I've also read that aluminum, when struck by a high-energy particle is easily capable of losing and loosing a neutron to go plowing into whatever is in the way, such as say, DNA.
Spacesuits are eventually going to have circulating water in suits for this reason. It auto-controls temperature, it protects against radiation, and place a water-activated polymer on the outside and if the suit is punctured by a microsatellite or mistake the suit can autoseal from the leakage of water.
Approximately two feet of water is a tenth thickness for gamma. That is it will reduce the dose to 1/10th of the previous dose.