Cosmic Radiation

--- In spacesettlers@yahoogroups.com, Andy Goddard
> Al wrote:
>
> >For radiation protect similar to Earth you need twice the mass of
the
> >atmosphere per unit surface area. You need 2x since the Earth
blocks
> >almost all cosmic radiation coming from below so the dosage
coming from
> >any one direction needs to be cut in half.
>
> Ummm...if I'm on the inside surface of a cylinder, I can presume
that the
> stuff "above" my local horizon is similar/greater in density than
that
> which is below my feet, so surely the minimum thickness that's
important
> here is the cylinder materials?
>
> Which, if I take a realistic atmospheric scale height (8.4km) and
density
> (1.225 kg/m3), means I only need 10 tonnes of "stuff" per square
metre for
> decent protection. Say 4m of concrete, 10m of ice...
>
> Regards,
>
> Andy G

Arghh. You guys got me curious about this.

What do we face on Earth? Some of you math wizards will have to
integrate this function if you want to get really exact,

http://hurri.kean.edu/~yoh/calculations/standatm/StdAtm.html

but at sea level the atmospheric density is 1.2 kg/m^3 and unlike
water, an atmosphere is compressable so at 9,000 m, the density is
0.47 kg/m^3. I'm going to use a uniform density of 0.76 kg/m^3 over
an altitude of 9,000 meters. This means you have an atmospheric mass
of 6842 kg/m^2. This is a rough estimate and you're free to check
me, but you'll have to do the math :)

Double this mass to replicate the Earth blocking factor. So we need
13.6 tonnes of protection per m^2 around a Habitat to replicate sea-
level.

The altitude of Denver is 5,280 ft. or 1,636 meters. At this
altitude the atmospheric density would be about about 1.04 kg/m^3.
Knocking out the mile of denser atmosphere below Denver's altitude
will yield a uniform density over the remaining 7,364 meters of 0.73
kg/m^3. This equates to an atmospheric mass of 5,375 kg. Doubled to
replicate the Earth's blocking and this means a mass of 10,750
kg/m^2.

http://www.geteams.com/WelcomeToDenver.htm

I'm using a lunar density of 3.3 g/cm^3 for the shielding material.
http://astrosun.tn.cornell.edu/courses/a102/Lectures/Lecture13.pdf

There are 1,000,000 cm^3 in 1m^3, so a m^3 of regolith masses 3,300
kg.

So 3.25 meters of radiation shielding will give you a protection
similar to living in Denver.

I haven't seen any specific references to the necessity to replicate
the Earth blocking feature that Al Globus mentioned but I've
incorporated it here. If this is modified downwards, so too will the
radiation shielding requirement.

In a larger Habitat, the atmosphere will play a part in radiation
ameleoration.

Taking an Island 3 with a diameter of 6.4 km and an atmospheric
composition of 50% O2 and 50% N2 and a atmospheric pressure of 50%
this would result in a mean molecular weight of 30, compared to
Earth's 29. This would be equivalent to living at an altitude of
4,958 meters but with an enriched O2 level.

Assuming a cylindrical Habitat configuration, we'd expect the
uniform density over the 6,400 meter diameter to be 1.052 kg/m^3,
then fctoring in the greater mean molecular weight, this should come
to 1.088 kg/m^3. So we'd have an atmospheric mass of 6,970 kg
directly overhead of each m^2. This of course does double duty
because directly overhead of you is another m^2 of land and the
atmosphere is flipped over and serves that land as well.

This atmosphere is the equivalent of 2.11 meters of lunar regolith,
leaving a 1.14 meter shielding requirement under your feet. This
could be the topsoil within the Habitat and the thickness of the
pressure shell could be an added bonus.

Hope this helps.

TangoMan