Physics

Radioactive decay, Nuclear fusion and fission, Nuclear power plants

Atomic Mass

Total number of protons and neutrons

Atomic Number

Total number of protons

Nucleons

Either a proton or neutron within the nucleus of an atom

Strong nuclear force

One of the four fundamental forces in nature, responsible for binding protons and neutrons together inside the nucleus of an atom

Electromagnetic force

A physical interaction that occurs between electrically charged particles, opposite charges attract each other, while identical charges repel each other

Radioactive decay

The spontaneous process by which an unstable atomic nucleus loses energy by emitting ionizing radiation (alpha, beta, gamma) in order to become stable

How does strong nuclear force + electromagnetic force relate to the stability of a nucleus

• The stability of a nucleus depends on the constant competition between the strong nuclear force holding the nucleus together, and the electromagnetic force attempting to split it apart

• Strong nuclear force binds protons and neutrons together, whereas electromagnetic force causes the positive protons within the nucleus to naturally repel each other

• Large nuclei eventually become unstable because the strong nuclear force only effects nucleons that are close to each other and balanced, and when a nucleus has too many protons, the electromagnetic force eventually causes it to split apart

Different isotopes have different levels of stability

Because of the balance between protons and neutrons inside the nucleus, and the competing strong nuclear force and electromagnetic force acting on them

Binding Energy

• The energy that needs to be supplied to split a nucleus into its constituent nucleons

• Binding energy is absorbed when an atom or nucleus is broken apart, and released when an atom or nucleus is formed

• Binding energy of products > binding energy of reactant = exothermic (energy released)

• Binding energy of products < binding energy of reactant = endothermic (energy absorbed)

How does Binding Energy relate to the stability of a nucleus and nuclei becoming unstable?

• Binding energy is the energy needed to split a nucleus into its constituent nucleons

• A higher binding energy per nucleon means a nucleus is more tightly bound and more stable, whereas a low binding energy per nucleon indicates instability and a tendency to undergo radioactive decay

Mass Defect

• The mass lost when separate nucleons bind to form a nucleus

• mass of nucleons - mass of nucleus

• The total mass of a stable nucleus is always less than the masses of the constituent nucleons, this difference in mass is known as the mass defect

• This lost mass is converted directly into released energy through E=mc²

Mass Defect & Binding Energy

• Binding Energy = mass defect x speed of light² (E=mc²)

• Energy = Mass x Speed of Light (3 × 10⁸)²

• To split a nucleus into nucleons, the binding energy must be supplied to their nucleus, to replace the mass defect

Alpha Radiation (α)

• 2 protons + 2 neutrons (a helium nucleus)

• Mass: 4 u (atomic mass units)

• Charge: +2

• Speed: 5-10% the speed of light

• Ionizing ability: Strongly ionizing, double positive charge & large mass allows them to strongly attract + strip electrons away from neutral atoms they pass

• Penetrating power: Weakly penetrating, travels 1-5cm in air, can be stopped by paper or the outer layer of human skin

Beta Radiation (β)

• High energy, high speed electron

• Mass: 1/1860 the mass of a proton

• Charge: -1

• Speed: aprox. 30-90% the speed of light

• Ionizing ability: Moderately to weakly ionizing, stronger than gamma rays but weaker than alpha particles

• Penetrating power: Moderately penetrating, travels a few metres in air, can be stopped by 5mm of aluminium

Gamma Radiation (γ)

• High frequency electromagnetic waves

• Mass: 0

• Charge: 0

• Speed: The speed of light

• Ionizing ability: Weakly ionizing, they do not frequently interact with matter due to their lack of mass and electric charge

• Penetrating power: Highly penetrating, travels for an infinite range through air, can be stopped by 10cm of lead or several metres of concrete

Alpha Decay

• Where an unstable atomic nucleus changes into a new element by shooting out an alpha particle

• Atomic mass reduces by 4 and atomic number reduces by 2 in daughter nucleus

Beta Decay

• When an atom’s nucleus decays and releases a beta particle, a neutron turns into a proton which stays in the nucleus, and a high energy electron is emitted

• Atomic mass remains the same, but atomic number increases by 1 in daughter nucleus

Gamma Decay

Where an unstable atomic nucleus drops from a high-energy excited state to a lower energy state by releasing gamma rays

Half Life

• The time it takes for half of the nuclei in a radioactive sample to decay (t½)

• The more unstable an isotope is, the faster it decays, resulting in a shorter half-life

Nuclear Fusion

• A nuclear reaction in which 2 or more light atomic nuclei combine to form one or more different, heavier atomic nuclei and subatomic particles

• The difference in mass between reactants & products is manifested as either the release or absorption of energy and results from the difference in nuclear binding energy

Nuclear Fission

• A nuclear reaction the occurs when an atomic nucleus splits into 2 or more pieces, which can happen spontaneously but is often triggered by the absorption of a neutron

• The total mass of fission products is slightly less than original reactants, with the loss of mass converting into energy

Main components of nuclear power stations

• Reactor vessels - encase and prevent radiation from escaping

• Control rods - absorb neutrons to control nuclear reactions

• Fuel rods - contain pellets of enriched uranium & generate heat through controlled nuclear fission

• Steam generator - a heat exchanger that uses heat from the reactor core to power a turbine and generate energy

• Moderator - slows down fast neutrons produced during fission so they can effectively cause nuclear fission

How do nuclear power stations work to generate electricity?

A nuclear reactor is a device in which nuclear reactions are generated, and the chain reaction is controlled to release large amounts of steady heat, thereby producing energy

Controlled vs Uncontrolled nuclear reactions

• Uncontrolled reactions occur when neutrons escape too quickly to maintain a chain reaction, resulting in the rapid release of nuclear energy, causing an explosion

• Controlled reactions occur when the neutrons produced from nuclear fission are slowed and absorbed to maintain a steady chain reaction

Advantages of using nuclear energy

• Nuclear plants have a longer operational lifetime than traditional coal power plants

• Nuclear plants are reliable and fuel efficient

Disadvantages of using nuclear energy

• Nuclear plants have lengthy development times, meaning they are unable to satisfy immediate electricity demands

• Nuclear plants produce dangerous radioactive waste which must be safely dealt with and disposed of securely underground