Radiation shielding and redirecting

[mfb]

the idea was not so much to generate enough power to make it a viable energy source as it was to make shielding more effective. my thought was that maybe by converting a portion of the energy into electricity, you could minimize the energy that carries through as damage.

I know - but it doesn't do that, as I explained. It won't even be neutral. It will make shielding worse because now the shielding can't just be effective with shielding, it must also allow extracting energy that would otherwise become heat.

 

[camondascia84]

But the prime objective would be to attenuate the incident energy. You are suggesting the equivalent of having an electrical generator coupled to the inertial reel of car seat belts to use some of the energy from a car crash to help charge the battery The cost (and payload) involved with the extra 'energy harvesting' system would really be a waste of time when the overwhelming need is for screening. Moreover, weight for weight, the screening would probably be less.

the difference being that seat belt systems are not made of a hundred pounds of lead. and if they WERE, auto companies might think such a system could be worth it if it only weighed a few pounds... I thought the main objective here was to find any way to reduce the need for such drastic shielding even if by only a small amount... or are we only interested if it is a complete and perfect solution? also any argument that only relies on the limitations of modern materials should fall flat on its face. these days science is finding new materials with new properties, all the time.

 

[sophiecentaur]

by only a small amount...

I can't see where you are trying to go with this.
I'm afraid that "a small amount" could be anything. Have you actually calculated how much energy is involved? You do not seem to have taken on board that an energy conversion system will have less shielding effect, per kilo of payload, than a specific screening system. It will be many generations of spaceflight before payload is not a very high priority (the second priority after biological safety.
My example of a seat belt reel was aimed at the present seatbelt design. If there were a large mass that was occasionally brought to a halt then energy harvesting could be worth while. We already use regen braking, so it is worth it but that's because the numbers are appropriate - it's called Engineering.
There is nothing in principle against getting electrical power from radiation but when the quantity is so small and the need for screening so great that there is no significance in your "small amount".

 

[camondascia84]

I can't see where you are trying to go with this.
I'm afraid that "a small amount" could be anything. Have you actually calculated how much energy is involved? You do not seem to have taken on board that an energy conversion system will have less shielding effect, per kilo of payload, than a specific screening system. It will be many generations of spaceflight before payload is not a very high priority (the second priority after biological safety.
My example of a seat belt reel was aimed at the present seatbelt design. If there were a large mass that was occasionally brought to a halt then energy harvesting could be worth while. We already use regen braking, so it is worth it but that's because the numbers are appropriate - it's called Engineering.
There is nothing in principle against getting electrical power from radiation but when the quantity is so small and the need for screening so great that there is no significance in your "small amount".

sigh... do i have to repeat myself every single time i post? all this was suggested to do is slightly reduce the strain on the actual shielding. it was never suggested as a complete solution nor as more than a different way to absorb energy that would otherwise have to be absorbed by shielding. radiation that is turned into electricity would not turn into heat. even a small increment of damage that the shielding does not have to take should be worth looking into. for all you know this could be implemented with a simple coat of currently unknown paint.
but instead, you would rather decide that what you know is definite. i was under the impression that the thing that makes us scholars is our understanding of what we DO NOT know. for gods sake, Ben Franklin KNEW electricity was a liquid... and because such a learned man said so and had "verifiable evidence" many scientists of the time agreed with him.

 

[phinds]

... all this was suggested to do is slightly reduce the strain on the actual shielding.

And you keep ignoring repeated statements that it will NOT reduce the strain on the actual shielding unless you increase the total mass involved, which makes it not a good idea.

 

[camondascia84]

And you keep ignoring repeated statements that it will NOT reduce the strain on the actual shielding unless you increase the total mass involved, which makes it not a good idea.

you've tried this have you? isn't that what science is about? testing things before we are absolutely certain of them? we do not know everything about everything. and it is those unknown discoveries that make science so wonderful. because we are still trying to figure out what is out there. we can run test after test. but until you try everything, you cannot be certain. try to keep an open mind. i cannot say it enough, materials science is making new findings all the time.

 

[sophiecentaur]

isn't that what science is about?

You aren't talking Science; you are talking ignorance of Engineering and Technology. What possible sort of system are you actually proposing that would be 'better' than lead / concrete or some other dense substance and which would make good use of the small amount of power that is carried by the cosmic rays? What sort of "strain" are you suggesting that the screening material is subjected to?

You are in the land of 'Wouldn't it be nice if', which has a rich supply of Unobtainium. Pretty much nonsense all round, I'm afraid. To follow PF rules you need to cite some evidence to support your ideas. Do you have a single credible reference to this?

 

[mfb]

To shield against radiation you need some material that converts the ionizing radiation to several low-energy particles. Once you have done this the radiation is not harmful any more.
To extract energy from radiation you need some material that converts the ionizing radiation to several low-energy particles and some additional material to use these low-energy particles. While this additional material can also do the initial conversion it won't be better in it (otherwise you would use it everywhere). Harvesting the energy cannot improve overall shielding because it is a step that happens downstream. In practice it will get worse because you are more limited in the material choice for some elements.

To make it worse: If you don't plan to extract energy you can just use any bulk material, stopping everything in the material. If you plan to extract energy you need to make sure the particles reach your setup. You are more limited in the material choice here as well and you need a more complex geometry. Your shielding will be worse.

 

[DBO]

X-ray optics just happens to be my field and by extension, gamma ray optics. Short answer about redirecting very short wavelength radiation.....Its really hard but not impossible. For most such energies, reflectivities are so low that you effectively just absorb the radiation. You could do it by reflecting at extreme grazing incidence with reflectivity of .999 and use hundreds of reflections, say 200 reflections at .01 degree or 2 degrees deflection. Still.999 to the 200th power is .81 meaning you've absorbed 19% just deflecting 2 degrees. Now try deflecting 180 degrees (around an object) and you get 1.5e-9 meaning you've absorbed all of it.

 

[Nik_2213]

IMHO, DBO's totally called it on the 'shadow angle'. An absorbing or grazing incidence system set out on a long pylon like the ultimate 'selfie stick' some-what shelters you from that one narrow vector.

Which, IIRC, is where those 'classic' inter-planetary rocket designs, their NERVA-ish nuclear engine and hab separated by a v-e-r-y--l-o-n-g trellis spine, got their start. Think '2001' book/movie and the 'Discovery-1'. They were more interested in minimising their neutron shield's mass, but same 'shadow angle' geometry applies...

Now, if you face multiple radiation sources from very predictable directions, I suppose you could have multiple 'selfie-sticks'. Even if you cross-tie those masts for stability, per 'Tall Ships' rigging, it soon gets a bit unwieldy, a tad wibbly. And, surely, there's a break-even point where, instead of multiple minimal shields on flimsy pylons, makes more sense to keep all that mass closer to the hab, mounted such it won't wibble at the least delta-V...

Bad news, you'd probably do better building a near-spherical bunker of asteroidal slag or, if beyond the ice-line, ice. Think 'swimming pool reactor', but inside-out. Extra thickness between you and your reactor, of course, of course. Requisite mass-haul hurts...

IMHO, if you want a 'force field-ish' whatsit that can efficiently 'steer' such high energy photons, it's probably related to the 'confinement system' around your 'Mr. Fusion Home Energy Reactor'. Requiring multiple major theory and tech advances, that's likely to remain hypothetical for a good while...
;-(

 

[DBO]

unfortunately, the most x-ray and gamma ray reflective materials are high Z and high density materials such as gold or Tungsten, etc. Because the number of reflections to direct a beam around an object is so high, the total absorption is also very high. You are better of using normal lead absorbers.
This is not a foolish question as I was paid in 1986 t do a study of the use of reflective materials to protect US satellites from a "hypothetical" Soviet nuclear pumped x-ray laser emitting a nominal 1 KeV beam with power density of 10E14 s/cm2 at a distance of 1000 Km. It was a $50,000 6 month program.
Here is my study. Assume a reflectivity of 99% meaning it absorbs 1%. This means it absorbs 10E13 watts/Cm2 of 1 KeV radiation in a time of 50 nanoseconds. Answer: No, no material will withstand that power density in 50 nS
I spent th remaining $49,000 becoming an expert on high heat load x-ray mirrors.

 

[DBO]

OOOps, should have been 10E14 watts/cm2 incident then 10E12 watts/cm2 is absorbed.
BTW, just out of interest, index of refraction for x and gammas is less than 1 and has a major imaginary part corsponding to absorption.

 

[bahamagreen]

To the degree that the exposure problem comprises mechanical damage impairing the functionality of genetic molecules, seeing that the human genome project is way ahead of schedule, and anticipating nanobots, the long term solution may be biological intervention rather than shielding.

The way forward may be to allow an otherwise lethal count of gamma ray passage through the astronauts; then mitigate the damage incurred to the genetic molecules continuously, repaired by the nanobots propagated, stationed, and operating together within every cell nucleus...?

 

[marcusl]

And now we’ve come full circle from one sci-fi fantasy to another.

 

[berkeman]

And now we’ve come full circle from one sci-fi fantasy to another.

Agreed. This is a good time to tie off this thread.