CHAPTER 2 – ATOMIC AND NUCLEAR PHYSICS 2.1 FUNDAMENTAL PARTICLES

CHAPTER 2 – ATOMIC AND NUCLEAR PHYSICS 2.1 FUNDAMENTAL PARTICLES • Physical world – combinations of subatomic (fundamental) particles

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)

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

Electron: • Rest mass me=9.10954x10-31kg • Charge e=1.60219x10+19 coulombs • Two types: negatrons (-e) and positrons (+e)

Electron Annihilation

Proton: • Rest mass mp=1.67265x10-27 kg • Positive charge equal to that of the electron

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

Photon: • Zero rest mass • Travels in vacuum with the speed of light (c=2.9975x108 m/sec) • Particles associated with electromagnetic waves

Neutrino: • Zero rest mass • No electrical charge • Appears in the decay of certain nuclei • Six types – electron neutrino and antineutrino

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

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

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

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))

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

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

Avogadro’s number – NA=0.6022045x1024 • m(12C) = 1.99268x10-23g • Atomic mass unit – amu – 1amu = (1/12) x m(12C) =1.66657x10-24g

2.4 ATOMIC AND NUCLEAR RADII • Average atomic radii = 2x10-10m • Electron density increases with the increase of Z

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)

2.5 MASS AND ENERGY • Einstein’s theory of relativity Erest = moc2 • Mass and energy are equivalent and convertible

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

Etotal=mc2 Ekin= mc2-moc2 = moc2 [(1/1-v2/c2)-1] • For neutrons: Ekin= (1/2) mo v2 Ekin 0.02 Erest

For photons E=h H – Plank’s constant = 4.136x10-12 eV-sec  - frequency of the electromagnetic wave, associated with photon

2.6 PARTCLE WAVELENGTHS •  = h/p p – momentum of the particle p=mv • p=2moEkin  = h/(2moEkin)

For neutrons:  = (2.860x10-9)/E • For photons:  = (1.240x10-6)/E

CHAPTER 2 – ATOMIC AND NUCLEAR PHYSICS 2.1 FUNDAMENTAL PARTICLES