Radioactivity

Question 1

How can we explain some of the properties of different elements?

Answer 1

By thinking about the particles that each element contains. We call these particles atoms. Chemical reactions occur when different atoms in a substance become joined in different ways

Question 2

What did the experiments that JJ Thompson (1856-1940) carried out show? And what did he do to support his evidence?

Answer 2

They showed that atoms contain much smaller subatomic particles called electrons. These have a negative charge and hardly any mass. Thompson supported using a new model that could explain this new evidence. The plum pudding model. The new model described that atom as a ‘pudding’ made of positively charged material, with negatively charged electrons (the ‘plums’) scattered through the it.

Question 3

Between 1909 and 1913 a team of scientists led by Ernest Rutherford (1871-1937) carried out a series of experiments called the gold foil experiment what did it involve? And what did they discover?

Answer 3

That involved studying what happens when positively charged subatomic particles called alpha particles passed through various substances, the scientists discovered that most of the alpha particles passed through the gold foil, a few bounced back. The plum pudding model couldn’t explain this. Rutherford suggested that atoms were mostly empty space, with most if their mass in a tiny central nucleus with a positive charge and electrons moving around the nucleus.

Question 4

Go to page 90 and 91

Answer 4

And look at the diagrams

Question 5

What is the radius of a nucleus and an atom?

Answer 5

Nucleus - 1 X 10 to the power of -15
Atom - 1 X 10 to the power of -10
So the atom itself is 100 000 times bigger than the nucleus inside it

Question 6

Where is the mass of an atom concentrated?

Answer 6

In its nucleus

Question 7

What is the nucleus itself made up of?

Answer 7

Smaller particles called nucleons. Nucleons can be protons or neutrons. All subatomic particles have very small masses so it is easier to describe their relative masses

Question 8

How do we describe subatomic particles relative masses?

Answer 8

We give the proton a mass of 1 and we compare the masses of the other subatomic particles relative to this

Question 9

Go to page 92

Answer 9

And look at the table carefully

Question 10

What does the atomic number or the proton number represent?

Answer 10

Atoms of a particular element that have the same number of protons, this number is the atomic number. Atoms of different elects have different numbers of protons and so have different atomic numbers

Question 11

What gives the nucleus its positive charge?

Answer 11

Neutrons have no charge so it’s the protons that give the needless its positive charge. Atoms have the same number of electrons as protons and so atoms are always electrically neutral (they have no overall charge)

Question 12

What is the mass number or the nucleon number?

Answer 12

The total number of protons and neutrons in the nucleus

Question 13

What are isotopes?

Answer 13

Two atoms of the same element will always have the same atomic number, but they can have different mass numbers if they contain different numbers of neutrons. Atoms of a single element that have different numbers of neutrons are called isotopes.

Question 14

What can electrons only exist in?

Answer 14

Certain orbits around the nucleus called electron shells, each electron she’ll is at a different energy level

Question 15

In a neon tube, what do the neon atoms do?

Answer 15

The neon atoms absorb energy transferred by the electricity because the electrons jump to higher shells. When the electrons fall back again they emit energy as electromagnetic radiation.

Question 16

What is the emission spectrum (the diagram is on page 94)

Answer 16

When each colour is a wavelength of light. The emission spectrum is different for each element

Question 17

Go to page 94 and 95

Answer 17

And look at the diagrams

Question 18

Turn to page 94 for this question. Gases can also also be energy transferred by electromagnetic radiation, such a s visible light. What does the bottom part of photo c show?

Answer 18

It shows the parts of the visible spectrum that neon gas absorbs when light passes through it. This is the absorption spectrum for neon. The wavelengths of light that neon gas absorbs are the same wavelengths that is emits

Question 19

How did Neils Bohr (1885-1962) amend rutherfordium model of the atom?

Answer 19

He amended it to explain observations by suggesting that electrons can only be in certain fixed orbits (electron shells) around the nucleus. They cannot be part-way between two orbits. This model could explain the lines in emission and absorption spectra

Question 20

Explain ionisation

Answer 20

Sometimes an atom gain so much energy that one or more of the electrons can escape from the atom altogether. An atom that has lost or gained electrons is called an ion. Radiation that causes electrons to escape is called ionising radiation

Question 21

What is a positive ion?

Answer 21

An atom has the same number of protons and electrons, so overall it has no charge. Is an atom loses an electron, it then has one more proton than it has electrons. It has an overall positive charge and is called a positive ion

Question 22

What is background radiation?

Answer 22

We are constantly being exposed to ionising radiation at a low level, from space and from naturally radioactive substances in the the environment. This is background radiation

Question 23

What is the main source of background radiation and how is it produced?

Answer 23

Radon gas. This radioactive gas is produced by rocks that contain small amounts of uranium. Radon diffuses into the air from rocks and soil and can build up in houses, especially where there is poor ventilation. The amount of radon in the air depends on the type of rock and its uranium content. Rock type and building stone vary around the country and so does the amount of radon

Question 24

How do some foods contribute to your exposure to back ground radiation?

Answer 24

Because they naturally contain small amounts of radioactive substances

Question 25

What do hospital treatments such as X-Ray's, gamma-Ray scans and cancer treatment contribute to?

Answer 25

Peoples exposure to back ground radiation

Question 26

high-energy, charged particles stream out if the sun and other stars. They are known as cosmic rays. What are they a form of?

Answer 26

Radiation, many cosmic rays are stopped in the upper atmosphere but some still reach the earths surface

Question 27

How can radioactivity be detected?

Answer 27

Using photographic film, which becomes darker and darker as more radiation reaches it. However, the film has to be developed in order to measure the amount of radiation (the dose). People who work with radiation often wear film badges (called dosimeters) to check how much radiation they are exposed to. Newer dosimeters use materials that change colour without needing to be developed

Question 28

How can the radioactivity of a source also be measured?

Answer 28

Using a Geiger-müller (GM) tube. Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow. A GM tube can be connected to a counter, to count the pulses of current, or the GM tube may give a click each time radiation is detected. The count rate is the number of clicks per second or minute

Question 29

When scientists measure the radioactivity of a source, they need to measure the background radiation first by taking several readings and finding the mean. What happens next?

Answer 29

This mean is then subtracted from measurements

Question 30

The nucleus of a radioactive substance is unstable, what does this mean? And what happens?

Answer 30

It can easily change or decay. When decay occurs radiation is emitted which can cause the nucleus to lose energy and become more stable. You cannot predict when a nucleus will decay - it's a random process

Question 31

What do alpha particles contain?

Answer 31

``` Two protons Two neutrons Relative mass of 4 No electrons Have a charge of +2 Can be written as alpha sign or helium sign ```

Question 32

What are beta particles?

Answer 32

High-energy, high-speed electrons. They have a relative mass of 1/1835 and a charge of -1. They can be written as B-

Question 33

What are positrons?

Answer 33

High-energy, high-speed particles with the same mass of electrons but a charge of +1. They can be written a B+

Question 34

What are gamma rays?

Answer 34

High-frequency electromagnetic waves (they travel at the speed of light). They do not have an electric charge

Question 35

What can also be emitted from an unstable nucleus?

Answer 35

Neutrons, they have a relative mass of 1 and no electric charge

Question 36

What are the characteristics of alpha particles?

Answer 36

Will travel a few cm in air Very ionising Chen be stopped by a sheet of paper

Question 37

Explain alpha particles

Answer 37

Alpha particles are emitted a high speeds. Due to this and their high routine mass, they transfer a lot of energy and so are good at ionising atoms they encounter. However, each time they ion side an atom they lose energy. Since they produce many ions in a short distance, they lose energy quickly and have a short penetration distance

Question 38

What are the characteristics of beta particles?

Answer 38

Will travel a few metres in air Moderately ionising Can be stopped by 3mm thick aluminium

Question 39

Explain beta particles

Answer 39

Beta particles are much less ionising than alpha particles and so can penetrate much further into matter that alpha particles can. Gamma rays are about 10 times less ionising than beta particles and can penetrate matter easily

Question 40

What are the characteristics of gamma rays?

Answer 40

Will travel a few Km in air Weakly ionising Need thick lead or several metres in concrete to stop them

Question 41

When an unstable nucleus changes and emits particles, the atomic number can change. What happens?

Answer 41

If this happens , the atom becomes a different elect

Question 42

What happens during beta decay?

Answer 42

A neutron changes into a proton and an electron. The electron is ejected from the atom. They atomic number increases by 1 but there is no change to the mass number

Question 43

What happens in positron decay?

Answer 43

A proton becomes a neutron and a positron, the atomic number goes down by 1 but the mass number does kit change

Question 44

If a neutron is ejected from a nucleus, what happens?

Answer 44

The mass number goes down but 1 bug the atomic number does not change

Question 45

When might the nuclei also lose energy a gamma radiation?

Answer 45

When the subatomic particles in the nucleus are rearranged. This helps to make them more stable

Question 46

What dies a nucleus equation show?

Answer 46

Shows what happens during radioactive decay. The equation must be balanced - the total mass number must be the same on each side and the total charges must be the same

Question 47

Go to page 101 and look at the

Answer 47

Table and the equations

Question 48

What is particle theory?

Answer 48

A model that helps explain the properties of solids, liquids and gases. The particles are usually represented as spheres

Question 49

What happens when an unstable nucleus undergoes radioactive decay?

Answer 49

It's nucleus changes to become more stable. The activity of a radioactive substance is the number of nuclear decays per second and is measured in becquerels (Bq). One becquerel is one nucleus decay each second

Question 50

What process is radioactive decay?

Answer 50

A random process - we cannot predict when it will happen

Question 51

What is the half-life?

Answer 51

The half-life is the time taken for half the unstable nuclei in a sample of radioactive isotope to decay. We cannot predict the decay of an individual nucleus because it is a random process. However, the half-life does allow us to predict the activity of a large number of nuclei. The half-life is the same for any mass of a particular isotope

Question 52

Go to page 102 and 103

Answer 52

And look at the half life diagram and look at the graphs

Question 53

After decaying, what might a nucleus become more of?

Answer 53

A nucleus may become more stable. The more stable nuclei a sample of a substance contains, the lower its activity. The half-life of an isotope is therefore also a measure of how long it takes for the activity to halve. It can be found by recording the activity of a sample over a period of time

Question 54

What can large amounts of ionising radiation cause?

Answer 54

It can cause tissue damage such as reddened skin (radiation burns) and also other effects that cannot be seen

Question 55

What can small amounts of ionising radiation over a long period of time do?

Answer 55

It can damage the DNA inside a cell. This damage is called a mutation. DNA contains the instructions controlling a cell, so some mutations can cause the cell to malfunction and may cause cancer. Gene mutations that occur in gametes can be passed on to the next generation. However, not all mutations are harmful and cells are often capable of repairing the damage if the radiation dose is low

Question 56

How is radiation a hazard?

Answer 56

Radiation is a hazard, because it can cause harm. We are exposed to background radiation all the time, but we are only exposed to small amounts so the risk of harm is low. However, people who work with radioactive materials could be exposed to more radiation and so must take precautions to minimise the risks from radiation

Question 57

How should you handle radioactive sources?

Answer 57

The intensity of radiation decreases with distance from the source, so sources are always handled with tongs. The risk can also be reduced but not pointing sources at people and storing them in lead-lined containers

Question 58

How do medical staff in hospitals try to limit themselves from the exposure to radiation?

Answer 58

Medical staff working with radioactive sources have their exposure limited in a number of ways, including increasing their distance from the source, shielding the source and minimising the time they spend in the presence of sources. Their exposure is also closely monitored using dosimeter badges

Question 59

Why are some patients exposed to a dose of radiation?

Answer 59

For medical diagnosis or treatment such as detecting and treating cancer. This is only done when the benefits are greater than the possible harm. The radiation could cause, and the minimum possible dose is used, and sources with short half-lives are used to minimise the time for which the patient is exposed

Question 60

What is it when someone is irradiated?

Answer 60

someone is irradiated when they are exposed to alpha, beta or gamma radiation from nearby radioactive materials. Once the person moves away the irradiation stops

Question 61

What is it if someone is contaminated?

Answer 61

Someone becomes contaminated if they get particles of radioactive material on their skin or inside their body. They will be expo side to radiation as the unstable isotopes in the material decay, and this will continue until the material has all decayed or until the source of contamination is removed (not always possible)

Question 62

How can contamination be spread to the food chain?

Answer 62

Because water and soils can also be contaiminated

Question 63

Why does contamination with radioactive materials with long half-lives poses a greater hazard?

Answer 63

Because the effects will last longer than for materials with shorter half-lives

Question 64

What are radioactive materials used to diagnose medical conditions instead of?

Answer 64

Instead of having to cut into a patients body. A radioactive traced, which emits gamma rays, is put into the patient

Question 65

What do tracers often contain?

Answer 65

Tracers often contain a radioactive isotope attached to molecules that will be taken up by particular organs in the body. The tracer is usually injected into the bloodstream, it it may be swallowed, inhaled or injected directly into an organ. The location of the tracer in the body is detected using one or more gamma cameras

Question 66

Tracers can be injected into the blood to find what?

Answer 66

Sources of internal bleeding

Question 67

What are gamma cameras used to detect?

Answer 67

Gamma cameras de text the highest gamma radiation, which is where the bleeding is occurring. They aare also used to detect tumours

Question 68

In medicine, what is the tracer made using?

Answer 68

The tracer is made using radioactive glucose molecules because very active cells, such as cancer cells, take up glucose more quickly than other cells

Question 69

Explain diagnosing with positrons

Answer 69

The tracer emits a positron. When this meets an electron, both it and the electron are destroyed and two gamma rays are emitted in opposite directions. The detector in a PET scanner moves around the patient, building up a set of images showing where different amounts of gamma radiation are coming from.

Question 70

Why do the radioactive isotopes used in all medical tracers need to have a short half-life?

Answer 70

So that the other parts of the body are affected little as possible. This means that they lose their radioactivity quickly and so must be made close to the hospital. They are often used within hours or even minutes of production

Question 71

Cancer cells divide more rapidly than most other cells in the body and so are more susceptible to being killed by what?

Answer 71

By radiation

Question 72

What is internal radiotherapy?

Answer 72

(To kill cancer) internal radiotherapy uses a beta emitter such as iodine-131 placed inside the body, within or very close to a tumour. This does not always require surgery - the patient stats in a room alone while the source us in place

Question 73

What is external radiotherapy?

Answer 73

(To kill cancer) most radiotherapy is external radiotherapy, which uses beams if gamma rays, X-rays or protons directed at the tumour from outside the body. Several lower strength beams may be directed at the tumour from different directions so that only the tumour absorbs a lit of energy and the surrounding tissues are harmed as little as possible

Question 74

What happens in nuclear fission?

Answer 74

In nuclear fission large nuclei (such as uranium-235) break up to form smaller nuclei and release energy. Fission reactions are used in nuclear power stations

Question 75

What happens in nuclear fusion?

Answer 75

In nuclear fusion two small nuclei join together (fuse) to form a large nucleus. Fusion reactions release energy inside the sun

Question 76

Nucleus fuels store a lot more energy per kilo gram than any other type of fuel. This makes them useful for navel ships and submarines. What else does nuclear fuel not do?

Answer 76

Nuclear fuels do not burn, so they do not need air to allow them to release energy and they do not produce carbon dioxide

Question 77

Where is most nuclear energy used?

Answer 77

Most nuclear energy is used in power stations to generate electricity. Uranium is a non-renewable fuel, but is estimated to last for over 200 years at their current use rate. This is much longer than other non renewables, such as oil, will last

Question 78

Conventional power stations that burn fossil fuels produce what? What does this contribute to?

Answer 78

Produces carbon dioxide, the increasing amount of carbon dioxide in the atmosphere is contributing to climate change. Conventional power stations can also produce other forms of pollution, such as soot and acidic gases

Question 79

Even though power stations do not emit gas, what do they still produce?

Answer 79

Produce waste that will stay radioactive for millions of years. This waste is expensive to treat, as it needs to be sealed into concrete or glass and buried safely

Question 80

Parts of a nuclear power station become radioactive as it is used, what does it make it?

Answer 80

Very expensive to decommission (dismantle safely) a power station at the end of its life

Question 81

Even though power stations are designed safely, what accidents sometimes occur?

Answer 81

Small leaks of radioactive materials and reactor explosions. Major accidents can have serious consequences for many people. Also many people do not think that the benefits of nuclear energy are worth the risks. At least 12 countries in Europe have voted to ban nuclear power stations

Question 82

Explain nuclear fission using an example

Answer 82

When a uranium-235 nucleus absorbs a neutron it immediately splits into two smaller daughter nuclei, which are also radioactive. Two or more neutrons are also released. Both daughter nuclei and the neutrons store a lot of kinetic energy because they are moving at high speeds.

Question 83

Using the first paragraph on page 112 to help, in nuclear fission, wah at happens if the neutrons released are absorbed by other uranium-235 nuclei?

Answer 83

These nuclei will become unstable and release more neutrons when their nuclei split. These neutrons can then be absorbed by yet more uranium nuclei, which in turn split up, releasing more neutrons. This is an un controlled chain reaction, such as occurs in an atomic bomb

Question 84

In nuclear fission, how can the chain reaction be controlled?

Answer 84

It can be controlled if other materials absorb some if the neutrons

Question 85

How is energy also transferred from fission?

Answer 85

By heating

Question 86

Explain nuclear reactors

Answer 86

In a nuclear reactor the fuel is made into fuel rods. As fission reactions occur, neutrons leave the fuel rods at high speed. They are slowed down to increase the chance they will be absorbed by another uranium-235 nucleus. Inside a reactor core, fuel rods are inserted into holes in a material called a moderator, which slows down the neutrons

Question 87

How is the chain reaction controlled in nuclear fission? Explain it

Answer 87

The chain reaction is controlled using control rods, which contain elements that absorb neutrons. These rods are placed between the fuel rods in the reactor core. If the rate of fission needs to be increased the control rods are moved out of the core so that fewer neutrons are absorbed, and vice versa. When the control rods are fully lowered into the core, the chain reaction stops and the reactor shuts down

Question 88

Go to page 113

Answer 88

And look at the diagrams

Question 89

How is electricity generated from the reactor core?

Answer 89

Energy released from the core is transferred to a coolant, which is pumped through the reactor. The coolant can be water, a gas or a liquid metal. The hot coolant is pumped to a heat exchanger where it is used to make steam. The steam drives a turbine, which turns a generator to produce electricity

Question 90

When does nuclear fusion occur?

Answer 90

It occurs when small nuclei combine to form larger ones. The mass of the new nucleus formed is slightly less than the total of the masses of the two smaller nuclei. The lost mass has been converted to energy.

Question 91

Fusion reactors in which hydrogen nuclei combine to form helium are the main source for what?

Answer 91

Stats, including our sun

Question 92

Go to page 114

Answer 92

And look at the diagram

Question 93

What is electrostatic repulsion?

Answer 93

A force between two electrical charges that have the same sign that pushes them apart

Question 94

In nuclear fusion, when are nuclei more likely to collide?

Answer 94

Nuclei are more likely to collide at higher temperatures, when they are moving faster. If nuclei are close enough or travelling fast enough, some can overcome their electrostatic repulsion and fuse

Question 95

What does a useful fusion reactor need?

Answer 95

A useful fusion reactor needs fusion to happen faster than it does in the sun, it is also difficult to produce very high pressure on earth, so the temperature inside a fusion reactor must be very high - hotter than the temperatures in the sun