Plotting/Sketching Decay Curves for Radioactive Materials

Half-life is a fundamental concept in understanding radioactivity. It is the time taken for the number of radioactive nuclei (or the activity) in a sample to decrease by half.
Decay curves are a graphical representation of how the radioactivity (or number of radioactive nuclei) in a substance changes over time.
The y-axis (vertical) usually represents the radioactivity count or the number of radioactive nuclei, while the x-axis (horizontal) represents time.
When plotting or sketching a decay curve, one must start from a fixed point on the y-axis which signifies the initial radioactivity or number of radioactive nuclei.
The curve should show a consistent decrease over time, indicating that the radioactivity or the number of radioactive nuclei in the sample is decreasing.
The curve should be smooth and should curve downwards, not straight. This is because the rate of decay is not linear, but exponential. This means that the amount of decay decreases over time, but never reaches zero.
At the half-life point on the x-axis, the radioactivity count or the number of radioactive nuclei should be half of the initial value. This is an important point on the decay curve and it is used to measure the half-life of a radioactive substance.
Consequently, every time you move along the x-axis by one half-life, the y-value should halve.
The curve goes on decreasing but never reaches zero, theoretically implying that radioactivity never completely disappears but keeps reducing infinitely.
A common mistake made when sketching decay curves is to make the curve too steep or too shallow. Remember, the curve should show a steady, consistent, and exponential decrease.
The longer the half-life of a radioactive substance, the shallower its decay curve would be.
It’s worth noting that if a decay curve is plotted on a graph with logarithmic scales, the decay will appear as a straight line. This represents the same relationship shown in a typical decay curve, but visualised in a different way.