CP6: radioactivity

• What was the early model of the atom?

  Plum pudding model which positively charged pudding and negatively charged plums.
• what is the structure of an atom?

  it has a positively charged nucleus made up of negatively charged neutrons and positively charged proton, with electrons floating in the electron shells.

  The nucleus has most of the mass of the atom.

  
• How did the model of the atom change over time?

  Rutherford shot atoms with alpha particles at gold foil. Most of the alpha particles went straight through, but some bounced off, which proves that there is lots of empty space in the atom with a small mass.
• How do you calculate atomic mass?

  P= atomic number 

  E= atomic number

  N= mass number - atomic number

  
• How does a Geiger-Müller tube work?


  It connects to the counter and contains argon gas so when radiation enters, the argon atoms are ionised, when the radiation enters the counter, it clicks and the counts are displayed on the screen, this is called a count rate.
• How does photographic film detect radioactivity?

  When it’s exposed to ionising radiation, it goes from transparent to dark and non-transparent
• What are the relative electric changes of protons, neutrons, electrons and positrons?

  Protons: +1 Neutrons: 0 Electrons: -1 Positrons: +1
• What is an isotope?

  Atoms of the same element that have the same number of protons but different numbers of neutrons
• how do charges work?

  • neutral - electrons = protons
  • negative - more electrons than protons
  • positive - more protons that electrons
• What is the history of the atom?

  • democritus - atomic theory
  • Dalton - solid spheres
  • JJ Thomson - plum pudding model
  • Rutherford - gold sheet experiment
  • Bohr - electrons orbit nucleus in shells (explained collapse issue from rutherfords cloud theory)
  • Rutherford - protons and electrons
  • Chadwick - neutrons
• What happens in radioactive decay?

  • unstable isotopes decay into other elements by emitting radiation (alpha, beta, gamma or neutron)
• what happens when an electron gets too much energy?

  • moves up am orbit as it absorbs EM radiation
  • falls back down and emits EM radiation
• what happens in ionisation?

  • outer electrons absorb lots of energy and leave atom leaving it as a ion
  • More protons so + charged
• what is ionising radiation?

  Radiation that has enough energy to remove knock electrons off of atoms
• what is the definition of radioactive a substance?

  A substance that Contains unstable isotopes that can decay
• how does decay occur?

  in a random process
• what is alpha radiation?

  • 2 protons and a neutron But no electrons
  • 2 + charge
  • Large so easily stopped by other particles
  • Absorbed by paper
  • Strongly ionising
• What is gamma radiation?

  • waves of EM radiation
  • Often emitted after Alpha/Beta radiation
  • Happens when nucleus has to bet rid of extra energy
  • No mass or charge
  • Weakly ionising
  • Stopped by lead
• What is neutron emission?

  • when an extra electron is causing instability so the atom gets rid of it
• what is the nuclear equations for alpha?

  4

  He

  2
• what is the equation for beta - decay?


  0

  e

  -1
• what is the formula for beta + decay?


  0

  E

  +1
• what is the formula for gamma decay?

  γ (gamma)

  doesn’t change as it has no mass or charge
• what is the equation for neutron decay?


  1

  n

  0
• what is the definition of activity?

  overall rate of decay of all the isotopes/number of decays in a sample per second
• what happens to activity over time?

  • starts high - more atoms = higher chance of decay
  • decreases as less unstable atoms are there
• what is the unit for activity?

  becquerel, Bq
• what is the definition of half life?

  Time taken for half of a radioactive substance to decay
• what is the relationship between activity and numbers of unstable particles?

  as the number of unstable particles decreases = rate of decay (activity) decreases
• what does a Geiger muller tube and counter do?

  • record decays per second = count rate
  • count rate determines activity
  • when absorbs radiation electrical pulse transmitted and produces a click
  • frequency of clicks = how much radiation
• how does photographic film detect radiation?

  • Originally white but film goes darker when it absorbs radiation
  • Worn as a badge for people who work with radiation
• what is irradiation?


  • when an object is exposed to radiation
  • Short term impact
  • Source emits radiation
  • Cant emit to others
• what is contamination?


  • radiative particles on the object
  • long term impact
  • material can decay and irradiate object
  • can harm others
• Why is ionisation so dangerous?

  • gets into your cells and interact with the molecules
  • Ionise DNA and cause mutation and cancer
  • UV rays can also cause cancer
• Which types of radiation are the most dangerous?

  • externally - beta and gamma as they can penetrate skin
  • Internally - alpha as can go into cells
• how can you be safe around radiation?

  • limit exposure - x rays leaving the room
  • gloves, overalls, tongs and lead lined pots
  • photographic film badges
• what are the main sources of background radiation?

  • radon gas
  • buildings and the grounds
  • cosmic rays
  • food and drink
  • medical
  • nuclear weapons and power