ASNT Industrial Radiography Radiation Safety Practice Test

When moving from 100 ft to 50 ft from a radiation source, by what factor does the exposure rate increase if the intensity is 50 mR/h?

1. 2 times

2. 3 times

3. 4 times

4. 5 times

The correct answer is: 4 times

When considering the exposure rate from a point radiation source, the inverse square law applies. This law states that the intensity of radiation exposure is inversely proportional to the square of the distance from the source. In the scenario of moving from 100 feet to 50 feet from a radiation source, the distances involved can be analyzed as follows: - Initial distance (d1) = 100 ft - Final distance (d2) = 50 ft According to the inverse square law, the intensity changes according to the formula: Intensity at distance d2 = Intensity at distance d1 × (d1/d2)² Substituting the given distances: Intensity at 50 ft = 50 mR/h × (100/50)² = 50 mR/h × (2)² = 50 mR/h × 4 = 200 mR/h The exposure rate increases from 50 mR/h to 200 mR/h when the distance is halved. Thus, the exposure at 50 ft is 4 times that of the exposure at 100 ft, confirming that the correct answer is the factor of 4. This understanding emphasizes the importance of distance in radiation safety