ATOMIC STRUCUTURE

• what is an isotope?


  atoms with the same number of protons but different number of neutrons
• what were atoms thought to be before the discovery of the electron?

  tiny spheres that could not be divided
• what did the plum pudding model suggest?

  that the atom is a ball of positive charge with negative electrons embedded in it

  
• how did they conduct the alpha particle scattering experiment?


  they shot alpha particles at a gold sheet; most particles went straight through, some were partially deflected and some were deflected back
• what did the alpha particle scattering experiment suggest?

  that the mass of an atom was concentrated at the center and that the nucleus was charged
• what did niels bohr suggest?


  that electrons orbit the nucleus at specific distances
• what did later experiments suggest?

  the positive charge of any nucleus could be subdivided into a whole number of smaller particles (protons)
• what did james chadwick discover?

  the neutron; 20 years after the nucleus became an accepted scientific idea
• what is radioactive decay?

  the random process in which unstable atomic nuclei gives out radiation as they change to become more stable
• what is activity?

  the rate at which a source of unstable nuclei decays
• what is activity measured in?


  becquerels (Bq)
• what is count-rate?


  the number of decays recorded each second by a geiger-muller tube
• what is an alpha particle?

  two neutrons and two protons, helium nucleus
• 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 are the properties of alpha radiation?


  weakly penetrating, strongly ionizing
• what is alpha radiation used for?


  smoke detectors
• what are the properties of beta radiation?

  moderately penetrating, moderately ionizing
• what is beta radiation used for?

  thickness control
• what are the properties of gamma radiation?


  strongly penetrating, weakly ionizing
• what is gamma radiation used for?


  medical tracers, radiotherapy
• how does alpha radiation change the mass or charge of the nucleus?

  decreases the mass and charge of the nucleus
• how does beta radiation change the mass or charge of the nucleus?

  mass stays the same but increases the charge of the nucleus
• how does gamma radiation change the mass or charge of the nucleus?


  both stay the same
• what is background radiation?

  the low-level radiation that is around us all the time
• where does background radiation come from?


  rocks, cosmic rays, nuclear fallout, nuclear accidents
• what is radiation dose measured in?

  sieverts or millisieverts (1000mSv = 1 Sv)
• how do medical tracers work?

  radioisotopes can be injected into the body and traced from the outside using an external detector
• what is perceived risk?

  how risky a person thinks something is
• what is the half-life of a radioactive isotope?

  the time it takes for the number of nuclei of the isotope in a sample to halve
• what is radioactive contamination?


  the unwanted presence of materials containing radioactive atoms on other materials
• what is irradiation?

  the process of exposing an object to nuclear radiation
• what can be used to protect us from contamination and irradiation?

  lead-lined suits, gloves, tongs, staying away,
• what is nuclear fission?


  the splitting of a large and unstable nucleus into two smaller nuclear, emitting two or three neutrons plus gamma rays
• what usually has to occur for nuclear fusion to happen?


  the unstable nucleus needs to first absorb a neutron
• why are chain reactions controlled in a nuclear reactor?


  to control the energy released
• what is nuclear fusion?


  the joining of two light nuclei to form a heavier nucleus; some mass may be converted into the energy of radiation
• Alpha particles


  Particles released during radioactive decay
• Alpha particles


  • Can travel around 5 centimeters in air before colliding with air particles and stopping
  • Relatively easy to stop, stopped by a single sheet of paper
  • Very strongly ionizing, can produce a lot of ions when colliding with material
• Beta particles


  Particles released during radioactive decay