Nuclear physics

• atoms


  a particle of matter that uniquely defines a chemical element
• atomic number 


  number of protons in the nucleus
• mass number 


  number of protons and neutrons in the nucleus
• element format

  X-element symbol

  A-atomic number

  Z-mass number
• isotopes


  when an element has a different number of neutrons in its nucleus
• isotopes of hydrogen 


  protium/hydrogen-1 proton

  deuterium-1 proton & neutron

  tritium-1 proton 2 neutrons
• radioisotopes


  some naturally occurring isotopes are unstable and may spontaneously emit a particle to become stable and will change into a different element or isotope which is radioactivity
• types of nuclear decay

  alpha decay

  beta (plus/minus) decay

  gamma decay
• in a nuclear reaction 


  atomic and mass numbers are conserved and energy is released
• nuclear transmutation 


  when and atom changes into another element
• alpha decay α


  when a heavy unstable nucleus undergoes radioactive decay, it may eject an alpha particle. This is a positively charged particle that consists of two protons and two neutron.
• alpha decay of uranium-238, 92P


  parent nucleus emits an alpha particle, thus giving off helium and Thorium-234,92 P
• weak nuclear force


  responsible for both types of beta decay. This allows the parent nucleus to become more stable by rearranging the number of protons and neutrons into a more energy-favourable ratio
• beta minus decay β-


  when an electron is emitted from the nucleus of a radioactive atom from than from the electron cloud/shell. written as 0B-1. The atomic number of -1 indicates that the beta particle(electron) has a single negative charge. Occurs if a nucleus has too many neutrons to be stable.
• beta minus decay of carbon 14

  C-14, 6 proton, 8 neutrons

  turns into N-14,7 proton,7 neutron

  antineutrino and electron added
• Beta plus decay β+


  occurs when the nucleus has too many protons. A proton spontaneously changes into a neutron and emits a neutrino(V) and a positively charged beta particle(positron)
• positrons


  same properties of electrons but the electrical charge is positive rather than negative
• Gamma decay γ


  after a radioisotope has emitter an alpha or beta particle, the daughter nucleus usually has excess energy. The protons & neutrons in the daughter nucleus then rearrange slightly & offload this excess energy by releasing a gamma ray.
• gamma ray


  high energy electromagnetic radiation and so have no mass are uncharged and travel at the speed of light (3.0 X 10^8ms^-1)
• strong nuclear force-isotope chart

  keeps the nucleus together as it is a force of attraction between nucleon regardless of charge, but this force only works over a small distance so as the nucleus gets bigger the force gets weaker and more neutrons are needed to dilute the repelling forces of the protons
• properties of alpha radiation

  mass-heavy

  speed-up to 20000 kms^1, 20% the Speed of light

  charge-+2

  range in air- a few cm

  penetration in matter-~10^-2mm

  ionising ability-high

  penetrating power-low

  stopped by-paper
• properties of beta radiation

  mass-lignt

  speed-90% the speed of light

  charge-+1

  range in air-1 or 2 m

  penetration in matter-a few mm

  ionising ability-medium

  penetrating power-medium

  stopped by-aluminium
• properties of gamma radiation

  mass-none

  speed-the speed of light

  charge-0

  range in air-many metres

  penetration in matter-high

  ionising ability-0

  penetrating power-high

  stopped by-lead
• when is radiation type most dangerous

  alpha-when source is inside the body

  beta-when source is outside the body

  gamma-when source is outside the body
• when nucleus has too many protons

  positron emission
• when nucleus has too many neutrons

  beta emission
• when nucleus is too big

  alpha emission or spontaneous fission
• nucleus is excited


  gamma emission
• half life


  the time is takes for half of the nuclei of the sample radioisotope to decay
• half life formula 


  N=N0(1/2)^n

  N-no. of radioactive nuclei remaining

  N0-initial number of radioactive nuclei

  n-no. of half lives elapsed
• Number of half lives

  n=T/t1/2

  n-no. of half lives elapsed

  T-period of time that the radioactive nuclei decayed

  t1/2-half life of the radioactive nuclei
• half life and activity

  activity is measured in becquerels, Bq

  1 Bq=1 disintegration per second
• activity formula 


  A=A0(1/2)n

  A-activity of radioactive nuclei remaining

  A0-initial activity of radioactive nuclei

  n-no. of HL elapsed
• radiation and the human body

  some types of radiation like radio waves are harmless. other types are danger to humans. Known as ionising radiation, these types of radiation interact with atom. They have enough energy to remove outer shell electrons and create ions
• what particles are ionising

  alpha beta particles and gamma rays are all ionsing
• when ionising radiation interacts with human tissue-


  it can lead to the development of cancers and tumours
• what happens when alpha beta or gamma radiation or x ray pass through a body cell?

  it may turn molecoles in the cell into an ion pair
• ions are


  highly reactive & can damage the DNA that forms chromosomes in the nucleus of a cell.
• somatic effects


  somatic(physical) effects arise when ordinary body cells are damaged, they depend on the size of the dose.

  very high dose=immidiate symptoms

  low dose=leas to symptoms develeping years later
• genetic effects


  when cells in the reproductive organs(testes or ovaries) are damaged the body suffers genetic effects. If DNA in the chromosomes of these cells is damaged this genetic change could be passed to a developing embryo