Cosmic rays and induced radioactivity

[rob60]

Homework Statement

90% of the cosmic rays that fall on Earth are protons. So the outside of the Earth is hit by a net positive charge but does not seem to be, in particular, positively charged. How do you explain this?
One last thing: I read that a body that is exposed to radiation becomes radioactive radiation source in turn ... I think it is generally false unless the body is contaminated with radioactive material. It is correct?
thank you

Homework Equations

The Attempt at a Solution

 

[daveb]

One last thing: I read that a body that is exposed to radiation becomes radioactive radiation source in turn ... I think it is generally false unless the body is contaminated with radioactive material. It is correct?

In general, you are correct. Material exposed to a neutron or proton flux can become activated, which usually makes some part of it radioactive, and energetic enough electron or gamma fluxes can also do it (but it in general takes a lot of energy).