A medical lab has a 16g of sample of radioactive isotopes. After 6 hours it was found that 12g of a sample have decayed. The half life of the isotope is:
Correct answer: D. 3 hours
- A. 12 hours
- B. 6 hours
- C. 2 hours
- D. 3 hours
Explanation
Original amount = 16gDecayed amount = 12gradioactive isotope left after 6 hours is, 16 g - 12 g = 4 gUse N = No/2nWhere N = 4g , No = 16gWithin 6 hours, the original amount of 16g was first halved to 8g and then it was halved to 4g16g ---3 hrs---- 8g ----3 hrs--- 4gThus the half-life of the sample is 3 hrs.
This question appeared on the ETEA MDCAT 2014 paper, which you can sit online with every answer explained.
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About Half-life and Rate of Decay
Half-life is the time required for half the unstable nuclei in a sample to decay, and it remains constant for a particular radioactive nuclide. Questions use the exponential decay law, decay constant, activity, remaining quantity and mean life. Radioactive decay is random for individual nuclei but predictable for large samples.
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