If Radiation Were Cookies...
...which one would you eat?
So if you had four cookies, and you could eat one, put one in your pocket, hold one in your hand, and throw the other away, what would you do?
This problem is used to help people understand the effects of different kinds of radiation. This has largely to do with each type of radiation's dose factor.
Gamma cookie: You would eat this one, because it doesn't cause much somatic damage.
Beta cookie: Your pocket is the choice for this one, as it will be shielded by one layer of clothing.
Alpha cookie: Hold this one in your hand, because it will be blocked by your first layer of skin.
Neutron cookie: Throw this sucker away.
The dose factor has to do with the size of the particle (photons have no mass, at least while at rest), its state of charge (an alpha particle is +2), and its penetration distance.