Radioactivity Flashcards
what is radioactivity?
random process where unstable nuclei decay by emitting ionising radiation
what are the three types of ionising radiation?
- alpha
- beta
- gamma
properties of alpha particles
- made of 2 protons and 2 neutrons (same as helium nucleus)
- Mass: 4/ Charge: +2
- heavy/ big/ slow moving
HIGH IONISING POWER
LOW PENETRATING ABILITY - blocked by paper/skin )only travels few cm in air)
properties of beta particles
- essentially an electron so charge of -1
- small/ fast-moving
MODERATE IONISING POWER
MODERATE PENETRATING ABILITY - blocked by thin aluminium (travels 20-30cm in air)
properties of gamma rays
- EM waves so have no mass/charge
LOW IONISING POWER
HIGH PENETRATING ABILITY - blocked by thin lead/ thick concrete
what is activity?
number of nuclei that decay per second
what is count rate?
number of radioactive emissions detected per unit of time
what happens during alpha decay?
loses 2 protons/ 2 neutrons
so atomic number decreases by 2 and mass number decreases by 4
what happens during beta decay?
neutron splits into proton and electron
so atomic number increases by 1 and mass number stays the same
why are alpha and beta particles deflected in opposite directions by magnetic/electric field?
because they have opposite charges
- alpha feel a greater force but are deflected less because of greater mass
what is radiation dose depend on and what is it measured in?
location and occupation
measured in sieverts (Sv)/ millisieverts (mSv)
give examples where exposed to high radiation doses
- radiography - stand behind lead screen/ wear lead aprons
- uranium miners/ nuclear industry - protective clothing
- underground rocks - release radon gas - mining in general is risk to health
- high altitudes - commercial pilots exposure to cosmic rays from sun
what contributes to background radiation?
- natural sources
- radon gas
- human acitivity: nuclear industry/ industrial waste
- cosmic rays
- medical X-rays
what is half-life?
average time for radioactive nuclei in a radioactive isotope sample to halve
unit of radioactivity
becquerels (Bq)
how is alpha radiation used for smoke alarms?
weak source of alpha radiation placed between two electrodes
- source causes ionisation so current flows through alarm
- if smoke, it absorbs radiation. cutting current and sounding alarm
how is beta radiation used for thickness control?
connected to control unit - fluctuating amounts of radiation adjusts rollers to give correct thickness- source has long half-life so doesnt decay too quickly
what is gamma radiation used for?
- sterilising equipment
- cancer treatment - radiotherapy
which type of radiation is most dangerous outside body?
beta/gamma - penetrate through get to delicate organs
which type of radiation is most dangerous inside body?
alpha - damages in localised area
what is nuclear fission?
splitting of atomic nuclei by absorbing slow moving neutron and also releases 2 more neutrons
how is nuclear fission used for generating electricity>
releases lots of energy heats water turns to steam which spins steam turbines and produces electricity
how are chain reactions regulated?
control rods absorb some of the neutrons to slow down reaction
what fuel is usually used for nuclear fission?
uranium- 235 or plutonium-239
what is the fission equation for uranium-235?
1/0 n + 235/92 U –> 236/92 U
–> 144/56 Ba + 90/36 Kr + 2 x 1/0 n
what is nuclear fusion?
joining smaller nuclei together to form larger one e.g. hydrogen isotopes
equation for fusion of hydrogen isotopes
1/1 H + 2/1 H –> 3/2 He
why is nuclear fusion signficant as energy source>
releases lots of energy but needs high temp/pressure which is hard to control
- used in hydrogen bombs
