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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 anucleus – 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 (Z

AX)/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