Question

9. Technetium-99m is an ideal radioisotope for scanning organs, because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 80.0 mg were prepared in the technetium generator this morning. How many milligrams would remain after: a. one half-Life b. two half-lives c. 18 hrs. d. 24 hrs.

Answer 1

a) half life t1/2 = 6 hr

t/t1/2 = n = 1

amount of reactanta remaining after n t1/2 = a/2^n

n= 1

= 80/2 = 40 mg

b) n= 2

= 80/2^2 = 20 mg

c) t = 18

t/t1/2 = n,   18/6 = 3

n = 3

= 80/2^3 = 10 mg

d) t = 24 hr  

24/6 = 4

= 80/2^4 = 5 mg