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

Question

131 Iodine 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 of131 Iodine. Assume that all of the iodine is absorbed by the 0.15 kg thyroid gland. Each 131Iodine 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? Include units.

Explanation / Answer

Here 1 Curie = 1 Ci =3.7*10^10 disintigrations/sec

Energy deposited in one hour

E(t)=3.7*10^10 disintigrations/sec* 3600 sec/hour * 0.05*10^(-3) Ci *0.5 (absorption fraction) * 0.97 Mev *        1.602*10^-13 J/MeV / 0.15 kg
E= 3.45*10^-3 J/kg = 3.45*10^-3 Gy
1 Gy = 1Sv for betas
therefore dose-equivalent = 3.45*10^-3 Sv

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