Question

The walls of a CT scanner room are coated with:

• A. Lead
• B. Glass
• C. Tungsten
• D. Iron

Hint:

Think dense, high atomic number, cheap, and easy to roll into sheets.

Answer 1

The Correct Option is A

Step 1: A CT scanner uses an X-ray tube, so the room must shield staff and the public from scattered X-ray photons.
Step 2: A good shielding material needs a high atomic number and high density so it absorbs photons by the photoelectric effect over a thin layer. It should also be cheap, workable into sheets, and chemically stable.
Step 3: Lead has atomic number 82 and very high density, attenuates X-rays efficiently, is inexpensive, and is easy to roll into sheets fixed inside walls and doors. This makes it the standard barrier material for diagnostic X-ray and CT rooms.
Step 4: Why the others are wrong. Glass is used only as leaded glass in viewing windows, not as the wall coating. Tungsten has an even higher atomic number and is used inside the X-ray tube as the target and as collimator material, but it is hard and expensive and is not used to line whole rooms. Iron has a lower atomic number and density than lead and gives poor X-ray shielding for the same thickness.
Step 5: So the walls of a CT room are coated with lead.
Answer: Option A, Lead.