Nuclear Radiation Flashcards
Radioactivity
Some isotopes have an unstable nucleus - gives out radiation to become stable - (Radioactive decay - random)
Activity
Measure in Bq
Rate at which a source of unstable nuclei decays
1 Bq = 1 decay per second
Count-rate
Number of decays recorded each second by a detector
E.g. Geiger-muller tube
Nuclear radiation
Alpha particles (Helium nucleus - 2 neutrons, 2 protons)
Beta particles (High speed electron ejected from nucleus - as neutrons turns into proton)
Gamma ray (EM radiation from nucleus
A neutron
Alpha Particles
Large
Travel 5 cm in air
Absorbed a sheet of paper
Strongly ionising - radiation collides with atoms, they lose electrons and form ions
Beta particles
Travel 1 m in air
Absorbed a few mm of aluminium
Moderately ionising
Gamma Radiation
Travel a long distance in air (km)
Absorbed by thick sheets of lead or metres of concrete
Weakly ionising
Nuclear Equations
Alpha decay: Mass & charge of nucleus decrease. Mass decreases by 4, proton number decreases by 2
Beta Decay: Mass doesn’t change, charge increases. Proton number increases by 1
Half life
Time it takes for number of nuclei of the isotope in a sample to halve
Time it takes for count rate (activity) from a sample containing the isotope to halve
Irradiation
Exposing an object to nuclear radiation (object doesn’t become radioactive)
Precautions: Shielding (lead-lined box/stand behind barriers) - Ionising radiation can cause cancer
Contamination
When unwanted radioactive isotopes end up on other materials
Precautions: Gloves & tongs when handling sources/protective suits
Background radiation
Around us all the time
Level affected by location/occupation
Comes from: Rocks, cosmic rays (space), fallout from nuclear weapons, nuclear accidents
Uses of nuclear radiation
Exploration of internal organs (tracers): emit radiation, passes out of body, not strongly ionising, short half life
Control, destruction of unwanted tissue (radiotherapy): gamma - less ionising to other cells
