Section 7- Radioactivity and Particles P1 Flashcards
What does the nucleus of an atom contain?
Protons
Neutrons
What does the number of protons in the nucleus determine the name of?
The atomic number
the proton number
What does the total number of protons and neutrons in the nucleus determine the name of?
The mass number
The nucleon number
What charge are electrons?
Negative
What is most of an atom?
empty space
Define isotope:
Isotopes are atoms with the same number of protons but a different number of neutrons
How many stable isotopes do each element tend to have?
One or two (e.g. Carbon-12)
What do the unstable isotopes of each element tend to be like?
Radioactive - the nucleus is unstable, so it decays and emits radiation (e.g. Carbon-14)
What is radioactive decay?
The nuclei of unstable isotopes break down at random
- you can’t say when they will decay
- you can’t do anything to make a decay happen
When a nucleus decays, what types of radiation does it split into?
alpha (α)
beta (β)
gamma (γ)
neutron (n)
What is background radiation?
Background radiation is low-level background nuclear radiation all around us all the time.
What are the sources of background radiation?
- substance on earth(air, food, building materials, soil, rocks)
- radiation from space(cosmic rays from the sun)
- living things(have a bit of radioactive substances in)
- radiation due to human activity(fallout from nuclear explosions, nuclear waste - only a tiny proportion of all background radiation though)
What does nuclear radiation cause?
Nuclear radiation causes ionisation by bashing into atoms and knocking electrons off them
-atoms are turned into ions, hence ‘ionisation’
What makes nuclear radiation less ionising?
The further the radiation can penetrate before knocking into an atom and getting stopped, the less damage it will do along the way (so it’s less ionising)
What can detect ionising radiation?
Geiger–Müller detector (gives a count rate of the amount of radioactive particles reaching it per second)
Photographic film
What are the four types of radiation?
Alpha radiation
Beta radiation
Gamma radiation
Neutron radiation
What does neutron decay consist of?
A neutron is emitted from the nucleus
- the mass number decreases by 1
- the proton number remains the same
What are alpha particles made up of?
α particles are made up of 2 neutrons and 2 protons
- the same as Helium nuclei
- they are big, heavy and slow-moving
What are the features of alpha particles and alpha radiation?
- don’t penetrate far into materials
- since they are big, they are strongly ionising (they bash into a lot of atoms and knock electrons off)
- they are electrically charge(positive), so they are deflected by electric and magnetic fields
What does alpha radiation do to the mass number and proton number of the atom it has been emitted from?
- the proton number decreases by 2
- the mass number decreases by 4
What is a beta particle made up of?
A β particle is an electron which has been emitted from a nucleus
-an electron is emitted from the nucleus when a neutron turns into a proton and an electron
What does beta radiation do to the mass number and proton number of the atom it has been emitted from?
- number of protons in the nucleus is increased by 1 (proton number is increased by 1)
- the mass number stays the same
What are the features of beta particles and beta radiation?
- quite fast and small
- moderately penetrating and ionising
- they are electrically charged(negative), so they are deflected by electric and magnetic fields
What are gamma rays?
γ rays have no mass and are just energy in the form of an electromagnetic wave
-always happen after beta or alpha decay, you never just get gamma radiation
What does gamma radiation do to the mass number and proton number of the atom it has been emitted from?
- has no effect on the proton or mass number
- if a nucleus has excess energy it emits it in the form of a gamma ray
What are the properties of gamma rays and gamma radiation?
- highly penetrating
- weakly ionising, but when they do hit atoms they are highly ionising
- have no charge, so not deflected by electric or magnetic fields
What are alpha particles blocked by?
paper, skin or a few centimetres of air
What are beta particles blocked by?
thin metal - aluminium
What are gamma rays blocked by?
thick lead or very thick concrete
Describe a practical for how you can investigate the penetration of radiation:
- set up the Geiger-Müller detector, radioactive source and have a space between them where you can put materials
- remove the source, to measure a background count over a minute (then divide by 60 to get the count per second), repeat and find a mean, subtract this from your results at the end
- measure the count rate of the source (-background) repeat and take a mean
- insert different materials and count the rate, repeat and take a mean
How should radioactive sources be dealt with?
- kept in a lead-lined box when not in use
- should only be picked up with long-handled tongs or forceps
- don’t point them at anyone, and keep a safe distance from them
What occur each time a decay happens?
- an alpha, beta particle or gamma ray is given out
- one more radioactive nucleus has reacted
Define half-life:
Half-life is the time taken for half of the radioactive atoms now present to decay.
The time taken for the activity(or count rate) to fall by half.
What does a short half-life mean?
A short half life means the activity falls quickly, because lots of the nuclei decay quickly
What does a long half-life mean?
- the activity falls more slowly
- most of the nuclei don’t decay for a long time
What unit is radiation recorded in from the Geiger–Müller tube?
Becquerels
What is the shape of a graph of a radioactive source’s activity (measured with a Geiger–Müller tube)?
a stretched out L
-the readings should only be plotted when the background radiation count has been subtracted from the values
How do you find half-life on a graph?
Find the time interval on the x axis corresponding to a halving of the activity on the y axis
What are the uses of nuclear radiation?
- medical tracers
- to treat cancer
- to sterilise food and equipment
- in industry for tracers and thickness gauges
What types of nuclear radiation do they use for medical tracers?
beta or gamma radiation
-they penetrate human skin
How is nuclear radiation used as a medical tracer?
- the source is injected or swallowed by the patient
- the radiation penetrates the tissue and can be directed externally, as the source moves around it is monitered
- doctors use this to see whether organs are working properly
What properties does the radiation used as a medical tracer need?
-short half-life - so initial levels are high enough to be detected but the radioactivity inside a patient quickly disappears
Why would an alpha source not be a good as a medical tracer?
- wouldn’t be detected because it’d be stopped by the body tissue
- stong ionising power makes it increasingly dangerous to be inside of you
How is nuclear radiation used to treat cancer?
Radiotherapy kills the cancer cells and stops them from dividing
- involves a high dose of gamma rays carefully directed into a tumour, minimising the effect to the rest of the body
- ionising radiation can kill or damage cells
How is nuclear radiation used to sterilise food and equipment?
Food and medical equipment can be sterilised with a high dose of gamma rays to kill all microbes
What is the advantage of sterilising food?
Food will have a longer shelf life and won’t go off as quickly
Why is irradiation a particularly good method for food and plastic apparatus?
-does’t involve high temperatures, so they won’t be damaged
What does the radioactive source for sterilising food and medical equipment need to be like?
- needs to be a very strong emitter of gamma rays
- a reasonable half-life, so it doesn’t need to be constantly replaces
How is radiation used in industry as tracers?
- used to find leaks in underground pipes
- the source flows down a pipe and is detected above ground (gamma radiation is used because it can penetrate through rocks or earth surrounding the pipe)
- if there’s a crack the radiation in that area will increase
How is nuclear radiation used in industry as thickness gauges?
Beta radiation is used for this
- you put the stuff being made through, with a detector on the other side, connected to a control unit
- when the level of radiation changes the detector sends a signal for the plates altering the thickness of the stuff being made
Why is beta radiation used in industry as thickness gauges?
it will be partly blocked by the stuff being made, so some will be detected but the reduced rate allows you to see how the radiation emits as the thickness of the product can vary
What are the risks of ionising radiation?
Ionising radiation can damage cells and tissues
What are the risks of beta and gamma radiation?
- can penetrate the skin and soft tissues to reach the delicate organs inside
- they are more hazardous than alpha outside of the body
- if they get inside the body, their radiation mostly passes out and doesn’t do much damage
What are the risks of alpha radiation?
- alpha radiation can’t penetrate the skin
- if an alpha source gets inside the body it is very dangerous since it’s highly ionising
What does collisions between radiation and molecules in your cells mean?
- cause ionisation, which damages or destroys these molecules
- the extent of the effect depends on how much exposure to radiation and it’s energy and penetration
What can low doses of radiation cause?
- tend to cause minor damage without killing the cell
- can cause mutations in cells which can divide uncontrollably - cancer
What can a high dose of radiation cause?
- tends to kill cells completely
- causing radiation sickness, if a large part of your body is affected at the same time
What is exposure to radiation called?
Irradiation
-irradiating something does not make it radioactive
What are ways of reducing the risk of irradiation?
- lead-lined boxes
- standing behind barriers
- being in a different room
- using remote control arms
What is contamination in terms of radiation?
If unwanted radioactive atoms get onto or into an object, the object is said to be contaminated
What is the danger of contaminating atoms?
- they might decay, releasing radiation which could cause you harm
- especially dangerous if it gets inside of your body
How can you reduce the risk of contamination?
- gloves and tongs should be used when handling sources (avoiding particles getting stuck on your skin or under your nails)
- protective suits and masks
Where is most radioactive waste from?
nuclear power stations and hospitals
-it is low level
How is low-level radioactive waste dealt with?
it is buried in secure landfill sites
How is high-level radioactive waste dealt with?
- sealed in glass blocks, which are sealed in metal canisters
- then buried deep underground
- have to be buried in a geologically stable place to stop the canister being disturbed and the waste leaking out into groundwater
What is nuclear fission?
The splitting of an atom, which releases energy
-it can be spontaneous but in a nuclear reactor it’s made to happen
How is uranium-235 used in nuclear fission?
- a neutron is fired into a uranium-235 nucleus
- uranium-236 is highly unstable,so the nucleus can split
- when this split happens it splits into 2 or 3(small amount) of neutrons, two daughter nuclei and a lot of energy
What is a chain reaction?
When a nucleus (for example Uranium-236) splits into two daughter nuclei and a small number of neutrons, these neutrons can then hit other uranium-235 nuclei causing them to split too…
What is the main problem with nuclear power?
- the new nuclei formed are also radioactive
- dealing with radioactive waste
What energy transfers occur in a nuclear reactor?
- when a split occurs the energy is in the kinetic energy stores of the fission products
- the reactor releases this energy in the form of thermal energy stores to produce steam to drive a turbine
In a nuclear reactor what happens to the neutrons released from a nuclear fission reaction?
to sustain the reaction the neutrons released have to be slowed down
What does the moderator do in a nuclear reactor and what is made of?
Slows down the neutrons
-made of graphite or water
What are the main components of a nuclear reactor?
- moderator
- control rods
- shielding
- source rods (for example Uranium rods)
- substance pumped around the reactor (for example carbon dioxide, water)
- heat exchanger
What does the control rods do in a nuclear reactor and what is made of?
Limit the rate of fission by absorbing excess neutrons
-made of boron
What does the shielding do in a nuclear reactor and what is made of?
Used to absorb the ionising radiation created from fission
-made of a thick concrete structure, which may also contain lead or other metals
What does the substance pumped around the reactor do in a nuclear reactor and what is made of?
Transfer the energy to the water in the heat exchanger
- water turns to steam which turns a turbine, which turns a generator and generates electricity
- carbon dioxide can be used for this
What is nuclear fusion?
In nuclear fusion, two light nuclei collide at high speed and join to create a larger, heavier nucleus
What is the mass of the created nucleus in comparison to the two separate nuclei?
- the larger created nucleus doesn’t have as much mass as the two separate nuclei
- this is because some of the mass is converted into energy (this energy is released as radiation)
What are the advantages of fusion?
- it releases a lot of energy (more than fission for a given mass of fuel)
- all the energy released from stars comes from fusion
What is the problem with fusion?
- can only happen at really high temperatures (about 10,000,000°C and pressures
- because the positively charged nuclei have to be very close to fuse, so they need to be moving very fast to overcome the force due to electrostatic repulsion
What problems have scientist got with using fusion to create energy for us?
-the pressures and temperature are too high so that fusion reactors are really hard and expensive to build
