If a radiographer has a reading of 60 mR at the surface of the exposure device, what would the reading be after 2 half-lives?

To determine the radiation reading after two half-lives from an initial exposure level, it's important to understand the concept of half-life in radioactive decay. A half-life is the time it takes for half of a radioactive substance to decay, which effectively reduces the radiation level by half.

Starting with an initial reading of 60 mR, after one half-life, the radiation level would reduce to half of that initial value. Therefore, after the first half-life, the reading would be 30 mR.

Continuing to the next half-life, we again take the current reading (30 mR) and reduce it by half. After the second half-life, the reading would then become 15 mR.

Thus, after two half-lives, the reading decreases from 60 mR to 30 mR and then to 15 mR, making 15 mR the final reading, confirming that this value accurately reflects the calculated decay based on the half-life principle.