Transcript atomic and nuclear physics

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CHAPTER 2 – ATOMIC AND NUCLEAR
PHYSICS
2.1 FUNDAMENTAL PARTICLES
• Physical world – combinations of
subatomic (fundamental) particles
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• Particles of interest to the NE:
– Leptons – subject to weak nuclear
forces (electron, positron, and
neutrino)
– Hadrons – subject to both weak
and strong nuclear forces (proton
and neutron – baryons)
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• Hadrons – composed of quarks, which
exchange gluons – strong nuclear forces
• For NE - we will consider a class of particles,
without studying in detail their structure
• Appendix I – Units and conversion Factors
• Appendix II – Fundamental Constants and
Data
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Electron:
• Rest mass me=9.10954x10-31kg
• Charge e=1.60219x10+19 coulombs
• Two types: negatrons (-e) and
positrons (+e)
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Electron Annihilation
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Proton:
• Rest mass mp=1.67265x10-27 kg
• Positive charge equal to that of the
electron
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Neutron:
• Rest mass mn=1.67495x10-27kg
• Electrically neutral
• Not stable, except when is bounded into an
atomic nucleus
• Free neutron decays (-decay) to a proton
with an emission of a negative electron and
an antineutrino
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Photon:
• Zero rest mass
• Travels in vacuum with the speed of
light (c=2.9975x108 m/sec)
• Particles associated with
electromagnetic waves
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Neutrino:
• Zero rest mass
• No electrical charge
• Appears in the decay of certain nuclei
• Six types – electron neutrino and antineutrino
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2.2 ATOMIC AND NUCLEAR
STRUCTURE
• Atoms – building blocks of the matter
• Atom – consist of nucleus, surrounded
by cloud of moving electrons
• Nucleus – composed of protons and
neutrons
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• Atomic number – total number of
protons in a nucleus – Z
• Total electrical charge - +Ze
• Neutron number – N
• Atomic mass number – nucleon
number = total number of nucleons in a
nucleus – Z+N=A
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• Nuclides – ZAX
(X – chemical symbol of the element)
• Isotopes – same Z and different A
• Isotopic abundance – in atom percent –
a/o – percentages of the atoms of an
element that are particular isotopes
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2.3 ATOMIC AND MOLECULAR WEIGHT
• Atomic weight – mass of neutral atom
relative to the mass of a neutral 12C
• The atomic weight of 12C is taken to
be = 12
• M(ZAX) = 12x(m (ZAX)/m(12C))
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• Atomic weight of element:
M =  IMi/100
• Molecular weight – sum of the atomic
weights of the constituent atoms
• Atomic and molecular weights – unit
less numbers
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• Gram atomic weight (gram molecular
weight)-mole-amount of a substance
having a mass in grams, equal to the
atomic (or molecular) weight of
substance
• Number of atoms (molecules) in a mole
of any substance is a constant –
Avogadro’s law
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• Avogadro’s number –
NA=0.6022045x1024
• m(12C) = 1.99268x10-23g
• Atomic mass unit – amu – 1amu =
(1/12) x m(12C) =1.66657x10-24g
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2.4 ATOMIC AND NUCLEAR RADII
• Average atomic radii = 2x10-10m
• Electron density increases with the
increase of Z
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• Nucleus radii:
R=1.25 fm x A1/3
Fm – fathometers (fm) = 10-13cm
• Uniform nuclear density (V of the
nucleus is proportional to A)
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2.5 MASS AND ENERGY
• Einstein’s theory of relativity
Erest = moc2
• Mass and energy are equivalent and
convertible
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• Unit of energy – electron volt – eV
Df. Kinetic energy of an electron,
when it falls through an electrical
potential of one volt
• 1eV=1.60219x10-19joule
MeV; KeV
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• Etotal=mc2
Ekin= mc2-moc2 = moc2 [(1/1-v2/c2)-1]
• For neutrons:
Ekin= (1/2) mo v2
Ekin  0.02 Erest
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• For photons
E=h
H – Plank’s constant = 4.136x10-12 eV-sec
 - frequency of the electromagnetic
wave, associated with photon
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• 2.6 PARTCLE WAVELENGTHS
•  = h/p
p – momentum of the particle
p=mv
• p=2moEkin
 = h/(2moEkin)
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• For neutrons:
 = (2.860x10-9)/E
• For photons:
 = (1.240x10-6)/E
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