P4 - Atomic structure

• Radius of atom


  1x10⁻¹⁰m
• Energy levels


  - Atoms can absorb energy. This energy can cause electrons to move up to a high energy level (shell). It has absorbed electromagnetic radiation.

  
  

  - These electrons may then fall back down to a lower energy level and emit energy in the form of an electromagnetic wave (visible light).
• 1800


  Dalton said everything was made of tiny spheres (atoms) that couldn't be divided.
• 1897


  J.J Thomson discovered the electron (Plum pudding model)

  
• 1911


  Rutherford discovered the nucleus and the proton (alpha scattering experiment)

  
• 1913


  Bohr discovered electron shells and produced the final model of the atom.

  
• Radioactive


  Has an unstable nucleus
• Decay


  Act of giving off the particle
• Radiation


  Particle or energy that is given off by an unstable nucleus
• Stable


  Non - radioactive isotopes that are naturally occurring form of elements.
• Alpha radiation


  -2 protons 2 neutrons

  -Charge 2+

  -Mass 4

  -Strongly ionising

  -Deflected by EM field

  -Stopped by paper/ few cm of air

  
• Beta radiation


  -An electron

  Charge 1-

  -Mass 1/1860

  -Weakly ionising

  -Deflected by EM field

  -Stopped by aluminium/ few m of air
• Gamma radiation


  -High energy electromagnetic radiations (wave)

  -Charge 0

  -Mass 0

  -Very weakly ionising

  -Not deflected by EM field

  -Stopped by lead, thick concrete/few km of air
• Reactivity is measured in

  Becquerels (Bq)
• Alpha decay


  - Proton number decreases by 2

  - Mass number decreases by 4

  
• Beta decay


  - A neutron turns into a proton which stays in the nucleus when an atom's nucleus decays and releases a beta particle.

  - Proton number increases by 1

  
• Gamma decay


  - When an atom's nucleus decays and emits gamma radiation (not a type of particle) it is a form of energy. There is no change to the make-up of the nucleus so a new element is not formed.
• Neutron decay


  - A neutron is ejected from the nucleus, reducing the mass of the element

  
• Half-life

  Time taken for half the nuclei in a sample to decay.

  
  

  Long: Remains weakly radioactive for a long period of time

  
  

  Short: Less long-term risk (doesn't remain strongly radioactive)
• Net decline


  (initial number - number after X half lives) / initial number
• Reducing dangers associated with ionising radiation

  - Short exposure time

  - Monitor exposure

  - Wear protective clothing

  - Label radioactive substances

  - Store sources in shielded containers

  
  

  Scientific reports published on radiation must be peer reviewed
• Radioactive contamination


  Unwanted presence of radioactive atoms on other materials, lasts for a long period of time.
• Irradiation


  Exposing an object to nuclear radiation but does not make it radioactive, lasts for a short period of time.
• Background radiation

  Weak radiation that can be detected from natural / external sources.

  
  

  e.g. cosmic rays, underground rocks, medical rays
• Effective dose


  Calculated Value (measured in micro Sieverts, mSv) that takes 3 factors into account;

  - Absorbed dose to all organs in the body

  - Relative harm level of radiation

  - Sensitivities of each organ to radiation
• Nuclear fission


  Splitting of a large and unstable nucleus into smaller nuclei.

  
  

  - Spontaneous fission is rare, for fission to occur it must first absorb a neutron

  - When the unstable nuclei absorbs a neutron, it splits into two smaller nuclei called daughter nuclei (roughly equal in size)

  - This is a chain reaction as one split causes another due to the neutrons being fired

  - If the chain reaction is not controlled, it will increase at an exponential rate- which is what happens in a nuclear weapon

  
• Nuclear fusion


  Two small nuclei fuse to dorm a heavier nucleus, releasing lots of energy (the sum of the masses of the two nuclei is more than the mass of the heavier one).

  
  

  - Some of the mass is converted into energy

  - How elements heavier than hydrogen are made

  - Happens inside stars and not on Earth

  
• Uses of ionising radiation in medicine

  - Radiotherapy

  - Medical tracers that are swallowed

  - Chemotherapy (gamma rays emitted onto certain areas of the body with cancerous cells, which absorb the energy and die) - however surrounding healthy cells may be effected too as it is hard to control/ direct accurately