p6 radioactive materials

P6 – Radioactive materials. Understand what ionising radiation is, the uses and dangers of it and how it can be used to produce electrical energy.

Radioactive materialsRecap of the atom:

Nucleus in the centre, contains protons and neutrons.

Electrons are in constant motion outside the nucleus in ‘shells’.

Electrons can be lost or gained which turns the atom into an ion with a positive (lost) or negative (gained) charge.


Radioactive materialsThe mass of an atom is found in its nucleus. Protons and neutrons each have a mass of 1. Electrons have almost no mass (negligible).

Protons have a positive charge (+ve)Neutrons are neutral Electrons have a negative charge (-ve)

If a nucleus was scaled up to the size of a pea, the electrons would be moving around it a kilometre away.


Radioactive materials

Particle Mass ChargeElectronProtonNeutron

• A grain of sand weighs 0.0026g. How many atoms are in a grain of sand?

• 78 000 000 000 000 000 000



• How can protons (with a positive charge) all inhabit the same tiny nucleus without repelling each other?

• Nuclear force



• https://www.youtube.com/watch?v=XBqHkraf8iE

• In 1909 Marsden and Rutherford discovered that: – The atom was mostly empty space.– There is a concentration of mass and positive

charge at the centre of the atom.



https://www.youtube.com/watch?v=XBqHkraf8iE

https://www.youtube.com/watch?v=XBqHkraf8iE

• Isotopes• Two atoms of the same element can have a

different number of NEUTRONS. These are isotopes.

• Eg Hydrogen always has one proton.



• Recap questions:• A uranium atom has 92 protons in its nucleus.

How many electrons does it have?• Oxygen has 3 stable isotopes 16O, 17O and 18O.

Oxygen has 8 protons. What is the other particle in the nucleus, and how many are there in each of these isotopes?

• What is the difference between an atom and an ion?



• Lesson 2 – Ionising radiation and its sources• https://www.youtube.com/watch?v

=6dKFs2lDgZs

• What is ionising radiation?



https://www.youtube.com/watch?v=6dKFs2lDgZs





• Ionising radiation is when energy hits an atom and ‘knocks’ an electron off the atom, turning it into an ion.

• Remember:Ions are atomsthat have gainedor lost an electron





• Marie Curie first isolated Polonium, Uranium and Radium.

• She was the first woman to win a Nobel prize and is the only person to have won Nobel prizes in both Physics and Chemistry (1903 & 1911)

• There is always background radiation• This means that there is low level radiation

surrounding us now. • Where does it come from?– Some from outer space (cosmic rays)– Most from rocks and soil– A small amount from human activity



• Rocks are used to build with – our buildings may emit some radiation.

• Plants absorb some radiation from the soil – we may eat these plants.

• Granite releases radon gas – if your house is built with granite you may be exposed to more radon.

• Airplane travel exposes you to more cosmic rays.



• We measure radiation with a geiger counter

• https://www.youtube.com/watch?v=v8wKbpsw-OE



https://www.youtube.com/watch?v=v8wKbpsw-OE





• 3 types of ionising radiation• Alpha particles (α)• Beta particles (β)• Gamma waves (γ)

• We’re going to learn about each of these in detail



• What is an alpha particle?

• 2 protons + 2 neutrons• = helium nucleus• Emitted from the nucleus of an atom

• What is its mass?• What is its charge?



• Alpha particles are heavy and slow• In air they can only travel about 1cm • They are highly ionising – easily knock

electrons off atoms• They can be stopped by a sheet of paper or

your skin.



• Uses of alpha radiation• Americium-241



• When Radon emits an alpha particle, what happens?

• Is alpha radiation dangerous?

• https://www.youtube.com/watch?v=v8wKbpsw-OE





• Beta particles• These are electrons• They come from the nucleus

• Electrons? That come from the nucleus?!• It is a decaying neutron which forms a proton

and an electron



• Beta particles are electrons and therefore are much lighter than alpha particles.

• They move very fast and can penetrate skin.• They can be stopped by an aluminium sheet

3mm thick.• They are not as ionising as alpha particles



• If magnesium undergoes beta decay, what does it become?



• Gamma rays/waves• Not a particle, this is a wave!



Gamma• Very short wavelength• Have no charge – cannot be deflected by

electricity or magnetism• They pass through most things – needs thick

lead to stop them• The are weakly ionising, but when they do hit

something they will knock an electron off.



• Gamma radiation does not change one element into another

• When an atom gives off a gamma ray, it has less energy and becomes more stable



• Gamma radiation can cure and cause cancer – how?



• Gamma radiation can be used to sterilise food and medical equipment.



• Compare alpha, beta and gamma– What they are made of– What happens to the atom they come from– How penetrating they are– How ionising they are– Their uses– Their danger

– Use the books to gather as much info as possible.



• Take a post it note and stick it to your work.

• Have a look at other people’s work and comment on their work if you think they have forgotten to include something, or if they have added something good.



• Lesson 3• Nuclear energy



• There are 2 ways in which we can release energy from single atoms.

• Fusion – joining 2 small atoms

• Fission – Splitting a large atom (this one is used in nuclear power stations)



• Fission – splitting – power stations



• Radioactive waste• Once the uranium rods are not useful in a

power station any more they need to be disposed of.

• They are still radioactive and will continue to be for a very long time.



• Used (spent) fuel rods are high-level waste.• They are mixed with molten glass and stored

in steel drums which are then encased in concrete.

• These large concrete blocks are then buried underground or in remote areas above ground.



• Fukushima after 2011 tsunami



• Nuclear fusion – not currently a viable way to produce energy

• Involves the fusion of two atoms – both are isotopes of hydrogen.



• Fusion is the reaction which happens inside the sun, and all stars.

• The reaction takes place under immense pressure and at extremely high heat. (>10,000,000 degrees K)

• It then gives off enough heat energy to keep the reaction going.



• Deuterium and a tritium nuclei are positively charged and therefore will repel each other.

• This is known as electrostatic repulsion. • The nuclei have to get very close in order to collide, which is

approximately a 0.000 000 000 001mm.• If the nuclei are moving very fast then they can overcome the

electrostatic repulsion. The hotter a molecule is, the faster it will move and the more likely it is to collide.

• For a nuclear fusion reactor to work, the temperature and pressure would each have to be very high. These extremely high temperatures and pressures are very difficult to reproduce and are very expensive. As a result, fusion as an energy source is a long way off.



• Are the by products of fusion radioactive?• No• Does fusion contribute to CO2 in the

atmosphere?• No

• More energy per kg than fossil fuels• Fuel will last for millions of years



Half life



• The half life is the time taken for half the radioactive atoms in a sample to decay.

• What do we mean by decay?• It gives off some ionising radiation.• Does the half life depend on how big your sample

is?• No• Does it mean that half your sample has

disappeared?• No



• Why does radioactive decay follow this pattern?• Radioactive decay is random• For each atom it can happen at any time –

immediately, or in millions of years. • Remember that there are 78 000 000 000 000

000 000 atoms in a tiny grain of sand? This means that a piece of radioactive material that small will at some point release 78 000 000 000 000 000 000 bursts of radiation over time.



• Since we can’t measure the entire lifetime of how long it takes a piece of radioactive material to have every last atom decayed, we use ‘half-life’.

• ie the time taken for half the atoms in the sample to decay.

• Half life varies for different substances





Investigation page 266-7

• Recap questions:• Describe how ionising radiation may cause cancer.• Why is alpha radiation most harmful when it is a gas?• Why are people who are exposed to lots of radiation

monitored for many years?• How can gamma radiation extend the shelf life of

food?• Challenge: why might a tumour show up on a brain

scan when the person has been injected with a radioactive tracer?



• Read pages 274-275• Identify the difference between hazard and

risk• Describe what we mean by contamination and

explain how it can enter the food chain. • Answer question 5



Higher tier only• This is to find out the energy lost in the fusion

reaction

• E = mc2

• E is the energy in joules• M is mass in kgs• C is a constant 3 x 108m/s (speed of light)• Follow the equation on page 281



Activity 1• Page 284 - foundation do questions 1-4, higher

do all questions.• Use the book if necessaryActivity 2• Use the checklist at the end of each chapter and

write down what you are unsure of – this will be your guide for revision

Activity 3• Have a go at the past paper I can give you



p6 radioactive materials

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