131I undergoes beta-minus decay with a subsequent gamma emission from the daught

Question

131I undergoes beta-minus decay with a subsequent gamma emission from the daughter nucleus. Iodine in the body is almost entirely taken up by the thyroid gland, so a gamma scan using this isotope will show a bright area corresponding to the thyroid gland with the surrounding tissue appearing dark. Because the isotope is concentrated in the gland, so is the radiation dose, most of which results from the beta emission. In a typical procedure, a patient receives 0.050 mCi of131I. Assume that all of the iodine is absorbed by the 0.15 kg thyroid gland. Each 131I decay produces a 0.97 MeV beta particle. Assume that half the energy of each beta particle is deposited in the gland.

What dose equivalent in Sv will the gland receive in the first hour?

Express your answer to two significant figures and include the appropriate units

Explanation / Answer

1 Curie = 1 Ci =3.7 e10 dis/s

Energy deposited in one hour

3.7e10 dis/s * 3600 s/h * 0.05e(-3) Ci *0.5 (absorption fraction) * 0.97 Mev * 1.602e-13 J/MeV / 0.15 kg

= 3.45e-3 J/kg = 3.45e-3 Gy

1 Gy = 1Sv for betas

therefore dose-equivalent = 3.45e-3 Sv

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