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A Level Physics OCR B > 19: Using the Atom > Flashcards

19: Using the Atom Flashcards

1
Q

Describe the number of protons and neutrons in isotopes of the same element

A

Same number of protons, different number of neutrons

Same Z, different A

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2
Q

What is the Z number in standard notation?

A

The proton number or atomic number

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3
Q

What is A in standard notation?

A

The nucleon number or mass number

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4
Q

What forces are balanced inside a stable nucleus?

A

Strong nuclear force holding it together

And the electrostatic force pushing the protons apart

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5
Q

What happens if the nucleus is unstable, how does it transform?

A

It transforms into a more stable isotope by emitting radiation

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6
Q

What can cause the nucleus to be unstable?

A

Too many neutrons
Too few neutrons
Too many nucleons in total, it’s too massive
Too much energy in the nucleus

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7
Q

What are the four types of nuclear radiation?

A

Alpha, beta–minus (beta), beta–plus, gamma

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8
Q

What is an atomic mass unit, u?

A

Roughly the mass of a proton or neutron

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9
Q

What is alpha radiation made of?

A

Two protons and two neutrons

Helium nucleus

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10
Q

What is the symbol for each type of nuclear radiation?

A

α
β⁺
β⁻
γ

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11
Q

What is the relative charge of each type of nuclear radiation?

A

Alpha: +2
Beta–minus: -1
Beta–plus: +1
Gamma: 0

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12
Q

What is the mass, in atomic mass units, or each type of nuclear radiation?

A

Alpha: 4
Beta–minus: negligible
Beta–plus: negligible
Gamma: 0

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13
Q

What is beta–minus radiation made from?

A

An electron

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14
Q

What is beta-plus radiation made from?

A

A positron

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15
Q

What is gamma radiation made from?

A

Short–wavelength, high–frequency EM wave

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16
Q

Describe the ionising power, speed, and penetrating power of alpha radiation

A

Strong ionising power
Slow speed
Absorbed by paper or a few cm of air

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17
Q

Describe the ionising power, speed, and penetrating power of beta-minus radiation

A

Weak ionising power
Fast speed
Absorbed by ~3 mm of aluminium

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18
Q

Describe the ionising power, speed, and penetration power of beta-plus radiation

A

Annihilated by electron – so virtually zero range

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19
Q

Describe the ionising power, speed, and penetrating power of gamma radiation

A

Very weak ionising power
Speed of light
Absorbed by many cm of lead, or several m of concrete

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20
Q

Which types of nuclear radiation are affected by magnetic fields?

A

Alpha and beta because they carry a charge

Gamma radiation isn’t affected by the magnetic field

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21
Q

What is the relationship between penetrating power and ionising power, of radiation? Why?

A

The penetrating power of radiation decreases with increasing ionising power.
This is because radiation loses energy as it ionises atoms. This means that the higher the ionising power of the type of radiation, the more energy it loses in a given distance, so the shorter its range

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22
Q

What safety procedures should be put in place when doing experiments with a radioactive sources?

A

Radioactive sources should be kept on a lead lined box when they’re not being used
They should only be picked up using long handled tongs or forceps
Take care not to point them at anyone

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23
Q

Describe the investigation for the penetration of different kinds of radiation in the lab

A

Measure the background count. Calculate a count rate. Subtract this from all your results. Set up the equipment. Insert different materials between the source and tube, and record the count rate over a sensible time interval.

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24
Q

How can you get an accurate reading for the count, of radiation? Why is it hard?

A

Radioactive decay is random, so to get an accurate reading the count needs to be measured over a long enough time interval

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25
Q

How do you calculate an accurate count rate, given the background count of radiation?

A

Divide your count by the time interval to get a count rate. Repeat this measurement at least three times been taken average.

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26
Q

Describe the possible outcomes of the investigation of penetration of different kinds of radiation

A

If the count rate remains about the same, then the radiation can penetrate the material. If the count rate drops by a large amount, then the radiation is being absorbed and blocked by the material. If the count rate drops to 0, the radiation is being completely absorbed

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27
Q

Describe the setup for the investigation of the penetration of different kinds of radiation

A

Radioactive source positioned a distance away from an absorber which is a distance away from a Geiger-Müller tube which is connected to a Geiger counter

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28
Q

How can you repeat this experiment with different sources?

Investigation of the penetration of different kinds of radiation

A

You’ll need to change the distance between the source and the Geiger-Müller tube for each source, as different kinds of radiation have different penetrating power is in air

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29
Q

Nuclear decay equations:

What is the parent nucleus?

A

The nucleus you start off with

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30
Q

Nuclear decay equations:

What is the daughter nucleus?

A

The nucleus it decays to

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31
Q

What must be conserved in the decay equations?

A

Charge, nucleon number and lepton number

Energy and momentum as well

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32
Q

How are beta-minus particles written in the decay equations?

A

They have a negative charge. They are written with a negative proton number

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33
Q

What variable does not have to be conserved nuclear equations?

A

Mass

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34
Q

Is an alpha particle heavier or lighter than its constituents added together?

A

The mass of an alpha particle is less than the individual masses of two protons and two neutrons

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35
Q

What is the mass defect, in nuclear equations?

A

The difference in mass on the different sides of the equation

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36
Q

What accounts for the missing mass in nuclear equations?

A

The energy released when the nucleons bond together to form the alpha particle

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37
Q

When does alpha emission happen?

A

Only happens in very heavy atoms, like uranium and radium

The nuclei of these atoms are too massive to be stable

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38
Q

What happens to the proton number and the nucleon number when an alpha particle is emitted?

A

The proton number decreases by two, and the nucleon number decreases by four

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39
Q

What is beta-minus decay? When does it occur?

A

The emission of an electron from the nucleus along with an antineutrino. It happens in isotopes that are ‘neutron rich’, have many more neutrons and protons in their nuclei
One of the neutrons in the nucleus decays into a proton and ejects a beta particle and an antineutrino

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40
Q

What happens to the proton number and nucleon number when a beta-minus particle is emitted?

A

Proton number increases by one

Nucleon number stays the same

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41
Q

When does beta-plus emission occur?

A

In proton rich nuclei

A proton gets changed into a neutron, releasing a positron and a neutrino

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42
Q

What happens to the proton number and nucleon number when a beta-plus particle is emitted?

A

Proton number decreases by one, and the nucleon number stays the same

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43
Q

Describe gamma radiation, when it occurs, what happens

A

From nuclei with too much energy. We say the nucleus is excited. This energy is lost by emitting a gamma ray. This often happens after an alpha or beta decay has occurred.

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44
Q

What happens to the proton number and nucleon number when a gamma ray is emitted?

A

There is no change to the nuclear constituents – the nucleus just loses excess energy

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45
Q

What are some useful things, that radiation can be used for?

A

Generate power, in medicine for diagnosis and treatment, and to kill harmful microorganisms that might contaminate our food

46
Q

What can radioactive materials cause?

A

Cancerous tumours, skin burns, sterility, radiation sickness, hair loss and even death

47
Q

The result of the advantages and disadvantages of radiation, is that it is only used when?

A

When the benefits outweigh the risks

48
Q

What two parts are there to the risks of radiation?

A

How likely it is that the radiation will cause a problem, and how bad the problem would be if it happened

49
Q

Describe the risk for a nuclear reactor

A

A nuclear reactor melting down would be catastrophic but it’s also very unlikely, so the risk might be acceptable

50
Q

Describe the risk of ionising radiation in medicine

A

Ionising radiation can cause cancer, but it can also be used in cancer treatments to destroy tumours. The risk of serious damage caused by the treatment is considered acceptable if the treatment is likely to prolong or improve a patient’s life

51
Q

Risk = probability * …..

A

Consequences

52
Q

What happens to the cells in your body, when affected by ionising radiation?

A

It can damage cells, and cause them to mutate or even kill them

53
Q

What does ionising radiation do? Briefly

A

Knock electrons of atoms, creating ions

54
Q

What is the absorbed dose?Units?

A

The amount of energy deposited per kilogram of tissue

Measured in grays (Gy)

55
Q

How do you calculate the absorbed dose?

A

You first need the energy of the radiation absorbed by a mass of tissue
You can find the energy released by a source from its activity, the energy of the radiation, and the time interval. If all of the release energy is absorbed by tissue, you can calculate the absorbed dose using the tissue’s mass

56
Q

Why can radiation treat cancer? What needs to be minimised or maximised?

A

The ability radiation to damage or kill cells

Minimise the dose absorbed by healthy tissue at the same time as maximising the dose absorbed by the cancer cells

57
Q

Describe how radiation can be used to treat cancer?

A

Place radioactive sources inside the patient, in all next to the tumour
Sources can either be inserted next to the tumour for a short period of time, all left within the patient permanently

58
Q

Describe the dosage and half life of sources left in the body to treat cancer

A

Sources left within a patient permanently are chosen to deliver a low-dose per hour than sources inserted for a shorter duration, to minimise damage to healthy tissue. They will also have a very short half life, around 20 days or so. This means they remain active for long enough for the cancer cells to be killed, typically a few months, without causing unnecessary damage to surrounding tissue

59
Q

What does the amount of tissue damage caused by exposure to radiation depend on?

A

The amount of energy absorbed, the type of ionising radiation, and the type of body tissue

60
Q

What does the effective dose measure allow you to do?

A

Lets you compare the amount of damage to body tissues that have been exposed to different types of radiation

61
Q

What is the unit of effective dose?

A

Sievert, Sv

62
Q

Effective dose =

A

Absorbed dose * quality factor

63
Q

What is the typical quality factor for alpha, beta, and gamma radiation?

A

Alpha: 20
Beta: 1
Gamma: 1

64
Q

What is the effective dose of 1 Gy of alpha, beta, and gamma radiation?

A

Alpha: 20 Sv
Beta: 1 Sv
Gamma: 1 Sv

65
Q

Describe the relationship between a radiation’s quality factor and its ionisation

A

The higher the radiation’s quality factor, the more ionising it is

66
Q

When beta or alpha particles ionise an atom, they transfer…

A

They transfer some of their energy to the atom being ionised

67
Q

Why can alpha particles easily pull electrons of atoms? What does this mean for ionisation and damage to the body?

A

They are strongly positive
An alpha particle quickly ionises many atoms (~10,000) and loses all its energy – that’s why it causes so much damage to body tissue

68
Q

Describe beta-minus ionisation and therefore the damage on the body

A

Has lower mass and charge than the alpha particle, but a higher speed. This means it can still knock electrons off atoms. Each beta particle ionise about hundred atoms, losing energy each interaction. This lower number of interactions means that beta radiation causes much less damage to body tissue then alpha radiation

69
Q

Describe the intensity and ionisation of gamma radiation

A

Most weekly ionising form of nuclear radiation, but also the most penetrating. Intensity of gamma radiation decreases with distance. Although its quality factor is generally low, it is more difficult to shield yourself from.

70
Q

What is the relationship between intensity and how far gamma radiation travels through and absorbing material?

A

When it travels through and absorbing material, its intensity, the amount of radiation per unit area, decreases exponentially

71
Q

Why does the intensity of gamma radiation decrease as you get further away?

A

A gamma source will also emit gamma radiation in all directions. However this radiation spreads out as it gets further away from the source, so the intensity will decrease. The radiation spreads out over a larger area.

72
Q

What is the half life of a source?

A

The time it takes for the number of radioactive nuclei in the source to halve. Or the amount of time it takes for the activity of the source to halve

73
Q

What needs to be considered when deciding whether or not to use nuclear power, and deciding where nuclear waste should be stored?

A

Radioactive waste often has a very long half life

74
Q

Describe the half life of a radioactive isotopes used as medical tracers

A

They need to have a short half life to minimise exposure of patients to radiation, and the chance of environmental contamination when the body excretes them

75
Q

What are radioactive tracers?

A

Radioactive sources that are ingested or injected into patients. The radiation release as they move through the body can then be used to generate images that are useful for medical diagnostics

76
Q

What is the mass defect?

A

The mass of the nucleus is less than the mass of its constituent parts – the difference is called the mass defect

77
Q

What does Einstein’s equation mean?

A

Mass and energy are equivalent

78
Q

What happens to mass and energy when nucleons join together?

A

The total mass decreases – this ‘lost’ mass is converted into energy and released

79
Q

What is the binding energy?

A

If you pull the nucleus completely apart into it separate nucleons, the energy you’d have to use to do it would be the same as the energy released when the nucleus formed. This is called the binding energy. The binding energy is equivalent to the mass defect.

80
Q

Are binding energy in mass negative or positive. Why?

A

They are both negative quantities. That’s because they correspond to maths, and thus energy, lost from the nucleus

81
Q

What value is used to compare the binding energies of different nuclei?

A

Look at the binding energy per nucleon

82
Q

At what value is the binding energy per nucleon at a maximum?

A

Around N = 50

83
Q

Describes a graph of binding energy per nucleon against nucleon number

A

The curve is called a nuclear valley

The graph curve steeply down from the origin to a minimum at N = 50 then the curve slowly rises again. Pg 176

84
Q

Where do you the most stable nuclei occur on the binding energy per nucleon against nucleon number graph?

A

Around the minimum point, which is it nucleon number 56 – iron. Nuclei with the nucleon number close to 56 are bound most strongly

85
Q

Nuclei undergoing nuclear reactions will tend to move where on the graph of binding energy per nucleon against nucleon number? Why?

A

They tend to move towards this valley of stability. The nuclear reactions tend to happen and those that make nuclei more stable

86
Q

What is nuclear fusion, what happens to the binding energy per nucleon on, and energy?

A

Combining small nuclei to create a larger nucleus
This makes the binding energy per nucleon much more negative, which means a lot of energy is released during nuclear fusion

87
Q

What is fission? What happens to the branding energy per nucleon, and energy.

A

Large nuclei are split into two
The nucleon numbers of the two new nuclei are smaller than the original nucleus. This makes the binding energy per nucleon more negative. So, energy is also released during nuclear fission (but not as much energy per nucleon is a nuclear fusion).

88
Q

How can you calculate the energy released in a nuclear fission or nuclear fusion reaction?

A

The energy released is equal to the difference between the binding energy of the parent nucleus and the daughter
Or, you can calculate the difference in mass between the parent nucleus and the daughter nucleus, then using E=mc2 to find the energy that this change in mass is equivalent to.

89
Q

Describe nuclear fission in more detail. What is the difference between spontaneous and induced nuclear fission?

A

Heavy nuclei are unstable and some can randomly split into two smaller nuclei, and sometimes several neutrons. This process is called spontaneous if it just happens by itself, or induced if we encourage it to happen

90
Q

Explain why energy is released during nuclear fission

A

Because the new, smaller nuclei have a higher binding energy per nucleon and a lower total mass

91
Q

Are larger or smaller nuclei more likely to spontaneously fission? What does this mean for nuclear fusion in all elements?

A

Larger, because they are more unstable

Spontaneous fission limits the number of nucleons that a nucleus can contain, it limits the number of possible elements

92
Q

What do nuclear reactors use as fuel?

A

Fuel rods of uranium that are rich in uranium 235

93
Q

Describe the nuclear reactions that happen is die a uranium nuclear reactor?

A

Decision of uranium produces more neutrons which then induce other new creative vision – this is called a chain reaction
The neutrons will only cause a chain reaction if they are slow down to thermal neutron energy levels, so they can be captured by the uranium nuclei. To do this the fuel rods need to be placed in a moderator, water,. You need to choose a moderator that will slow down some neutrons enough so they can cause further session, keeping your action going at a steady rate

94
Q

How do control rods control the chain reaction, in a nuclear reactor?

A

They limit the number of neutrons in the reactor. They absorb neutrons so that the rate of fission is controlled. Control rods are made up of material that absorbs neutrons (boron), and they can be inserted by varying amounts to control the reaction rate

95
Q

What is the critical mass?

A

The amount of fuel you need to keep the chain reaction going at a steady rate, where one vision follows another. This means that for each nuclei that fissions, exactly one of the neutrons released triggers another fission.

96
Q

What happens if you have any less than the critical mass (sub-critical mass)?

A

Too few neutrons will be captured by other nuclei and the reaction will just peter out.

97
Q

Describe the sub/super/critical mass used in nuclear reactors

A

Nuclear reactor is use a super critical mass of fuel, were several new fissions normally follow each fission, and control the rate of fission using fuel rods

98
Q

What is coolant used for, in a nuclear reactor?

A

It is sent around reacted to remove heat produced in the fission – often the coolant is the same water that is being used in the reactor as a moderator.

99
Q

Briefly, how is heat used from the nuclear reactor?

A

The heat from the reactor can then be used to make steam for powering electricity-generating turbines

100
Q

Explain what could happen if the chain reaction in a nuclear reactor is not effectively managed

A

Large amounts of energy are released in a very short time. Many new fissions will follow each fission, causing a runaway reaction which could lead to an explosion. This is what happens in a fish and (atomic) bomb

101
Q

What is the advantage of using nuclear fission over fossil fuels or renewable sources?

A

It doesn’t produce carbon dioxide, unlike burning fossil fuels, so it doesn’t contribute to global warming. It also provides continuous energy supply, unlike many renewable sources.

102
Q

Describe the disadvantage of nuclear waste, when using a nuclear active

A

Some of the waste products are highly radioactive and difficult to handle and store.
When waste material is removed from the reactor, it is initially very hot, so it is placed in cooling pond until the temperature falls to a safe level. The radioactive waste is installed in sealed containers in a specialist facilities until its activity has fallen sufficiently. This can take many years, and there is a risk that material could escape from these containers.

103
Q

What could happen if radioactive material escapes the container where it is stored?

A

A leak of radioactive material could be harmful to the environment and local human populations both now and in the future, particularly if the material were to contaminate water supplies

104
Q

What events pose a risk to nuclear reactors?

A

Accidents or natural disasters

105
Q

Explain the disadvantage of time and money with nuclear reactors?

A

Because of all the safety precautions necessary building and decommissioning nuclear power plants is very time-consuming and expensive

106
Q

When can nuclei fuse?

A

They can only fuse if they have enough energy to overcome the electrostatic repulsion between them and get close enough to the strong interaction to bind them

107
Q

Describe the difference in conditions in order for nuclear fission and fusion to take place

A

Fusion reactions require much higher temperatures than fission, as well as higher pressures or densities

108
Q

Describe the state of matter, when the conditions are met for nuclear fusion

A

Generally only found inside stars, matter turns into a state called plasma

109
Q

Describe the energy released in nuclear fusion

A

A lot of energy is released because the new, heavier nucleus has a much higher binding energy per nucleon and, and so a lower total mass. The energy released helps to maintain the high temperatures needed for further fusion reactions

110
Q

Why does fusion release more energy than fission, considering the energy released per reaction is generally low in nuclear fusion than fission?

A

The nuclei used in fusion have a lower mass, so a mole of the reactants in the fusion reaction weighs less than a mole of the reactants and fission reaction

111
Q

What would be the advantage of a nuclear fusion reactor over a fission reactor?

A

We could generate nuclear electricity without the waste you get from fission reactors

A Level Physics OCR B (61 decks)

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