SP6: radioactivity Flashcards
atom size
10^-10 m
what happens when electrons absorb energy?
they move to higher energy levels (bigger distances from the nucleus), in time they jump back down to a lower level and release energy
what does a stable nuclei have?
have almost equal numbers of neutrons and protons
what will happen to nuclei with too many or too little neutrons?
they will decay & release radiation, as they are unstable
formation of alpha particles
when a nucleus is unstably large, it emits a “package” of two protons and two neutrons called an alpha particle
alpha particle
atomic mass = 4
atomic number = 2
what does alpha decay do?
-mass number decreases by 4
-atomic number to decrease by 2
beta minus (ß-)
atomic mass = 0
relative charge = -1
formation of beta minus:
-in a nucleus with too many neutrons, a neutron splits into a proton (same mass but positive charge) and and an electron, which is then emitted at a high speed, this electron is a beta minus particle
-a beta particle is an electron
what does beta minus decay do?
-mass number stays the same
-atomic number increase by one
positron (ß+)
mass number = 0
relative charge = +1
formation of a positron:
-in a nucleus with too little neutrons, a proton will turn into a neutron and emit a fast-moving positron
-a positron is the antimatter version of an electron
what does positron decay do?
-mass number stays the same
-atomic number decreases by one
gamma ray
atomic mass: 0
atomic number: 0
formation of gamma rays
-after emitting an alpha or beta particle, the nucleus will often still have excess energy and will again lose energy
-a nuclear re-arrangement will emit the excess energy as a gamma ray
what does gamma decay do?
nothing
neutron emissions
emitted by radioactive decay, or artificially caused
what does neutron decay cause?
-atomic mass decreases by one
-atomic number remains the same
penetrating power of alpha
stopped by paper/skin
ionising power of alpha
high
range of alpha in air
few cm
penetrating power of beta
stopped by aluminium
ionising power of beta
moderate
range of beta in air
around 1m
penetrating power of gamma
stopped by thick lead or concrete
ionising power of gamma
low
range of gamma in air
around 1km
how can radioactive decay be detected?
photographic film
-it’s chemically changed by radiations so it can be developed to see if there has been exposure
G-M tube (geiger-muller tube)
-radiation ionises the particles and the charged particles are counted as charges
can radioactive decay be predicted?
no, it is random
half-life
-the time it takes for half the unstable nuclei in a sample to decay
-the time it takes for activity to half
-the time it takes for the count rate to half
what is the activity of a
radioactive substance measured in?
becquerel
irridation
exposing objects to beams of radiation
advantages and disadvantages of irridation
advantages
-sterilisation can be done w/o high temperatures
-it can be used to kill bacteria on things that would melt when exposed to high temps
disadvantages
-may not kill all bacteria
-can be very harmful, standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation
irridation for sterilisation of fruit
gamma rays emitted by a radioactive source & will destroy any bacteria on the fruit but will not change the fruit in any significant way
medical irridation
-sterilisation of medical equipment
-external radiotherapy (gamma beams are aimed at the tumour from many different directions to maximise the dose on the tumour but to minimise the dose on the surrounding soft tissue, this technique can damage healthy tissue, so careful calculations are done to establish the best dose)
what aspects are considered when using radioactive sources?
-the nature of decay (alpha, beta or gamma)
-the half-life (long enough for the isotope to produce useful measurements, but short enough for the radioactive sources to decay to safe levels soon after use, a half-life that is too long will extend effects of radiation)
-toxicity
contamination
the introduction of radioactive materials into something
medical contamination
-cancer tumours can be treated by injecting them with a radioactive material
-the cancer cells absorb radiation from the material and receive a high dose of energy
-doctors must work out the danger to nearby healthy tissue before giving this treatment
-injected radioactive sources can be used as tracers to make soft tissues, show up through medical imaging processes
-an isotope emits gamma rays that easily pass through the body to a detector outside the body
-changes in the amount of gamma emitted from different parts would indicate how well the isotopes are flowing, or if there is a blockage, perhaps caused by a cancer
-isotopes need to be chosen with short half-lives & that aren’t poisonous
PET scanners
-use a positron emitter as a tracer
-the tracer materials, have very short half-lives and injected into the patient’s blood soon after manufacture
-the positrons emitted will react with electrons in the patient’s body and produce gamma rays which can be detected outside the body
contamination to check for leaks
-water supplies can be contaminated with a gamma-emitting radioactive isotope to find leaks in pipes
-where there is a leak, contaminated water seeps into the ground, causing a build-up of gamma emissions in that area
-the build-up of gamma emissions can be found using a G-M tube
the isotope for this must be:
-a gamma emitter
-have a half-life of at least several days to allow the emissions to build up in the soil
-not be poisonous to humans as it will form part of the water supply
advantages and disadvantages of contamination
advantages:
-radioactive isotopes can be used as medical and industrial tracers
-Use of isotopes with a short half-life means exposure can be limited
-imaging processes can replace some invasive surgical procedures
disadvantages:
-radioactive isotopes may not go where they are wanted
-it can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind
-exposure to radioactive materials can potentially damage healthy cells
smoke alarms
(usually americium-241)
-a household smoke alarm measures the movement of alpha particles across a small gap
-if smoke enters the detector, it will absorb the alphas and the detector will measure a drop in the number getting across the gap, this drop in measurement will trigger the alarm to sound
thickness monitoring
(beta minus emitters in industry, for paper milling and the production of aluminium foil)
-if the foil is too thick it absorbs more beta particles
-the detector receives less beta particles and then sends a signal to the rollers to increase the force on the foil, making it thinner
-if the foil is too thin it absorbs less beta particles
-the detector receives more beta particles and then sends a signal to the rollers to decrease the force on the foil, making it thicker
background radiation
ionising radiation that occurs naturally in the environment
background radiation sources
cosmic rays
-radiation from space
rocks & soil
-radioactive rocks that give off radioactive radon gas
living things
-plants that absorb radioactive materials from the soil & pass these up the food chain
medical procedures
-x-rays
nuclear missiles & power
effects of radiation on the human body
eyes:
-high doses can cause cataracts
lungs:
-breathing in radioisotopes can damage DNA
reproductive organs:
-high doses can cause sterility or mutations
skin:
-skin burns or cancer
managing risks of radiation
-keep radioactive sources in a lead-lined box when not in Use
-wear protective clothing to prevent the body becoming contaminated
-avoid contact with bare skin
-wear face masks to avoid breathing in materials
-limit exposure time - so less time is spent around radioactive materials
how does background radiation affect people
-mostly by irridation
-a small amount is from being contaminated by radioisotopes in the food and drink that is consumed
one becquerel
one decay per second
sievert (Sv)
-the unit to measure radiation dose
-the amount of damage that would be caused by the absorption of 1 joule of energy in each kilogram of body mass
1000 mSv
1 Sv
nuclear fission
-a slow-moving neutron is absorbed into a nucleus (typically uranium-235), this causes the nucleus to become unstable (uranium-236)
-the entire nucleus splits into two daughter nuclei, two or three neutrons also explode out of the fission reaction
-these neutrons can collide with other uranium nuclei to cause further fission reactions -> chain reaction
fission reactor
producing electrical energy by means of a controlled fission reaction
nuclear fuel in a nuclear reactor
-uranium or plutonium isotope that will split when triggered by an incoming neutron
-the fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods
moderator in a nuclear reactor
slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod (eg: graphite core)
control rods in a nuclear reactor
these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction
coolant in a nuclear reactor
heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station
concrete shield in nuclear reactor
the daughter products of the fission reaction are radioactive and can be a hazard
an uncontrolled fission reaction is
the basis of an atomic bomb
advantages and disadvantages of nuclear power stations
advantages:
-no pollution
-doesn’t add to global warming
-very low fuel costs
-power station has long lifetime
disadvantages:
-waste is reactive, products are hard & expensive to remove
-large scale accidents can be catastrophic
-public perception of nuclear power is negative
-costs of building and safely decommissioning are very high
nuclear fusion
two small, light nuclei join together to make one heavier nucleus, some mass changes to energy
conditions needed for nuclear fusion
-nuclear fusion requires the fusing of nuclei, which are positive particles, as two nuclei approach each other, they will repel because they have the same charge
-the fusion of the nuclei has to happen under intense pressure and very high temperatures in order to force the nuclei together and overcome this electrostatic repulsion.
-this is why it’s very difficult to build a fusion power station, for fusion to occur at the lower pressures in a reactor on earth, the temperature would need to be between 100 and 200 million degrees
