.

Nearby solar flares and whatnot are a different matter, but I'm okay with abstracting them and lumping them in with generic GURPS radiation (high energy gurpsons? Generic Unidirectional Radioactive Particle Spray?)

[Anthony]

Originally Posted by callen

Ah, yes, you're right. The alpha particles in both cases are quite comparable. I had forgotten. Still, aren't the 17.6-MeV neutrons a threat?

Not for solar neutrons in space, they decay into protons long before they reach anything. If you're next to a fusion reactor, sure, but they can pretty much be treated as identical to gamma rays, while different types of shielding are optimal for one vs the other, they're pretty comparable in general behavior.

[callen]

I went back and double-checked. I'm not so sure I was right to accept the lack of threat from roughly 3.5-MeV alpha particles. We need to remember that we're not talking about a few, nor even a few hundred, particles. We're talking about a beam. In my case, with fusion drives, it's quite a beam, too. I'm pretty sure even non-charged particles moving at those speeds, when placed into a beam, would cause serious problems. In the case of alpha particles, they interact strongly with their target, too, much more so than neutral particles do. So the alpha particle beam is actually probably fairly dangerous but shouldn't be treated as radiation damage by GURPS.

Chris