If the radiation intensity at 6 feet from an unshielded iridium-192 source is 5 mR/h, what is the approximated activity of the radioisotope?

To determine the activity of the iridium-192 source based on the radiation intensity measured at a specific distance, one can use the relationship between activity (measured in curies, Ci) and dose rate (in mR/h) at a known distance, utilizing the inverse square law of radiation.

In this scenario, the intensity is provided as 5 mR/h at a distance of 6 feet from the source. An established estimation is that for iridium-192, the dose rate in mR/h at 1 meter (approximately 3.28 feet) is roughly proportional to its activity in curies. From data tables and radiation standards, the dose rate at 1 meter from a 1 Ci source of iridium-192 is approximately 462 mR/h.

Given this information, one can deduce the relationship:

1. Convert the distance from feet to meters: 6 feet is approximately 1.83 meters.

2. Use the dose rate at 1 meter to ascertain the expected intensity at 1.83 meters.

3. Given that the radiation follows the inverse square law, the intensity will decrease with the square of the distance. Therefore, the intensity measured at 6 feet can help approximate the activity