In article <79cf0a8.0310171314.1a9d8696@posting.google.com>,

Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a *****. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon.

You got some confusion here. There are protons in all possible
energies. There is little if any evidence for any significant amount
of heavy ions at hig energy (heavy ion is an ion with *Z > 1*).
Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does
not* mean that you've heavy ions at high energies.

Certainly since all protons above 10 MeV or so will give
you spallation. Nothing to do with "heavy ions".

COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments.

No you don't yyou need a primary shield which is thick enough to stop
all (or nearly all) charged particles). Then you need a moderation
layer thick enough to slow all neutrons in generated within the first
layer (or neutrons incoming into the first layer) to thermal or near
thermal velocities. Then you need something to absorb these neutrons
and absorb the gammas generated by the neutron absorption.

In article <79cf0a8.0310171314.1a9d8696@posting.google.com>,

Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a *****. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon.

You got some confusion here. There are protons in all possible
energies. There is little if any evidence for any significant amount
of heavy ions at hig energy (heavy ion is an ion with *Z > 1*).
Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does
not* mean that you've heavy ions at high energies.

Certainly since all protons above 10 MeV or so will give
you spallation. Nothing to do with "heavy ions".

COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments.

No you don't yyou need a primary shield which is thick enough to stop
all (or nearly all) charged particles). Then you need a moderation
layer thick enough to slow all neutrons in generated within the first
layer (or neutrons incoming into the first layer) to thermal or near
thermal velocities. Then you need something to absorb these neutrons
and absorb the gammas generated by the neutron absorption.

mmeron@cars3.uchicago.edu wrote in message news:<kEskb.179$O4.60832@news.uchicago.edu>...

In article <79cf0a8.0310171314.1a9d8696@posting.google.com>,

mmeron@cars3.uchicago.edu wrote in message news:<gkmib.50$O4.12116@news.uchicago.edu>...

Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a *****. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon.

You got some confusion here. There are protons in all possible
energies. There is little if any evidence for any significant amount
of heavy ions at hig energy (heavy ion is an ion with *Z > 1*).
Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does
not* mean that you've heavy ions at high energies.

Not my confusion. Need for you to read up on the subject, since you're
way out of date. 98% of extragalactic cosmics are H and He, but the
remaining 2% (which is better than our own solar system for
metalicity) are ions all the way up the periodic table, at any energy
you like (and as far up as has been measured). Mostly below Z=30, as
expected, but also going higher. Relative abundances for even elements
look a lot like what we're used to. All evidence for the supernova
shock origin theory.

http://www.wkap.nl/prod/a/ISBN_0-7923-7196-8_29.PDF

Certainly since all protons above 10 MeV or so will give
you spallation. Nothing to do with "heavy ions".

Heavy ions are important to the extent you have to do your shielding
with other than hydrogen. If you're sheilded with a big ball of frozen
H2 on the voyage out, heavy ions are your most important source of
neutrons.

COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments.

No you don't yyou need a primary shield which is thick enough to stop
all (or nearly all) charged particles). Then you need a moderation
layer thick enough to slow all neutrons in generated within the first
layer (or neutrons incoming into the first layer) to thermal or near
thermal velocities. Then you need something to absorb these neutrons
and absorb the gammas generated by the neutron absorption.

Yes, and since you have three different sets of materials available to
do some of these jobs in three different mission phases (cruise, early
surface, late surface), again you get three different designs. The
moderator will be of different thicknesses depending on how much
neutron radiation has to be dealt with, which is a function of
radiation type atmosphere interactions, and type of primary sheild
(how much hydrogen).

If you are in space this will be a lot of
hydrogen, so your moderator has to deal with only those neutrons
produced by heavy elements in the primary sheild, and neutrons
produced by high Z cosmics in the primary sheild. But on the Martian
surface things are very different, and you have neutrons produced by a
primary sheild of sand, and in the atmosphere before that. Neutrons
from that may need to be moderated, but with later carry-down
sheilding in the dig-in phase, but only sand absorption after that.

Remember, with enough sand you not only don't need a gamma sheild
(certainly you dont' need to carry down from orbit whatever you used
in space),you also don't even need a dedicated neutron absorber, and
won't use it any more than one is used in modern power plants.