radioactivity Flashcards
what did J.J Thomson discover
electrons could be removed from atoms, so atoms must be made up of smaller bits
what did J.J thomson call his model
plum pudding - atoms were spheres of positive charge with tiny negative electrons stuck in them
what experiment did rutherford and marsden do
the gold foil test
they shot alpha beams of alpha particles at a thin gold foil, they expected the particles to pass straight through or only be slightly reflected
what results did they get from the gold foil test
although most of the particles did go straight through some were deflected more than they expected and were deflected back to where they came from
what did rutherford conclude
most of the mass of the atoms was concentrated at the centre in a nucleus, most of the atom is just empty space and must have a positive charge
what did bohr do to rutherford design
the electrons were in fixed orbit at set distances from the nucleus, the most normal atom we know now
3 factors of the current model
protons
neutrons
electrons
factors of the new atom
positively charge nucleus
negatively charged electrons
electrons are in shells
protons and neutrons in the centre
atoms are neutral
atoms join together to form molecules
relative mass and relative change of a proton
1
+ 1
relative mass and relative change of a neutron
1
0
relative mass and relative change of a electron
0.0005
-1
how can electrons move shells
if it absorbs EM radiation with the right amount of energy, it moves up to an empty or partially filled shell
however it does quickly fall back
what happens to an atom to make it becomes ionised and how
looses an electron
absorbs enough energy which can move so far it leave the atom, now a free electron and the atom is ionised
now it’s a positive ion
what ionises atoms
nuclear radiation
what is ionising radiation
any radiation that can knock electrons from atoms
what is an isotope
different forms of the same element by having the same number of protons but different number of neutrons
what is radioactive decay
when unstable isotopes decay into other elements and give out radiation as they try to become more stable
what do radioactive substances spit out
one or more types of ionising radiation when they decay - alpha, beta and gamma
what are alpha particles
helium nuclei
alpha particle facts
emitted from the nucleus
don’t penetrate very far into materials and are stopped quickly
they are strongly ionising due to their size
only travel a few cm and are absorbed by a thin sheet of paper
what are beta particles
electrons and positrons
beta particles facts
beta minus is a fast moving electron released by the nucleus
beta positive is a fast moving positron
beta minus - both moderately ionising - range in air for a few metres and absorbed by a sheet of aluminium
positrons - smaller range, hit an electron and destroy eachother and produce gamma rays
what are gamma rays
EM waves with a short wavelength
gamma rays facts
penetrate far into materials and will travel long distance in air - absorbed by thick sheet of lead or metres of concrete
weakly ionising and tend to pass through rather than collide with atoms
the nucleus decays and undergoes nuclear rearrangement and releases energy
what is a nuclear equation
a way of showing radioactive decay by using element symbols
what does alpha decay decrease
the charge and mass of the nucleus
what happens when a nucleus emits an alpha particle
loses 2 protons and 2 neutrons
mass number decreases by 4
atomic number decreases by 2
what does beta minus decay increase
the charge of the nucleus
what happens during beta minus decay
a neutron changes into a proton and an electron
mass number doesn’t change as it hasn’t lost a neutron
atomic number increases by 1
what does positron emission decrease
the charge of the nucleus
what happens in beta plus decay
a proton changes into a neutron and a positron
mass number doesn’t change - lost a proton and gained a neutron
atomic number decreases by 1
what does neutron emission decrease
the mass of the nucleus
what happens when a nucleus emits a neutron
mass number decreases by 1 - lost a neutron
atomic number stays the same
what happens in both alpha and beta emission
a new element will be formed as the number of protons changes
what do gamma rays not change
the charge or mass of the nucleus
what is a totally random process
radioactivity
why is radioactivity random
you cannot say when any radioactive isotopes is going to decay and you cannot say which will decay next
what is half-life
the average time taken for there number of radioactive nuclei in an isotope to halve
how can activity be measured
the geiger - muller tube
how does the geiger-muller tube work
clicks each time it detects radiation, the tube can be attached to a counter, which displays the number of clicks per second
how else can you detect radiation (photographic film)
using photographic film, the more radiation the films exposed to, the darker it becomes
what happens to the radioactivity of a source over time
decreases
what does a short half life mean
the activity falls quickly because the nuclei are very unstable and rapidly decay
they are also dangerous due to high amount of radiation
what does a long half life mean
the activity falls more slowly because most of the nuclei don’t decay for a long time
dangerous as nearby areas are exposed to radiation for millions years of years
how can you measure half life
plotting a graph
found from the graph by finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis
what is background radiation
low level radiation that’s around us all the time
examples of background radiation
radioactivity - air, some foods, building materials, rocks
space - cosmic rays
radiation due to human activity
what is absorbed radiation dose
amount of radiation your exposed to, it also varies due to where you live or jobs which involve radiation
what is exposed to radiation called
irradiation
ways to reduce irradiation
keeping sources in lead lined boxes
standing behind barriers
being in a different room, using remote controlled resources
wearing photographic film badges to monitor exposure
how does radiation damage cells
radiation can enter living cells and ionise atoms and molecules in them, leading to tissue damage
what do lower doses of radiation cause
minor damage without killing cells which can cause cell to mutate and divide uncontrollably, causing cancer
what do higher doses of radiation cause
tend to kill cells completely, causing radiation sickness
what radiation are the most dangerous outside the body and why
beta and gamma as they can penetrate the body and get to the delicate organs
what radiation are the least dangerous outside the body and why
alpha is less dangerous as it can’t penetrate the skin
what radiation are the most dangerous inside the body and why
alpha as they are strongly ionising, all do damage in a very localised area which means contamination
what is contamination
radioactive particles getting on objects
why is contamination dangerous
because radioactive particles could get inside your body
there’s a risk until the contamination is removed or all the atoms have decayed
what can prevent contamination
using gloves and tongs
protective suits
what do hazards associated with radioactive source depend on
it’s half life
what do household fire alarms use
alpha radiation
what can be sterilised by using gamma rays
food - kill microbes
equipment - sterilise medical equipment
what is used in tracers and thickness gauges
radiation
what can PET scanners help with
diagnose illnesses
how do pet scanners work
1) inject the patient with a substance used by the body
2) positrons emitted by the isotope meet electrons in an organ and annihilate high energy gamma rays in opposite directions are detected
3) the distributions of radioactivity matches up with metabolic activity
4) the isotopes used in PET scanning have short half lives
5) could be no longer useful if left too long due to transportation
what is internal radiation therapy
a radioactive material is placed inside the body into or near a tumor
how can tumors be treated externally
using gamma rays aimed at the tumor
why can gamma rays sometimes cause more harm than gold
because if they are being used to treat tumors if they hit healthy cells they could potentially cause them to become tumors
what are alpha emitters injected near
the tumor
how are beta emitters used
in implants placed inside or next to the tumor
what is nuclear fission
a type of nuclear reaction that is used to release energy from uranium or plutonium atoms
what is the chain reaction
1) slow moving neutron is fired at a large unstable nucleus
2) the neutron is absorbed by the nucleus - makes the atom more unstable causing it to split
3) when it splits it forms 2 new lighter elements and energy is released - all nuclei is radioactive
4) every time it splits up, it splits out 2 or 3 neutrons which can hit other nuclei causing them to split - a chain reaction
why must chain reactions be carefully controlled
neutrons will only cause other nuclear fissions if they are moving slowly enough to be captured by nuclei
what are nuclear power stations powered by
nuclear reactions that control chain reactions
what is nuclear fission
two light nuclei collide at high speed and join to create a larger, heavier nucleus
when does fusion happen
only at high temperatures and pressures
what are the pros of nuclear power
pretty safe
very reliable
nuclear power doesn’t release gases like fossil fuels
cheap and readily available
what are the cons of nuclear power
public perception can be very negative
nuclear waste can never be disposed safely
risk of leaks - cause major catastrophe
