Final answer:
The cutoff in millicurie for major spills of technetium or thallium is not specified but is determined by regulatory bodies. A millicurie is a unit of radioactive decay, and different thresholds for major spills depend on the isotope, its activity, and spill area.
Step-by-step explanation:
The specific cutoff in millicurie (mCi) for a major spill of technetium or thallium is not mentioned in the provided reference, but the term millicurie is described as a larger unit for the rate of radioactive decay frequently used in medicine, where 1 Ci equals 3.7 x 10¹⁰ disintegrations per second. In a medical context, radioisotopes for use often have the information of mCi per milliliter (mCi/mL). When managing radioactive materials, different regulatory bodies have varying thresholds for what constitutes a 'major' spill, and it usually depends on multiple factors including the radioisotope, its activity, and the area of the spill. For example, the U.S. Nuclear Regulatory Commission (NRC) provides specific guidance on these matters. It’s essential for individuals working with these substances to follow their institution's protocols and the regulations set forth by the appropriate health and safety authorities.