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physics > Radioactivity - topic 5 > Flashcards

Radioactivity - topic 5 Flashcards

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1
Q

what does an atom consist of

A

protons, neutrons and electrons

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2
Q

charge of a proton

A

+1

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3
Q

charge of an electron

A

-1

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4
Q

charge of a neutron

A

0

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5
Q

mass of proton and neutron

A

1

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6
Q

mass of an electron

A

1/2000

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7
Q

what are isotopes

A

atoms of the same element with the same number of protons but different number of neutrons

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8
Q

mass number

A

protons + neutrons (top number)

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9
Q

atomic number

A

number of protons

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10
Q

what is the plum pudding model

A

large positive proton with negative electrons inside

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11
Q

which experiment disproved the plum pudding model

A

Rutherford’s gold foil experiment

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12
Q

what is the gold foil experiment

A

when alpha particles were shot through thin gold foil

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13
Q

findings of the gold foil experiment

A

majority of alpha particles went through because most of the atom was empty space, some were deflected because centre of atom was positively charged and some alpha particles bounced directly back as the centre had a concentrated mass

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14
Q

the further away the electron from the nucleus …..

A

the more easily the electron can change its energy level

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15
Q

why do electrons further away from nucleus easily change electron levels

A

the further away the electron is from the nucleus, the weaker the force of attraction between nucleus and electron

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16
Q

ionisation

A

when atom with neutral charge becomes positively charged as it loses an electron

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17
Q

what is an ion

A

atom that loses or gains an electron

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18
Q

radiation

A

emission of energy in the form of waves or particles through space

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19
Q

unstable atom

A

contains surplus of energy and is called radioactive

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20
Q

what is used in external radiotherapy

A

gamma

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21
Q

dangers of radioactivity

A

tissue damage, skin burns, DNA mutation and sometimes cancer

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22
Q

contamination

A

where ionising radiation gets in contact with skin or enters their body

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23
Q

safety procedures with radioactive sources

A

shielding
minimise exposure time
maximise distance
wear protective clothing
use of dosimeters
use materials with short half lives

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24
Q

advantages of nuclear power

A

alternative to fossil fuels
doesn’t release carbon dioxide
doesn’t cause acid rain

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25
Q

disadvantages of nuclear power

A

high overall costs
risk of radioactive materials leaking
danger of polluting land and rivers

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26
Q

nuclear fission

A

high energy neutron collides with isotope. Nuclei absorbs high energy neutron and splits it into 2 smaller daughter nuclei. Daughter nuclei are radioactive and 2 or more neutrons are released which go on to collide with more isotopes causing an uncontrolled chain reaction.

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27
Q

where nuclear fission takes place

A

inside a nuclear reactor

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28
Q

what is steam released during nuclear fission used for

A

to power turbines which turn a generator to produce electricity

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29
Q

graphite moderator

A

slow down neutrons so uranium can absorb them so chain reaction can keep going

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30
Q

control rods

A

control rate of reaction by absorbing neutrons. Control rods can be lowered into the reactor to slow reaction down.

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31
Q

nuclear fusion

A

smaller nuclei combine under high pressure and high temperature to form a larger nuclei.

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32
Q

example of nuclear fusion

A

in the sun

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33
Q

what is needed for nuclear fusion

A

high temp and pressure

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34
Q

for the nuclei to fuse …

A

they must overcome the strong electrostatic forces of repulsion

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35
Q

why is high temp needed for nuclear fusion

A

high temperature means high energy, which is needed to overcome forces of repulsion between nuclei

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36
Q

what is the radius of an atom

A

1 x 10 ^-10 m

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37
Q

why are atoms neutral

A

atoms have the same number of protons and electrons

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38
Q

what is the relative mass of a positron

A

1/2000

39
Q

what is the relative electric charge of a positron

A

+1

40
Q

how far away are electrons from the nucleus

A

in each atom, electrons orbit the nucleus at different set distances from the nucleus

41
Q

when do electrons change orbit

A

when there is absorption or emission of EM radiation

42
Q

how do atoms form positive ions

A

by losing outer electrons

43
Q

what happens when electrons release EM radiation

A

they lose energy and fall to a lower energy level closer to the nucleus

44
Q

how are alpha, beta minus, positrons, gamma rays and neutron radiation emitted

A

they are emitted from unstable nuclei in a random process

45
Q

what is an alpha particle

A

a helium nucleus

46
Q

what is a beta particle

A

an electron emitted from the nucleus

47
Q

what is a gamma ray

A

electromagnetic radiation

48
Q

what is the ionising power of alpha particles

A

highly ionising

49
Q

what is the penetration power of alpha particles

A

low

50
Q

what is the ionising power of beta minus particles

A

moderately ionising

51
Q

what is the penetrating power of beta minus particles

A

medium

52
Q

what is the ionising power of gamma ray

A

weakly ionising

53
Q

what is the penetrating power of gamma rays

A

high

54
Q

what is the effect on the mass number and atomic number of alpha decay

A

atomic number decreases by 2 and mass number decreases by 4

55
Q

what is the effect on the mass number and atomic number of beta minus decay

A

atomic number increases by 1 and mass number in unchanged

56
Q

what is the effect on the mass number and atomic number of beta plus decay

A

mass number does not change, and atomic number decreases by 1

57
Q

what is the effect on the mass number and atomic number of gamma decay

A

atomic number and mass number remain unchanged

58
Q

what is the effect on the mass number and atomic number of neutron emission

A

mass number decreases by 1 and atomic number stays the same

59
Q

what happens in beta minus decay

A

a neutron turns into a proton plus an electron

60
Q

what happens in beta plus decay

A

a proton becomes a neutron plus a positron

61
Q

how can you measure and detect radioactivity

A

with a geiger muller tube or photographic film

62
Q

how do you use a geiger muller tube

A

place the object in front of the geiger muller tube and then count the number of ticks from the object and take into consideration the radiation from the background. Then repeat and average

63
Q

how does photographic film work

A

the more radiation the film is exposed to, the darker it becomes

64
Q

why can you not predict radioactive decay

A

because it is entirely random, so you cannot predict when or which nucelus in a sample will decay next but you can find out the half life

65
Q

what is half life

A

the time it taken for the activity of a source to decay by half

66
Q

what does half life enable you to work out

A

the activity of a very large number of nuclei to be predicted during the decay process

67
Q

what is activity measured in

A

becquerels, Bq

68
Q

how does the activity of a sample decrease over time

A

each time a radioactive nucleus decays to become a stable nucleus, the activity will decrease

69
Q

what is background radiation

A

low level radiation that is present at all times, all around us, wherever we go

70
Q

where does background radiation come from

A

cosmic rays, from space
man made sources
naturally occurring unstable isotopes all around us

71
Q

what are the dangers of ionising radiation

A

tissue damage and cell mutations, cancer

72
Q

what is irradiation

A

if radiation from a radioactive source reaches an object

73
Q

what is contamination

A

if unwanted radioactive atoms get onto and into a material

74
Q

what are the precautions to reduce the risk of harm from irradiation

A

keep radioactive sources in lead lined boxes
wearing shielding
stay as far away from the source as possible
monitor exposure

75
Q

what are the precautions to reduce the risk of harm from contamination

A

gloves and tongs should be used
wear protective suits
chose sources with appropriate half lives

76
Q

what is the effect of half life on potential danger of a source

A

the lower the activity of a radioactive source, the safer it is to be around because the activity of a source with a short half life will have fallen more

77
Q

what type of radiation is used in fire alarms

A

alpha radiation

78
Q

what type of radiation is used in gauging thickness

A

beta radiation

79
Q

what type of radiation is used in sterilisation

A

gamma

80
Q

what type of radiation is used in tracers

A

gamma

81
Q

why are isotopes used in PET scanners made near by

A

they have short half lives so need to be used as quickly as possible

82
Q

how can tumours be treated externally

A

using gamma radiation aimed at the tumour from a source outside the body

83
Q

how can tumours be treated internally

A

placing a radioactive material inside the body into or near a tumour

84
Q

difference in half lives of sources used in external and internal tumour treatment

A

in external treatment, half life is long and in internal treatment, half life is short

85
Q

what happens in the fission of uranium-235

A

a slow moving neutron is fired at a large, unstable U-235 nucleus.

The neutron is absorbed by the nucleus , which makes the atom unstable and causes it to split

When the atoms splits, it forms two identical daughter nuclei which are radioactive

Two or more neutrons are also released and if any of the neutrons are moving slowly enough to be absorbed by another nucleus, the can cause more fission to occur

86
Q

what do graphite moderators do

A

control the speed of neutrons and slow down fast moving neutrons

87
Q

why are graphite moderators important

A

they allow more fissions and the chain reaction to continue as they make sure the neutrons are moving slow enough to be absorbed

88
Q

what do control rods do

A

they absorb excess neutrons to prevent the chain reactions from getting out of control

89
Q

what is the difference between nuclear fusion and fission

A

in fusion, two daughter nuclei fuse to create a larger nucleus and in fission it is the opposite

90
Q

what is nuclear fusion

A

the creation of larger nuclei resulting in a loss of mass from smaller nuclei accompanied by a release of energy

91
Q

why does fusion only happen at high temperatures and high pressure

A

because the positively charged nuclei have to get very close to fuse, so the strong force due to electrostatic repulsion has to be overcome and this takes a lot of energy which comes from high temperatures

92
Q

how is thermal energy from a chain reaction used in the generation of electricity in a nuclear power station

A

energy released by chain reaction is transferred to the thermal energy of the moderator

some of this energy is then transferred to the thermal energy store of the coolant

the coolant flows around the boiler and transfers energy to the thermal energy store of cold water passing through the boiler

this causes water to boil, generating steam

this steam causes a turbine connected to a generator and the turning generator produces electricity

93
Q

what are the advantages of using nuclear power

A

no acid rain
no carbon dioxide emission

94
Q

what are the disadvantages of using nuclear power

A

nuclear waste can leak out and pollute land, river and oceans

high cost of setting up power plant and decommissioning it

nuclear waste cannot be disposed of safely

physics (14 decks)

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