(A) 131 I is a emitter used as a tracer for radioimmunoassays in biological systems....

(A) ¹³¹I is a β^– emitter used as a tracer for radioimmunoassays in biological systems. Use information in Table 25.1 to determine 

(a) The decay constant in s^–1; 

(b) The activity of a 2.05 mg sample of ¹³¹I;

(c) The percentage of ¹³¹I remaining after 16 days; 

(d) The rate of β^– emission after 16 days.

(B) ²²³Ra has a half-life of 11.43 days. How long would it take for the activity associated with a sample of ²²³Ra to decrease to 1.0% of its current value?

Table 25.1

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TABLE 25.1 Some Representative Nuclide Half-Lifea Nuclide H 12.33 a 10K 14C 5715 a ¹30 8.7 x 10-³ s 21 h 14.3 d 87.9 d Mg Br 3 Sr 131 13 Cs Half-Lives Half-Lifea 1.26 x 10° a 17.6 min 29.1 a 8.021 d 30.2 a Nuclide 214 Po 84 222Rn 86 22 Ra 88 234 Th 90 239 U Half-Lifea 1.64 x 10-4 s 3.823 d 1.599 × 10³ a 24.10 d 4.47 × 10° a