Topic 6 - Using Radioactive Materials Flashcards Preview

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Flashcards in Topic 6 - Using Radioactive Materials Deck (31)
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1
Q

Where does background radiation come from?

A
  • 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
2
Q

How does where you live affect how much background radiation from radon you get?

A
  • 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
3
Q

What is meant by the term “half-life”?

A

The half-life of a radioactive isotope is the time taken for half of the undecayed nuclei to decay.

4
Q

How does the radioactivity of a source decrease over time?

A
  • 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
5
Q

What does a short half-life tell us about the activity of the radioactive isotope?

A

activity falls quickly, lots of nuclei decay quickly

6
Q

What does a long half-life tell us about the activity of the radioactive isotope?

A

activity falls slowly, most nuclei don’t decay for a long time

7
Q

What is the activity of a radioactive isotope measured in?

A

Becquerels (Bq)

8
Q

What measures activity of a radioactive isotope?

A

Geiger-Muller (G-M) tube

9
Q

What does 1 Bq mean in terms of speed of decay?

A

1 decay per second

10
Q

The activity of a radioisotope is 640 Bq. Two hours later it has fallen to 40 Bq. Find the half-life of the sample.

A

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)

11
Q

How would a Geiger-Muller tube be used to measure the half-life of a radioactive source?

A

Take several readings and plot them on a graph and then drawing a line of best fit

12
Q

How is the half-life of a radioactive source found from a graph?

A
  • 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
13
Q

How is alpha radiation used in household fire alarms?

A
  • 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
14
Q

How are gamma rays used in the sterilisation of food & equipment?

A
  • 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
15
Q

How is radiation used as a medical tracer?

A
  • 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
16
Q

How is gamma radiation used in industry to detect leaks in underground pipes?

A
  • Gamma put in liquid underground
  • Can be detected at surface
  • Can see the leak as gamma will be detected where it shouldn’t be
17
Q

How is beta radiation used in thickness gauges?

A
  • 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
18
Q

How are gamma rays used to treat cancer?

A
  • High doses of gamma kill all living cells

- Radiotherapists need to ensure they target them at cancerous cells to minimise damage to healthy cells

19
Q

What effect on the body do lower doses of ionising radiation have on the body?

A
  • Minor damage without killing cells

- Can rise the number of mutant cells which divide uncontrollably: cancer

20
Q

What effect on the body do higher doses of ionising radiation have on the body?

A
  • Kill cells completely

- Which causes radiation sickness if lots of cells are killed at once

21
Q

What are the two main factors that affect the extent of harm from radiation?

A
  • Amount of exposure to the radiation

- Energy & penetration of the radiation

22
Q

Which ionising radiation is the most dangerous inside the body and why?

A
  • Alpha
  • Does all damage in a localised area
  • Beta & gamma are less dangerous as they mostly pass straight out without doing much damage
23
Q

How can you minimise your exposure to radioactive sources when working with them in a laboratory?

A

-Never allow skin contact with a source; handle with tongs

24
Q

How would you protect yourself if you were working with nuclear radiation?

A
  • 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
25
Q

Why is nuclear waste such a problem?

A
  • 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
26
Q

How do nuclear power stations usually deal with most dangerous nuclear waste?

A

-Vitrification

27
Q

What is meant by vitrification?

A
  • Melt radioactive waste with other materials to form a type of glass
  • Liquid glass is sealed inside steel canisters and buried deep underground
28
Q

What ways are there to deal with nuclear waste?

A
  • Vitrification

- Pack it into thick metal containers &/or bury in a deep hole & fill hole with concrete

29
Q

What important thing must you consider when storing radioactive nuclear waste?

A

-There are plenty of materials to absorb radiation before it can reach Earth’s surface

30
Q

What are the advantages of working with nuclear power?

A
  • 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
31
Q

What are the disadvantages of working with nuclear power?

A
  • 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)