Atomic and Nuclear Physics

Geiger-Marsden experiment

Experiement that proved that the atoms was a mostly empty space with tiny, dense, positively charged nucleus. It led to the proposed nuclear model of the atom

Photon

a discrete unit or package of light energy

\*Nuclide

a particular type of nucleus with a certain number of protons and neutrons

\*Isotope

nuclei with the same number of protons (Z) but different number of neutrons (N)

\*Nucleon

a proton or neutron (NOTE: Do **not** say “a particle in the nucleus” since that would include quarks as well.)

\*Nucleon Number (Mass Number) (A)

number of nucleons (protons + neutrons) in nucleus

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\*Proton Number (Atomic Number) (Z)

number of protons in nucleus

\*Neutron Number (N)

number of neutrons in nucleus (N = A – Z)

Coulomb interaction (Coulomb force, electrostatic force)

electrostatic force of repulsion between the protons in the nucleus

Radioactive Decay

when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a **random** and a **spontaneous** process.) (NOTE: The rate of radioactive decay decreases exponentially with time.)

Alpha Particle (α)

helium nucleus (2 protons + 2 neutrons)

Beta Positive Particle (β+)

electron

Beta Negative Particle (β-)

positron (antielectron)

Gamma Radiation (γ)

high energy (high frequency) electromagnetic radiation

\*Radioactive Half-life (T1/2)

a.     the time taken for ½ the number of radioactive nuclei in sample to decay  

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      b.     the time taken for the activity of a sample to decrease to ½ its initial value

\*Unified Atomic Mass Unit

1/12th the mass of a carbon-12 nucleus

\*Mass Defect

difference between the mass of the nucleus and the sum of the masses of its individual nucleons

\*Binding Energy

energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is separated into its individual components)

\*Binding Energy per Nucleon

energy released **per nucleon** when a nuclide is assembled from its individual components (OR: energy required **per nucleon** when nucleus is separated into its individual components)

\*Nuclear Fission

a heavy nucleus splits into two smaller nuclei of roughly equal mass

\*Nuclear Fusion

two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun’s energy.)

\*Photoelectric Effect

the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the surface

Threshold Frequency (f0)

minimum frequency of light needed to eject electrons from a metal surface

Work Function (Φ)

minimum energy needed to eject electrons from the surface of a metal

\*de Broglie Hypothesis

All particles can behave like waves whose wavelength is given by **λ = h/p** where h is Planck’s constant and p is the momentum of the particle.

\*Matter Waves

All moving particles have a “matter wave” associated with them whose wavelength is the de Broglie wavelength.

Wave-Particle Duality

Both matter and radiation have a dual nature.  They exhibit both particle and wave properties.

Schrödinger Model of the Atom

This model assumes that electrons in the atom may be described by wavefunctions.  The electron has an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electron at a particular point.

Heisenberg Uncertainty Principle

Conjugate quantities (position-momentum or time-energy) cannot be known precisely at the same time.  (NOTE: There is a link between the uncertainty principle and the de Broglie hypothesis.  For example, if a particle has a uniquely defined de Broglie wavelength, then its momentum is known precisely but all knowledge of its position is lost.)

\*Radioactive Decay Law

1.  The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei present in the sample at any one time. (A = λN)    
2. N = N0e-λt  OR A = λ N0e-λt  (as an exponential function)

\*Decay Constant (λ)

\*Decay Constant (λ)

Activity (A)

number of radioactive disintegrations (decays) per unit time