PROBLEMS
1) By direct measurement of the activity of the thyroid gland in several patients who had received ¹³¹I for diagnostic purposes, it was observed that the biological elimination half-life for the radionuclide was 5.22 days. What is the efficient half-life and what is the value of the effective decay constant?
2) find out for 3H the mean energy per nuclear disintegration, Δ. SI unit for Δ is kg Gy Bq^-1 s^-1 identical with J Bq^-1 S^-1. Efficient half-life for tritium in body water is 10.5 days. Suppose the injection of 50 MBq of tritium labelled water. What is the average absorbed dose in water after the elapse of three half-lives? Suppose equilibrium conditions of energy deposition as defined in this chapter.
3) find out the mean energy per nuclear disintegration, Δ, for ^99mTC if 2.0 x 10⁹ Bq of this isotope is injected into a patient. Suppose that one-half of the administered dose is taken up by the thyroid and that the removal kinetics follow first-order exponential form with a biological half-life of 4 h. What is the dose to the thyroid? Suppose for purposes of this problem that the specific absorbed fraction is 0.5 and the thyroid weighs 80 g. Express the dose in gray.