Nuclear Physics

Learn how atoms split and fuse — interactively

Drag, drop, collide, and discover

²³⁵U

⚛️

Fission Lab

Split U-235 with a neutron. See what comes out.

STEP 1 →

🔥

Fusion Lab

Fuse hydrogen isotopes into helium.

STEP 2 →

💥

Chain Reaction

Watch neutrons cascade through fuel.

STEP 3 →

🏭

Build a Reactor

Place fuel rods, control rods & coolant. Keep it critical.

STEP 4 →

⚡

Accelerator

Fire particles at nuclei. Discover transmutation.

STEP 5 →

⏱️

Half-Life

Watch atoms decay in real-time with exponential curve.

STEP 7 →

🔬

Isotope Builder

Build any isotope and check if it's stable.

STEP 8 →

🛡️

Shielding

Test materials to block α, β, γ, and neutrons.

STEP 9 →

📊

Compare

Fission vs Fusion side by side.

STEP 10 →

🧠

Quiz

Test your knowledge.

STEP 11 →

0

Energy per fission of U-235

17.6 MeV

Energy per D-T fusion

10⁸ °C

Temperature for fusion ignition

Nuclear Fission

STEP 1: Drag the neutron into the U-235 nucleus

Particles

n

Neutron

mass ~ 1 amu, charge: 0

²³⁵U

Uranium-235

92p + 143n

A fissile isotope. When it absorbs a neutron, it becomes unstable U-236 and splits.

²³⁵U

Drop neutron here

Reaction Info

How Fission Works

A slow neutron is absorbed by U-235, forming an unstable U-236 compound nucleus that vibrates violently and splits into two smaller nuclei plus extra neutrons.

Conservation Laws

• Charge is conserved (protons in = protons out)

• Nucleons are conserved (mass number)

• Mass -> Energy via E=mc^2

Mass Defect

The products weigh slightly less than the reactants. This "missing mass" becomes ~200 MeV of kinetic energy.

Nuclear Fusion

STEP 1: Drag Deuterium and Tritium into the reaction zone

Hydrogen Isotopes

²H

Deuterium

1p + 1n

³H

Tritium

1p + 2n

Plasma Temperature

0 0 million C 200M

Cold plasma (0M C)

Deuterium

+

Tritium

Reaction Info

How Fusion Works

Two light nuclei must overcome Coulomb repulsion (both positively charged). At ~100 million C, they move fast enough for the strong nuclear force to bind them.

Why It Releases Energy

He-4 has higher binding energy per nucleon than D or T. The difference becomes kinetic energy.

Where It Happens

• The Sun's core (15M C + immense pressure)

• Hydrogen bombs (uncontrolled)

• Tokamak / Stellarator reactors (experimental)

Chain Reaction

Click any U-235 atom to fire a neutron at it — watch the cascade

Controls

Fuel Density

Control Rods

Rods: 0

Statistics

Fissions0

Generation0

Active Neutrons0

Energy (MeV)0

Critical Mass

When each fission causes >=1 more fission on average, the reaction is self-sustaining. More fuel = more likely to go critical.

Control Rods

Absorb neutrons to slow or stop the chain. In power plants, operators raise/lower rods to control the reaction rate.

Build a Reactor

Click a tool, then click cells to place. Keep k ~ 1.0

offline

Toolbox

Control Rod Height

Inserted 50% Withdrawn

Gauges

Temperature 25 °C

k-factor 0.000

subcritical k=1 supercritical

Power 0 MW

Fissions 0

Neutrons 0

How It Works

Fuel rods — U-235, fissions when hit by slow neutrons

Moderator — water, slows fast neutrons

Control rods — absorb neutrons, insert to slow reaction

Goal: k ~ 1.0 for steady power

Particle Accelerator

Fire projectiles at target nuclei. Adjust energy to see different interactions.

Low Energy (<50 keV)

Particle bounces off — Coulomb repulsion wins

Coulomb Barrier

Quantum tunneling possible near barrier energy

Ultra-High Energy

Deep inelastic — shatters the nucleus into fragments

Projectile

Target Nucleus

Beam Energy

10 keV 100 keV 1 MeV

Medium — near Coulomb barrier

Coulomb barrier: —

Shots fired: 0

Famous Experiments

α + N-14 — Rutherford's first transmutation (1919)

p + Li-7 — Cockcroft-Walton (1932)

n + U-238 — Try for fission!

Radioactive Half-Life

Watch atoms decay in real-time and compare with theoretical exponential curve

Isotope

Time Speed

0.25x 1x 5x

Stats

Isotope: Iodine-131

Real T½: 8 days

Decay type: β-

Used for: —

Alive atoms0

Decayed0

Initial total400

Sim time0.0s

Half-lives elapsed0.00

Expected (theory)400

Exponential Decay

N(t) = N₀ × (½)^t/T½

After 1 half-life, 50% remain. After 2 half-lives, 25%. After 10, only 0.1%.

Isotope Builder

Add/remove protons and neutrons. See if your isotope is stable or what decay mode it has.

C

Carbon

C-12

Protons (Z)

6

Neutrons (N)

6

Mass number A = 12

Stability

✓ STABLE

STABLE — this isotope exists in nature

Quick Presets

Radiation Shielding

Test how different materials block different types of radiation

Slot 1

Slot 2

Slot 3

Radiation Type

Alpha (α)

He nucleus (2p + 2n)

Very low — stopped by paper

Detector

Intensity 0 CPS

Fired0

Reached0

Blocked0

Transmission0%

Stopping Rules

α — paper stops it (heavy, +2 charge)

β — aluminum stops it (light, charged)

γ — lead (dense, high Z)

n — concrete (hydrogen-rich)

Fission vs Fusion

Side-by-side comparison

Binding Energy per Nucleon

This curve explains why both fission and fusion release energy. Both move nuclei toward Fe-56 (the peak), where binding energy per nucleon is highest.

Property	Fission	Fusion
Process	Splits heavy nuclei	Combines light nuclei
Fuel	U-235, Pu-239	Deuterium, Tritium
Energy per reaction	~200 MeV	~17.6 MeV
Energy per unit mass	~82 TJ/kg	~337 TJ/kg (4x more)
Temperature needed	Room temp (+ neutron)	~100,000,000 C
Chain reaction?	Yes (neutrons)	No (self-limiting)
Radioactive waste	Significant (long-lived)	Minimal (short-lived)
Fuel abundance	Limited (mining)	Abundant (seawater)
Controlled use today?	Yes (power plants)	Experimental (ITER, NIF)
Meltdown risk	Yes	No (self-stopping)

Key Insight

Both processes release energy because the products have higher binding energy per nucleon than the reactants. Fission moves heavy nuclei (right side of the curve) toward the peak, while fusion moves light nuclei (left side) toward the peak. The peak at Iron-56 is the most stable nucleus — you can't extract energy from it by splitting or fusing.

Test Your Knowledge

Drag each statement to the correct category

Score: 0 / 0

Nuclear Physics

Fission Lab

Fusion Lab

Chain Reaction

Build a Reactor

Accelerator

Half-Life

Isotope Builder

Shielding

Compare

Quiz

Nuclear Fission

Particles

Products

Reaction Info

Nuclear Fusion

Hydrogen Isotopes

Products

Reaction Info

Chain Reaction

Controls

Statistics

Build a Reactor

Toolbox

Control Rod Height

Gauges

Particle Accelerator

Projectile

Target Nucleus

Beam Energy

Radioactive Half-Life

Isotope

Time Speed

Stats

Isotope Builder

Protons (Z)

Neutrons (N)

Stability

Quick Presets

Radiation Shielding

Radiation Type

Detector

Fission vs Fusion

Binding Energy per Nucleon

Test Your Knowledge

Statements

Categories