http://www.nytimes.com/aponline/scie...Radiation.html

The explanation of the mode of operation of this stuff seems incoherent to
me.

Mark Folsom

"Mark Folsom" wrote in message ...
http://www.nytimes.com/aponline/scie...Radiation.html

The explanation of the mode of operation of this stuff seems incoherent to
me.

I agree.

"The shield, composed of several sheets of polyethylene heavily
impregnated with hydrogen, is called a material composite...The
hydrogen breaks down, or diffuses, harmful radiation that could
cause cancer by reducing heavy ions into lighter ones...
Exposure to lighter ions is less harmful to people than cosmic
radiation..."

What?

I put the keywords "material composite radiation shield" into
Google. That got me some more coherent explanations. Here's
one:
http://science.nasa.gov/newhome/head...d20jul98_1.htm
"Radiation actually comprises electromagnetic radiation
- X-rays and gamma rays - and particulate radiation
- high-speed particles like electrons, protons, neutrons,
and atomic nuclei. Low-energy radiation can be stopped
by a spacecraft wall, but at higher energies the wall
helps produce showers of secondary radiation, like
splinters from a wall hit by a bullet. So, even more
shielding is needed to absorb that, until eventually
the radiation is worn down.

"Oddly, one of the better ways to stop radiation is
with lightweight materials - hydrogen, boron, and lithium.
The nuclei of heavy elements in cosmic rays can be shattered
by lightweight atoms without producing additional hazardous
recoil products like neutrons."

This one's more specific about the problem, namely
"high charge and energy (HZE) ions".
http://spacescience.spaceref.com/colloquia/ mmsm/wilson_pos.pdf

"Sixty percent of the astronaut cancer risks are from the
ions of C, O, Mg, Si, and Fe (with an added 30 percent from
the other HZE ions and only about 8 percent from GCR protons).
These five dominant ions will be the focus of laboratory
testing in the most important energy range between 500 MeV
per nucleon and 2000 MeV per nucleon."

And here's one more interesting link.
http://spaceresearch.nasa.gov/docs/h...adpt2_2003.pdf

Didn't find one to explain exactly what reaction constitutes
the "shattering" of energetic C, O, Mg, Si and Fe by H.

- Randy