Half-Life | Physics for GCSE/IGCSE - Year 11 PDF Download

Half-Life Basics

• Predicting the exact moment when a specific unstable nucleus will decay is impossible.
• However, it's feasible to determine the rate at which the activity of a sample decreases.
• This rate is quantified as the half-life.
• Half-life is defined as the duration required for half of the nuclei of a particular isotope in any sample to decay.
• In simpler terms, it's the time for the activity of a sample to reduce to half of its initial level.
• Various isotopes exhibit different half-lives, ranging from fractions of a second to billions of years.
• Half-life can be deduced from an activity–time graph.

• The half-life is the duration needed for the activity of a sample to decline from 100% to 50%.
  • This period is equivalent to the time required for the activity to drop from 50% to 25%.
  • The half-life remains consistent for a specific isotope.
• Half-life data can also be illustrated in tabular format.
  • With each successive half-life, the proportion of remaining isotopes halves.

Half-Life Graphs

• Begin by identifying the initial activity of the sample, noted where the line intersects the y-axis, labeled as A₀.
  • Halve this value and locate where this halved activity occurs on the graph.
  • Trace horizontally from this halved value on the y-axis to the nearest point on the curve.
  • Then, draw a vertical line downwards from that point until it intersects the x-axis.
  • The intersection point on the x-axis denotes the half-life.
• In essence, the half-life represents the time taken for the activity to diminish to half of its original value.

Background Radiation

• Background radiation constitutes the constant radiation inherent in the surrounding environment.
• Consequently, during any radiation-related experiment, a portion of the detected radiation will be attributed to background radiation.
• In experiments aimed at measuring half-life, it's imperative to consider the existence of background radiation.

• To do this you must:
  • Begin by assessing background radiation levels (without any additional sources) – referred to as the background count.
  • Proceed with the experiment as planned.
  • Adjust each reading by subtracting the background count, yielding a corrected count.
  • The corrected count serves as the most accurate estimation of radiation emitted by the source, essential for half-life measurement.