@ Georgesplane- Although Alpha particles are not very dangerous outside of the body, once inhaled or ingested, they become extremely dangerous. The reason alpha particle radiation is so dangerous when they are inhaled is due to their so strongly ionizing. The atoms that the alpha particles emitted from are in a state of recoil, causing these cations to have a positive charge. These cations then become attracted to the negative charge of DNA, causing genetic mutations.
This type of nuclear radiation is the biggest threat in terrorist attacks. To be effective in an attack, terrorists do not need fissionable nuclear material. Those in the immediate vicinity of the attack will likely suffer from radiation sickness. Those that survive will likely bear the effects for the rest of their lives. When the dust settles, the environment will hold these radioactive particles; creating a hazard every time someone stirs the earth. This can cause genetic damage to generations of people.