Alpha Decay and Nuclear Stability

• Atoms consist of protons, neutrons, and electrons.
• Protons and neutrons reside inside the nucleus.
• Two forces act within an atom's nucleus: electrostatic repulsion and strong nuclear force.
• Atoms are stable and do not emit anything from their nucleus where the strong nuclear force is greater than electrostatic repulsion.
• Atoms are unstable and will emit particles and/or wave from its nucleus when the strong nuclear force is less than electrostatic repulsion.
• The emitted particles and/or waves from unstable nuclei are radiation.
• Atoms can be written in two different ways.
• The +1 indicates a positive charge, making the atom a cation. It has one more proton than electron to create a +1 charge.

Alpha Decay (α)

• Reason for decay: Isotope is unstable due to being too large.
• An alpha particle contains two protons and two neutrons.
• Particle Symbol: α or He
• During alpha decay, the number of protons and nucleons is conserved.
• The starting atom is called the Mother.
• The final atom is called the Daughter.

Beta Minus Decay (β −)

• Reason for decay: Isotope is unstable due to having too many neutrons.
• A neutron changes into a proton, an electron, and antineutrino (v).
• The electron and antineutrino are emitted, while the proton remains in the nucleus.
• An antineutrino accounts for an apparent energy loss.
• Particle Symbol: -β or e

Beta Positive Decay (β +)

• Reason for decay: Isotope is unstable due to having too many protons
• A proton will change into a neutron, a positron (+₁e) and an uncharged massless particle called a neutrino (v).
• The positron and neutrino are emitted while the neutron remains in the nucleus.
• Symbol: +1β or +1e

Gamma Decay (γ)

• Reason for decay: Isotope is left in a temporary energized, metastable state following alpha or beta decay.
• Gamma rays are electromagnetic waves with no charge and do not alter the mass number of the nucleus.

Radiation Properties

• Alpha particle structure: 2 protons + 2 neutrons (Helium nucleus).
• Beta particle structure: Electron.
• Gamma structure: Electromagnetic wave. -Alpha range through air: Low (a few cm). -Beta range through air: Moderate (1-2m).
• Gamma range through air: High (almost unlimited).
• Alpha transmission ability: Low, stopped by paper or skin.
• Beta transmission ability: Moderate, stopped by a few mm of aluminium.
• Gamma transmission ability: High, stopped by thick lead or concrete.
• Alpha charge: +2
• Beta charge: -1
• Gamma charge: 0
• Alpha ionizing ability: High.
• Beta ionizing ability: Moderate.
• Gamma ionizing ability: Low.
• Alpha danger to humans: Dangerous if ingested.
• Beta danger to humans: Moderate danger, can pass through skin if within range.
• Gamma danger to humans: Most dangerous externally, easily passes through skin.
• Alpha speed through air: 10% of the speed of light (0.1c).
• Beta speed through air: 90% of the speed of light (0.9c).
• Gamma speed through air: speed of light (c).
• Alpha effect of fields: Deflects towards a negative charge.
• Beta effect of fields: Deflects towards a positive charge.
• Gamma effect of fields: No deflection.
• Alpha typical energy: High (5 MeV).
• Beta typical energy: Moderate (1 MeV).
• Gamma typical energy: Low (0.1 MeV).

Half-Life

• Radioactive samples contain billions of atoms that decay at different rates, following a similar decay pattern.
• Half-life is the time taken for half the radioactive nuclei in a sample to decay.

Inverse Square Law

• A physical quantity (like intensity, force, or radiation) is inversely proportional to the square of the distance from the source.
• If the distance from the source is doubled, the intensity reduces to one-fourth of its original value.
• If the distance is tripled, the intensity becomes one-ninth of its original value.

Decay Series

• After alpha, beta, or gamma radiation emission, some isotopes remain unstable.
• Daughter nuclei will continue to emit radiation until stable.

Radiation Effect on Humans

• Ionising radiation is dangerous because it creates chemically reactive ions within cells.
• These ions can start undesirable chemical reactions, possibly leading to cancers, tumours, and cell death.
• Charge strength order: Alpha (+2), Beta (-1), Gamma (neutral)
• Ionising power order: Alpha, Beta, Gamma (due to charge strength)

Fission

• An isotope splits into two or more daughter nuclei (fragments).
• Triggered by neutron absorption.
• The binding energy supplying the strong nuclear force is released as heat and light.
• Free neutrons are released.
• Chain Reaction: Free neutrons can trigger a chain reaction
• Applications: nuclear power, nuclear weapons

Fusion

• Two or more nuclei combine to form one nucleus.
• Energy releases as heat and light as electrostatic forces are overcome.
• Applications: Sun, hydrogen bombs, fusion reactors

Mass Defect

• In fusion and fission, there is a mass defect where the number of particles before and after is conserved, their mass is reduced
• The lost mass converts to energy

Electron Volt

• Electron volt (eV) is a unit to measure kinetic energy (KE) acquired when an electron accelerates in an electric field.
• 1eV equals the KE an electron acquires when it accelerates in an electric field by a potential difference of one volt.