P6 - Radioactivity

• What order of magnitude is the diameter of an atom?

  10-10 m
• What order of magnitude is the size of a molecule?

  10-9 m
• What does the nucleon number of an atom tell you?

  Number of protons and neutrons
• atomic number tells us that protons=electrons
• isotopes have different number of neutrons
• the relative mass of a positron is 1/1840
• atoms are neutral because they have the same number of protons and electrons
• atoms form ions by loosing or gaining electrons
• the five types of radiation that can be emitted from unstable nuclei:alpha, β– (beta minus), β+ (positron), gamma rays and neutron radiation
• the types of ionising radiation

  alpha, β– (beta minus), β+ (positron), gamma rays 
• photorgraphic film and a GM tube are used to measure radioactivity
• an alpha particle is equivalent to a helium nucleus
• a beta particle is a high speed electron that has been emitted from the nucleus
• a gamma ray is a type of EM radiation
• gamma is the most penetrating
• alpha is the most ionisng
• rutherfords findings: Most of the atom is empty space, most of the mass of the atom is concentrated in the nucleus which has a positive charge.
• Most of the alpha particles went straight through the gold foil=most of atom is empty space
• beta minus decay is when a neutron turns into a proton and an electron
• beta plus decay is when a proton becomes a neutron plus a positron
• in alpha decay the Atomic number decreases by 2, mass number decreases by 4
• in beta minus decay the Atomic number increases by 1, mass number stays the same
• in beta plus decay the Atomic number decreases by 1, mass number stays the same
• in neutron emission the atomic number stays the same and mass number decreases by 1
• What do nuclei that have undergone radioactive decay often undergo?

  Nuclear rearrangement with a loss of energy as gamma radiation
• a half life is the time taken for half of the undecayed nuclei to decay or the acitivity of the source to decay by half
• ionising radiation can cause tissue damage and possible mutations
• six precautions is handling a radioactive source:Keep a safe distance, point the source away from people, handle the source with tongs, limit exposure time, use shielding, wear a film badge
• Contamination is when the source is inside the object
• irradiation is when the source is outside the object.