Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Hannah LS on 12/12/2018 10:50:08
-
A school class ask:
We've been tasked with the assignment of resolving a physical or social problem astronauts encounter in space. We would like your input on our project and possible solution...
Gamma radiation from the sun is a huge problem faced in outer space that greatly deteriorates the human body. Our solution to this problem is designing and constructing a wall that maintains the growth of Chaga mushrooms (radiation-eating fungi) and build it into the ISS. Water pouches will be designed to be used manually for hydrating the mushrooms. The outer-most component of the wall will be made of silica tiles, the material space ships are already constructed of, and lined lead to further limit the presence of radiation. Our “wall” will be constructed into the US Lab and Columbus section of the ISS, which our team designed to rotate in a manner that will always face towards the direction of the sun.
What do you think?
-
It is conceivable that chaga mushrooms may absorb and concentrate radioactive heavy metals in the soil, just like Brazil nuts, but they can't "eat radiation" in the sense of absorbing gamma radiation from a distant source, any better than any other material.
Lead is OK for absorbing gamma radiation but at high energies (above 100 keV) it is the mass of material rather than its atomic number that determines the effectiveness of a gamma shield, so you may as well use a structural material like steel, which can serve two purposes, The silica tiles will mop up most of the low energy gamma and charged particle radiation.
Neutrons will happily penetrate silica and steel, but are strongly absorbed by hydrogen so an inner layer of water or polyethylene would be useful.
-
Neutrons are not much of a problem in space.
Once you are a few times 10.3 light minutes away from everything there aren't many neutrons.
-
True, but the interest is in stuff, not space, and the most interesting stuff is close to neutron sources!
-
It is conceivable that chaga mushrooms may absorb and concentrate radioactive heavy metals in the soil, just like Brazil nuts, but they can't "eat radiation" in the sense of absorbing gamma radiation from a distant source, any better than any other material ...
Fungi may not block ionizing-radiation better than similar material, but apparently some can use it as an energy-source ...
https://en.wikipedia.org/wiki/Radiotrophic_fungus
-
I've just been intrigued by the ability of common edible mushrooms to synthesise vitamin D with ultraviolet irradiation.
-
True, but the interest is in stuff, not space, and the most interesting stuff is close to neutron sources!
Most of the dose is accrued while in transit to the interesting stuff.
Once you are somewhere really interesting you might be able to hide behind an atmosphere.
-
The idea of taking your own atmosphere to Mars is intriguing. Mars is about 12 - 15 light-minutes from the sun. The half-life of a free neutron is about 10 minutes, so there will be plenty arriving at the surface.
-
Mars is about 12 - 15 light-minutes from the sun. The half-life of a free neutron is about 10 minutes, so there will be plenty arriving at the surface.
Neutrons are emitted in nuclear fission (from decay of heavy radioactive elements on the surface of Mars, for example).
However, the form of nuclear fusion in the Sun:
- Occurs in the core; radiation emitted in the core is well-shielded by the surrounding layers of the Sun
- Does not release neutrons, but primarily releases gamma rays and positrons (which have a very short range in the dense core) plus neutrinos, which don't interact with the Sun (or us, to any measurable extent).
See: https://en.wikipedia.org/wiki/Nuclear_fusion#Nuclear_fusion_in_stars
-
There's no obvious reason why another planet would do a better job of producing neutrons than ours does nd, of course, a lot of the neutrons that are formed here are absorbed by the rocks before they reach the surface.
There's a small neutron flux from spallation in the upper atmosphere
https://en.wikipedia.org/wiki/Background_radiation#Neutron_background
-
Googling "solar neutrons" produces several papers explaining not only how they are formed in the solar photosphere, but also how their flux has been measured.
-
Googling "solar neutrons"
This is a free paper on the subject: https://www.sciencedirect.com/science/article/pii/S1384107614001936
Neutrons < 200MeV don't make it through the Earth's atmosphere.
- However, Mars has a much thinner atmosphere (1% of Earth), so lower-energy neutrons will make it to ground level
Fortunately, most neutrons produced in solar flares collide with protons in the outer solar atmosphere to produce deuterium, releasing gamma rays with a characteristic spectrum.
-
So we are agreed, then, that a spacecraft or habitation on a Mars-like planet, should have a neutron shield. The question is whether a wall of mushrooms and moist, sterilised horse dung is preferable to an inch of polyethylene. I guess it depends on whether you are a farmer or an engineer.
-
If you are going to shield from fast neutrons do it right.
Polythene will moderate them quite well- though an inch just isn't enough: the halving thickness for 4MeV neutrons is about 2 1/2 inches (6.6 cm) . They use a few inches for neutron detectors. Bonner spheres are the size of bowling balls for a reason.
Neither carbon, nor hydrogen has a good capture cross section for absorbtion.
So polythene will not absorb neutrons.
If all you plan to do is moderate the neutrons then the easy way is to hide behind the water tank (you were planning to take water with you, right?).
That means that the travellers are hit by slow neutrons- which is only a marginal improvement.
So, you still need an actual neutron trap.
Chlorine's quite good. Boron is better. If you have the sort of money that goes into making spacecraft then gadolinium is excellent.
On a practical, basis using PVC for some structural things might be a good idea.
So, we are agreed, any ship that is going to spend time in deep space doesn't really need a neutron shield- because the cosmic ray shield will afford adequate shielding by default (On an inch by inch comparison, lead is as good as polythene. Water, of which you will have plenty, is slightly better). If there's a good reason to have some of that water trapped in mushrooms then it will still act as a shield, but the mushrooms will suffer radiation damage.
If you are on a planet, dig a deep hole and live in that (unless there's a thick atmosphere).
If the rock of the planet is so radioactive that living in a cave offers a higher radiation dose than living on the surface then you should probably pick a different planet
-
B10 is a good absorber for thermal neutrons but the product does tend to decay into Li and α-particles, which, added to the inherent chemical toxicity of boron, makes for a fairly unhealthy environment. Not that cadmium is much better.
Part of the art of space exploration (indeed exploration in general) is minimisation and conservation of water supplies, because this essential stuff has a habit of sloshing around (dangerously unbalancing even slow vehicles like fire trucks), freezing, and condensing on everything from beards to electronics. It might nevertheless be possible to construct a space vehicle with ice walls, like a hollow comet, which I humbly suggest is no more bizarre than one made from horse poo and mushrooms. And whilst we are in the province of Wallace and Gromit, how about cheese?
-
added to the inherent chemical toxicity of boron, makes for a fairly unhealthy environment. Not that cadmium is much better.
If we have to put signs on the walls saying "please do not eat the neutron shielding" then I think we are sending the wrong people.
B10 is a good absorber for thermal neutrons but the product does tend to decay into Li and α-particles,
Yes- sort of.
They have a range of under 10 microns in solid materials.
If you can make your nuclear shielding problem into one that can be solved with a coat of paint you have pretty much sorted it.
And whilst we are in the province of Wallace and Gromit, how about cheese?
The characteristic component of cheese would probably be calcium - which has a fairly poor neutron capture cross section.
-
Cheddar cheese (sorry I don't have the figures for Wensleydale) is about 50% water, 30% fat (plenty of thermalising protons)and 15% protein. It contains less than 0.5% calcium. Obviously the perfect neutron shield.
Way off the subject, but when we were first establishing the national breast screening service, I needed a precisely reproducible substitute for breast tissue for testing new x-ray installations. It turned out that Gouda cheese has a very tight specification, is just the right density, and with two wedges, you can simulate a range of breast thicknesses. No neutrons, but I learned a lot about the photon scattering and absorption properties of cheese.
-
. Obviously the perfect neutron shield.
In the very real sense of not stopping neutrons.
It's a good moderator, but a poor shield.
-
intrigued by the ability of common edible mushrooms to synthesise vitamin D with ultraviolet irradiation
We're very similar: 7-dehydrocholesterol in the skin is acted on by UVB to produce cholecalciferol; a couple of OH groups are added by the kidney and liver respectively, yielding 1,25-dihydroxycholecalciferol aka "vitamin D" - this is why most high-latitude inhabitants - the UK population - are vitamin D deficient by the end of winter...
-
A school class ask:
We've been tasked with the assignment of resolving a physical or social problem astronauts encounter in space. We would like your input on our project and possible solution...
Gamma radiation from the sun is a huge problem faced in outer space that greatly deteriorates the human body. Our solution to this problem is designing and constructing a wall that maintains the growth of Chaga mushrooms (radiation-eating fungi) and build it into the ISS. Water pouches will be designed to be used manually for hydrating the mushrooms. The outer-most component of the wall will be made of silica tiles, the material space ships are already constructed of, and lined lead to further limit the presence of radiation. Our “wall” will be constructed into the US Lab and Columbus section of the ISS, which our team designed to rotate in a manner that will always face towards the direction of the sun.
What do you think?
I think that's very cool! :)