See
http://www.cnn.com/2002/TECH/science/11/13/radiation.suit.reut/index.html

I think that seemingly small things like this could have a big impact on
feasibility of long-duration human space ventures.

Ron

It sounds a bit like the polyethylene that was used out on the ISS. It
does work to some extent- it cuts the radiation by a few percent, and
weighs comparatively little, but apparently it doesn't work as well as
was hoped.

Still, the types of radiation found in space are a little different from
that found on the ground- cosmic rays tend to be much higher energies;
so it may be far more useful and effective down on the ground.

It sounds a bit like the polyethylene that was used out on the ISS. It
does work to some extent- it cuts the radiation by a few percent, and
weighs comparatively little, but apparently it doesn't work as well as
was hoped. I'm beginning to think that we're never going to get around the fact that more protection is always going to mean more mass. On the other hand, some people go too far with that. They advocate burrowing many meters into the interior of asteroids, and tout protection from radiation as an advantage of that approach. I always tell them that anything over 2 meters is overkill.

Regards,

Mike Combs

Message Let me explain some physical principles of shielding. Radiation that can damage living cells is usually divided into two categories, charged particles (such as solar wind protons, alpha particles and others) and photons (gamma and x-rays). Both interact mostly with electrons, so any material that holds lots of electrons in a small volume will work for stopping them. The materials we have for shielding here is atomic, andatoms are roughly all the same size, around an angstrom (or 0.1 nanometer) in diameter. So which atoms have the most electrons and are not too expensive? Pick the atoms with the highest number of protons, because each neutralatom has the same number of protons and electrons. So of the naturally occurring elements, uranium would be the best, except it is radioactive, expensive and can be used to make bombs. So pick some other abundant and non-radioactive elements. That would be (the highest non-radioactive element, which is) Bismuth, with 83 protons and electrons, and a density of 9.8 gram/cc. Another good choice is Lead, with 82 protons and electrons, and a density of 11.4. Now not all electrons are the same for stopping gamma rays. The more tightly bound ones work better for photonsproviding that the gamma ray energy exceeds the electron binding energy. And more loosely bound electrons are better for stopping charged particles. But ignoring these complicating factors, the best shielding in a small space is provided by materials which have the highest mass density. The mass comes mostly from the protons and neutrons, but the shielding comes from the electrons. Now, how wouldplastic and organic compounds, with a density of roughly 1, work. Okay for charged particles if they were maybe 10 times as thick as a piece of lead, but not as well for gamma rays. One could try and lower the mass to electron ratio by using lighter isotopes, such as hydrogen 1 instead of hydrogen 2, which we mostly do with out trying with hydrogen, but most elements don't differ nearly so much and separating isotopes willmake the shielding very expensive. So without having seen any technical data on this "radiation-proof" fabric, my guess is that it incorporates some higher elements into it, but will stillnot be very good at stopping radiation or be very light-weight either. The Earth's atmosphere is equivalent to about 76 cm of Mercury (remember barometers?), which would be about 90 cm of lead. We suspect we need such shielding for the long term. Sincerely, Jay Huebner

It sounds a bit like the polyethylene that was used out on the ISS. It
does work to some extent- it cuts the radiation by a few percent, and
weighs comparatively little, but apparently it doesn't work as well as
was hoped. I'm beginning to think that we're never going to get around the fact that more protection is always going to mean more mass. On the other hand, some people go too far with that. They advocate burrowing many meters into the interior of asteroids, and tout protection from radiation as an advantage of that approach. I always tell them that anything over 2 meters is overkill.

Regards,

Mike Combs

Thanks for your explanation. I found it very informative.

> Let me explain some physical principles of shielding.
Radiation that
> can damage living cells is usually divided into two categories,
charged
> particles (such as solar wind protons, alpha particles and others)
and
> photons (gamma and x-rays). Both interact mostly with electrons,
so any
> material that holds lots of electrons in a small volume will work
for
> stopping them. The materials we have for shielding here is
atomic, and
> atoms are roughly all the same size, around an angstrom (or 0.1
nanometer)
> in diameter. So which atoms have the most electrons and are not
too
> expensive? Pick the atoms with the highest number of protons,
because each
> neutral atom has the same number of protons and electrons. So of
the
> naturally occurring elements, uranium would be the best, except it
is
> radioactive, expensive and can be used to make bombs. So pick
some other
> abundant and non-radioactive elements. That would be (the highest
> non-radioactive element, which is) Bismuth, with 83 protons and
electrons,
> and a density of 9.8 gram/cc. Another good choice is Lead, with
82 protons
> and electrons, and a density of 11.4.
> Now not all electrons are the same for stopping gamma rays.
The more
> tightly bound ones work better for photons providing that the
gamma ray
> energy exceeds the electron binding energy. And more loosely bound
> electrons are better for stopping charged particles. But ignoring
these
> complicating factors, the best shielding in a small space is
provided by
> materials which have the highest mass density. The mass comes
mostly from
> the protons and neutrons, but the shielding comes from the
electrons.
> Now, how would plastic and organic compounds, with a density of
roughly
> 1, work. Okay for charged particles if they were maybe 10 times
as thick as
> a piece of lead, but not as well for gamma rays. One could try
and lower
> the mass to electron ratio by using lighter isotopes, such as
hydrogen 1
> instead of hydrogen 2, which we mostly do with out trying with
hydrogen, but
> most elements don't differ nearly so much and separating isotopes
will make
> the shielding very expensive.
> So without having seen any technical data on this "radiation-
proof"
> fabric, my guess is that it incorporates some higher elements into
it, but
> will still not be very good at stopping radiation or be very light-
weight
> either. The Earth's atmosphere is equivalent to about 76 cm of
Mercury
> (remember barometers?), which would be about 90 cm of lead. We
suspect we
> need such shielding for the long term.
> Sincerely, Jay Huebner
>
radiation-pr
> oof"
>
> It sounds a bit like the polyethylene that was used out on the
ISS. It
> does work to some extent- it cuts the radiation by a few percent,
and
> weighs comparatively little, but apparently it doesn't work as
well as
> was hoped.
>
> I'm beginning to think that we're never going to get around the
fact that
> more protection is always going to mean more mass.
>
> On the other hand, some people go too far with that. They advocate
> burrowing many meters into the interior of asteroids, and tout
protection
> from radiation as an advantage of that approach. I always tell
them that
> anything over 2 meters is overkill.
>
> Regards,
>
> Mike Combs
>
7050835
>
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