The atom and radioactivity Flashcards
history of theories on structure of atom
Democritus: all matter made up of identical lumps, couldn’t be broken down
John Dalton: each element made up of different type of atom
Thomson: plum pudding theory (sphere of positive charge with negative electrons scattered in it)
Rutherford: mostly empty space, positive charge concentrated at centre of nucleus
Rutherford experiment
fired alpha particles at thin sheet of gold
most went through
some bounced right back
nuclide definition
atoms comprised of particles number of proton and neutrons
ionisation definition
when atom/molecule loses electrons
forms ions
ionising radiation
high-energy radiation able to cause atoms/molecules to lose electrons
EM spectrum able to cause ionisation
UV
X-rays
gamma rays
radioactive meaning
decay and give out ionising radiation to become more stable
nature of different types of radiation
alpha = 2 protons, 2 neutrons beta = electron gamma = EM wave
charge of different types of radiation
alpha = 2+ beta = -1 gamma = 0
mass of different types of radiation
alpha = He nucleus (relatively large) beta = very small (negligible) gamma = zero
range of different types of radiation
alpha = 3-5cm beta = 2-3m gamma = 100s of metres
ionising effect of different types of radiation
alpha = very strong due to size beta = moderately ionising gamma = very weak, tends to pass through rather than interact with particles
penetration of different types of radiation
alpha = slow moving, stopped by paper, skin beta = moderate, blocked by thin plate of metal gamma = high, blocked by thick metal plates
different types of radiation in magnetic/electric field
alpha: larger charge + feels greater force in these fields+ deflected less due to greater mass than beta, deflected in opposite direction to beta
beta: deflected in opposite direction to alpha (opposite charge)
gamma: doesn’t get deflected (no charge)
danger of different types of radiation
alpha: most dangerous inside of body due to low penetration power
beta + gamma most dangerous outside due to higher penetration power
why emitting gamma rays doesn’t change element of nucleus
gamma ray is just energy
alpha decay
atomic number -2
mass number -4
beta decay
atomic number +1
mass number 0
neutron turns into proton + electron, electron emitted
background radiation definition
low level radiation around us all the time
main causes of background radiation
natural radioactive substances (rocks, soil, living things, cosmic rays human activities (nuclear waste, power stations, medical uses of radiation)
irradiation uses
make medical equipment/food sterile
destroy cancer cells in patients’ bodies
alpha radiation uses
smoke alarm
alpha radiation ionises air
small electric current flows in smoke detector
in fire, smoke particles absorb alpha radiation
current drops
alarm sets off
beta radiation uses
monitor thickness of materials
radiation passes through given material
thicker material = more radiation absorbed =less radiation reaches detector
detector on other side sends signals to control unit that adjusts thickness of material
gamma rays uses
cancer treatment (wide beam focused on tumour to limit damage to healthy cells) sterilise food / medical equipment (kills pathogens)
beta or gamma emitting sources as tracers in medicine
diagnostics
tracer swallowed or injected into patient
releases radiation periodically
progress monitored by radiation detector
has to have short half-life so radioactivity disappears quickly
beta or gamma emitting sources as tracers in industry
radioactive source placed in underground pipes
tracer tracked by detector above ground
leak or blockage shown by reduction in activity
carbon dating
all organisms have around 1/10000000 of carbon as carbon-14
organisms dies, no more carbon-14 gained from environment
carbon-14 decays with half-life of 5730 years
half-life of uranium-238
4.5 billion years
relative proportions daring
radioactive uranium changes into stable lead after series of half-lives
measure relative proportion of uranium and lead isotopes in rock
approximate age can be worked out
radiation dose units
sieverts (Sv) or millisieverts (mSv)
how radioactive materials handled carefully
using tongs
holding them far from body as possible
avoid looking at material directly
keep exposure to minimum
how radioactive materials stored
stored in lead box
lead absorbs alpha and beta radiation
reduces gamma radiation
dangers of radiation
may cause cancer
radiation sickness
fission definition
splitting of atom into smaller atoms
how fission occurs
large isotope bombarded by slow-moving neutron
atom absorbs neutron
nucleus becomes unstable
atom splits into smaller atoms (2-3 high-speed neutrons) and large amount of energy
chain reaction continues
how nuclear fission is controlled
moderators slow down the produced neutrons
prevents reactor from overheating and exploding
nuclear fuel advs
small amount of nuclear fuel gives large amount of energy relatively inexpensively
how nuclear waste is disposed of
low level: bury in secure landfill sites
intermediate level: sealing into concrete blocks, in steel canisters, buried underground
high level: sealed in glass and steel, stored underground, cooled for 50 years, moved to more permanent storage
fusion definition
joining of 2 lighter atoms into larger atom under extremely high pressure and temperature
why nuclear fusion is hard
requires high pressure and temperatures
takes a lot of energy (no source on Earth can reach these levels)
nuclear fusion uses
potential future energy source
hydrogen bombs
how fusion works
nuclei approach each other and fuse
nuclei repel each other as both positively charged
requires a lot of pressure and temperature to overcome this to fuse
releases enormous amounts of energy with minimal radioactive waste
cold fusion
2 scientists claimed to undergo fusion in room temp. in 1989
been unable to reproduce this, never been validated
half-life of radioactive isotope definition
average time taken for number of unstable nuclei to halve
time taken for count rate from original isotope halve
radioactive of sample measured in
becquerel (Bq)
one nucleus decaying per second
radioactivity of sample over time
older sample = less radiation
