"The total dose deposition in silicon is only 10 rads/year when the GCR environment is at its peak. However, when the GCR dose is converted to dose equivalent in units of rem for biological systems, it can reach dangerous levels for humans. This can be true even for low earth orbits where the effect of the magnetospheric attenuation on the fluence levels of cosmic ray particles is significant."
http://radhome.gsfc.nasa.gov/radhome/Nat_Space_Rad_Haz.htm

"The principal ionizing radiations to be found in space are summarized in table 2-2. Ionizing radiation endangers humans because it is capable of breaking chemical bonds in tissue. The damaging power depends upon the amount of energy deposited per unit volume, the rapidity with which the energy is transferred, and its concentration along the track of the particle of radiation. Radiation which deposits 100 ergs of energy (3) per g is said to deliver a dose of 1 rad. Because different forms of radiation may deposit this energy at different rates and with different intensities along the track, the biological damage of a dose of 1 rad varies with the type of radiation. To correct for this effect the radiation dose in rads is multiplied by the "relative biological effectiveness" (RBE) of the particular kind of radiation."
http://lifesci3.arc.nasa.gov/SpaceSettlement/75SummerStudy/2appendB.html

"Dec. 17, 1999: If it rains, you put up an umbrella. If you expect a meteor shower, you build the spacecraft with shielding that blunts the blow when particles arrive. But what do you do for radiation?
After almost four decades of human spaceflight, we still are grappling with the challenge of protecting space crews from cosmic rays and other radiation hazards. Part of the problem is understanding
fully the composition and energies of cosmic rays."
http://www.spaceref.com/redirect.ref?id=0&url=spacescience.spaceref.com/newhome/headlines/ast17dec99_1.htm

Btw, Keith your link: CREME96 results, http://www.spaceref.com/redirect.ref?id=0&url=coffee.phys.unm.edu/~dima/creme/table.html
doesn't work.
[I used to have more references on radiation but those links also don't work {http://members.tripod.com/~gbaikie/1.html}]
-gb