Radiation

• Nucleon is something that makes up the nucleus
• Excitation:

  • Electrons absorb energy from collisions with free electrons, causing them to 'jump up' energy levels
  • Excited electrons are very unstable
• De-excitation:

  • Excited electrons lose energy, causing them to fall back energy levels
  • This process results in the emission of photons
• 1897 - JJ Thompson discovered the electron
• 1904 - Plum pudding model:

  • Negatively charged 'plums' embedded into a positively charged 'pudding'
  • Electrons were thought to be mobile
• 1909 - Alpha particle scattering experiment:

  • Attempted to prove the plum pudding model
  • Some alpha particles deflected dramatically, while others did not deflect at all
  • Led to the realization of an extremely dense positively charged matter in the centre of the atom (nucleus) by Rutherford
• 1911 - Rutherford proposed the nuclear model
• 1913 - Bohr atom:

  • Proposed that electrons were located in circular orbitals at specific distances from the nucleus
• 1932 - James Chadwick discovered the neutron
• Stable isotopes remain the same over time

  Unstable isotopes decay into another type of atom, ionizing part of them, becoming more stable
• Alpha radiation:

  • Helium nucleus
  • Relative mass of 4u, relative charge of 2+
  • Slow speed, high ionizing power
  • Weak penetrating power, can travel around 2cm in air
  • Absorbed by thin sheets of paper or skin, deflects towards the negative plate in an electric field
• Beta radiation:

  • Electron emitted from the nucleus
  • Small relative mass of 1/1845u, relative charge of -1
  • Fast speed, moderate ionizing and penetrating power
  • Travels about 1m in air
  • Absorbed by an aluminum sheet, deflects towards the positive plate in an electric field
• Gamma radiation:

  • High frequency electromagnetic wave from the nucleus
  • No mass or relative charge
  • Speed of light (3x10^8 m/s), weak ionizing power
  • High penetrating power, infinite range in air
  • Absorbed by thick lead or concrete, does not deflect in an electric field
• As each nucleus decays, the number of atoms decreases, so the activity falls
• The Geiger counter gives a count rate from the sample (counts per sec)
• Radioactive decay is a spontaneous and random process, not influenced by environmental factors
• Half-life is the time it takes for half of the unstable nuclei in a sample to decay
• Isotopes with a short half-life have a high activity
• Radiation is the emissions of energy as electromagnetic waves or as moving subatomic particles
• Ionisation is the process of becoming ions
• Ionising radiation can damage human cells and tissues, leading to cell death and potential tumor formation
• Acute radiation exposure symptoms include: skin burns, reduction of white blood cells, and radiation sickness
• Higher dose equals a higher risk of cancer or cell death
• Risk can never be zero due to background radiation
• Irradiation is the exposure of an object to ionising radiation, without making the object radioactive
• Contamination is the unwanted presence of radioactive material on an object through physical contact
• Precautions for handling radioactive material include: keeping sources shielded, wearing protective clothing, avoiding skin contact, wearing a mask, limiting exposure time, using tongs, and monitoring exposure
• To measure radiation dose absorbed by the body, the sievert (Sv) is used
• Background radiation is the low-level radiation always present from natural and man-made sources
• Unstable atoms can become more stable by decaying and releasing ionising radiation
• Binary Fission is when unstable nuclei break apart
• Nuclear Fission is the process of splitting a large and unstable nucleus
• Fissionable isotopes are isotopes that can be split via nuclear fission
• Firing a neutron into the nucleus can make a fissionable isotope split
• When a nucleus undergoes fission, it splits into two smaller daughter nuclei, some individual neutrons, and a small amount of matter converts into energy in the form of gamma rays
• Daughter nuclei are extremely radioactive
• A moderator can slow neutrons
• Thermal neutrons have already been slowed down, increasing the chance of neutron absorption
• Control rods control the rate of reaction
• Superheating a gas causes the atoms to have so much energy that their electrons become excited and 'shed' off, ionizing the particles and allowing the gas to conduct electricity