Plotting/Sketching Decay Curves for Radioactive Materials

Plotting/Sketching Decay Curves for Radioactive Materials

Decay Curves for Radioactive Materials

The concept of a decay curve

• Decay curves are graphical representations that show the decay of radioactive substances with time.
• The decay curve drops steeply for a radioactive material with a short half-life, and more slowly for a material with a longer half-life.

Plotting a Decay Curve

• On the y-axis, plot either the count rate (how many decays are detected per second) or the mass of the radioactive substance.
• On the x-axis, plot time.
• As the quantity of radioactive material decreases, draw a curve heading downwards from the point representing the initial amount of the material.

Interpreting a Decay Curve

• The half-life of a material can be found by finding the time interval on the x-axis where the y-axis value (quantity of material or count rate) becomes half of what it was.
• The curve becomes less steep as time progresses because the rate of decay decreases as there are fewer radioactive atoms.

The impacts of half-life

• Radioactive material with a short half-life will have a steep curve, as the material decays rapidly.
• Radioactive material with a longer half-life will have a gradually sloping curve, showing that it decays over a longer period.
• The half-life is the same no matter the total amount of material. This means that whether you start with 2 grammes or 2 kilogrammes of a radioactive material, its half-life remains the same.

Mathematics in Decay Curves

• Decay curves involve exponential decay, which means the rate of decay at any point is proportional to the quantity of material at that point.
• An understanding of how to manipulate and plot exponential curves is crucial for this part of the WJEC Physics (Combined) GCSE.