Question

You are shown two nice, identical-looking pieces of clothing. You are told that one is made of cotton and the other of polyester (a textile derived from petroleum). You want to determine which is which but you are not allowed to touch them. But you have your Geiger counter at hand which you always carry around with you. How can you use that to find out the answer? Explain briefly what you would do and what the reasoning is behind your idea.

Answer 1

Geiger counter is an instrument used to detect radiation. Note that plants and animals have very little amount of radioactive ¹⁴C which decays into ¹²C. This is replenished from the environment continously due by processes like food intake. Once they die, the ¹⁴C concentration decreases in their dead bodies due to its decay to ¹²C. In fossil derived products like polyester, the ¹⁴C concentration is far less than that of cotton which is clearly not thousands of years old like petrol.

Hence, the Geiger counter beeps more when taken near cotton (as it has more ¹⁴C).