Nuclear Physics

• Atom


  The building blocks of all matter, incredibly small with a radius of 1 x 10^-10 m
• Atom


  • Has a tiny, dense nucleus at the centre, with electrons orbiting around the nucleus
  • The radius of the nucleus is over 10,000 times smaller than the whole atom, but it contains almost all of the mass of the atom
  • Consists of a small dense positively charged nucleus, surrounded by negatively charged electrons
• An atom is a small positive nucleus, surrounded by negative electrons
• The atom is around 100,000 times larger than the nucleus
• Rutherford's Experiment


  Involved the scattering of alpha (α) particles by a sheet of thin metal, which supported the nuclear model of the atom
• Rutherford's Experiment


  1. A beam of alpha particles (He2+ ions) were directed at a thin gold foil

  2. Most of the alpha particles passed straight through the foil

  3. Some of the alpha particles changed direction but continued through the foil

  4. A few of the alpha particles bounced back off the gold foil
• The bouncing back of alpha particles could not be explained by the Plum Pudding model, so a new model had to be created
• Rutherford's experiment was the first evidence of the structure of the atom
• Ion


  An electrically charged atom or group of atoms formed by the loss or gain of electrons
• Positive ion


  Formed when atoms lose electrons, resulting in more protons than electrons
• Negative ion


  Formed when atoms gain electrons, resulting in more electrons than protons
• A stable atom is normally electrically neutral, with the same number of protons and electrons
• The term 'net charge' refers to the overall charge of an atom
• Atom


  Structure made up of a positively charged nucleus at the centre (made up of protons and neutrons) and negatively charged electrons in orbit around the nucleus
• Protons


  Positively charged particles found in the nucleus of an atom
• Neutrons


  Particles with no charge found in the nucleus of an atom
• The nucleus is overall positive due to the positive charge of the protons
• Proton number (Z)


  The number of protons in an atom, which determines the element
• The atomic number is always the same for a particular element
• The atomic number is equal to the number of electrons in a neutral atom
• Nucleon number (A)


  The total number of protons and neutrons in the nucleus of an atom
• Calculating the number of neutrons


  Nucleon number - Proton number
• Electrons have a tiny mass compared to protons and neutrons, so their mass is negligible when considering the mass of the nucleus
• Isotopes


  Atoms of the same element that have the same number of protons but a different number of neutrons
• Isotopes tend to be more unstable due to their imbalance of protons and neutrons, making them more likely to decay
• Hydrogen has three naturally occurring isotopes
• Deuterium and Tritium are rare isotopes of Hydrogen
• Nuclear fission

  The splitting of a large, unstable nucleus into two smaller nuclei
• Isotopes of uranium and plutonium

  • They undergo fission and are used as fuels in nuclear power stations
• Nuclear fission


  1. Neutron collides with unstable nucleus

  2. Nucleus splits into two smaller nuclei (daughter nuclei)

  3. Two or three neutrons emitted

  4. Gamma rays emitted
• Large nuclei can decay by fission


  Produces smaller nuclei and neutrons with a lot of kinetic energy
• Nuclear potential energy


  Converted into kinetic energy in the products of fission
• The mass of the products (daughter nuclei and neutrons) is less than the mass of the original nucleus
• The remaining mass has been converted into energy which is released during the fission process
• Nuclide equation for fission

  • 235U + n → 92Kr + 141Ba + 3n + energy
• Nuclear fusion


  When two light nuclei join to form a heavier nucleus
• Nuclear fusion requires extremely high temperatures to maintain
• Stars use nuclear fusion to produce energy
• Nuclear fusion


  Two hydrogen nuclei fusing to form a helium nucleus
• Mass-energy equivalence


  E = m × c^2