Atomic and Nuclear Physics

1. `The Atom and Nuclear Structure Describe the model + evidence Limitations of simple model Evidence of energy levels (spectra)

Define nuclides, isotopes, nucleon number A, proton number Z, neutron number N

Interactions (strong force, weak force and Coulomb force)

Geiger-Marsden (Rutherford) :alpha particles fired at gold foil

Result:occasionally alpha particles detected at large scattering angles (bounce back) because of coulomb force of repulsion. Evidence for a positive atomic charge of 10-15 m in diameter.

Rutherford model:

Problem:Accelerating charges radiate energy. Electrons should therefore lose energy and spiral into nucleus.

Niels Bohr:Electrons have discrete energy levels. They can only gain/lose energy by transitioning.

Emission Spectra:the set of wavelengths emitted by the excited atoms of an element.Absorption Spectra:the set of wavelengths absorbed by the atoms of an element. The same as of the emission spectra.

E=hf=hc/

Nuclear Structure

Interactions in nucleus

2. Radioactive DecayRadioactivity Describe radioactive decay particles, properties, ionizing properties nucleus stabilityHalf-lives

Radioactivity: Unstable nuclei spontaneously emit a particle, decay and become different nuclei.

: ::photon

Characteristicalphabetagamma

naturehelium nucleusfast electron + antineutrino photon

Penetrating Powerfew cm of airfew mm of metalmany cm of lead

Ions per mm of air for 2 MeV particles10 0001001

Energydiscrete valuescontinuous values=hc/ (nuclear energy levels)

decay: +

decay: +

decay: +

Stablity

More protons electrostatic replusion grows BUT strong force has a small range SO we add neutrons because they provide strong force but no electromagnetic force.

HOWEVER if we have too many neutrons than decay is more likely to happen.

So need more neutrons than protons but nuclides can only reach a certainsize.

Half-Life

Radiactive decay:is random and spontaneous. And the rate of decay (activity, A; units: Bq) decreases exponentially wit time.Half-Life:after each half-life the number of undecayed nuclei is halved.

3 Nuclear Reactions, Fissions and Fusion

Nuclear Reactions unified atom mass unit E=mc2 Mass defect/ binding energy/ binding energy per nucleon Graph of binding energy per nucleon against nucleon number A

Fission and Fusion Describe process (plant/stars) Solve problems

Unified atom mass unit:u, 1/12 mass of a Carbon-12 atom=931.5MeVMass defect: = total mass of nucleons mass of nucleus

Eg. C-12.=(6*mp + 6*mn) (12u-6*me)

Binding energy:Eb= c2 = energy required to completely separate nucleons.

Binding energy per nucleon:Eb/A . energy required to remove one nucleon. MeV

For decay to take place, the mass of the decaying nucleus must be greater thanthe combined masses of the products.

TWO types of nuclear activity: Decay and nuclear reactions

DECAY: +Less mass on right hand side which means the products have kinetic energy.

MV(Pb)=mv(alpha).

NUCLEAR REACTION:

artificial/induced transmutation:If a nucleus cannot decay by itself, it can still do so if energy is supplied to it.

+ +

Less mass on the left hand side which means the reactants have kinetic energy.

NOTE: the kinetic energy of the alpha particle would have to more than make up for the mass deficit because the products would have kinetic energy too.

ENERGY PRODUCING nuclear reactions (i.e. fission and fusion)

Nuclear fission:the process by which a heavy nucleus splits into lighter nuclei.Nuclear fusion:the joining of two light nuclei into a heavier one.

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