P6- Radioactive Materials

Question 1

Isotopes?

Answer 1

• Many elements have a few different isotopes- atoms with the same number of protons but different numbers of neutrons.
• Usually each element only has one or two stable isotopes. Like carbon 12.
• The other isotopes tend to be radioactive- the nucleus is unstable so it decays and emits radiation.
• Carbon 14 is an unstable isotopes of carbon.

Question 2

Radioactive elements and ionising radiation?

Answer 2

• Some elements emit ionising radiation all the time. These elements are radioactive.
• Radioactive atoms are unstable- they decay to make themselves more stable.
• Unstable atoms decay at random so you can’t predict when it will happen. It is unaffected by physical conditions.
• When an atom does decay it splits out one or more of three types of ionising radiation- alpha,beta and gamma.
• In the process, the atom often changes into a new element.
• Ionising radiation can transfer enough energy to break an atom or molecule into bits called ions - this is ionisation.
• These ions can take part in other chemical reactions.

Question 3

Alpha radiation?

Answer 3

• Alpha particles are relatively big and heavy and slow moving.
• They don’t penetrate far into materials- they’re stopped quickly.
• Alpha particles are released by very heavy nuclei.
• An alpha particle is a helium nucleus made of 2 protons and 2 neutrons.
• Alpha particles have a mass of 4 and a charge of +2.
• Alpha decay always changes the element of the atom that’s decaying since it loses protons.

Question 4

Beta radiation?

Answer 4

• Beta particles move quite fast and they are quite small.
• They penetrate moderately into materials before they’re stopped.
• Beta particles are released by nuclei that have too many neutrons.
• During beta decay, a neutron in the nucleus turns into a proton. So the element changes and a beta particle is emitted.
• A beta particle is identical to an electron with no mass and a charge of -1.

Question 5

Gamma radiation?

Answer 5

• After spitting out an alpha or beta particle the nucleus might need to get rid of some extra energy.
• It does this by emitting a gamma ray- a type of electromagnetic wave. They have no mass.
• They can penetrate a long way into materials without being stopped.
• Since a gamma ray is just energy it doesn’t change the element of the nucleus that emits it.

Question 6

What blocks the three types of radiations?

Answer 6

• Alpha particles are blocked by paper.
• Beta particles are blocked by thin aluminium.
• Gamma rays are blocked by thick lead.

Question 7

What is a half life?

Answer 7

Half life is the time taken for half of the radioactive nuclei now present to decay.

Question 8

What is a “short half life”?

Answer 8

It means the activity falls quickly because lots of the nuclei decay in a short time.

Question 9

What is a “long half life”?

Answer 9

It means the activity falls more slowly because most of the nuclei don’t decay for a long time.

They sit there and they are unstable.

Question 10

Radioactivity deceases over time?

Answer 10

• Each time an unstable nucleus decays and emits radiation that means one more radioactive nucleus isn’t there to decay later.
• As more unstable nuclei decay the radioactivity of the source as a whole decreases so the older a radioactive source the less radiation it emits.
• How quickly the activity deceases varies. For some isotopes it takes just a few seconds before all the unstable nuclei have decayed. For others it takes millions.
• It is a problem trying to measure this as the activity never reaches zero. So we use half life.

Question 11

Half life calculation?

Answer 11

(Look in CGP book)

Question 12

Half life graph?

Answer 12

(Look in CGP book)

Question 13

Rutherfords scattering?

Answer 13

• In 1909, Ernest Rutherford, Hans Geiger and Ernest Marsden tried firing alpha particles-Which are positively charged- at thin gold foil.
• Most of the alpha particles just went straight through but the odd one came straight back at them.
• This meant most of the mass of a gold atom was concentrated at the centre in a tiny nucleus. The rest of the atom was empty space- as most alpha particles went straight through the foil.
• The nucleus had to have a positive charge- otherwise the positively charged alpha particles wouldn’t be repelled by the nucleus and wouldn’t scatter.

Question 14

Nucleus held together by strong forces?

Answer 14

• The nucleus contains positively charged proton particles which repel each other.
• The nucleus doesn’t fly apart because it’s held together by an attractive force much greater than the repulsive electrostatic force between protons. These are called strong forces.
• The strong force has a short range- it can only hold protons and neutrons together when they’re separated by tiny distances.
• At larger separations, the strong force is so weak that it effectively disappears.

Question 15

Nuclei by fuse?

Answer 15

• Two nuclei can combine (fuse) to create a larger nucleus, releasing energy when they do- this is called nuclear fusion.
• Nuclei can only fuse if they overcome the repulsive electrostatic force and get close enough for the strong force to hold them together.
• For this you need lots of energy- which means high temperatures.

Question 16

Energy equation?

Answer 16

Energy(J) = mass (kg) * speed squared (m/s squared)

OR

E= mc squared.

Question 17

Nucleus power stations splitting atoms?

Answer 17

• A nuclear fuel releases large amounts of energy when it’s nuclei split apart.
• This process is nuclear fission. It starts when neutrons are fired at the fuel causing some of its large unstable nuclei to split into two smaller nuclei of roughly equal size.
• Each split nucleus also releases 2 or 3 more neutrons and lots of energy.

Question 18

How much energy does nuclear fission release?

Answer 18

• Nuclear reactions release a lot more energy than chemical reactions like burning.
• Splitting a gram of uranium releases over 10 000 times more energy than burning a gram of oil.
• You can calculate how much is released my using E=mc squared.

Question 19

Describe nuclear power stations?

Answer 19

• In nuclear power reactors a chain reaction is set up.
• A neutron splits a nucleus- releasing more neutrons. These can then split more nuclei and release more neutrons.
• The uranium (or plutonium) fuel is used in nuclear reactors is contained in fuel rods.
• These fuel rods capture the neutrons and emit neutrons when nuclei in the rod split.
• The chain reaction in the reactor has to be controlled or the reactor would overheat.
• Control rods absorb some of the neutrons and slow down the reaction. They can move further into and out of the reactor to absorb more or less neutrons.
• Coolant is used to take away the hart produced by the fission process.
• This heat is used to produce steam to drive a turbine and generator.
• And we get electricity 😜

Question 20

How to deal with radioactive waste?

Answer 20

• Most waste from power stations is “low level” (slightly radioactive). This waste can be disposed of by burying it in a secure landfill site.
• Intermediate level waste includes things like the metal cases of used fuel rods and some waste from hospitals. It’s quite radioactive so is sealed into concrete blocks and put in steel canister for storage.
• High level waste from nuclear power stations is so radioactive that it generates a lot of heat. The waste is sealed in glass and steel then cooled for 50 years before moving to permanent storage.
• The canisters of intermediate and high level waste could be buried deep underground. However it is difficult to find a suitable place.
• The site has to be geologically stable since big movements in the rock could break the canisters and radioactive material could “leak out”.
• When geologists do find a site people live nearby.
• At the moment- most intermediate and high level waste is kept “on site” at nuclear power stations.

Question 21

Ionising radiation can damage living cells?

Answer 21

• Alpha, beta and gamma radiation are all ionising radiation. They can break up molecules into smaller bits called ions.
• Ions can be very chemically reactive so they go off and text with things.
• In humans ionising radiation can cause serious damage to the cells in the body.
• A high dose of ionising radiation can kill cells directly. Causing radiation sickness.
• Low doses of ionising radiation damage cells without killing them. Which can cause cancer.

Question 22

Irradiation?

Answer 22

Being exposed to radiation without coming into contact with the source. The damage to your body stops as soon as you leave the radioactive area.

Question 23

Contamination?

Answer 23

Picking up some radioactive material. (Drinking it, breathing it etc.)

You’ll still be exposed to the radiation once you’ve left the radioactive area.

Question 24

What is radiation dose measured in?

Answer 24

It’s measured in sieverts (Sv). Or millisieverts (mSv).

Question 25

Radiation doses and affects on the body?

Answer 25

(Look in CGP book)

Question 26

People who are at higher risks of radiation exposure?

Answer 26

• Uranium miners and processors.
• Workers in nuclear power plants.
• Airline staff (comes from cosmic Rays)
• miners and medical staff like radiographers.
• Nuclear researchers.

Question 27

Background radiation?

Answer 27

• Natural radioactive elements in the air, in soil, in living things and even under our feet.
• Space (cosmic rays) these come from the sun.
• Human activity- eg from nuclear explosions or waste from nuclear power stations.

Question 28

When are radioactive materials considered “safe”?

Answer 28

They are considered “safe” when the radiation they are emitting is at about the same level as the background radiation.

The half life of a source gives an idea of how long it will take for this to happen.

Question 29

What is ionising radiation useful for?

Answer 29

• Treating cancer
• Sterilising medical equipment
• Sterilising food
• Detecting diseases using tracers.

Question 30

Treating cancer with ionising radiation?

Answer 30

• High doses of gamma rays will kill any living cells. So they can treat cancers.
• The gamma rays have to be directed carefully. And at the right dosage so to kill the cancer cells without damaging normal cells.
• However, a small amount of damage is done to the normal cells. Which makes the patient feel very ill.
• But if the cancer is successfully killed off in the end - it’s worth it.

Question 31

Sterilising medical equipment with ionising radiation?

Answer 31

• Gamma rays are used to sterilise medical instruments by killing all the microbes.
• This is better than to boil plastic instruments which might be damaged by high temperatures.
• You need to use a strongly radioactive source that has a long half life so it doesn’t need replacing too often.

Question 32

Sterilising food with ionising radiation?

Answer 32

• Food can be sterilised in the same way as medical instruments- killing all microbes.
• This keeps food fresh for longer without having to freeze it or preserve it in other ways.
• The food is not radioactive afterwards and is safe to eat.

Question 33

Detecting diseases using tracers with ionising radiation?

Answer 33

• Tracers are radioactive molecules that can be injected into people.
• Their process around the body is followed using an external detector.
• They can detect cancer or if an organ is working properly.
• Isotopes used as tracers must be gamma or beta emitters so the radiation passes out of the body.
• They should have a short half life so the radioactivity inside the patient quickly disappears.

Question 34

Describe an atom?

Answer 34

• The nucleus contains protons and neutrons.
• The nucleus takes up the mass of the atom. However, it takes up limited space- it’s tiny.
• The electrons are tiny.
• Electrons whizz around the outside of the atom. Their paths take up a lot of space- giving the atom its overall size.