P4

• What is the basic structure of an atom

  A positively charged nucleus composed of protons and neutrons surrounded by negatively charged electrons
• Where is the most of the mass of an atom concentrated

  Nucleus
• How can the electron arrangements of the nucleus change

  The absorption of electromagnetic radiation causes electrons to move further from the nucleus

  The emission of electromagnetic radiation causes electrons to move closer
• Why do atoms have no overall charge

  The number of protons is equal to the number of electrons
• What is atomic number?

  The number of protons in an atom's nucleus.
• What is a mass number?

  The total number of protons and neutrons in an atomic nucleus.
• How do atoms form positive ions

  Losing electron(s)
• What is radioactive decay


  The random process by which nucleus gives out radiation to become stable
• What is activity


  The rate at which a source of unstable nuclei decay
• What is the unit for activity

  Baquerel, Bq
• What is count rate


  The number of decays recorded each second by a detector
• What is an alpha particle

  A helium nucleus which is two neutrons and two protons
• What is a beta particle

  A high-speed electron ejected from the nucleus as a neutron turns into a proton
• What is a gamma ray

  Electromagnetic radiation from the nucleus
• What is half life

  The time it takes for number of nuclei of the isotope in a sample to half
• What is contamination


  The unwanted presence of materials containing radioactive atoms on other materials
• What is irridation 


  The process of exposing an object to nuclear radiation

  The irridated object does not become radioactive