Like I said, "radiation" has a very broad definition today. Going from memory: Alpha particles are helium nuclei, and tend to be very easy to shield against. non-critical Plutonium emits alpha particles, which can be stopped by a thick sheet of paper. Beta particles are electrons, I believe, and typically can be shielded by a few inches of wood. Gamma radiation is true electromagnetic radiation, on the short wavelength end of the spectrum, and needs a lot of mass to stop it.
Then in space there are high-energy protons and other charged particles, which can be deflected by a magnetic field. Neutrons are sometimes also lumped in as radiation. Neutron flux has the nasty property of making things it hits radioactive themselves, and neutrons cannot be deflected by magnetic fields. I don't know if there are a lot of neutrons free in space, typically they are the product of intensive nuclear reactions.
Again, this is from memory, so catch me if I'm wrong.
Space/Science » in reply to Bad news once again, Mark
Re: Bad news once again, Mark