Physics Topic 4

• EARLIEST DEVELOPMENT OF THE ATOM

  1800s dalton said everything was made form tiny spheres that could not be divided
• What did JJ Thomson discover?

  electron, leading to the plum pudding model
• describe the plum pudding model


  The plum pudding model suggested that an atom is a ball of positive charge with negative electrons in embedded in it
• What did Rutherford discover?

  Nucleus and protons
• What's the alpha scattering experiment?

  fired a beam of alpha particles at a thin gold foil

  most went through= atoms mostly empty space

  some alpha particles were deflected= the center of the atom has the most concentrated mass

  some alpha particles bounced back= atom was mostly positively charged
• What did Niel Bohr do?

  made a nuclear model and suggsested electrons were orbitting at energy levels
• What is an isotope?


  different version of an element with the same number of protons different number of neutrons
• what is ionizing radiation


  process by which electrons can be added or removed from an atom to create an ion
• alpha radiation


  made up of alpha particles (two neutrons and two protons)

  helium nuclei

  penetrate far

  absorbed by a sheet of paper

  travels only a few cm

  strongly ionising
• beta particle


  high speed electrons

  no mass no charge

  moderatley ionising

  absored by aluminium (5mm)
• gamma rays


  waves of electromagnetic radiation

  penetrate far into materials

  weakly ionising

  absorbed by lead or aluminum
• does alpha decay decrease or increase the charge and mass

  decreases
• does beta decrease or increase the charge

  increase
• What is radioactivity?


  unstable atomic nuclei decay over time, releasing particles and energy
• what is half life

  time it takes for the nuclei of the isotope in a sample to halve
• what is nuclear fission

  The splitting up of large unstable nuclei into smaller nuclei
• how does nuclear fission happen

  hitting the nucleus with a neutron to make it more unstable

  - When this happens, the original nucleus breaks apart into two smaller 'daughter' nuclei, along with two or three neutrons

  - these products carry away the energy released in the form of kinetic energy
• what are nuclear reactors


  where the rate of fission is carefully controlled

  through control rods, which are lowered into the reactor to absorb neutrons (slows down reaction)
• what happens to the energy released in nuclear fission

  heats up water which causes steam and drives the turbines

  turbines are connected to an electricity generator
• pros of nuclear fission

  uranium or plutonium feul is cheap

  produces a large steady amount of energy

  doesnt produce greenhouse gases
• cons of nuclear fission

  nuclear power plants are expensive to build

  nuclear waste is expensive to get rid of

  risk of major disaster
• what is nuclear fusion

  joining of two light nuclei to form a heavier nucleus
• nuclear fusion


  happens in conditions of high temperature and pressure,
• pros of nuclear fusion

  no radioactive waste

  easily makes the hydorgen thats need a feul
• cons of nuclear fusion

  only happens at high temps and pressure
• compare nuclear fusion and fission

  nuclear fusion is the fusing of light nuclei to make heavier nuclei

  releases tons of energy

  happens inside stars due to high temp and pressures required

  
  

  nuclear fisson

  large unstable nuclear splits into two smaller nuclei

  produces lots of energy

  NOT AS MUCH AS FUSION

  uses it on earth to generate electricity
• What's irradiation?


  when an object is exposed to nuclear radiation
• whats contamination


  the unwanted presence of materials containing radioactive atoms on other materials
• whys contamination bad


  risk of contaminating atoms decaying, realising radiation causing harm
• difference between irradiation and contamination

  radioactive contamination occurs when there is direct contact with radioactive substances, whereas irradiation occurs when there is indirect exposure to radioactive substances.