Isotopes & nuclear radiation stuff

• isotopes


  different forms of the same element
• isotopes of an element - atoms with the same number of protons but different number of neutrons
• all elements have different isotopes but usually only a few stable ones and the rest are unstable
• radioactive Decay


  unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable.
• radioactive substances spit out one or more types of ionizing radiation from the nucleus - they are called alpha, beta and gamma.
• ionising power


  radioactive substances can also release neutrons when they decay, as they rebalance their atomic and mass number. The ionising power of a radiation source is how easily it can do this
• alpha particles are helium nuclear
• Alpha radiation

  • when an alpha particle (α) is emitted from the nucleus.
  • An alpha particle is two neutrons and two protons (like helium)
  • They don't penetrate very far into my take materials and are stopped quickly.
  • they can only travel a few cm in air and are absorbed by a sheet of paper
  • because of their size they are strongly ionising
• Beta radiation

  • a beta particle (β) is a fast-moving electron released by the nucleus
  • beta particles have virtually no mass and the charge of -1
  • they are moderately ionising
  • they penetrate moderately for Inter materials before colliding and have an air range of a few meters
  • they are absorbed by a sheet of aluminium
  • for every beta particle emitted, a neutron in the nucleus has turned into a proton
• Gamma rays (γ)

  • they are waves of electromagnetic radiation released by the nucleus
  • they penetrate far into materials without being stopped and will travel long distances through air
  • this means that they are weekly ionizing because they tend to pass through rather than collide with atoms eventually they hit something and do damage
  • thick sheets of lead or meters of concrete can absorb them
• mass and atomic numbers have to balance.
• alpha decay

  decreases the charge and mass of the nucleus

  alpha particles are made up of two protons and two neutrons so when an atom Emits an alpha particle it's atomic number reduces by 2 and its mass number by 4
• beta decay

  increases the charge of the nucleus

  a neutron in the nucleus turns into a proton and releases a fast-moving electron (the beta particle)

  the number of protons in the nucleus increases by one - this increases the positive charge of the nucleus(atomic number)

  because the nucleus has lost a neutron and gained a proton during the decay, the mass of the nucleus doesn't change.

  e ₋₁$^0$
• equation for beta decay


  e ₋₁$^0$
• equation for alpha decay


  H$^2$₄
• gamma rays don't change the charge or mass of the nucleus
• radioactivity is a totally random process
• radiation can be measured using a Geiger Muller tube and counter, which records the count rate - the number of radiation counts reaching it per second.
• Half life


  the amount of time it takes for the amount of radiation emitted by a source to half

  it can be used to make predictions about radioactive sources
• each time a radioactive nucleus decays to become a stable nucleus that activity as a whole will decrease ( older sources emit less radiation)

  for some isotopes it takes just a few hours whilst some take millions of years
• why do we measure half-life?

  the activity of an isotope never reaches zero so we have to use that idea of half-life to measure how quickly that activity drops off
• half-life


  the time taken for the number of radioactive nuclei in an isotope to half
• short vs long half-life

  Short: the activity Falls quickly. They are more dangerous because of the high amount of radiation they emit at the start but they quickly become safe

  Long: the activity Falls more slowly - the source just sits there, releasing small amounts of radiation for a long time. can be dangerous because nearby areas are exposed to radiation for many years
• where does background radiation come from?

  • naturally occurring unstable isotopes - which are in air, food, building materials and rocks
  • in space - known as cosmic rays - mostly come from the sun - Earth's atmosphere protects us from this radiation
  • human activity such as nuclear explosions or nuclear waste (but this represents a tiny portion)
• radiation doses tell you the risk of harm to body tissues due to radiation exposure. it is measured in sieverts (Sv). the dose from background radiation is small so millisieverts are used. radiation dose depends on where you live or if you have a job that involves radiation.
• exposure to radiation is called irradiation
• preventing irradiation

  keeping sources in lead-lined boxes

  standing behind barriers

  being in a different room
• contamination

  radioactive particles getting into objects
• avoiding contamination

  using

  • gloves
  • tongs
  • to avoid the particles from getting inside your body
• radiation risks


  ionise atoms within your cells - can lead to tissue damage.

  lower doses cause minor damage - can give rise to mutant cells which divide uncontrollably - cancer

  higher doses cill cells - causes radiation sickness
• gamma sources can be used as a medical tracer


  can be injected and followed by an external detector. A computer converts the reading to find where the strongest reading is coming from
• radiotherapy - treating cancer with radiation


  gamma rays are directed carefully and at the right dosage to kill the cancer cells without damaging too many normal cells. damage is inevitably done to the cells, making the patient feel ill.
• Nuclear Fission - splitting a large, unstable nucleus


  a new type of nuclear reaction that is used to release energy from large and unstable atoms by splitting them into smaller atoms

  drawing fishing the nucleus has to absorb a neutron before it splits
• Nuclear fusion - joining small nuclei

  two light nuclear collide at high speed and fuse to create a larger heavier nucleus

  fusion releases a lot of energy so far scientists haven't found a way of using fusion to generate energy - too expensive