ASNT Industrial Radiography Radiation Safety Practice Test

After how many half-value layers would the percentage of radiation received be reduced to 1.6%?

1. 4 half-value layers

2. 5 half-value layers

3. 6 half-value layers

4. 7 half-value layers

The correct answer is: 6 half-value layers

The concept of half-value layers (HVL) is fundamental in understanding how radiation intensity is reduced as it passes through materials. Each half-value layer represents the thickness of a given material required to reduce the radiation intensity by half. To find out how many half-value layers are necessary to reduce the radiation to 1.6%, one can utilize the formula related to half-value layers, which is: \[ \text{Remaining Radiation} = \text{Initial Radiation} \times \left( \frac{1}{2} \right)^n \] where \( n \) is the number of half-value layers. Starting from 100% radiation, we want to know how many layers are needed to arrive at 1.6%. Setting up the equation: 1. **For 1 half-value layer:** 100% → 50% 2. **For 2 half-value layers:** 50% → 25% 3. **For 3 half-value layers:** 25% → 12.5% 4. **For 4 half-value layers:** 12.5% → 6.25% 5. **For 5 half-value layers:** 6.25% →