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## Homework Statement

The count-rate from a gamma source is measured to be 1000 counts per minute. When 1.0 cm of lead is placed between the source and the detector, the count rate is reduced to 100 counts per minute. What additional thickness of lead would have reduced the count-rate to 50 counts per minute?

## Homework Equations

C= Cinital e^-μx

## The Attempt at a Solution

I'm not really sure how to approach the question I tried using the first equation to find the attenuation coeffecient by subbing in 100= 1000 e^-μ(0.01) and getting 230.26. And then I used that to find x by doing 50= 1000e^-230.26x and I got 13 mm, but the answer is 3 mm. Not sure where I'm going wrong or if I am even using the right formula...