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Physics > Topic 6 - radioactivity > Flashcards

Topic 6 - radioactivity Flashcards

1
Q

What is the radius of an atom?

A

1x10^-10 metres

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2
Q

What are the stree subatomic constituents of an atom?

A

Proton
Neutron
Electron

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3
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus

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4
Q

What proportion of the total radius of an atom is the radius of the nucleus?

A

1/10,000

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5
Q

Where are protons found?

A

In the nucleus

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6
Q

Where are electrons found?

A

In discrete energy levels (shells) around the nucleus

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7
Q

Where are neutrons found?

A

In the nucleus

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8
Q

What charge does the nucleus of an atom have? Why?

A

A positive charge
It contains protons and neutrons
Protons are positive
Neutrons have no charge

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9
Q

Give two ways that an atom’s electron arrangement can be changed

A

Absorbing electromagnetic radiation

Emitting electromagnetic radiation

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10
Q

Explain how an atom’s electron arrangement changes when it absorbs EM radiation

A

The electrons move to higher energy levels (away from the nucleus)

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11
Q

Explain how an atom’s electron arrangement changes when it emits EM radiation

A

Electrons move to a lower energy level (towards the nucleus)

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12
Q

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

A

The number of protons is equal to the number of electrons

Protons are positive and electrons are negative so it evens out

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13
Q

What do all forms of the same element have in common?

A

The number of protons

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14
Q

What is the name given to the number of protons in an atom?

A

Atomic number

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15
Q

What is an atom’s mass number?

A

The total number of protons and neutrons in an atom

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16
Q

What is an isotope of an atom?

A

An atom of an element that has a different number of neutrons, but the same number of protons

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17
Q

What property differs between isotopes of an atom?

A

The mass of the atom

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18
Q

How do atoms turn into positive ions?

A

The lose one or more of their outer electrons

Electrons are negatively charged, so the resultant charge of the atom is positive

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19
Q

What are the relative masses of a proton, neutron and electron?

A 
Proton = 1
Neutron = 1
Electron = 1/1850
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20
Q

What is the relative charge of a proton?

A

+1

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21
Q

What is the relative charge of an electron?

A

-1

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22
Q

State four types of nuclear radiation

A

Alpha particles
Beta particles
Gamma rays
Neutrons

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23
Q

What is background radiation?

A

Radiation that is always present

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24
Q

Give four sources of background radiation

A

Rocks
Cosmic rays
Nuclear accidents
Nuclear weapon testing

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25
How do you measure and detect background radiation?
Photographic film | Geiger-Müller counter
26
How is photographic film used to measure radiation?
It turns dark when it absorbs radiation
27
How are Geiger muller tubes used to measure radiation?
When it absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends of how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation
28
What constitutes an alpha particle?
Two protons and two neutrons | Same as a helium nucleus
29
What is the range of an alpha particle through air?
A few centimetres
30
What will block beta radiation?
A thin sheet of aluminium | Several metres of air
31
What will block gamma radiation?
Several centimetres of lead | A few metres of concrete
32
Which type of radiation is most ionising?
Alpha radiation
33
Which type of radiation is least ion ionising?
Gamma radiation
34
How does gamma emission affect mass/charge of an atom?
Both mass and charge remain unchanged
35
Describe the plum-pudding model of the atom
A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it
36
Prior to the discovery of the electron what was believed about the atom?
That is was indivisible
37
Which experiment led to the plum-pudding model being discarded?
Rutherford’s alpha scattering experiment
38
What is the name given to the currently accepted model of the atom?
The Bohr model
39
Describe Rutherford’s experiment
Alpha particles were fired at a thin sheet of gold foil Most particles went straight through Some particles were deflected by small angles A few particles were deflected by large angles
40
What are the conclusions of rutherfors’s experiment?
Most of an atom is empty space The nucleus has a positive charge Most of the mass is concentrated in the nucleus
41
What happens in the process of beta plus decay?
A proton turns into a neutron and a positron
42
What is the process called when a neutron changes into a proton and an electron?
Beta minus decay
43
When alpha decay occurs, what happens to the atomic number and the mass number of the atom?
The atomic number decreases by 2 | The mass number decreases by 4pa new element is made since the atomic number has changed
44
What effect does beta minus decay have on the mass number and atomic number of an atom?
The mass number stays the same as the total number of neutrons and protons hasn’t changed The atomic number increases since there is one more proton
45
Define the activity of an unstable nucleus
Activity is the rate at chich a source of unstable nuclei decays
46
What is the unit of radioactive activity?
Becquerel (Bq)
47
What is count rate?
The number of radioactive decays per second for a radioactive source
48
Give an example of a detector that may be used to measure count rate
Geiger muller tube
49
Give example uses of radioactivity
``` Household fire alarms Irradiating food Sterilisation of equipment Tracing and gauging thicknesses of materials Diagnosis and treatment of cancer ```
50
How do smoke alarms work?
A radioactive substance is in the alarm which emits alpha radiation The emitted alpha particle ionised the air in the detector and causes a current to flow between the plates When smoke interferes with the radiation the air is no longer ionised so no current can flow. This reduction in current flow triggers the alarm
51
State two uses of nuclear radiation in the field of medicine
Examining of internal organs | Radiotherapy in the treatment of cancer
52
What is the role of beta radiation in tracers?
The tracer is inserted in your body, and targets a specific part of the body The radioactive substance in the tracer releases beta radiation which can be detected by external machines
53
How is beta radiation used to determine thickness?
A beta source is placed above the material and a detector is placed below it If there is an increase in radiation detected by the detector, too much radiation is passing through the material and so it is too thin If a decrease in radiation is detected then the material blocks too much radiation so it too thick
54
Why is ionising radiation dangerous?
It can cause cell mutations | It can damage tissue and kill cells
55
What is a consequence of cell mutation?
Cancer
56
What precautions should people tale when using ionising radiation?
Avoid handling the source directly Wear radiation protective clothing Keep the radiation in lead containers to reduce the amount of radiation that can escape Keep exposure time to a minimum
57
What precautions are takenTo reduce harm for doctors and patients using ionising radiation?
Only a small does is given It has a short half life They wear protective clothing
58
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials
59
What is irradiation?
The process of exposing a material to nuclear radiation | The material does not become radioactive
60
How is a radioactive tracer used in medicine?
It placed inside the body It releases gamma radiation which is detected by a detector which moves around the body Can then be used to produce a picture of the patient’s body
61
How does a PET scanner work?
It uses a tracer The scanner selects the gamma rays which are released by the tracer Multiple images are taken and this Is used to form a 3C image of the patient’s body
62
Isotopes are used I. PET scanners. What is important about where they are produced and why?
They must be produced near the hospital because they have a short half life so must be used soon after production
63
What are the advantages of nuclear power for generating electricity?
Doesn’t produce carbon dioxide Fuel is readily available Less nuclear fuel used to produce the same amount of energy Does not contribute to global warming
64
What are the disadvantages of using nuclear power to generate electricity?
Unpopular Security risks Expensive to commission and decommission the stations Radioactive waste can be hard to dispose of Risk of nuclear accidents
65
Hat is nuclear fission?
The splitting of large, unstable nuclei to form smaller, more stable nuclei
66
What usually needs to happen to induce fission?
The unstable nuclei must absorb a neutron
67
What is emitted in a fission reaction?
Gamma rays Energy 2 or three neutrons 2 smaller nuclei
68
Name a common fissile nuclei
Uranium - 235
69
What are the three main components of the core of a nuclear reactor?
Fuel rods Control rods Moderator
70
What takes place during a chain reaction in a nuclear reactor?
An unstable nucleus absorbs a neutron The nucleus undergoes fission and releases 2 or 3 further neutrons These induce more fission, which results in a chain reaction
71
What is the consequence of an uncontrolled chain reaction?
The rate of fission events becomes to high and results in the production of too much energy This can lead to a nuclear explosion
72
How is the chain reaction in a fission reactor kept under control?
Control rods are positioned in between the fuel rods The rate of fission is controlled by moving these rods up and down The lower the rods are inserted, the slower the rate of fission
73
What is the role of the moderator in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by simile nuclei and cause fission
74
How is electricity produced in a nuclear power station?
The reactions release thermal energy which is used to boil water and produce steam which turns a turbine, starting the generator

Physics (12 decks)

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