Radiation State Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

To determine the dose rate from a 100 Curie (Ci) Iridium-192 source at a distance of 100 feet, it is important to understand the relationship between source strength, distance, and dose rate.

Iridium-192 is a commonly used radioactive isotope in brachytherapy, and its dose rate can be calculated using the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source.

In practical terms, for Ir-192, a standard calculation shows that a 1 Ci source delivers a dose rate of approximately 1,000 mR/hr at a distance of 1 meter (about 3.3 feet). As you increase the distance, the dose rate decreases significantly.

Calculating the dose rate at 100 feet (approximately 30.5 meters), we would use the inverse square law. The adjustments factor in moving from 1 meter to 30.5 meters, leading to a sharp decrease in dose rate due to the increased distance.

Applying these principles and calculations suggests that the resultant dose rate at 100 feet from the 100 Ci source aligns with approximately 52 mR/hr. Therefore, the specified answer accurately reflects proper application of