Shadow wrote in part:
"You don't want heavy stuff like lead because they high energy
particles will create *multiple* lower energy particles when they hit
a nucleus. These result in *higher* radiation doses!"
This is the working principle behind "neutron" bombs ... a 'small' a-bomb triggers the enhanced nuke which then does nasty things of metal in the area - which thoughts in turn may lead to ships being constructed of ceramics, poly, and other attempts to reduce too much metal ...
Tim