Frontier physics

Radioactivity and decay modes

Watch an ensemble of unstable nuclei decay and verify the exponential law $N(t)=N_0e^{-\lambda t}$ with half-life $T_{1/2}=\ln2/\lambda$ , while observing how random individual decays build the smooth average.

High school

⚠ Ionizing radiation is invisible and cumulative; real sources are handled only with shielding, distance, time limits and dosimeter badges in licensed labs.

Equipment

3D population model of parent nuclei with decay events
Sliders “Tham số” and “Tham số vật lý” (decay-rate parameters)
Slider “Độ nhiễu” (noise level) for statistical fluctuations
“Chạy thời gian” (run time) control

Procedure

Measure the half-life
Start the time evolution with default parameters and let the parent-nucleus count run down. Note the time at which N crosses $N_0/2$ , then $N_0/4$ : equal ratios take equal times — the defining property of $N(t)=N_0e^{-\lambda t}$ .
Extract λ and the activity
From your measured $T_{1/2}$ compute $\lambda=\ln2/T_{1/2}$ and the activity $A=\lambda N$ at two instants. Check that A falls by the same factor as N — activity is proportional to the surviving population.
Explore the randomness
Raise the noise slider and rerun: individual decays become visibly irregular around the mean curve. Then change the decay-rate parameter and predict the new half-life before measuring — a larger λ means faster decay, $T_{1/2}=\ln2/\lambda$ .

Simulation

Experiment history

Henri Becquerel discovered radioactivity in 1896 when uranium salts fogged photographic plates in a dark drawer — no phosphorescence required. Marie and Pierre Curie isolated polonium and radium by 1898, showing some elements transform themselves; Marie coined the term “radioactivity.” Ernest Rutherford and Frederick Soddy explained the phenomenon around 1902–03 as transmutation of elements with a statistical decay law, and Rutherford separated α, β and later γ radiation. The exponential law with constant half-life became the clock of nuclear physics — dating rocks, calibrating medical doses, and powering deep-space probes.

Related physicists

Marie Curie Niels Bohr Henri Becquerel Pierre Curie

Equipment

Procedure

Simulation

Experiment history

Related physicists

Related library topics