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Further Additional Physics > Topic 3 - Radioactivity and Ionising Radiation > Flashcards

Topic 3 - Radioactivity and Ionising Radiation Flashcards

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1
Q

What is the relative mass of a neutron?

A

1

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2
Q

What is the relative mass of a proton?

A

1

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3
Q

What is the relative mass of an electron?

A

1/2000

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4
Q

What is the relative charge of a proton?

A

+1

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5
Q

What is the relative charge of a neutron?

A

0

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6
Q

What is the relative charge of an electron?

A

-1

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7
Q

In ab atom, what is always equal?

A

The number of protons and electrons

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8
Q

What is alpha radiation?

A

A helium nucleus
4
He
2

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9
Q

Is alpha radiation heavy or light, slow or fast?

A

Slow + heavy

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10
Q

How ionising is alpha radiation?

A

Strongly ionising

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11
Q

How penetrating is alpha radiation and what stops it?

A
  • Not very penetrating

- Stopped by paper, skin etc

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12
Q

What is beta radiation?

A

An electron
0
e
-1

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13
Q

Is beta radiation heavy or light, slow or fast?

A

Light + fast

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14
Q

How ionising is beta radiation?

A

Moderately ionising

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15
Q

How penetrating is beta radiation and what stops is?

A
  • Moderately penetrating

- Stopped by thin metal

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16
Q

What is gamma radiation?

A

Electromagnetic radiation

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17
Q

Is gamma radiation heavy or light, slow or fast?

A

No mass + very fast

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18
Q

How ionising is gamma radiation?

A

Weakly ionising

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19
Q

How penetrating is gamma radiation and what stops it?

A
  • Very penetrating

- Stopped by thick lead or very thick concrete

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20
Q

What is a positron?

A

The antiparticle of an electron, so has same relative mass but opposite relative charge (+1)

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21
Q

Is a positron heavy or light, slow or fast?

A

Light + fast

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22
Q

How ionising is a positron?

A

Moderately ionising

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23
Q

How penetrating is a positron and what stops it?

A
  • Moderately penetrating

- Stopped by thin metal

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24
Q

What happens when an electron and a positron meet?

A

Annihilation

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25
Q

How penetrating is neutron radiation?

A

More penetrating than alpha, beta or gamma
1
n
0

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26
Q

How does neutron radiation cause ionisation?

A
  • Not directly ionising
  • Absorbed by nuclei of atoms
  • Absorbing a neutron can make nucleus radioactive
  • Radioactive nuclei emit ionising radiation (alpha, beta or gamma)
  • Meaning neutrons sometime calles indirectly ionising
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27
Q

What is used to make neutron radiation shielding and why?

A
  • Water, polythene or concrete

- Neutrons absorbed best by light nuclei + these have lost of hydrogen (lightest nucleus)

28
Q

Why is thick lead sometimes added to neutron shielding?

A
  • Neutron absorption often makes nucleus emit gamma

- Lead absorbs gamma

29
Q

What causes a nucleus to become unstable?

A
  • Too many neutrons
  • Too few neutrons
  • Too many protons + neutrons altogether, too heavy
  • Too much energy
30
Q

On the curve of stability, what does it mean if an isotope is not on the curve?

A

Unstable

31
Q

What does it mean if an isotope is unstable?

A

Radioactive (particles or radiation emitted)

32
Q

On the curve of stability, what does it mean if an isotope is above the curve?

A

It has too many neutrons to be stable, beta-minus emitter

33
Q

On the curve of stability, what does it mean if an isotope is below the curve?

A

It has too few neutrons to be stable, beta-plus emitter

34
Q

What causes beta-minus decay?

A

When there are too many neutrons in relation to protons in the nucleus

35
Q

What happens when an isotope undergoes beta-minus decay?

A

-Emission of an electron from nucleus
-Neutron in the nucleus changes into a proton
-The proton (atomic, smaller) number increases by 1, + the nucleon (mass, bigger) number stays the same
e.g.
187 187 0
Re –> K + B
75 76 -1

36
Q

What causes beta-plus decay?

A

When there are too few neutrons in relation to protons in the nucleus

37
Q

What happens when an isotope undergoes beta-plus decay?

A

-Emission of a positron from the nucleus
-Proton changed to a neutron in the nucleus
-Proton (atomic, smaller) number decreases by 1, nucleon (mass, bigger) number stays the same
e.g.
37 37 0
Ca –> K + B
20 19 +1

38
Q

What causes alpha decay?

A

Very heavy atoms w/ atomic numbers (smaller) >82 + nuclei too big to be stable

39
Q

What happens when an isotope undergoes alpha decay?

A 
Proton number (smaller) decrease by 2, nucleon (bigger) number decreases by 4
e.g.
238            234           4
    U  -->            Th   +    a
92               90            2
40
Q

What causes gamma radiation?

A
  • After alpha/beta decay, nucleus has excess energy
  • Loses energy by emitting a gamma ray
  • Gamma emission always goes w/ alpha/beta, never just gamma
41
Q

What happens when an isotope gives out gamma rays?

A

No change to the proton or nucleon number of the nuclei

42
Q

What are protons and neutrons made up of?

A

Quarks

43
Q

How many quarks makes up a neutron or proton?

A

3

44
Q

What quarks make up a proton and neutron?

A

Up-quarks + down-quarks

45
Q

What is the relative charge of an up-quark?

A

+2/3

46
Q

What is the relative mass of an up-quark?

A

1/3

47
Q

What is the relative charge of a down-quark?

A

-1/3

48
Q

What is the relative mass of a down-quark?

A

1/3

49
Q

Which quarks are protons made from and how does this give them their charge and mass?

A

up-quark + up-quark + down-quark
Charge = 2/3 + 2/3 + (-1/3) =+1
Mass = 1/3 + 1/3 + 1/3 = 1

50
Q

Which quarks are neutrons made from and how does this give them their mass and charge?

A

up-quark + down-quark+ down-quark
Charge = 2/3 + (-1/3) +(-1/3) = 0
Mass = 1/3 + 1/3 + 1/3 = 1

51
Q

Through quarks, how does a nucleus become stable when it is unstable?

A
  • Neutron converted to proton/proton converted to a neutron
  • To do this, up-quark changes to down-quark or vice versa
  • Overall charge has to be equal
  • When neutron changes to proton (down to up), -vely charged electron emitted so overall charge = 0, beta-minus decay
  • When proton changes to neutron (up to down), +ve charge emitted so overall charge = +1, positron, beta-plus decay
52
Q

How are radioactive isotopes used as tracers?

A
  • Radioactive isotopes used as tracers to diagnose some medical conditions
  • Tracer injected to patient/swallowed
  • External detector follow progress around body
  • Computer uses readings to create image showing where strongest reading of radiation coming from
  • e.g. iodine-131 absorbed by thyroid gland. Gives out radiation that can be detected to see if thyroid gland taking in iodine as it should
53
Q

What radioactive isotopes are used as tracers and why?

A
  • Isotopes that emit beta or gamma
  • They can pass out of the body
  • Short half lives to reduce radioactivity in patient
54
Q

What is PET scanning used for?

A
  • Show areas of damaged tissue in heart by detecting areas of decreased blood flow
  • Can reveal coronary artery disease + damaged/dead heart muscle from heart attacks
  • Record blood flow + activity to the brain helping diagnose illnesses like epilepsy
  • Can identify active tumour cells by showing metabolic activity in tissue. Cancer cells have higher metabolism than healthy cells (because they grow a lot)
55
Q

How does PET scanning work?

A
  • Inject patient w/ substance body uses e.g. glucose, containing positron-emitting radioactive isotope w/ short half-life so acts as a tracer
  • Over an hour or so tracer moves through body to organs
  • Positrons meet electrons + annihilate emitting high-energy gamma rays that are detected
  • Distribution of radioactivity matches up w/ metabolic activity as more radioactive substance (e.g. glucose) injected to patient taken up + used by cells doing more work (increased metabolism)
56
Q

What type of isotopes need to be used in PET scan and how are they sometimes made?

A
  • Short half-lives
  • Need to be made close to where used
  • Some hospitals have own cyclotron to make isotopes on site
  • If not they’d have to be transported over large distances + activity could be too low when reach hospital so cannot be used
57
Q

What effect can ionisation have on cells?

A
  • Kill a cell completely
  • Damage it so it cannot divide causing tissue damage
  • Radiation can alter genetic material in cell
  • Can cause mutations
  • Can make cell divide + grow uncontrollably; cancer
58
Q

Why is it advised that patients don’t get a PET scan too often and only when necessary?

A
  • Any exposure to radiation increases risk of tissue damage + cancer
  • Uses 7 millisieverts (mSv) per PET scan compared to 2.2 mSv per year background radiation UK
59
Q

During medical scanning using ionising radiation, in what ways are patient’s exposure minimised?

A
  • Given lowest possible doses of radiation
  • Short exposure time
  • May also wear lead shielding to protect areas not being treated
60
Q

In what ways are the medical personnel’s exposure to ionising radiation minimised when doing medical scanning?

A
  • Should stand away from equipment or control remotely (as intensity of radiation decreases w/ distance)
  • May stand behind lead screens or wear protective lead-lined clothing
  • Radiation does must be closely monitored
61
Q

How can internal radiation therapy be used to treat a tumour?

A
  • Radioactive material placed inside body into/near tumour
  • Injected/implanted small amount of radioactive substance
  • Gives high dose to small part of body so damage to normal cells near tumour is limited
62
Q

How can external radiation therapy be used to treat a tumour?

A
  • High energy X-rays/gamma rays fired at tumour

- Carefully focussed on tumour but some damage to normal cells

63
Q

Why might internal radiation therapy be used to treat a tumour over external radiation therapy?

A
  • Shorter than external, so reduces no. of visits patient has to make to hospital + time to wait for further surgery
  • Generally no side effects other than discomfort
  • Very limited no. of healthy cells affected
  • External can have short + long lasting effects
64
Q

Why might external radiation therapy be used to treat a tumour over internal radiation therapy?

A
  • Sessions only last 10 mins

- Patient doesn’t emit radiation after

65
Q

What are the benefits of using radiation in medical physics?

A
  • Often cures
  • Even if doesn’t cure, reduces suffering of patient close to death (treatment reducing suffering w/out cure is palliative care)
66
Q

What are the drawbacks of using radiation in medical physics?

A
  • Always some damage to normal cells causing side effects (radiotherapy, hair loss, sickness, irritation), only minor + only during treatment
  • Can get serious side effects years after treatment e.g. bowel damage, infertility
  • Some argue of qol after treatment, worth it? Some refuse it for this reason
  • May develop 2ndncer from radiation to treat 1st, but w/out person’s life expectancy is dramatically shorter
67
Q

What are the ethical arguments around testing new medical techniques on people?

A
  • Could have harmful side effects so patients should be warned of possible side effects before taking part, but doctors don’t know all side effects to be aware of
  • Lots of ill patients may want to take part in medical trials but places are limited
  • When trial is shown a new technique works, how long before offered to everyone?

Further Additional Physics (5 decks)

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