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radioactivity Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

what did J.J Thomson discover

A

electrons could be removed from atoms, so atoms must be made up of smaller bits

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2
Q

what did J.J thomson call his model

A

plum pudding - atoms were spheres of positive charge with tiny negative electrons stuck in them

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3
Q

what experiment did rutherford and marsden do

A

the gold foil test

they shot alpha beams of alpha particles at a thin gold foil, they expected the particles to pass straight through or only be slightly reflected

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4
Q

what results did they get from the gold foil test

A

although most of the particles did go straight through some were deflected more than they expected and were deflected back to where they came from

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5
Q

what did rutherford conclude

A

most of the mass of the atoms was concentrated at the centre in a nucleus, most of the atom is just empty space and must have a positive charge

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6
Q

what did bohr do to rutherford design

A

the electrons were in fixed orbit at set distances from the nucleus, the most normal atom we know now

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7
Q

3 factors of the current model

A

protons
neutrons
electrons

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8
Q

factors of the new atom

A

positively charge nucleus
negatively charged electrons

electrons are in shells
protons and neutrons in the centre

atoms are neutral

atoms join together to form molecules

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9
Q

relative mass and relative change of a proton

A

1
+ 1

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10
Q

relative mass and relative change of a neutron

A

1
0

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11
Q

relative mass and relative change of a electron

A

0.0005
-1

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12
Q

how can electrons move shells

A

if it absorbs EM radiation with the right amount of energy, it moves up to an empty or partially filled shell

however it does quickly fall back

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13
Q

what happens to an atom to make it becomes ionised and how

A

looses an electron

absorbs enough energy which can move so far it leave the atom, now a free electron and the atom is ionised

now it’s a positive ion

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14
Q

what ionises atoms

A

nuclear radiation

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15
Q

what is ionising radiation

A

any radiation that can knock electrons from atoms

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16
Q

what is an isotope

A

different forms of the same element by having the same number of protons but different number of neutrons

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17
Q

what is radioactive decay

A

when unstable isotopes decay into other elements and give out radiation as they try to become more stable

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18
Q

what do radioactive substances spit out

A

one or more types of ionising radiation when they decay - alpha, beta and gamma

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19
Q

what are alpha particles

A

helium nuclei

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20
Q

alpha particle facts

A

emitted from the nucleus

don’t penetrate very far into materials and are stopped quickly

they are strongly ionising due to their size

only travel a few cm and are absorbed by a thin sheet of paper

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21
Q

what are beta particles

A

electrons and positrons

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22
Q

beta particles facts

A

beta minus is a fast moving electron released by the nucleus

beta positive is a fast moving positron

beta minus - both moderately ionising - range in air for a few metres and absorbed by a sheet of aluminium

positrons - smaller range, hit an electron and destroy eachother and produce gamma rays

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23
Q

what are gamma rays

A

EM waves with a short wavelength

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24
Q

gamma rays facts

A

penetrate far into materials and will travel long distance in air - absorbed by thick sheet of lead or metres of concrete

weakly ionising and tend to pass through rather than collide with atoms

the nucleus decays and undergoes nuclear rearrangement and releases energy

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25
Q

what is a nuclear equation

A

a way of showing radioactive decay by using element symbols

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26
Q

what does alpha decay decrease

A

the charge and mass of the nucleus

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27
Q

what happens when a nucleus emits an alpha particle

A

loses 2 protons and 2 neutrons

mass number decreases by 4
atomic number decreases by 2

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28
Q

what does beta minus decay increase

A

the charge of the nucleus

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29
Q

what happens during beta minus decay

A

a neutron changes into a proton and an electron

mass number doesn’t change as it hasn’t lost a neutron

atomic number increases by 1

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30
Q

what does positron emission decrease

A

the charge of the nucleus

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31
Q

what happens in beta plus decay

A

a proton changes into a neutron and a positron

mass number doesn’t change - lost a proton and gained a neutron

atomic number decreases by 1

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32
Q

what does neutron emission decrease

A

the mass of the nucleus

33
Q

what happens when a nucleus emits a neutron

A

mass number decreases by 1 - lost a neutron

atomic number stays the same

34
Q

what happens in both alpha and beta emission

A

a new element will be formed as the number of protons changes

35
Q

what do gamma rays not change

A

the charge or mass of the nucleus

36
Q

what is a totally random process

A

radioactivity

37
Q

why is radioactivity random

A

you cannot say when any radioactive isotopes is going to decay and you cannot say which will decay next

38
Q

what is half-life

A

the average time taken for there number of radioactive nuclei in an isotope to halve

39
Q

how can activity be measured

A

the geiger - muller tube

40
Q

how does the geiger-muller tube work

A

clicks each time it detects radiation, the tube can be attached to a counter, which displays the number of clicks per second

41
Q

how else can you detect radiation (photographic film)

A

using photographic film, the more radiation the films exposed to, the darker it becomes

42
Q

what happens to the radioactivity of a source over time

A

decreases

43
Q

what does a short half life mean

A

the activity falls quickly because the nuclei are very unstable and rapidly decay

they are also dangerous due to high amount of radiation

44
Q

what does a long half life mean

A

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

dangerous as nearby areas are exposed to radiation for millions years of years

45
Q

how can you measure half life

A

plotting a graph

found from the graph by finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis

46
Q

what is background radiation

A

low level radiation that’s around us all the time

47
Q

examples of background radiation

A

radioactivity - air, some foods, building materials, rocks

space - cosmic rays

radiation due to human activity

48
Q

what is absorbed radiation dose

A

amount of radiation your exposed to, it also varies due to where you live or jobs which involve radiation

49
Q

what is exposed to radiation called

A

irradiation

50
Q

ways to reduce irradiation

A

keeping sources in lead lined boxes

standing behind barriers

being in a different room, using remote controlled resources

wearing photographic film badges to monitor exposure

51
Q

how does radiation damage cells

A

radiation can enter living cells and ionise atoms and molecules in them, leading to tissue damage

52
Q

what do lower doses of radiation cause

A

minor damage without killing cells which can cause cell to mutate and divide uncontrollably, causing cancer

53
Q

what do higher doses of radiation cause

A

tend to kill cells completely, causing radiation sickness

54
Q

what radiation are the most dangerous outside the body and why

A

beta and gamma as they can penetrate the body and get to the delicate organs

55
Q

what radiation are the least dangerous outside the body and why

A

alpha is less dangerous as it can’t penetrate the skin

56
Q

what radiation are the most dangerous inside the body and why

A

alpha as they are strongly ionising, all do damage in a very localised area which means contamination

57
Q

what is contamination

A

radioactive particles getting on objects

58
Q

why is contamination dangerous

A

because radioactive particles could get inside your body

there’s a risk until the contamination is removed or all the atoms have decayed

59
Q

what can prevent contamination

A

using gloves and tongs

protective suits

60
Q

what do hazards associated with radioactive source depend on

A

it’s half life

61
Q

what do household fire alarms use

A

alpha radiation

62
Q

what can be sterilised by using gamma rays

A

food - kill microbes

equipment - sterilise medical equipment

63
Q

what is used in tracers and thickness gauges

A

radiation

64
Q

what can PET scanners help with

A

diagnose illnesses

65
Q

how do pet scanners work

A

1) inject the patient with a substance used by the body

2) positrons emitted by the isotope meet electrons in an organ and annihilate high energy gamma rays in opposite directions are detected

3) the distributions of radioactivity matches up with metabolic activity

4) the isotopes used in PET scanning have short half lives

5) could be no longer useful if left too long due to transportation

66
Q

what is internal radiation therapy

A

a radioactive material is placed inside the body into or near a tumor

67
Q

how can tumors be treated externally

A

using gamma rays aimed at the tumor

68
Q

why can gamma rays sometimes cause more harm than gold

A

because if they are being used to treat tumors if they hit healthy cells they could potentially cause them to become tumors

69
Q

what are alpha emitters injected near

A

the tumor

70
Q

how are beta emitters used

A

in implants placed inside or next to the tumor

71
Q

what is nuclear fission

A

a type of nuclear reaction that is used to release energy from uranium or plutonium atoms

72
Q

what is the chain reaction

A

1) slow moving neutron is fired at a large unstable nucleus

2) the neutron is absorbed by the nucleus - makes the atom more unstable causing it to split

3) when it splits it forms 2 new lighter elements and energy is released - all nuclei is radioactive

4) every time it splits up, it splits out 2 or 3 neutrons which can hit other nuclei causing them to split - a chain reaction

73
Q

why must chain reactions be carefully controlled

A

neutrons will only cause other nuclear fissions if they are moving slowly enough to be captured by nuclei

74
Q

what are nuclear power stations powered by

A

nuclear reactions that control chain reactions

75
Q

what is nuclear fission

A

two light nuclei collide at high speed and join to create a larger, heavier nucleus

76
Q

when does fusion happen

A

only at high temperatures and pressures

77
Q

what are the pros of nuclear power

A

pretty safe

very reliable

nuclear power doesn’t release gases like fossil fuels

cheap and readily available

78
Q

what are the cons of nuclear power

A

public perception can be very negative

nuclear waste can never be disposed safely

risk of leaks - cause major catastrophe

physics (7 decks)

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