Final answer:
The thresholds for major spills of radioactive isotopes like I-131 and others are set based on the isotope's half-life, activity, and potential health effects. The masses for medical use, such as in thyroid scans, can be calculated from these values. Adhering to these thresholds is crucial for safety and environmental protection.
Step-by-step explanation:
The thresholds for major spills of various radioactive isotopes such as I-131, Tc99m, Tl-201, Ga-67, In-111, and I-123 are critical to ensure safety and to initiate appropriate decontamination procedures. These thresholds depend on regulatory guidelines which can vary by country and are determined based on the radioisotope's half-life, its activity, the potential for environmental contamination, and its biological effects. For example, I-131, which is used in thyroid scans, may have a specific activity threshold that initiates a major spill protocol when exceeded.
Given the half-lives and activities mentioned for I-131 and I-123 in thyroid scans, one can calculate the masses of these isotopes required for medical procedures. Similarly, quantities like that for 99m Tc used in brain scans can also be determined. The mass of a radioactive isotope for a given activity can be found by applying the concept of half-life and the isotope's specific activity.
Considering the health risks associated with radioactive spills, it is important to understand and adhere to the thresholds for spills of these isotopes. These thresholds are often part of a radiation safety program to minimize exposure to personnel and the environment.