Half-Life (t½)
The time for half the undecayed nuclei in a sample to decay. After 1 half-life: 50% remain. After 2: 25%. After 3: 12.5%. Half-life is constant for each isotope.
Random Decay
Radioactive decay is random and unpredictable for individual atoms. We cannot say when a particular nucleus will decay, only the probability. This is why each simulation run gives slightly different results.
Exponential Decay
N(t) = N₀ × (½)^(t/t½). The number of undecayed atoms decreases exponentially. The rate of decay is proportional to the number of atoms remaining.
Types of Radiation
Alpha (α): 2 protons + 2 neutrons, stopped by paper. Beta (β): fast electron, stopped by aluminium. Gamma (γ): electromagnetic wave, reduced by thick lead.
Activity
The rate of decay measured in Becquerels (Bq). 1 Bq = 1 decay per second. Activity halves with each half-life since fewer atoms remain to decay.