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# Radioactivity Problem Examples - Radioactive Decay Example...

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Radioactive Decay Example PHY213 1 Radioactivity Problem Example 1: The half-life of an isotope of phosphorusis 14 days. If a sample contains 3.0 × 10 16 suchnuclei, determine its activity. Express your answer incuries. The decay constant is 1 2 ln2 T λ = , so the activity is ( ( 29 ( 29 16 10 4 1 2 3.0 10 ln2 ln2 1.7 10 decays s 14 d 8.64 10 s d N R N T λ × = = = = × × or ( 29 10 10 1 Ci 1.7 10 decays s 0.46 Ci 3.7 10 decays s R = × = × Radioactivity Problem Example 2: A drug tagged with (half-life = 6.05 h) is prepared for a patient. If the original activity of the sample was 1.1 × 10 4 Bq, what is its activity after it has sat on the shelf for 2.0 h? The activity is 0 t R R e λ - = where 1 2 ln2 T λ = . Thus, ( 29 ( 29 ( 29 1 2 2.0 h ln2 ln2 4 3 6.05 h 0 1.1 10 Bq 8.7 10 Bq t T R R e e - - = = × = ×

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Radioactive Decay Example PHY213 2 Radioactivity Problem Example 3: The half-life of 131 I is 8.04 days. (a) Calculate the decay constantfor this isotope. (b) Find the number of 131 I nucleinecessary to produce a sample with an activity of 0.50 μ Ci. (a) The decay constant is ( 29 ( 29 7 1 4 1 2 ln2 ln2 9.98 10 s 8.04 d 8.64 10 s d T λ - - = = = × × (b) R N λ = , so the required number of nuclei is
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Radioactivity Problem Examples - Radioactive Decay Example...

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