Nuclear Physics
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Transcript of Nuclear Physics
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Nuclear Physics
The atom and its nucleus
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Discovery of the nuclear atom
1909-Geiger and Marsden, working under Rutherford Scattering of alpha particles shot at a thin gold foil Alpha particle 4x mass of H atom Alpha particles-emitted when unstable elements
decay Used radon – source of alpha particle
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Rutherford, Geiger, and Marsden
Found that sometimes alpha particles were detected at very large scattering angles
This couldn’t be understood in terms of the prevailing model Thomson
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Geiger-Marsden-Rutherford experiment
Deflection indicative of enormous force of repulsion between alpha particle and carrier of positive charge of atom
Positive charge resided on a tiny object Alpha particle could approach + charge at a
small d, and the Coulomb force of repulsion, would be enormous
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Rutherford model
Massive, positively charged nucleus Electrons orbited nucleus Force keeping electrons in orbit
Electrical force between negative electron charge and positive nuclear charge
Couldn’t explain why matter is stable, i.e. why atoms exist
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Bohr model
Examined hydrogen Realized electron could exist in certain specific
states of definite energy, without radiating away energy
Electron lose energy when makes transition from one state to a lower
Emitted energy is difference between states Evidence-emission and absorption spectra
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Spectra
Normal conditions-lowest energy level Atoms excited higher level As soon as they do, transition back down to
lower state Energy allows wavelength of emitted light to
be calculated
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Spectra
Emission spectrum set of wavelengths of light emitted by the atoms of an element
Send a light of specific wavelength through an atom Doesn’t correspond to any of the wavelengths Light transmitted without absorption
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Nuclear Structure
Protons and neutrons # of protons is Z (atomic number) Protons + neutrons = mass (A) Electric charge is Z IeI # of neutrons N= A-Z Nucleon
Proton or neutron
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Isotopes
Nuclei that have the same number of protons, but different number of neutrons
Same number of electrons Identical chemical properties, different
physical Mass spectrometer
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Forces within the nucleus
Nucleons bound by nuclear force Attractive force Stronger than electrical force if separation
between 2 nucleons is small Larger separation-small force
Nuclear radius R = 1.2 A1/3 x 10-15m A is total number of p and n
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Forces within the nucleus
Weak nuclear force Responsible for decay of a neutron into a proton Called beta decay