There are radioactive gases in the air we breathe. Our own bodies - muscles, bones, and tissue - contain naturally occurring radioactive elements. Man has always been exposed to natural radiation ...

Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper or a human hand. Gamma radiation is the most penetrating. It can penetrate air, paper or thin metal.

If the thickness of the sheet remains constant the activity will ... A beta source is used because beta radiation can penetrate paper or thin aluminium, but the amount of penetrating will vary ...