One reason radiation is dangerous is that it can’t be detected with the senses. You normally can’t see it, smell it, hear it, or feel it. Fortunately, there are devices such as Geiger counters that can detect radiation. A Geiger counter, like the one in Figure below , has a tube that contains atoms of a gas. If radiation enters the tube, it turns gas atoms to ions that carry electric current. The current causes the Geiger counter to click. The faster the clicks occur, the higher the level of radiation.
Bob is an environmentalist studying the old Chernobyl site. He is particular interested in seeing how much radiation remains decades later. He took a Geiger counter with him and as he got closer to the area were the accident occurred the Geiger counter started to click. When he reached the site of the accident the Geiger counter clicked even faster.
Is there still radiation in the area or is it clean?