Topic 6 - Using Radioactive Materials

Question 1

Where does background radiation come from?

Answer 1

• 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

Question 2

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

Answer 2

• 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

Question 3

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

Answer 3

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

Question 4

How does the radioactivity of a source decrease over time?

Answer 4

• 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

Question 5

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

Answer 5

activity falls quickly, lots of nuclei decay quickly

Question 6

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

Answer 6

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

Question 7

What is the activity of a radioactive isotope measured in?

Answer 7

Becquerels (Bq)

Question 8

What measures activity of a radioactive isotope?

Answer 8

Geiger-Muller (G-M) tube

Question 9

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

Answer 9

1 decay per second

Question 10

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

Answer 10

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)

Question 11

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

Answer 11

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

Question 12

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

Answer 12

• 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

Question 13

How is alpha radiation used in household fire alarms?

Answer 13

• 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

Question 14

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

Answer 14

• 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

Question 15

How is radiation used as a medical tracer?

Answer 15

• 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

Question 16

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

Answer 16

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

Question 17

How is beta radiation used in thickness gauges?

Answer 17

• 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

Question 18

How are gamma rays used to treat cancer?

Answer 18

• High doses of gamma kill all living cells

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

Question 19

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

Answer 19

• Minor damage without killing cells

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

Question 20

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

Answer 20

• Kill cells completely

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

Question 21

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

Answer 21

• Amount of exposure to the radiation

- Energy & penetration of the radiation

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

• 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

Question 25

Why is nuclear waste such a problem?

Answer 25

• 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

Question 26

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

Answer 26

-Vitrification

Question 27

What is meant by vitrification?

Answer 27

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

Question 28

What ways are there to deal with nuclear waste?

Answer 28

• Vitrification

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

Question 29

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

Answer 29

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

Question 30

What are the advantages of working with nuclear power?

Answer 30

• 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

Question 31

What are the disadvantages of working with nuclear power?

Answer 31

• 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)