ASNT Industrial Radiography Radiation Safety Practice Test

What would the reading be after 2 half-lives if a radiographer has 60 mR (0.6 mSv) at the surface of the exposure device?

1. 30 mR (0.3 mSv)

2. 15 mR (0.15 mSv)

3. 7.5 mR (0.075 mSv)

4. 3 mR (0.003 mSv)

The correct answer is: 15 mR (0.15 mSv)

To understand how to determine the radiation reading after two half-lives, it's essential to grasp the concept of half-life in the context of radioactive decay. A half-life is the time required for half of the radioactive material in a sample to decay. Starting with an initial exposure reading of 60 mR, after the first half-life, this amount will reduce to half, which equals 30 mR. After another half-life, the reading will again be halved. Halving the 30 mR results in 15 mR. Therefore, after two half-lives, the radiation reading would be 15 mR (0.15 mSv), which aligns with the correct answer. This understanding of radioactive decay and the systematic way to calculate exposure levels over time is crucial in the field of industrial radiography, especially in ensuring safety protocols are followed and understood.