Appendix 2: Answers to Chapter 2

(b) ²⁰¹Tl decays by electron capture with gamma emissions of 0.135 MeV and 0.167 MeV.

(c) Stannous chloride is a reducing agent which changes the valence state of Tc in pertechnetate. It has no effect on either the amount of Al³⁺ or the radiation dose.

(b) The half-life of ¹³¹I is 8.06 days. Since the time elapsed is about two half-lives, the original activity would be halved twice (50 mCi/2 = 25 mCi, 25 mCi/2 = 12.5 mCi).

(b) 20 mCi × 0.62 = 12.4 mCi

(d) To find the effective half-life, we use the formula