Starches as Radiation Shielding

[kerbiloid]

4 hours ago, RainDreamer said:

Side question: is irraditated potato safe to eat?

Conserved food is often sterilized by gamma-rays.

Edited June 24, 2016 by kerbiloid

[p1t1o]

6 hours ago, RainDreamer said:

Side question: is irraditated potato safe to eat?

2 hours ago, kerbiloid said:

Conserved food is often sterilized by gamma-rays.

What about neutron activation?

[lajoswinkler]

5 hours ago, RainDreamer said:

Side question: is irraditated potato safe to eat?

Depends on what rays were used, how long, etc.

For example, if you irradiate a potato with infrared rays from a typical oven for one hour, you'll get a tasty potato (and you'll destroy its toxicity; potatos are actually toxic).

But if you put that potato in a strong neutron flux inside a nuclear fission reactor for a few days, it won't be safe at all. It will have, just to name one radioisotope, phosphorus-32 inside.

[Kobymaru]

On 23.6.2016 at 6:41 AM, DBowman said:

ah interesting - I should read the paper I guess! it sounds like they are not planing to eat it and then use the poop.

fwiw here is my mental model: Molecules are like little masses joined by springs. They have resonant frequencies, some frequencies you shake them at will damp out the energy but the resonant ones will amp up any oscillation of the springs (like pushing someone on a swing, the length of the 'hang' determines the frequency you have to push at). The 'spring's are 'good at' absorbing photons of particular frequencies and converting that energy into various motions of the masses joined to the spring, intra molecular motion if you like. If you have molecules waggling and bumping into each other then some 'waggle energy' will get converted to 'whole molecule motion' = heat by collisions of bits of molecules (is this 'friction'? even the waggle might be heat). Microwaves are tuned/chosen to resonate with H2O, so they directly heat the water. The heating they do to conductors is via a different mechanism, like an antenna picking up energy?

That's all good and well, and the Microwaves are somewhere *around* the resonance frequency of water. But they aren't actually. Resonance does not play a large part in the energy transfer, mostly it's just plain old absorption.

 

On 23.6.2016 at 8:39 AM, Bill Phil said:

Very correct. However, starches are large molecules, and they consist partly of hydrogen and carbon, which can help against neutron radiation. It's not very effective against most ionizing radiation, though. But it's likely that the sheer mass in a thick enough layer would do some good. Depends on the halving thickness of the starch you use...

The only question that matters is: is it better or worse than an equivalen mass of aluminum, steel or lead?

 

7 hours ago, cubinator said:

If it's irradiated with microwaves, it is definitely unsafe and should not be consumed, breathed, or looked at.

.... Joke?

[kerbiloid]

1 hour ago, p1t1o said:

What about neutron activation?

Negligible.

https://en.wikipedia.org/wiki/Food_irradiation

[p1t1o]

35 minutes ago, kerbiloid said:

Negligible.

https://en.wikipedia.org/wiki/Food_irradiation

It may be negligible, but that link does not mention neutron radiation at all (except for use in the production of gamma sources via neutron capture...). According to the link, all food irradiation is done via gamma/X-rays, occasionally electron beams.

Oh there might be a misunderstanding here. I know that food is often preserved using radiation, but in this context "irradiated" referred to space radiation, since the thread is about starch as radiation shielding. My question was about whether or not the neutron flux from space would risk inducing radioactivity in something that might later be consumed by the crew, if for example the starch was from a "potato-shield".

 

[Bill Phil]

2 hours ago, Kobymaru said:

The only question that matters is: is it better or worse than an equivalen mass of aluminum, steel or lead?

The density of starches is about half the density of aluminum.

[kerbiloid]

Probably, the second. I thought, you had meant "neutron activation by gamma-rays".

[p1t1o]

50 minutes ago, kerbiloid said:

Probably, the second. I thought, you had meant "neutron activation by gamma-rays".

Word.

What is the neutron flux like in an average (say in-system, interplanetary) bit of space? Is activation a likely problem?

[kerbiloid]

12 minutes ago, p1t1o said:

What is the neutron flux like in an average (say in-system, interplanetary) bit of space? Is activation a likely problem?

Probably, not activation the food, but activation of the hull and food containers material.
They may (should) contain metals which can be activated by the neutrons.

[Zhetaan]

21 hours ago, lajoswinkler said:

Starch would be a poor cosmic ray absorber. It's best to just use water.

Doesn't this imply that one can get shielding simply by surrounding the vessel with a well-watered greenhouse?  Since a food supply is a concern anyway, doesn't that make this a multiple-purpose solution?

[cubinator]

4 hours ago, Kobymaru said:

.... Joke?

Of course!  Why aren't microwave ovens totally illegal?

[p1t1o]

18 minutes ago, Zhetaan said:

Doesn't this imply that one can get shielding simply by surrounding the vessel with a well-watered greenhouse?  Since a food supply is a concern anyway, doesn't that make this a multiple-purpose solution?

You should read Seveneves by Neal Stephenson

[lajoswinkler]

46 minutes ago, Zhetaan said:

Doesn't this imply that one can get shielding simply by surrounding the vessel with a well-watered greenhouse?  Since a food supply is a concern anyway, doesn't that make this a multiple-purpose solution?

Hydroponics bay, thick one.

[SinBad]

How about a huge lump of ice (a few dozen kilotons) in a big ball shape with an elastic  blanket stretched over the top. Put the crew in the centre, and a hot thorium reactor on the end of a long stick. Circulate some warm water (heated with a portion of the reactor heat in a tertiary loop) through veins in the blanket, which uniformaly melts the outside of the ice ball. elasticity squeezes the water into a pipe and sends it down the stick to the reactor core where hundreds of thorium pebbles do their thing and make anything from high pressure super heated steam, all the way up to "oops we broke the water, better throw in a match" and lets it out an exhaust bell. Not the best reaction mass, but it does double as a shield well. And we know where to get more. Lots more.

 

 

[p1t1o]

9 minutes ago, SinBad said:

How about a huge lump of ice (a few dozen kilotons) in a big ball shape with an elastic  blanket stretched over the top. Put the crew in the centre, and a hot thorium reactor on the end of a long stick. Circulate some warm water (heated with a portion of the reactor heat in a tertiary loop) through veins in the blanket, which uniformaly melts the outside of the ice ball. elasticity squeezes the water into a pipe and sends it down the stick to the reactor core where hundreds of thorium pebbles do their thing and make anything from high pressure super heated steam, all the way up to "oops we broke the water, better throw in a match" and lets it out an exhaust bell. Not the best reaction mass, but it does double as a shield well. And we know where to get more. Lots more.

You can use the reactor to electrolyse the water to hydrogen and oxygen, use just the hydrogen as remass for increased ISP and Im sure we can think of a use for the oxygen, I'm thinking mainly industrial applications rather than breathing gas which can be regenerated.

[DBowman]

17 hours ago, Kobymaru said:

That's all good and well, and the Microwaves are somewhere *around* the resonance frequency of water. But they aren't actually. Resonance does not play a large part in the energy transfer, mostly it's just plain old absorption.

oh interesting, thanks, I'll read up on it.

[NuclearNut]

Actually starch would do just fine, but solids with a high hydrogen content would do better.  You see, the radiation you are dealing with is ultimately high energy nuclear particles such as protons and alpha particles.  These particles have to be slowed down via elastic scattering, that is to say that they need to bounce off of a large number of atoms.  Thankfully hydrogen is great at this and is rather common.  It also can slow down neutrons via the same means, though it is terrible at absorbing neutrons, so usually an element with a high neutron cross section is included (boron).

 

[kerbiloid]

On 24.06.2016 at 4:59 PM, lajoswinkler said:

On 24.06.2016 at 4:11 PM, Zhetaan said:

Doesn't this imply that one can get shielding simply by surrounding the vessel with a well-watered greenhouse?  Since a food supply is a concern anyway, doesn't that make this a multiple-purpose solution?

Hydroponics bay, thick one.

This could also provide them with a spacelift

 

[cubinator]

12 hours ago, kerbiloid said:

This could also provide them with a spacelift

 

"Hey, check it out, I threw these magic beans here on the ground yesterday and now there's a space elevator!"

Edited June 27, 2016 by cubinator