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Radioactive Decay: The spontaneous decomposition of an unstable nucleus into a a more stable one, emitting energized particles and/or electromagnetic radiation as a byproduct.
Radioactivity: The process of emitting energy from an unstable nucleus.
Alpha Radiation (α)
Occurs when a heavy nucleus needs to lose mass.
Products: Energized helium-4 nuclei.
Penetration: Low, can be stopped by a sheet of paper.
Ionizing Power: High.
Beta-Plus Radiation (β⁺)
Occurs when a lighter, proton-rich nucleus has too many protons.
Products: Energized positrons and neutrinos.
Penetration: Moderate, can be stopped by a thin sheet of low-density metal.
Ionizing Power: Moderate.
If positron emission isn't energetically favorable, electron capture may take place. This is when an electron falls into the nucleus, converting a proton into a neutron and decreasing the atomic number.
Beta-Minus Radiation (β⁻)
Occurs when an unstable nucleus has too many neutrons.
Products: Energized electrons and antineutrinos.
Penetration: Moderate, can be stopped by a thin sheet of low-density metal.
Ionizing Power: Moderate.
Neutron Radiation (n)
Occurs during nuclear reactions.
Products: Energized neutrons.
Penetration: Moderate, can be stopped by a few centimeters of low-density metal.
Ionizing Power: Moderate.
Gamma Radiation (γ)
Occurs when a nucleus releases energy during radioactive decay.
Products: High-energy photons (gamma rays).
Penetration: High, can be stopped by a thick sheet of high-density metal.
Ionizing Power: Low.
Why Do Nuclei Decay?
Why Do Nuclei Decay?
Strong Nuclear Force: The strongest fundamental force. Exists between nucleons, has extremely short range.
Electromagnetic Force: The fundamental force that governs attraction and repulsion between charged particles. Significantly weaker than the strong force, but has a much wider area of effect.
Pauli Exclusion Principle: No two identical fermions (particles with half-integer spins) can occupy the same quantum state simultaneously within a quantum system.
Nucleons (protons and neutrons) are fermions, so the principle applies to them. Therefore, protons and neutrons have their own energy levels within a nucleus, like electrons in an atom.
Beta-Plus Decay: Caused by too much protons. The strong nuclear force only acts between nearby particles, while the electromagnetic force (responsible for proton repulsion) acts over longer distances. As atomic number increases, the overall repulsion force increases in strength due to the increase of positive charge density, while the strong force remains constant due to its short range of influence. Because of that, excessive protons lead to a net repulsion that overwhelms nuclear binding, causing instability.
Beta Minus Decay: Caused by too much neutrons. Neutrons in a nucleus occupy energy levels, each with a limited capacity. As more neutrons are added, they fill higher energy levels, increasing their overall energy. When too many neutrons are in a nucleus, the energy of the outermost ones can exceed the binding strength of the strong nuclear force, resulting in instability.
Alpha Decay: Caused by increasing electromagnetic repulsion between protons and the Pauli exclusion principle, which limits how nucleons can be arranged. When these forces exceed the binding energy, the nucleus may eject a stable He-4 nucleus (alpha particle) to quickly reduce mass and restore stability.
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