Chemistry Figures

Identify the isotope from its half-life: three decay curves

An example figure from the Half-Life Graph generator.

Three decay curves, solid, dashed and dotted, named Isotope A, Isotope B and Isotope C in a key, against time in years from 0 to 160
Three radioactive isotopes decaying on one graph, percent remaining against time in years. The curves are solid, dashed and dotted so they read apart in black and white, and the key calls them only Isotope A, B and C. Students read each half-life off the curve where it crosses 50% and match the isotopes to a table of half-lives.
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Answer key

  • Isotope A is hydrogen-3: half-life 12.3 years, λ = 0.0564 per year; beta decay to helium-3
  • Isotope B is cesium-137: half-life 30.1 years, λ = 0.023 per year; beta decay to barium-137
  • Isotope C is cobalt-60: half-life 5.27 years, λ = 0.132 per year; beta decay to nickel-60

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