Studied by 3 people
What is an atom made of
protons, neutrons and electrons
Which particles are found in the nucleus of the atom and what particle is found in the orbitals
nucleus - protons and neutrons orbitals - electrons
What is the charge of a proton, neutron and electron
proton +1 neutron 0 electron -1
What is the mass of a proton, neutron and electron
proton 1 neutron 1 electron 1/1836
What is the atomic/proton number
the number of protons in an atom
there are the same number of electrons
the atomic number is found at the bottom of the atomic symbol
What is the mass/nucleon number
the number of protons and neutrons in an atom
the number of neutrons can be found by taking away the atomic number from the mass number
the mass number is found at the top of the atomic symbol
What are isotopes
atoms of the same element which have the same number of protons but a different number of neutrons (same atomic number, different mass number)
Why are some nuclei unstable
sometimes it is due to their large size or
because the number of protons or neutrons within them are out of balance
Why does an isotope decay
due to the unstable nuclei the isotope decays emitting radiation in order to reduce the size or bring them back to balance
What are alpha, beta and gamma
ionising radiations emitted from unstable nuclei in a random process
what does ionising mean
if the radiation hits other particles, it can knock out electrons
Why is ionisation bad
it can cause chemical changes such as mutations in materials and damage/kill cells and cause cells to become cancerous
What is an alpha particle
2 protons and 2 neutrons, a helium nucleus
What charge does an alpha particle have
+2
What is the range of an alpha particle
a few centimetres
What is alpha absorbed by
it is absorbed by paper/card
How ionising is alpha radiation
strongly
What is a beta particle
an electron
What is the charge of a beta particle
-1
What is the range of a beta particle
around 1 metre
What is beta absorbed by
a few millimetres of aluminium
How ionising is a beta particle
medium
What is gamma
an EM wave
What charge do gamma waves have
0
What is the range of a gamma ray
infinite
What is gamma absorbed by
it is not absorbed by anything but instead reduced by metres concrete or a few millimetres of lead
How ionising is gamma
low
How do you investigate the relative penetration of different types of radiation
connect a Geiger-Muller tube to a counter
measure the background radiation over a one minute period
repeat 3 times and take an average
place a radioactive source a fixed distance away from the tube
take a reading over a 1 minute period
place different absorbers between the source and tube
take a reading over 1 minute period for each absorber
if the count over an interval falls to background levels (allow random variation) then the radiation has been absorbed
repeat this for the other radioactive sources
What is an absorber
a material that absorbs radiation such as paper, aluminium and lead
What are safety points when handling radioactive isotopes
when a source is not in use, keep it in a lead lined container when a source is in use, keep it a good distance away from yourself use tongs when handling the source point the source away from you
What are the conclusions to the experiment
stopped by paper = alpha radiation stopped by aluminium = beta radiation reduced by lead = gamma radiation
What effect does alpha emission have on its atom
the nucleus loses 2 protons and 2 neutrons the atomic number is decreased by 2 and so is the mass number
What effect does beta emission have on its atom
the nucleus gains a proton the atomic number increases by 1 the mass number stays the same
What effect does gamma emission have on its atom
it has no effect on the atom as gamma is a wave the atomic and mass numbers stay the same
What effect does neutron emission have on its atom
the nucleus loses 1 neutron the mass number decreases by 1 the atomic number stays the same
How do radiation detectors work
they detect atoms which have been ionised due to radiation or the chemical changes that they produce
What are examples of radiation detectors
photographic film
Geiger-Muller tubes
ionisation chambers
scintillation counters
spark counters
What is background radiation
it is the radiation that is always present everywhere in the environment
What are natural sources of background information
radon gas (underground gases) rocks food humans cosmic rays
What are man-made sources of radiation
building materials medical uses (x-rays) nuclear power
What is activity
the number of decays occurring in an isotope every second
What is activity measure in
Becquerels, Bq
What happens to activity over time
it decreases
What is the formula for activity
activity = number of decays/time
What is the half-life of an isotope
it is the time taken for the activity of that isotope to drop to half of its initial value
In what way can decay be predicted
the probability of the decay is known however it can never be predicted when it will happen
Why does the activity of an isotope decrease over time
because although there is a fixed probability that an isotope will decay per unit of time the number of nuclei available drops over time as previous nuclei have decayed meaning there are less remaining to decay
What will the activity and number of nuclei never drop to
0
Do all isotopes have the same half-life
different isotopes have different half lives
What is a constant in exponential graphs
the time for activity to halve in value
How can you find half-life from a graph
look at the value of activity the isotope starts with
half the value and find it on the y-axis
draw a line from that number across until you reach the activity curve
draw a line from that point down to the x-axis to find the half life time
What are the different uses of radioactivity in industry and medicine
smoke detectors
thickness monitoring
tracers
radiotherapy
sterilisation
How do smoke alarms work
use alpha radiation
alpha particles ionise the air inside the detector, allowing a small current to flow within it
when smoke enters the detector, the alpha particles are absorbed and the current no longer flows
the alarm is the triggered
Why is alpha radiation used for smoke alarms
because it is easily absorbed by smoke which then triggers the alarm it has a short rage and cant penetrate through the casing and damage humans
How does thickness monitoring work
use beta radiation
they can be used to measure the thickness of thin materials such as paper
the material moves above the beta source
the beta particles are partly absorbed by the material
the thickness is monitored by the count of beta particles the detector counts
if the material gets thinner, less beta particles are absorbed meaning more pass through and the count rises
if the material gets thicker, more beta particles are absorbed meaning less get through and the count goes down
this allows the machine to make adjustments to keep the thickness the same
Why is beta used for thickness monitoring
it is partly absorbed meaning some still pass through the material if alpha was used all of the particles would be absorbed if gamma was used all of the particles would get through therefore not detecting change in thickness
How do tracers work
use gamma radiation
radioactive isotopes are added to fluids so the flow of the fluid can be monitored
the amount of the isotope used is kept to a minimum
isotopes which are chosen have short half lives of around a few hours, which is long enough to carry out the procedure but not so long that they cause long term harm
What are the uses of tracers
can be added to blood to check the blood flow and search for blockages such as blood clots can be added to an oil pipeline in order to check for any leaks
Why is gamma used for tracers
it is highly penetrating and can be easily detected
How does radiotherapy work
uses gamma radiation
it is the treatment of cancer using radiation
gamma is highly effective at treating cancer even though it causes it
bacteria and cancer cells are more susceptible to radiation than other cells
beams of gamma are directed at the cancerous tumour
the beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour
Why is gamma used for radiotherapy
highly penetrating and can kill bacteria and cancer cells it can also reach the tumour by penetrating through the body
How does sterilisation work
uses gamma radiation
medical instruments are sterilised by exposing them to gamma radiation
gamma kills the bacteria and viruses
penetrates the instrument, reaching areas that may otherwise not be properly sterilised
Why is gamma used in sterilisation
highly penetrating and can kill bacteria and viruses can also penetrate the instrument
What is contamination
when small amounts of the radioactive isotope leaks onto material
What happens because of contamination
small amounts of the isotope in the contaminated areas will give off radiation
What is irradiation
the process of exposing a material to alpha, beta or gamma radiation
How can a material become radioactive
if the material becomes contaminated
Does irradiating a material make it radioactive
no, it will not make a material radioactive regardless of the strength of the radiation or how long the material has been exposed to radiation for
What factors need to be taken into consideration when disposing nuclear waste
-some waste is highly reactive = thick shielding requires -some waste have very long half lives = need to be stored for long periods of time -containers holding the waste must not corrode or degrade over time = no nuclear waste leaks
must be stored in geologically safe areas, away from dangers of earthquakes
must be stored away from water sources so they wouldn't get contaminated if there was a leak
storage areas should be clearly marked using meaningful pictures = future societies can understand the nature of what is stored
What are the dangers of ionising radiation
can cause mutations in living organisms
can damage cells and tissue
problems about disposing radioactive waste
What can fission, fusion and radioactive decay be a source of
they can be a source of energy
What is required for nuclear fission to happen
the nucleus requires energy, this can be given by hitting the nucleus with a neutron
What does nuclear fission produce
2 smaller, daughter nuclei and 2/3 neutrons
What does nuclear fission release
it releases energy as kinetic energy of the fission products
What isotope is usually used for nuclear fission
Uranium 235 U-235
How can a chain reaction be set up for fission
one fission occurs, producing 2/3 neutrons
one of these neutrons could then go on to hit another U-235 nucleus causing another fission
What is the purpose of control rods
absorb neutrons, decreasing the number of fissions happening
so that fissions don't increase over time and cause the reactor to melt
What is the purpose of the moderator
slow down neutrons preventing them from being absorbed by U-238
these slowed down neutrons can still go on to create further fissions
Which substances can be used as moderators
carbon and water
What does U-238 do
nuclear reactors contain a large amount of U-238 as well as U-235
U-238 absorbs high energy neutrons released by fission
this prevents the rector from exploding
however it can stop chain reactions from occurring
What is the purpose of shielding in a reactor
fission releases lots of radiation (neutrons and beta particles)
if left unshielded, the radiation given off would be extremely hazardous to anyone nearby
the shielding absorbs the radiation preventing it from leaving the reactor
What is the difference between fission and fusion
fission is where large nuclei are split into smaller nuclei
fusion is where small nuclei are brought together to form a larger nucleus
What is the mass of the nucleus like after fusion
the mass is slightly smaller than the combined mass of the 2 original nuclei
this mass decreased is caused by a release of energy
What is fusion the energy source for
stars
hydrogen nuclei are fused together to form helium nuclei at the centre of stars, releasing energy
Why does nuclear fusion not happen at low temperatures and pressures
due to electrostatic repulsion of protons
in order for protons to overcome the repulsion, they have to travel at high speed (high temp)
there also needs to be lots of successful collisions (high pressure and density)
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