ASNT Industrial Radiography Radiation Safety Practice Test

How many curies remain if a source starts with 48 Ci and undergoes 2 half-lives?

1. 12 Ci

2. 24 Ci

3. 36 Ci

4. 42 Ci

The correct answer is: 24 Ci

To determine how many curies remain after a source has undergone two half-lives, it is crucial to understand the concept of half-life in radioactive decay. The half-life of a radioactive substance is the time it takes for half of the radioactive material to decay. In this case, starting with 48 curies, we analyze the decay process step by step: 1. After the first half-life, half of the original material will have decayed. This can be calculated as 48 Ci / 2 = 24 Ci. Therefore, after the first half-life, 24 curies remain. 2. After the second half-life, again, half of the remaining material will decay. So, we take the 24 curies that are left and divide it by 2, yielding 24 Ci / 2 = 12 Ci. After completing two half-lives, you arrive at 12 curies remaining. Thus, the correct reasoning leads to the conclusion that the amount of radioactive material remaining is 12 Ci, which corresponds to a correct understanding of how radioactive decay operates through half-lives. This approach rationalizes the changes in the amount of the radioactive substance, illustrating a clear relationship between the number of half-lives elapsed and