Sievert - 100 rem. Sieverts are not as commonly used as rems, and perhaps have come into use to make the numbers appear less threatening. Curie - a measure of radioactivity. It is defined as 37 billion disintegrations per second. This radiation readily penetrates matter.
Shielding requires dense materials such as lead.
Gamma radiation occurs in the decay of elements such as cobalt60 and cesium137. Beta radiation - electrons discharged in the decay of some radioactive isotopes. Amount of shielding required depends on the energy level. Plastics usually provide good shielding. Alpha radiation - the emission of the equivalent of the helium nucleus, consisting of 2 neutrons and 2 protons.