Question

11. A small quantity of solution containing 24Na radionuclide (half life 15 hours) of activity 1.0 microcurie is injected into the blood of a person. A sample of the blood of volume 1 cm3 taken after 5 hours shows an activity of 296 disintegrations per mimute. Deterimine the total volume of blood in the body of the person. Assume that the radioactive solution mixes uniformly in the blood of the person. (1 Curie - 3.7 x 1010 disintegrations per second) 12. At a given instant there are 25% undecayed radio-active nuclei in a sample. After 10 sec the number of undecayed nuclei remains to 12.5% Calculate: (i) mean - life of the nuclei and (ii) The time in which the number undecayed nuckxar wil l iur her reduce to 6.25% of ũheroduccc1 number.

Answer 1

15 x 3600 Activity of 24Na after 5 hours A = 1 × 10-6 × 3.7× 1010 1 cm3296 x cm3-296 x And 296 x 3.7 x 104 x e-n2/3 x-6 liters

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25 -i10 100 2 In 2 10 2. = 10 sec. 2 10 tan g = ln 2 t = 40 sec.