2 marksExplain why the effective half-life of a radionuclide in a biological system is always less than the physical half-life.
4 marksThe physical half-life of a radionuclide is 20 days. The nuclide was administered to a patient. Initially the corrected count rate at the patient’s body was 2700 counts s−1. Five days later, the corrected count rate at the same place on the patient was 1200 counts s−1.
Calculate the biological half-life of the nuclide.
4 marksTable 1 gives the properties of two radionuclides.
Table 1
Technetium 99 m | Iodine 131 | |
Emitted radiation | gamma | beta− and gamma |
Half life / hrs | 6.0 | 190 |
Energy of gamma ray / keV | 140 | 610 |
By considering information in Table 1 suggest which of these nuclides is more suitable for use as a tracer in medical diagnosis.
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