Final answer:
California state regulations require a gonadal shield to have a minimum thickness of 0.50 mm lead equivalent for protection against gamma rays. The effectiveness of lead shielding increases with its thickness, and lead aprons are commonly used for protection in medical and dental settings. Therefore, the correct answer is option 4. 0.50 mm lead equivalent
Step-by-step explanation:
According to California state regulations, the minimum thickness of a gonadal shield may not be less than 0.50 mm lead equivalent. When it comes to protecting against gamma rays, such as those emitted by 99m Tc, high-density materials like lead are most effective. The principle here is that a thicker layer of lead absorbs more gamma rays, thereby providing greater protection.
For instance, if a 0.170-mm-thick layer of lead absorbs half the gamma rays, then two layers of this thickness would absorb 75% of the gamma rays, because each layer absorbs half of what passes through the previous one. Consequently, as the number of layers increases, or equivalently, as the total thickness increases, the percentage of gamma rays absorbed also increases.
In practice, medical and dental protection often employs the use of lead aprons and other lead-shielded equipment to minimize exposure to radiation. This demonstrates the importance of using protective equipment of the regulated thickness for safety against gamma radiation.
Therefore, the correct answer is option 4. 0.50 mm lead equivalent