Subatomic PhysicsSubatomic PhysicsChapter 25-1

Properties of the NucleusProperties of the NucleusThe nucleus is

the small, dense core of an atom.

Atoms that have the same atomic number but different neutron numbers are called isotopes.

Properties of the Nucleus Properties of the Nucleus A particle has a certain amount

of energy (rest energy) associated with its mass.

Nuclear StabilityNuclear Stability

The nucleus of an atom is able to exist because of a nuclear force called a strong force.

Strong force is the attractive force between the protons and neutrons.

Nuclear StabilityNuclear StabilityNeutrons help to stabilize a

nucleus.

Binding EnergyBinding EnergyEnergy involved when

components of a nucleus are forced together or split (fusion/fission).

Nuclear DecayNuclear DecayCh. 25-2

Nuclear Decay Nuclear Decay Nuclear decay

can happen in nature or induced artificially.

When a nucleus decays radiation is emitted as particles, photons or both.

Nuclear Decay ModesNuclear Decay ModesAn unstable nucleus can decay in

three ways:

Measuring Nuclear DecayMeasuring Nuclear DecayThe decay

constant indicates the rate of radioactive decay.

Half-life measures how long it takes half a sample to decay

Decay ExampleDecay Example

Nuclear ReactionsNuclear ReactionsCh. 25-3

Nuclear ReactionsNuclear ReactionsA change in the nucleus of an

atom is called a nuclear reaction.

Fission – a nucleus splits into two or more nuclei.

Fusion – one or more nuclei combine.

Nuclear Chain ReactionNuclear Chain Reaction

Nuclear BombNuclear BombIf a chain

reaction happens too fast, it could result in a violent explosion.

This is the principle behind the first nuclear bomb.

Nuclear ReactorsNuclear ReactorsA nuclear reactor

is a system designed to maintain controlled self sustained chain reactions.

All nuclear reactors operate through fission.

Fusion occurs naturally only for light atoms.

Particle PhysicsParticle PhysicsCh. 25-4

Four Fundamental Four Fundamental InteractionsInteractionsAll particles in nature are subject to four fundamental interactions :

Strong – “glue” that holds nucleons together ; strongest

Electromagnetic – attraction of unlike and repulsion of like charges.

Weak – beta decay

Gravitational – holds planets, stars, and galaxies together; weakest

Four Fundamental Four Fundamental InteractionsInteractions

Classification of ParticlesClassification of ParticlesElectrons and

neutrinos are leptons.

Protons and neutrons are baryons.

Standard ModelStandard Model