Topic 6 - Using Radioactive Materials Flashcards
Where does background radiation come from?
- unstable isotopes all around us
- space (known as cosmic rays), mostly from sun. (Earth’s atmosphere protects us from much of this radiation & its magnetic field deflects them away)
- human activity i.e. nuclear explosions/dumped nuclear waste
How does where you live affect how much background radiation from radon you get?
- certain underground rocks cause higher background radiation levels at surface(i.e. granite), especially ones that release radioactive radon gas - gets trapped inside people’s houses
- radon concentration in people’s houses depends on the rock they’re built on which depends on your region
What is meant by the term “half-life”?
The half-life of a radioactive isotope is the time taken for half of the undecayed nuclei to decay.
How does the radioactivity of a source decrease over time?
- each time radioactive nucleus decays & radiation is emitted, one more radioactive nucleus disappears
- as unstable nuclei disappear, activity decreases, so older source=less radiation emitted
- some isotopes this is few hours, some millions of years
What does a short half-life tell us about the activity of the radioactive isotope?
activity falls quickly, lots of nuclei decay quickly
What does a long half-life tell us about the activity of the radioactive isotope?
activity falls slowly, most nuclei don’t decay for a long time
What is the activity of a radioactive isotope measured in?
Becquerels (Bq)
What measures activity of a radioactive isotope?
Geiger-Muller (G-M) tube
What does 1 Bq mean in terms of speed of decay?
1 decay per second
The activity of a radioisotope is 640 Bq. Two hours later it has fallen to 40 Bq. Find the half-life of the sample.
Initial = 640 Bq (divide by 2)
After one half-life = 320 Bq (divide by 2)
After two half-lives = 160 Bq (divide by 2)
After three half-lives = 80 Bq (divide by 2)
After four half-lives = 40 Bq
Half-life is 30 minutes (four half-lives in two hours)
How would a Geiger-Muller tube be used to measure the half-life of a radioactive source?
Take several readings and plot them on a graph and then drawing a line of best fit
How is the half-life of a radioactive source found from a graph?
- Results are plotted on a graph
- Find the time (on x axis) for activity (on y axis) to half
- Important background radiation is measured first to subtract from measured radiation to prevent false readings
How is alpha radiation used in household fire alarms?
- Weak source of alpha radiation is placed in a smoke detector, close to 2 electrodes
- Source causes ionisation & a current flows
- Fire will absorb the radiation so current stops & alarm sounds
How are gamma rays used in the sterilisation of food & equipment?
- Food can be irradiated with high doses of gamma rays which kill microbes so food doesn’t go bad as quickly
- Medical equipment can be sterilised with gamma rays instead of being boiled; good as high temps can damage fruit/plastic instuments
- Radioactive source needs to be a strong emitter of gamma rays with reasonably long half-life so it doesn’t need replacing too often
How is radiation used as a medical tracer?
- Medical tracer injected/swallowed by patient and progress monitored by an external detector
- Computer uses detector’s reading to produce an image of isotope’s flow
- Can detect & diagnose medical conditions e.g. cancer
- All isotopes in the body must be gamma or beta so it passes out the body
- Should have a short half-life so they quickly disappear
How is gamma radiation used in industry to detect leaks in underground pipes?
- Gamma put in liquid underground
- Can be detected at surface
- Can see the leak as gamma will be detected where it shouldn’t be
How is beta radiation used in thickness gauges?
- Used in thickness control
- Direct radiation through things and put detector on the other side
- When amount of detected radiation changes, means paper is too thick/thin so control is adjusted to go back to correct thickness
- Needs relatively long half-life so it doesn’t decay too quickly
- Need to be beta so paper partly blocks radiation as if all/none went through the reading wouldn’t change
How are gamma rays used to treat cancer?
- High doses of gamma kill all living cells
- Radiotherapists need to ensure they target them at cancerous cells to minimise damage to healthy cells
What effect on the body do lower doses of ionising radiation have on the body?
- Minor damage without killing cells
- Can rise the number of mutant cells which divide uncontrollably: cancer
What effect on the body do higher doses of ionising radiation have on the body?
- Kill cells completely
- Which causes radiation sickness if lots of cells are killed at once
What are the two main factors that affect the extent of harm from radiation?
- Amount of exposure to the radiation
- Energy & penetration of the radiation
Which ionising radiation is the most dangerous inside the body and why?
- Alpha
- Does all damage in a localised area
- Beta & gamma are less dangerous as they mostly pass straight out without doing much damage
How can you minimise your exposure to radioactive sources when working with them in a laboratory?
-Never allow skin contact with a source; handle with tongs
How would you protect yourself if you were working with nuclear radiation?
- Wear full protective suits; prevents tiny radioactive particles being inhaled/lodging in the skin/under fingernails etc
- Use lead lined suits, lead/concrete barriers & thick lead screens to prevent exposure to gamma rays
- Use remote-controlled robot arms for highly radioactive areas
Why is nuclear waste such a problem?
- Usually can’t be recycled to create more energy
- Long half-lives so radioactive for a long time
- Can be dangerous so needs to be placed far away from people
How do nuclear power stations usually deal with most dangerous nuclear waste?
-Vitrification
What is meant by vitrification?
- Melt radioactive waste with other materials to form a type of glass
- Liquid glass is sealed inside steel canisters and buried deep underground
What ways are there to deal with nuclear waste?
- Vitrification
- Pack it into thick metal containers &/or bury in a deep hole & fill hole with concrete
What important thing must you consider when storing radioactive nuclear waste?
-There are plenty of materials to absorb radiation before it can reach Earth’s surface
What are the advantages of working with nuclear power?
- Relatively safe method of generating electricity
- Very reliable
- Reduces need for fossil fuels that are running out
- Very clean (fossil fuels release CO2 when burnt, greenhouse effect, reduces sulphur dioxide too [acid rain])
- Lots of energy can come from small nuclear material
- Cheap and readily available
What are the disadvantages of working with nuclear power?
- Often perceived to be dangerous
- Some worry it cannot be disposed safely & can leak & pollute land, rivers & seas
- Have been serious accidents that contaminated large areas with radioactivity & some believe it’s not worth the risk
- Risk of leaks=major catastrophes (e.g. Chernobyl)
- Higher overall costs from cost of power plant & final decommissioning (to dismantle a nuclear power plant safely takes days)
