Nuclear structure
A nucleus contains \(Z\) protons and \(N\) neutrons. The mass number is \(A=Z+N\). Isotopes share the same \(Z\) but differ in \(N\).
Nuclear physics
Nuclei, radiation, fission, fusion, and detectors from first principles.
Nuclear physics studies the structure and transformations of atomic nuclei. It connects quantum mechanics, the strong force, electromagnetic repulsion, weak decay, astrophysics, medicine, energy, and radiation measurement.
Interactive nucleus
Change protons and neutrons.
The panel visualizes a simplified nucleus and estimates qualitative stability regions. It is intended for learning, not nuclear engineering or isotope production planning.
Strong force
The residual strong interaction binds nearby nucleons. It is short-ranged, attractive at nuclear distances, and much stronger than electromagnetic repulsion there.
Binding energy
Binding energy is the energy needed to separate a nucleus into free nucleons. Higher binding energy per nucleon generally indicates a more tightly bound nucleus.
Radioactive decay
Unstable nuclei can transform through alpha decay, beta decay, gamma emission, electron capture, spontaneous fission, or chains of multiple decays.
Fission
Fission splits a heavy nucleus into lighter fragments, releasing energy because the fragments are usually more tightly bound per nucleon.
Fusion
Fusion combines light nuclei. It powers stars and releases energy when the product has greater binding energy per nucleon than the reactants.
Core equations
Nuclear physics language.
These equations define quantities used across nuclear structure, reactions, and radiation measurement.
Mass energy
\[E=\Delta m c^2\]
Energy release in nuclear reactions comes from a mass difference between initial and final bound systems.
Decay law
\[N(t)=N_0 e^{-\lambda t}\]
The number of undecayed nuclei falls exponentially for a single radioactive species with decay constant \(\lambda\).
Half-life
\[T_{1/2}=\frac{\ln 2}{\lambda}\]
Half-life is the time required for half of a radioactive population to decay in the simple exponential model.
Radiation and detectors
How nuclear events become measurable signals.
Radiation detection converts particle or photon interactions into electrical, optical, or track-based records.
Alpha particles
Helium nuclei with high ionization and short range in matter. They are stopped easily but hazardous if alpha emitters enter the body.
Beta particles
Electrons or positrons emitted through weak interactions. Their penetration and shielding behavior differ from alpha and gamma radiation.
Gamma rays
High-energy photons from nuclear transitions. Gamma detection often uses scintillators, semiconductors, or spectroscopy systems.
Neutrons
Uncharged particles that interact through nuclear collisions and capture. Detection commonly uses moderation and capture reactions.
Scintillation
A scintillator emits light when radiation deposits energy. Photodetectors convert that light into electronic pulses.
Semiconductors
Ionizing radiation creates charge carriers in a semiconductor. The collected charge can estimate deposited energy.
Criticality link
Learn the chain-reaction modes separately.
Supercriticality is part of reactor and criticality-safety physics. The separate page explains subcritical, critical, delayed supercritical, and prompt-supercritical regimes with an interactive population model.