Structure Of Matter

Structure of Matter Two years of Physics in one hour

A lump of coal

Mass is the ability of an object to resist acceleration Force = mass x acceleration

Mass is also the force felt from gravity (weight)

Coal is made of Carbon atoms

Mass = 2×10-29 kg ≡12 amu

How much force is needed to accelerate a carbon atom to Mass of Carbon Atom: 2×10-26kg Speed of light: 3×108 meters/sec (m/s) Acceleration = Δv/Δt= 3×108 m/sec/sec (m/s2) Force = m a = 2×10-26kg × 3×108 m/s2

Objects are made out of atoms Mass is the ability to resist acceleration Scientiﬁc notation lets us work with the very large and very small

The nucleus is very small – – + +

Frequency = number of cycles per sec

O shell N shell M shell L shell Pauli Exclusion principle: at most two electrons in each level K shell

Energy of emitted photon 1 neV 1µeV 1meV 1eV 1keV 1MeV 1GeV (eV)

Objects are made out of atoms Mass is the ability to resist acceleration Scientiﬁc notation lets us work with the very large and very small Electrons on the outsides of atoms give all the chemical properties Electrons live in standing wave states each with a particular energy/ frequency No more than two electrons in each state Putting energy into an atom can raise an electron to a high state An electron falling to a low state releases a characteristic photon with a deﬁned energy With massive atoms, these characteristic photons can be in the 100 keV medical interest range.

A=Z+N Symbol also gives 12 6C6 number of protons Z: number of protons N: number of neutrons

Nuclear Shell Model pnpnpnpnpnpn pnpnpnpnpnpn pnpn pnpnpnpn pnpn

Nuclear Shell Model • Nuclei should have about pppppp the same number of protons and neutrons pppppp pnpnpnpnpnpn pnpn pnpnpnpn pnpn

Nuclear Shell Model • Nuclei should have about the same number of protons and neutrons pnpnpnpnpnpn • Nuclei with magic numbers pnpnpnpnpnpn of protons or neutrons are more stable pnpn • Nuclei with even numbers pnpnpnpn of protons and neutrons are more stable pnpn

Nuclear Shell Model • Nuclei should have about n the same number of protons and neutrons pnpnpnpnpnp • Nuclei with magic numbers pnpnpnpnpnpn of protons or neutrons are more stable pnpn • Nuclei with even numbers pnpnpnpn of protons and neutrons are more stable pnpn • Nuclei can be excited

Heavy nuclei tend to have more neutrons than protons

– – + +

Nucleus is held together by “Strong Force” Strong force must be stronger than electric repulsion between protons Neutrons and protons both make strong force

Is the mass of a nucleus the sum of its parts? + + m=1.0073×2 m=1.0087×2 m=4.0026 total=4.0320 amu difference = .0302 amu

Attraction between neighboring nuclei Surface tension Repulsion between positive protons Same number of protons as neutrons

Objects are made out of atoms Mass is the ability to resist acceleration Scientiﬁc notation lets us work with the very large and very small Electrons on the outsides of atoms give all the chemical properties Electrons live in standing wave states each with a particular energy/ frequency No more than two electrons in each state Putting energy into an atom can raise an electron to a high state An electron falling to a low state releases a characteristic photon with a deﬁned energy With massive atoms, these characteristic photons can be in the 100 keV medical interest range. Z=protons, N=neutrons, A=N+Z, 12C has 6 neutrons, 14C has 8. Shell model explains why N≳Z, shell bands Strong force holds nuclei together Nuclei have less mass than constituent protons and neutrons. The difference is the binding energy. Liquid drop model part of semi empirical mass formula, explains binding energy with contributions from strong force interactions, surface tension, electric repulsion from protons, N~Z

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Structure Of Matter

by David Graff on Jul 09, 2009

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Structure Of Matter — Presentation Transcript