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Nuclear Physics

Inside every atom is an astonishingly energetic nucleus. Nuclear physics is the science of how those nuclei hold together, transform and release energy. This category covers radioactive decay chains, neutron-driven fission chain reactions, thermonuclear fusion, the binding energy curve and reactor neutron kinetics. By adjusting parameters in each interactive Nuclear Physics model — enrichment, plasma temperature, control-rod position or half-life — you can see directly why some reactions die out while others run away. You will learn the exponential decay law, the neutron multiplication factor, the Lawson criterion and why iron-56 sits at the peak of stability. It matters because these same principles power reactors, medical imaging, radiometric dating and the stars themselves, making this one of the most consequential branches of modern science.

7 simulations Fission · Decay Monte Carlo · Chain Reactions

Category Simulations

Open a simulation — it runs right in your browser

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New ★★★ Advanced
Ising Model
Statistical mechanics of a 2D ferromagnet: Metropolis-Hastings Monte Carlo on a square lattice. Dial temperature through the critical point and watch phase transitions and domain walls emerge.
Statistical Mechanics Monte Carlo Phase Transition
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New ★★☆ Moderate
Nuclear Fission Chain Reaction
Neutron-induced fission with configurable enrichment and moderator. Watch the chain reaction go subcritical, critical or supercritical.
Fission Neutron Transport Canvas 2D
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New ★☆☆ Beginner
Radioactive Decay Simulator
Start with N₀ unstable nuclei and watch them decay stochastically. Compare exponential decay law with the actual random simulation.
Half-Life Stochastic Canvas 2D
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New ★★☆ Moderate
Binding Energy Curve
The Bethe-Weizsäcker semi-empirical mass formula plotted interactively. Understand why iron-56 is the most stable nucleus and where fusion/fission releases energy.
Binding Energy SEMF Canvas 2D
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New ★★★ Advanced
Nuclear Fusion — Tokamak
D-T fusion in a tokamak reactor. Adjust plasma temperature, density and confinement time to meet the Lawson criterion and achieve ignition. Real-time Q factor and fusion power density output.
Tokamak Lawson Criterion Q Factor
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★★★ Advanced New
Nuclear Reactor — Neutron Kinetics & Control Rods
Point kinetics model of a nuclear reactor. Insert or withdraw control rods, change reactivity and watch neutron population, delayed neutron precursors and power evolve in real time.
Point Kinetics Control Rods Delayed Neutrons

Related Articles

The physics behind nuclear reactions

About Nuclear Physics Simulations

Radioactive decay, chain reactions, fission, and fusion modelled

Nuclear physics simulations model the behaviour of atomic nuclei and the reactions that release nuclear energy. Radioactive decay simulations place hundreds of unstable nuclei on screen and allow each to decay stochastically with its empirical half-life, directly demonstrating the exponential decay law and statistical fluctuations. Nuclear chain-reaction simulations track neutron multiplication in a fissile slab under subcritical, critical, and supercritical conditions.

Fission and fusion cross-section visualisers show how reaction probability varies with incident particle energy, explaining why fusion requires plasma temperatures above 100 million Kelvin. These models draw on data from the ENDF nuclear reaction database and use Monte Carlo neutron-transport techniques — the same methods employed in reactor safety codes and nuclear-weapon simulation programs (declassified educational versions).

Each simulation in this category is built with accuracy and interactivity in mind. The underlying mathematical models are the same ones used in academic research and professional engineering — just made accessible through a web browser. Changing parameters in real time and observing the results is one of the most effective ways to build intuition for complex scientific and engineering concepts.

Key Concepts

Topics and algorithms you'll explore in this category

Interactive ModelReal-time browser simulation with live parameter controls
WebGL / Canvas 2DHardware-accelerated rendering in the browser
Mathematical FoundationDifferential equations and numerical integration
Open SourceMIT-licensed code — inspect, fork, and learn
No Install RequiredRuns directly in Chrome, Firefox, Safari, Edge
Educational FocusBuilt to explain the underlying science clearly

Frequently Asked Questions

Common questions about this simulation category

What is radioactive half-life and how does the simulation model it?
Half-life T½ is the time for half of a radioactive sample to decay. The exponential decay law N(t) = N₀·exp(−λt) describes the average behaviour, but individual nuclei decay randomly. The Radioactive Decay Simulator places N₀ unstable nuclei on screen and decays each one stochastically with probability λΔt per timestep, letting you see statistical fluctuations around the theoretical exponential curve — and why small samples show larger relative fluctuations.
What determines whether a fission chain reaction goes critical?
The neutron multiplication factor k_eff determines the chain reaction regime: k_eff < 1 is subcritical (reaction dies out), k_eff = 1 is critical (steady power), and k_eff > 1 is supercritical (exponential growth). k_eff depends on enrichment (fraction of fissile U-235), moderator (slowing neutrons improves fission cross-section), and geometry (minimising neutron leakage). The Fission Chain Reaction simulation lets you adjust all three parameters and watch the neutron population evolve.
Why does nuclear fusion require such extreme temperatures?
Fusion requires two positively charged nuclei to come close enough (~1 fm) for the strong nuclear force to bind them, overcoming the Coulomb repulsion barrier. At temperatures above ~100 million K, particle kinetic energies exceed the barrier height via quantum tunnelling. The Lawson criterion — nτT ≥ threshold — specifies the plasma density n, confinement time τ, and temperature T needed to sustain a burning plasma with Q > 1 (energy gain). The Tokamak Fusion simulation shows you how to meet this criterion.
Why does the binding energy curve peak at iron-56?
The Bethe-Weizsäcker formula shows that binding energy per nucleon rises steeply for light nuclei (strong force wins over surface tension), peaks near iron-56, then falls for heavier nuclei (Coulomb repulsion between protons grows). This means fusing hydrogen up to iron releases energy, while splitting uranium or plutonium down toward iron also releases energy. Iron is therefore the thermodynamic endpoint of stellar evolution and the reason neutron stars and supernovae exist.

Other Categories

Every Nuclear Physics simulation in this collection runs straight in your browser, so you can learn Nuclear Physics online without any installation or specialist hardware. Each interactive Nuclear Physics model — from stochastic radioactive decay to a critical fission chain reaction, tokamak fusion and reactor neutron kinetics — lets you turn abstract equations into something you can watch unfold in real time. The same physics underpins real-world applications such as cancer-treating radiotherapy, carbon-free reactor power and radiocarbon dating, making these models a practical way to build genuine intuition for how the atomic nucleus behaves.