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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper I covers inorganic chemistry.

UPSC Combined Geo-Scientist, Mains · 2024 · Mains Paper I

Q9(d). Time for activity to fall

Question

A sample of radioactive isotope with t₁/₂ of 1600 y has an activity of 20 mCi (Ci = curie). How long would it take the activity to be reduced to almost 1 mCi (≈1.25 mCi)?

Answer in brief

To reach the specified 1.25 mCi takes four half-lives, or 6400 y; to reach exactly 1.00 mCi would take about 6915 y.

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Topic notes: nuclear chemistry: radioactive decay, binding energy, radiocarbon dating and the GM counter, with every Civil Services, IFoS and Geo-Scientist PYQ →

Covershalf-life calculationradioactive activitycurienumber of half-lives

All parts of Question 9