38. Iodine-131, t1/2 = 8.0 days, is used in diagnosis and treatment of thyroid gland diseases. If a laboratory sample of iodine-131 initially emits 9.95 \(\times\) 1018 \(\beta\) particles per day, how long will it take for the activity to drop to 6.22 \(\times\) 1017 \(\beta\) particles per day? (ln 2 = 0.693)
(A)48 days
(B)32 days
(C)16 days
(D)128 days
(E)2 days

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