CP6

• What is the nucleus of an atom?


  The tiny centre of an atom where almost all of the mass and all of the positive charge is found
• What is the mass and charge of a proton?


  Mass of 1, charge of +1
• What is the mass and charge of a neutron?


  Mass of 1, charge of 0
• What is the mass and charge of an electron?


  Mass of 1/1800, charge of -1
• What is the size of an atom?


  1x10$^{-10}$ m
• What is a nucleon?


  A particle found in the nucleus (proton or neutron)
• What are isotopes?


  Atoms that have the same number of protons, but different numbers of neutrons
• What is the atomic number?


  The number of protons in the nucleus
• What is the mass number?


  The number of protons plus neutrons in the nucleus
• What is a positron?


  An antimatter electron with a mass of 1/1800 and a charge of +1
• Why are atoms neutral?


  Because the number of protons must equal the number of electrons
• How do electrons orbit the nucleus?


  Electrons orbit the nucleus at different set distances from the nucleus
• What happens if an electron absorbs electromagnetic radiation?


  It will move to an orbit at a higher energy level
• What happens if an electron emits electromagnetic radiation?


  It will move to an orbit at a lower energy level
• What occurs when an atom loses an outer electron?


  It will become a positive ion
• What can unstable nuclei emit?


  Ionising radiation
• What is nuclear decay?


  A random process
• What is background radiation?


  The ionising radiation that is always present around us
• Name two sources of background radiation.

  Cosmic rays from space and radon gas from rocks
• How can ionising radiation be detected?


  By photographic film or a Geiger-Muller tube
• What is an alpha particle?


  A helium nucleus made from 2 protons and 2 neutrons
• What is a beta minus particle?


  A high speed electron emitted from the nucleus
• What is a gamma ray?


  A high-energy electromagnetic wave emitted from the nucleus
• How can alpha radiation be stopped?


  By a few cm of air or a sheet of paper
• How can beta minus radiation be stopped?


  By a few mm of aluminium
• How can gamma radiation be stopped?


  By cm of lead or metres of concrete
• Which type of radiation is the most strongly ionising?

  Alpha radiation
• Which type of radiation is the least strongly ionising?


  Gamma radiation
• What did the plum pudding model of the atom propose?


  The positive charge as a cloud with electrons scattered throughout the atom
• What experiment did Rutherford conduct?


  He fired alpha particles at very thin gold foil
• What did Rutherford find from his gold foil experiment?


  Most of the mass and positive charge of the atom must be concentrated in one spot
• What occurs in beta minus decay?


  A neutron turns into a proton and an electron which is fired out of the nucleus
• What occurs in beta plus decay?


  A proton turns into a neutron and a positron which is fired out of the nucleus
• What happens in alpha decay?


  The mass number decreases by 4 and the atomic number decreases by 2
• What happens in beta minus decay regarding mass and atomic numbers?


  The mass number stays the same and the atomic number increases by 1
• What happens in beta plus decay regarding mass and atomic numbers?


  The mass number stays the same and the atomic number decreases by 1
• What happens in gamma decay regarding mass and atomic numbers?


  The mass and atomic numbers stay the same but the nucleus drops to a lower energy level
• What happens in neutron emission regarding mass and atomic numbers?


  The mass number decreases by one and the atomic number stays the same
• What happens to the activity of a radioactive source over time?


  It will decrease
• What is the unit of activity?

  Becquerel, Bq