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GCSE AQA Physics 9-1 > P7 Radioactivity > Flashcards

P7 Radioactivity Flashcards

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1
Q

what is the radius of an atom?

A

1 x 10^-10 m

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2
Q

what is the radius of the nucleus?

A

less than 1/10000 of the radius of the atom

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3
Q

what does the nucleus contain?

A

protons - positive particles
neutrons - neutral particles

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4
Q

what is the overall charge of the nucleus?

A

positive overall charge due to the protons

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5
Q

where are electrons found?

A

in energy levels orbiting the nucleus

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6
Q

how is the energy of the energy level and the distance from the nucleus related?

A

energy levels further from the nucleus are at a higher energy than those closer

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7
Q

how can electrons move from energy levels?

A

if an electron absorbs EM radiation the electron can move from a lower energy level to a higher one
the atom can then emit EM radiation and the electron returns back to the lower energy level

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8
Q

what is the atomic number?

A

the number of protons
all atoms of each element have the same number of protons (same atomic number)

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9
Q

how is an atom neutral overall?

A

the number of electrons equals the number of protons
this means the negative charge on the electrons cancels out the positive charge of the protons

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10
Q

what does the mass number of an atom equal?

A

it equals the number of protons and neutrons in the atom

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11
Q

what is an isotope?

A

atoms of the same element with different numbers of neutrons

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12
Q

what is an ion?

A

atoms which lose electrons to become positively charged

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13
Q

what did the ancient Greeks think about atoms?

A

everything is made of atoms
atoms are tiny spheres that cannot be divided

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14
Q

what happened in 1897?

A

electrons were discovered
this showed that atoms must have an internal structure

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15
Q

what did the plum-pudding model suggest?

A

an atom is a ball of positive charge with negative electrons embedded in it

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16
Q

why was gold foil used in the alpha scattering experiment?

A

it can be hammered out very thin (a few atoms thick)

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17
Q

what did scientists do during the alpha scattering experiment?

A

fire positive alpha particles at gold foil

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18
Q

what were the observations made during the alpha scattering experiment?

A

most alpha particles passed straight through the foil
some particles were deflected
some particles bounced straight back off the foil

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19
Q

what told the scientists that atoms are mostly empty space? (in the alpha scattering experiment)

A

most of the particles passed straight through the gold foil
this meant the plum-pudding model had to be wrong

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20
Q

if some alpha particles were deflected, what does this mean?

A

the centre of the atom must have a positive charge that repelled the alpha particles

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21
Q

if some alpha particles bounced back, what does this say about the structure of an atom?

A

the mass of the atom must be concentrated in the centre. this central mass is known as the nucleus

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22
Q

what did Niels Bohr propose about electrons?

A

electrons orbit the nucleus at specific distances known as energy levels or shells

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23
Q

what did James Chadwick discover?

A

the nucleus contains neutral particles called neutrons

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24
Q

what is radioactive decay?

A

some isotopes have an unstable nucleus.
in order to become stable, the nucleus gives out radiation

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25
Q

can scientists predict when a nucleus will decay?

A

no
radioactive decay is completely random

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26
Q

what is the activity?

A

the rate at which a source of unstable nuclei decay

27
Q

what is the symbol/unit for activity?

A

the becquerel (Bq)
1 Bq = 1 decay per second

28
Q

what is the count rate?

A

the number of decays recorded each second by a detector

29
Q

what is an alpha particle?

A

a radioactive particle with the structure of 2 protons and 2 neutrons (the same as a helium nucleus)

30
Q

what is a beta particle?

A

an electron ejected from the nucleus at high speeds

31
Q

how is a beta particle formed?

A

when a neutron turns into a proton and an electron

32
Q

what is gamma radiation?

A

a type of electromagnetic radiation from the nucleus

33
Q

what other radiation type is given out by the nucleus?

A

a neutron

34
Q

what happens to the atomic number during alpha decay?

A

it decreases by 2

35
Q

what happens to the mass number during alpha decay?

A

it decreases by 4

36
Q

what is the rule for beta decay?

A

the atomic number increases by 1 but the mass number stays the same

37
Q

what happens to the mass/atomic number during gamma decay?

A

they are not changed

38
Q

what are alpha particles’ range in air? (and why)

A

alpha particles are large
they can travel around 5 cm before colliding with air particles and stop

39
Q

what are beta particles’ range in air?

A

up to a metre

40
Q

what are gamma rays’ range in air?

A

several metres before stopping

41
Q

what are the penetrating powers of the three types of radiation?

A

alpha - stopped by paper
beta - stopped by a few mm of aluminium
gamma - stopped by thick lead or concrete

42
Q

what is ionising?

A

when radiation collides with atoms, it can cause the atoms to lose electrons and form ions

43
Q

what are the ionising powers of radiation types?

A

alpha - very strongly ionising
beta - quite strongly ionising
gamma - weakly ionising

44
Q

what is half life?

A

the time it takes for the number of radioactive nuclei in an isotope in a sample to halve
half life is also the time it takes for the count rate (or activity) for a sample containing the isotope to fall to half its initial level

45
Q

what is the risk of ionising radiation?

A

it can increase the risk of cancer in humans

46
Q

what is irradiation?

A

exposing an object to nuclear radiation
the object does not become radioactive

47
Q

how is irradiation used to sterilise objects?

A

the object is exposed to gamma radiation
this kills any bacteria present

48
Q

what are the precautions when working with ionising radiation?

A

shielding - using gloves, lead apron, lead glass screen/container
monitoring - measure how much radiation has been received

49
Q

what is radioactive contamination?

A

when unwanted radioactive isotopes end up on other materials

50
Q

why is radioactive contamination hazardous?

A

the radioactive atoms decay and emit ionising radiation

51
Q

how are alpha particles dangerous?

A

very strongly ionising
can cause a lot of damage if inhaled or swallowed

52
Q

which radiation types can pass through the skin?

A

alpha - stopped by dead skin cells
beta - can penetrate skin
gamma - can penetrate body by likely to pass straight through

53
Q

what does peer reviewing allow?

A

it allows other scientists to check the findings of other scientists

54
Q

what is background radiation?

A

the low level nuclear radiation that is always present from natural or man-made sources

55
Q

what are some natural forms of background radiation?

A

rocks
cosmic rays

56
Q

what are cosmic rays?

A

very high energy particles which travel through space and crash into the earth’s atomosphere

57
Q

what are some man made sources of background radiation?

A

fall out from nuclear weapons testing
nuclear accidents

58
Q

what affects your exposure to background radiation?

A

location and occupation

59
Q

what is radiation dose measured in?

A

sieverts (Sv)
or
milisieverts (mSv) = 1/1000 of a Sv

60
Q

what are some features that a radioactive isotope must have to be used in medical tracers?

A

must emit a radiation type which can pass out of the body (beta/gamma)
not be strongly ionising to minimise damage to tissue
must not decay into another radioactive isotope
short half life so the isotope is not present in the body after a long time

61
Q

how does radiotherapy work?

A

gamma rays pass into the body and destroy a tumour

62
Q

what is the problem with radiotherapy?

A

healthy tissue may also be damaged when the gamma rays pass through the body

63
Q

how can the damage to healthy tissue be reduced in radiotherapy?

A

the radioactive isotope can be implanted into the body
this means the radiation is targeted precisely to the tumour

GCSE AQA Physics 9-1 (17 decks)

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