Topic 6 - Radioactivity

• Give an approximation for the radius of an atom.

  1x10⁻¹⁰ metres
• What are the three subatomic constituents of an atom?

  1. Proton

  2. Neutron

  3. Electron
• Where is most the mass of an atom concentrated?

  its nucleus
• Approximately what proportion of the total radius of an atom is the radius of the nucleus?

  1/10,000

  This equals 0.01%. The nucleus is very small compared to the whole atom
• Describe the arrangement of protons, neutrons and electrons in an atom.

  ● The protons and neutrons are found in the atom's nucleus

  ● The electrons are found in discrete energy levels around the nucleus
• What type of charge does the nucleus of an atom have? Why?

  ● Positive charge

  ● The nucleus contains protons and neutrons

  ● Protons have a positive charge

  ● Neutrons have no charge
• Give two ways that an atom's electron arrangement can be changed.

  1. Absorbing electromagnetic radiation

  2. Emitting electromagnetic radiation
• Explain how an atom's electron arrangement changes when it absorbs EM radiation.

  Electrons move to higher energy levels

  They move away from the nucleus
• Explain how an atom's electron arrangement changes when it emits EM radiation.

  Electrons move to a lower energy level

  They move towards the nucleus
• How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

  ● The number of protons is equal to the number of electrons

  ● Protons and electrons have equal and opposite charges, so charge cancels
• What do all forms of the same element have in common?

  They all have the same number of protons.
• What is the name given to the number of protons in an atom?

  atomic number
• What is an atom's mass number?

  The total number of protons and neutrons in the atom.
• What is an isotope of an atom?

  An atom of an element that has a different number of neutrons, but the same number of protons.
• What property differs between isotopes of an atom

  mass of the atom
• How do atoms turn into positive ions?

  ● They lose one or more of their outer electrons

  ● Electrons are negatively charged, so the resultant charge of the atom is positive
• What are the relative masses of a proton, neutron and electron?

  1, 1, and 1/1840 respectively
• What is the relative charge of a proton?

  +1
• What is the relative charge of an electron?

  -1 (negative)
• State four types of nuclear radiation.

  1. Alpha particles

  2. Beta particles

  3. Gamma rays

  4. Neutrons
• What is meant by background radiation?

  ● Radiation that is always present

  ● It is in very small amounts and so not harmful
• Give 4 sources of background radiation

  1. Rocks

  2. Cosmic rays from space

  3. Nuclear weapon testing

  4. Nuclear accidents
• How do you measure and detect background radiation?

  1. Photographic film

  2. Geiger-Müller counter
• How is photographic film used to measure radiation?

  A photographic film turns dark when it absorbs radiation. This is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes. Therefore the workers know when they have been exposed to too much radiation.
• How is Geiger-Muller tubes used to measure radiation?

  When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends on how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation.
• What constitutes an alpha particle?

  ● Two protons and two neutrons

  ● It is the same as a helium nucleus
• What is the range of an alpha particle through air?

  A few centimetres (normally in the range of 2-10cm).
• What will block beta radiation?

  ● A thin sheet of aluminium

  ● Several metres of air
• What will block gamma radiation?

  ● Several centimetres of lead

  ● A few metres of concrete
• Which type of radiation is the most ionising?

  alpha radiation
• Which type of radiation is least ionising?

  gamma radiation
• How does gamma emission affect the mass/charge of an atom?

  Both mass and charge remain unchanged.
• Describe the plum pudding model of the atom

  sphere of positive charge with negative electrons embedded in it
• Prior to the discovery of the electron what was believed about the atom?


  The atom was believed to be indivisible.
• Which experiment led to the plum-pudding model being discarded?

  Rutherford's alpha-scattering experiment
• What is the name given to the currently accepted model of the atom?

  Bohr model
• Describe Rutherford's gold foil experiment

  Alpha particles (Helium nuclei) are fired at thin gold foil. Photographic film is placed around the foil. The main area on the film where the alpha particles hit the film were THROUGH the foil in a straight line. Other areas were scattered around the film, and even back by the alpha particle source.
• What are the conclusions of Rutherford experiment?

  Most of an atom is empty space

  The nucleus has a positive charge

  Most of the nucleus is concentrated in the nucleus
• What happens in the process of beta plus decay?

  A proton turns into a neutron and a positron (in order to conserve charge).
• What is the process called when a neutron changes into a proton and an electron?

  beta minus decay