Question

Below are data from the research study done on 28 individuals. Each individual was injected with a dose of iodine-131 with an initial count rate of 18 000 cpm. The averaged daily count data for all 28 individuals appears in the table. Make a graph of the data and answer the following questions:

a) What is the effective half-life of I-131?

b) What is the biological half-life of I-131?

[NOTE: Day 0 is pre-injection count rate (i.e background).]

Day	Avg. CPM
0	50
1	10610
2	8040
3	6093
4	4618
5	3500
6	2653
7	2010
8	1523
9	1154
10	875
11	663
12	502
13	380
14	289
15	219
16	166
17	127
18	95
19	72
20	55

Answer 1

Graph Shows the daily average count of iodine along the y axis, plotted against the number of days in the x axis

Half Lives:-

Physical Half Life is the time for a quantity of radioisotope to decay by half.

Physical Half Life of IODINE – 131 is 8.1 days

Biological Half Life is the time for half of the amount of radionuclide to be expelled from the body.

Biological Half Life of IODINE – 131 is 138 days

Effective half life takes into account both physical and biological half.

Effective Half Life of Iodine – 131 is 7.60 days