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Chapter 8

MEDRADSC 2Z03 Chapter Notes - Chapter 8: Nuclear Medicine, Radionuclide, Half-Life


Department
Medical Radiation Sciences
Course Code
MEDRADSC 2Z03
Professor
Dawn Danko
Chapter
8

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HALF-LIFE OF A RADIOISOTOPE
Every radioisotope has a characteristic half-life (t12) which is the time required for the
radioactivity to decay to 50% of its original value. The half-lives of some of the common
radioisotopes used in nuclear medicine are presented in Table 2.
Radioisotope Half-life
Carbon-11 20 minutes
Fluorine-18 110 minutes
Copper-64 12.7 hours
Gallium-67 78.3 hours
Gallium-68 68 minutes
Technetum-99m 6.02 hours
Indium-111 67.3 hours
Iodine-123 13.22 hours
Thallium-201 72.9 hours
Table 2: Examples of half-lives of some of the common radioisotopes used in nuclear
medicine
In one half-life, the activity A is reduced by A2
In two half-lives, the activity A is reduced by A22 (so the activity is reduced by a quarter)
In three half-lives, the activity A is reduced by A23 (so the activity is reduced by an
eighth)
In n half-lives, the activity A is reduced by A2n
The activity of a radioisotope at any time t is given by:
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