Texas Industrial Radiography Gamma Practice Test

How many half-value layers of shielding are needed to reduce the intensity from 8,192 mr/hr to 8 mr/hr at a distance of 10 feet from a Cobalt 60 source?

1. 8

2. 10

3. 16

4. 20

The correct answer is: 10

To determine the number of half-value layers needed to reduce radiation intensity from 8,192 mR/hr to 8 mR/hr, it is essential to understand the concept of half-value layer (HVL). A half-value layer is the thickness of a specified material that reduces the intensity of radiation to half its original value. Starting with the intensity of 8,192 mR/hr, we can calculate how many times we need to halve this value to reach 8 mR/hr. 1. The first step involves finding how many times we can divide 8,192 by 2: - 8,192 / 2 = 4,096 - 4,096 / 2 = 2,048 - 2,048 / 2 = 1,024 - 1,024 / 2 = 512 - 512 / 2 = 256 - 256 / 2 = 128 - 128 / 2 = 64 - 64 / 2 = 32 - 32 / 2 = 16 - 16 / 2 = 8 Each division represents the