If the operator stands behind a portable shield, the approximate total dose reduction would be about:

• A. 50%
• B. 75%
• C. 92%
• D. 99%

Answer: (C)

The main point is how effectively a shield blocks radiation. A portable lead shield dramatically cuts the operator’s exposure by attenuating photons, especially the scatter that would otherwise reach the operator behind the shield. Typical shielding performance for a portable barrier yields a reduction on the order of about tenfold, which corresponds to roughly 90% reduction in dose. In practice, some residual exposure remains because of small gaps around the shield, scatter that can reach the shield’s edges, and any leakage through seams, so the reduction isn’t perfect. Therefore, about 92% is a representative value for the dose reduction when the operator stands behind a portable shield—significantly lower than unshielded exposure but not zero.