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

[vicky_molokh]

Greetings, all!

Noticed a bug:
A quick pulse of radiation, shaped as a typical beam (i.e. non-AE, non-Cone Tox Innate Attack modified to deal Rad damage) hits a target. The beam doesn't have enough power to penetrate the target completely, and is absorbed fully. Now, look at two different situations: (1) target is a mouse, weighting less than a kg; (2) target is a whale. How does it happen that in both cases they get the same number of Rads?

Thanks in advance!

[lexington]

Rad damage should probably scale with HP like various other things do.

[Blind Mapmaker]

I have no idea why the radiation rules use Rads. Gray and Sievert wouldn't have added much more complication. They could have even used "effective Sievert" if they really wanted to avoid using another unit.

As for the mouse and whale problem, dividing by HP/10 would probably be the most reasonable course. Beams are pretty easy though. Hit that mouse and that whale with a big cone and things would get even more complicated. I don't think just getting barely hit by the cone should give you the same dose as standing right in the middle of the blast, but I guess that's how it works by RAW.

[vierasmarius]

Part of the problem is that Rads are discrete units. A less massive creature would absorb fewer from a single exposure, but would also feel the same effects from a much smaller dose. You could multiply Rads by HP/10, but you'd also have to multiply all the thresholds by the same value. It might be best to treat radiation dosage as "Virtual Rads", ie a theoretical radiation dose normalized to the human body mass. So 200 rads to a mouse, a human, and an elephant would represent different amounts of energy, but equivalent dosage in comparison to body mass.

But then, that's what Sieverts are, isn't it?

[Anthony]

Originally Posted by vicky_molokh

Now, look at two different situations: (1) target is a mouse, weighting less than a kg; (2) target is a whale. How does it happen that in both cases they get the same number of Rads?

Most radiation is fairly penetrating, so most of it goes through the mouse. In practice, the penetration is probably less than the thickness of the whale so a whale would take a lower dose, but that could be handled by radiation resistance, most modest size critters will take the same dose.

[Nosforontu]

Originally Posted by Blind Mapmaker

I have no idea why the radiation rules use Rads. Gray and Sievert wouldn't have added much more complication. They could have even used "effective Sievert" if they really wanted to avoid using another unit.

Probably because Gray and Sievert are not terms that a lay person are familiar with while rads are a fairly commonly known term.

[Flyndaran]

Most people have heard the word, "rad", but that doesn't mean they know what it means. I know that I forget.

[Lord Carnifex]

Having grown up in the '80s, I'm comfortable working in rads <grin>.

More seriously, I think this is legacy from 3e, which established measuring radiation in rads. At that time, it made sense because characters were more commonly assumed to be humans. Also, using rads allowed standardized measurement and comparison of sources. So if one was standing at ground zero of a smallish nuclear event, one would receive x rads. If the event were twice as large, one would receive 2x rads. The focus was on the source, not the character. I suppose wit the change to a greater character focus in 4e might have spurred a change to siverts, but I guess that was overlooked.

Linking effective exposure levels to HP makes sense to me, if it's worth nitpicking over.

[Blind Mapmaker]

I haven't heard of rad outside of GURPS and browsing wikipedia, but then we hardly did anything interesting in highschool physics.

With the ongoing reporting about Fukushima I would say the average person is now more familiar with sievert and the fact that once you drop the milli-prefix things start getting not so nice.

Anyway, rads are easily convertible and I guess it was easier to write 10 rad than 0.1 Gray.

[callen]

What would probably work best would be to start based on particle number and kinetic energy, scaled based on severity of the type (alpha is much worse than gamma for the same dosage). Take this value of some sort and compare it to the size of the target to determine the results. I'm not going to try to figure this out, though.

Originally Posted by Anthony

Most radiation is fairly penetrating

This really isn't true, though. For example, proton beam therapy specifically takes advantage of the heavy absorption at the surface. Alpha particles from radioactive decay have quite minimal penetration, too. Meanwhile gamma particles from radioactive decay penetrate extremely well. Overall there is a huge amount of variation.

Chris