atomic structure and radiation

• Rutherford directed a beam of alpha particles at a very thin gold sheet suspended in a vacuum.

  
  

  Vacuum -> any deflections of particles is due to gold atoms and not particles in the air

  
  

  Screen -> shows where alpha particles strike it

  A) scintillation screen

  B) gold foil

  C) alpha particles

  
• Niels Bohr revised Rutherford's model by suggesting that electrons orbited the nucleus in different energy levels or at specific distances from the nucleus.
• Niels Bohr proposed that electrons in an atom have fixed levels of energy and release energy in a pattern that is unique to each element. This explains why certain chemicals burn with specific colors of flames, as the energy released by the electrons is consistent across all atoms of that element.
• Most atoms are stable. However, radioactive atoms are not - they are unstable.

  
  

  They 'want' to become stable. So to try achieve this state they emit energy in the form of radiation.
• Some atomic nuclei are unstable. the nucleus gives out ionising radiation as it changes to become stable. This is a random process call radioactive decay
• The rate at which a source of unstable nuclei decays is called it's 'activity' and is measured in Bequerel (Bq)
• Count rate is the number of decays recorded each second by a detector e.g. Geiger-muller tube
• alpha particle is α

  beta particle is β

  gamma ray is γ

  neuron is n
• Isotopes are forms of an element that have the same number of protons but different numbers of neutrons.
• an atom which loses or gains an electron is called a ion
• alpha particle is identical to a helium nucleus

  
  

  It contains 2 protons and 2 neutrons
• A beta particle is a fast moving electron which is emitted from the nucleus undergoing radioactive decay
• beta decay occurs when a neutron changes into a proton and electron
• gamma rays are electromagnetic radiation with high frequency
• When atoms decay by emitting an alpha or beta particle to form a new atom, the nuclei of the new atom may still have too much energy to be completely stable.

  
  

  Excess energy is emitted as gamma rays
• Stable isotopes stay as they are - they do not decay over time

  
  

  Unstable atoms decay - they lose mass and or energy over time
• Nuclear equations show radioactive decay

  
  

  The total mass and atomic number on both sides of the arrow must be equal

  
  

  atomic mass-> on top

  atomic number-> on bottom

  
• exposure to radiation is called irradiation
• Irradiated objects do not become radioactive themselves as the atoms are not decaying and emitting radiation
• You can reduce irradiation by keeping the source far away as possible and using barriers to absorb the radiation
• contamination is where radioactive atoms get onto or into an object

  
  

  these atoms might decay and emit radiation
• Contamination is more dangerous as the particles may continue to give out radiation for a long time
• You can stop contamination by wearing special gloves and suits when handling radioactive substances
• The half-life of an isotope is the time taken for the number of radioactive nuclei in an isotope to halve

  
  

  It is also the time taken for the activity of a radioactive isotope to halve
• Short half life -> activity will fall quickly -> dangerous because emits large amount of radiation at the start -> quickly becomes safe
• Long half life -> activity falls slowly -> nearby areas exposed to radiation for many years -> dangerous in the long term
• natural sources of background radiation:

  cosmic rays

  rocks and soil

  Radon gas

  plants absorbing radioactive material from the air and soil
• Artificial sources of radiation:

  nuclear power

  medical scans, etc.

  nuclear weapons test
• effect of radiation on eyes:

  cataracts
• effect of radiation on thyroid:

  radioactive iodine can build up and cause cancer
• effect of radiation on reproductive organs:

  infertility, birth defects / mutations
• effect of radiation on skin:

  radiation burns, skin cancer
• effect of radiation on bone marrow:

  leukaemia / blood diseases
• radiation dose is a measure of the amount of damage that would be caused by the absorption of radiation from different sources
• radiation is measured in Sieverts (Sv) or more usually milliSieverts (mSv)
• The greater the radiation dose the bigger the risk of harm
• How to reduce risk of radiation dose:

  Shield radioactive sources when not in use

  Wear protective clothing

  Handle with care

  Limit exposure time

  Avoid ingesting/breathing in

  Monitor exposure using radiation detector badges
• nuclear fission is the splitting of a large and unstable nucleus

  
• Nuclear fission steps->

  Unstable atom absorbs a neutron -> the nucleus splits into smaller nuclei -> emits 2 or 3 neutrons + gamma radiation -> neutrons are absorbed by other unstable nuclei -> causes a chain reaction
• nuclear fission is used in nuclear power stations, atomic bombs and stars