The study of atomic nuclei, their structure, reactions and interactions. Nuclear forces between nucleons and nuclear binding energies connect it to the low-energy consequences of Quantum chromodynamics.
An energetically allowed weak transition converts a neutron into a proton, emitting an electron and an electron antineutrino. Free neutron decay is an example; in nuclei, the nuclear binding energy determines whether the transition is possible.
Fusion combines nuclear reactants into heavier compound nuclei or products. A net decrease in rest mass releases energy; heavier fusion reactions can instead require energy. Stellar nuclear fusion uses exothermic networks to power stars, and quantum tunnelling through the Coulomb barrier permits many charged-particle reactions at stellar temperatures.
Repulsion between positively charged nuclei creates this electrostatic energy barrier outside the short-range nuclear interaction. Quantum tunnelling allows reaction at thermal energies below its classical height and contributes the penetration factor in the Gamow peak.
A sufficiently energetic photon can break up a nucleus, consuming energy for an endothermic breakup. In neon burning and silicon burning, such steps combine with captures to form a larger reaction network whose net energy balance can be positive.
An energetically allowed weak nuclear transition converts a proton into a neutron, emitting a positron and electron neutrino. Positron annihilation deposits additional electromagnetic energy, while the neutrino can escape. These transitions are steps of the CNO cycle and the pp III branch; an isolated free proton cannot undergo this decay.
A nucleus can capture an electron when energetically allowed, converting a proton into a neutron and emitting an electron neutrino. Beryllium-7 electron capture participates in one of the proton-proton chain branches. Stellar capture rates depend on ionization, mass density and electron phase space.
The residual strong interaction between nucleons. Its long-distance part involves pion exchange and depends on spin and isospin. It is distinct from directly exchanging gluons between color-singlet nucleons.
The central system of protons and neutrons in an atom. Its mass number is its baryon number in ordinary nuclear states; is the proton number and the neutron number.
The helium-four atomic nucleus, containing two protons and two neutrons. Its ground-state spin and isospin are zero. A quantized cubic four-Skyrmion supplies a corresponding nuclear state in the soliton description.
The bound atomic nucleus containing one proton and one neutron. Its ground-state spin is one and its isospin is zero. The appropriately quantized toroidal two-Skyrmion models these quantum numbers.
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Nuclear physics is the branch of physics that deals with the study of atomic nuclei, their constituents (protons and neutrons), and the interactions that occur between them. It encompasses a variety of topics, including: 1. **Structure of the Nucleus**: Understanding the arrangement of protons and neutrons within an atomic nucleus, including models that describe nuclear stability and the forces that hold the nucleus together (strong nuclear force).
Nuclear physics is basically just the study of the complex outcomes of weak interaction + quantum chromodynamics.