A radiation worker inhales a large volume of alpha-emitting radon gas (Wr = 20), resulting in an absorbed dose of 1.02 Gy to the lungs. What is the equivalent dose?

• A. 20.4 Sieverts (Sv)
• B. 1.02 Gray (Gy)
• C. 2448 millisieverts (mSv)
• D. 1.02 milligrays (mGy)

Answer: (A)

The key idea is converting the absorbed dose to an equivalent dose using the radiation weighting factor. For alpha radiation, the weighting factor is 20. The equivalent dose H_T = D_T × w_R, where D_T is the absorbed dose in grays. Here, D_T = 1.02 Gy and w_R = 20, so H_T = 1.02 × 20 = 20.4 Sv. This shows why the equivalent dose is measured in sieverts, not grays, because the weighting factor accounts for the higher biological impact of alpha particles. In other units, 20.4 Sv equals 20,400 mSv.

So the correct reasoning yields 20.4 Sv, not the other values listed.