Radiation shielding

[Anthony]

The most penetrating threat ordinarily encountered is what's called galactic cosmic rays; they don't really behave like any of the three types of nuclear radiation, because they're at very high energy levels (often hundreds of times greater than nuclear radiation). In this case the primary threat is protons and heavier nuclei with energies exceeding about 1 GeV/nucleon. At those energies, the primary interaction with matter is strong force interactions which occur when the particle hits a nucleus in the target or shielding material. Since nuclei are very small, a cosmic ray can pass through a quite substantial amount of matter before being stopped, and when it does stop, it produces a spray of secondary particles which can also have considerable penetration. In general, getting the GCR background in deep space (outside a reasonably strong planetary magnetic field) down to OSHA-legal levels requires about 5 tons per square meter of concrete. Other materials are better or worse shielding depending on the ratio of nucleus size to nucleus area; assuming you could solidify it somehow, a mere 2 tons per square meter of hydrogen would do the job, though in practice it's hard to get much below 4 tons (various plastics) and metals would generally require 6-8 tons.

[Agemegos]

Originally Posted by Anaraxes

That depends a lot on the material. Metals are bad in this regard. Polyester and other plastics are a common modern-day suggestion.

I am thinking in terms of a few metres of methane ice outside the pressure hulls of space stations, and of bulldozing ice over the roofs of surface stations on gas-giant moons. I just don't want to mention it if canon implies that it isn't necessary.

Liquid hydrogen is also pretty good radiation shielding in this regard. Traveller ships certainly haul around vast quantities of the stuff. (We finally know why! It's flushed into jumpspace to get rid of the isotopes with induced radiation :)) Most of the deck plans put the fuel conformally along the hull, which is convenient for this bit of handwaving.

True, but you don't want to put it in a metal tank for that purpose. Charged particle shielding has to go on the outside, then neutron shielding (if you're planning to hang around nuclear explosions, that is), and x-ray/gamma-ray shielding innermost.

I have this idea for ships that they ought to be sheathed in polythene feathers with a good standoff from the true surface, which would act both at Whipple shielding against meteroid impact and intercept charged particle radiation. When something makes a hole, you can "ruffle" the shielding to cover it over.

It occurs to me that most of the crew's time in spent in jumpspace.

Yeah, but the same is not true of people living in orbital habitats or on the surfaces of airless moons.

They're only exposed to cosmic rays during the transition to and from the 100D limit.

Yes, but they may be caught by a solar storm at any time, and they blithely traverse the radiation belts both of habitable planets and (when skimming a gas giant for fuel) gas giants.

[Agemegos]

Originally Posted by Anthony

The most penetrating threat ordinarily encountered is what's called galactic cosmic rays; they don't really behave like any of the three types of nuclear radiation, because they're at very high energy levels (often hundreds of times greater than nuclear radiation). In this case the primary threat is protons and heavier nuclei with energies exceeding about 1 GeV/nucleon. At those energies, the primary interaction with matter is strong force interactions which occur when the particle hits a nucleus in the target or shielding material. Since nuclei are very small, a cosmic ray can pass through a quite substantial amount of matter before being stopped, and when it does stop, it produces a spray of secondary particles which can also have considerable penetration. In general, getting the GCR background in deep space (outside a reasonably strong planetary magnetic field) down to OSHA-legal levels requires about 5 tons per square meter of concrete. Other materials are better or worse shielding depending on the ratio of nucleus size to nucleus area; assuming you could solidify it somehow, a mere 2 tons per square meter of hydrogen would do the job, though in practice it's hard to get much below 4 tons (various plastics) and metals would generally require 6-8 tons.

Interesting. Four tonnes per square metre of methane ice would amount to a layer about eight metres thick, wouldn't it?

[far_trader]

Originally Posted by Brett

I am thinking in terms of a few metres of methane ice outside the pressure hulls of space stations, and of bulldozing ice over the roofs of surface stations on gas-giant moons. I just don't want to mention it if canon implies that it isn't necessary.

Canon seems to imply it's not required, at least for hull material at the appropriate TL. For ships and small craft. Though it might be interpreted as part of the properties of the power plant (iirc, some vague CT recall of radiation exposure danger if you run out of power, not sure though).

That said, it would be a good idea, especially where such material is cheap and abundant and easy to use, as either a backup (for if the power fails) or simply to cut costs.

[hcobb]

Originally Posted by far_trader

Canon seems to imply it's not required, at least for hull material at the appropriate TL. For ships and small craft. Though it might be interpreted as part of the properties of the power plant (iirc, some vague CT recall of radiation exposure danger if you run out of power, not sure though).

I.e. the incoming radiation goes wherever the waste heat from your power plant winds up...

[far_trader]

Originally Posted by hcobb

I.e. the incoming radiation goes wherever the waste heat from your power plant winds up...

Yup :-D

(obligatory superfluous characters for post minimum, they're probably for waste heat and radiation control too ;-) )

Well, actually I was thinking artificially generated magnetic shielding, but a subspace soak works too.

[Anaraxes]

ought to be sheathed in polythene feathers

Now I have go to stat up the Zhodani Bird of Prey.

For habitats, I'd stick with the methane ice. No matter how the starships deal with the problem, if you gots tons of ice handy, might as well use it. It's simple and cheap.

[thrash]

Originally Posted by far_trader

Canon seems to imply it's not required, at least for hull material at the appropriate TL. For ships and small craft. Though it might be interpreted as part of the properties of the power plant (iirc, some vague CT recall of radiation exposure danger if you run out of power, not sure though).

Can't find the quote in a quick search, but it's a throwaway remark that the ship is protected from radiation during gas giant skimming as long as the maneuver drive doesn't fail. It may be in Beltstrike or Tarsus, or one of the equally obscure CT sources.

Maybe someone with the CT CD-ROM can turn it up more quickly?

[martinl]

Originally Posted by Brett

I have this idea for ships that they ought to be sheathed in polythene feathers with a good standoff from the true surface, which would act both at Whipple shielding against meteroid impact and intercept charged particle radiation. When something makes a hole, you can "ruffle" the shielding to cover it over.

That is an awesome setting detail. Totally divergent from any previous hard sci-fi I've encountered, hard science, visibly evocative, and weird.

Kudos.