Question

Suppose 128 radioactive atoms have a half-life of 15 seconds. Approximately how many radioactive atoms will be left after 60 seconds?

Answer 1

A half life is how long it takes for half of the amount you have to go away. So 60 seconds is really just 4 half lives, right? So halve 128 four times.

Answer 2

Which of the following is the best definition of half-life for a radioactive substance?


Half of the amount of time required for all of the radioactive atoms to decay.
The amount of time required for half of the radioactive atoms to decay.
The amount of time required for each radioactive atom to decay halfway.
All of the above.