An individual's thyroid absorbs 0.1 joules of energy. The thyroid mass is 0.03 kg. What is the absorbed dose to the thyroid?

An individual's thyroid absorbs 0.1 joules of energy. The thyroid mass is 0.03 kg. What is the absorbed dose to the thyroid?

• A. 0.003 gray (Gy)
• B. 0.03 gray (Gy)
• C. 0.3 gray (Gy)
• D. 3.3 gray (Gy)

Answer: (D)

Absorbed dose equals energy deposited per unit mass, with the gray defined as joule per kilogram. Here the thyroid receives 0.1 joules of energy and has a mass of 0.03 kilograms. So the dose is 0.1 J divided by 0.03 kg, which equals 3.333... J/kg, i.e., about 3.3 gray (Gy) when rounded to two significant figures. This matches the correct value because dose depends solely on how much energy is deposited per unit mass, not on how that energy is distributed within the tissue. If you tried smaller numbers like 0.003 Gy or 0.03 Gy, that would require a much larger mass to reach the same energy deposit; conversely, a much larger dose would require a smaller mass.

Absorbed dose equals energy deposited per unit mass, with the gray defined as joule per kilogram. Here the thyroid receives 0.1 joules of energy and has a mass of 0.03 kilograms. So the dose is 0.1 J divided by 0.03 kg, which equals 3.333... J/kg, i.e., about 3.3 gray (Gy) when rounded to two significant figures.

This matches the correct value because dose depends solely on how much energy is deposited per unit mass, not on how that energy is distributed within the tissue. If you tried smaller numbers like 0.003 Gy or 0.03 Gy, that would require a much larger mass to reach the same energy deposit; conversely, a much larger dose would require a smaller mass.