p4 atoms and radiation

• Beta Particles are negatively charged and have a very small mass. They travel very fast and are electrons.
• During the decay of beta particles, the mass number is unchanged and the nucleus contains one less neutron .It contains one more proton and the atomic number increases by 1.
• Alpha particles are positively charged.
• alpha particles have a large mass and are helium nucleus'.
• Alpha particles have helium gas around them and have 2 protons and 2 neutrons.
• Half-life is the average time taken for the number of radioactive nuclei to halve.
• alpha radiation only travels a few centimetres in air
• beta radiation travels tens of centimetres in air
• gamma radiation travels very large distances
• Alpha, beta and gamma radiation are all ionising radiation
• Ionising radiation can break molecules into small particles called ions
• substance radiation = total radiation - background radiation
• Radioactive contamination is when radioactive atoms or molecules get onto other materials.
• The types of exposure to radiation are contamination and irradiation
• Beta is not very harmful as it can pass out of the body.
• • Gamma is the least harmful radiation.
  • It is the most penetrative (passes through things most easily), and so it will easily pass out of the body.
• • Alpha is the most dangerous form of radiation inside the body.
  • It cannot penetrate (pass through) the skin and so stays in the body.
  • This can cause cell mutations.
  • Alpha radiation is also the most ionising of the 3 types of radiation
• the nucleon number is the total number of neutrons and protons in the nucleus of an atom.
• Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation
• alpha radiation has low penetrating power because it has a high mass
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• alpha is the most ionising radiation
• the radius of an atom is about 0.1 nm (1 × 10-10m)
• a radioactive material has unstable isotopes that can decay
• 20th century, Chadwick discovered neutrons in the nucelus
• Rutherford developed nuclear model:

  In Rutherford's experiments, alpha particles were fired at a thin sheet of gold foil.

  
  

  Most particles passed through, but some were deflected off course. 

  
  

  This caused him to hypothesise that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles.

  
  

  As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surround by negative electrons. 
• 1. Electrons orbit the nucleus at specific energy levels which are also called shells.
  2. The shells get progressively further from the nucleus and increase in energy level.
  3. Electrons can absorb electromagnetic radiation and jump to a higher energy level / shell. In these cases we say that the electron has become 'excited'.
  4. Excited electrons can later fall back to a lower energy level, and emit electromagnetic radiation in the process.
  5. Electrons can also absorb enough energy to leave the atom altogether, this is known as ionisation.
• 'mass number', which is the number of protons and neutrons combined
• 'atomic number', which is the number of protons
• Isotopes are atoms with the same number of protons but different number of neutrons.
• Some isotopes are unstable and can decay into other elements. Decay involves emitting radiation such as alpha, beta, and gamma radiation.
• An alpha particle is the same as a helium nucleus. It has no electrons, and has a charge of 2+.
• In the 1800's John Dalton described atoms as solid spheres, and suggested that different types of spheres make up the different elements.
• In 1897 J J Thomson theorised that an atom consists of a ball of positive charge, with negative electrons mixed throughout it : plum pudding model
• a beta particle consists of 1 electron
• the emission of a neutron is caused when the nucleus has too many neutrons; making it unstable
• neutrons and protons have a relative atomic mass of 1
• unstable nuclei give out radiation because they undergo decay to become more stable and as they release radiation, their stability increases
• radioactive decay is the process in which an unstable nucleus gives out radiation to become more stable
• activity is the radioactive decay of a source of unstable nuclei