ASNT Industrial Radiography Radiation Safety Practice Test

If you have 73 Ci of Co-60, what would be your exposure rate at 2 ft from the source?

1. 145 R

2. 255.5 R

3. 320 R

4. 250 R

The correct answer is: 255.5 R

To understand the correct answer regarding the exposure rate from a Co-60 source, it's essential to grasp how radiation exposure decreases with distance from the source. Co-60 is a radioactive isotope that emits gamma radiation, and the exposure rate can be calculated using a specific formula that incorporates the activity of the source and the distance from it. In the case of a Co-60 source, the exposure rate at a certain distance can be derived using the known exposure rate constant for Co-60, which is approximately 13.07 R/hr per Ci at 1 meter. This conversion factor allows us to calculate the exposure rate for any distance by applying the inverse square law, which states that exposure rate decreases with the square of the distance from the source. In this scenario, 73 Ci at a distance of 2 feet (which is approximately 0.61 meters) would have an exposure rate that can be calculated as follows: 1. First, convert the activity into exposure rate: - Exposure rate at 1 meter = 13.07 R/hr/Ci, hence at 73 Ci, it becomes 13.07 R/hr/Ci * 73 Ci. 2. Then, adjust for the distance using the inverse square law: