Topic 3 - Radioactivity and Ionising Radiation Flashcards
1
Q
What is the relative mass of a neutron?
A
1
2
Q
What is the relative mass of a proton?
A
1
3
Q
What is the relative mass of an electron?
A
1/2000
4
Q
What is the relative charge of a proton?
A
+1
5
Q
What is the relative charge of a neutron?
A
0
6
Q
What is the relative charge of an electron?
A
-1
7
Q
In ab atom, what is always equal?
A
The number of protons and electrons
8
Q
What is alpha radiation?
A
A helium nucleus
4
He
2
9
Q
Is alpha radiation heavy or light, slow or fast?
A
Slow + heavy
10
Q
How ionising is alpha radiation?
A
Strongly ionising
11
Q
How penetrating is alpha radiation and what stops it?
A
- Not very penetrating
- Stopped by paper, skin etc
12
Q
What is beta radiation?
A
An electron
0
e
-1
13
Q
Is beta radiation heavy or light, slow or fast?
A
Light + fast
14
Q
How ionising is beta radiation?
A
Moderately ionising
15
Q
How penetrating is beta radiation and what stops is?
A
- Moderately penetrating
- Stopped by thin metal
16
Q
What is gamma radiation?
A
Electromagnetic radiation
17
Q
Is gamma radiation heavy or light, slow or fast?
A
No mass + very fast
18
Q
How ionising is gamma radiation?
A
Weakly ionising
19
Q
How penetrating is gamma radiation and what stops it?
A
- Very penetrating
- Stopped by thick lead or very thick concrete
20
Q
What is a positron?
A
The antiparticle of an electron, so has same relative mass but opposite relative charge (+1)
21
Q
Is a positron heavy or light, slow or fast?
A
Light + fast
22
Q
How ionising is a positron?
A
Moderately ionising
23
Q
How penetrating is a positron and what stops it?
A
- Moderately penetrating
- Stopped by thin metal
24
Q
What happens when an electron and a positron meet?
A
Annihilation
25
How penetrating is neutron radiation?
More penetrating than alpha, beta or gamma
1
n
0
26
How does neutron radiation cause ionisation?
- 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
27
What is used to make neutron radiation shielding and why?
- Water, polythene or concrete
| - Neutrons absorbed best by light nuclei + these have lost of hydrogen (lightest nucleus)
28
Why is thick lead sometimes added to neutron shielding?
- Neutron absorption often makes nucleus emit gamma
| - Lead absorbs gamma
29
What causes a nucleus to become unstable?
- Too many neutrons
- Too few neutrons
- Too many protons + neutrons altogether, too heavy
- Too much energy
30
On the curve of stability, what does it mean if an isotope is not on the curve?
Unstable
31
What does it mean if an isotope is unstable?
Radioactive (particles or radiation emitted)
32
On the curve of stability, what does it mean if an isotope is above the curve?
It has too many neutrons to be stable, beta-minus emitter
33
On the curve of stability, what does it mean if an isotope is below the curve?
It has too few neutrons to be stable, beta-plus emitter
34
What causes beta-minus decay?
When there are too many neutrons in relation to protons in the nucleus
35
What happens when an isotope undergoes beta-minus decay?
-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
What causes beta-plus decay?
When there are too few neutrons in relation to protons in the nucleus
37
What happens when an isotope undergoes beta-plus decay?
-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
What causes alpha decay?
Very heavy atoms w/ atomic numbers (smaller) >82 + nuclei too big to be stable
39
What happens when an isotope undergoes alpha decay?
```
Proton number (smaller) decrease by 2, nucleon (bigger) number decreases by 4
e.g.
238 234 4
U --> Th + a
92 90 2
```
40
What causes gamma radiation?
- 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
What happens when an isotope gives out gamma rays?
No change to the proton or nucleon number of the nuclei
42
What are protons and neutrons made up of?
Quarks
43
How many quarks makes up a neutron or proton?
3
44
What quarks make up a proton and neutron?
Up-quarks + down-quarks
45
What is the relative charge of an up-quark?
+2/3
46
What is the relative mass of an up-quark?
1/3
47
What is the relative charge of a down-quark?
-1/3
48
What is the relative mass of a down-quark?
1/3
49
Which quarks are protons made from and how does this give them their charge and mass?
up-quark + up-quark + down-quark
Charge = 2/3 + 2/3 + (-1/3) =+1
Mass = 1/3 + 1/3 + 1/3 = 1
50
Which quarks are neutrons made from and how does this give them their mass and charge?
up-quark + down-quark+ down-quark
Charge = 2/3 + (-1/3) +(-1/3) = 0
Mass = 1/3 + 1/3 + 1/3 = 1
51
Through quarks, how does a nucleus become stable when it is unstable?
- 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
How are radioactive isotopes used as tracers?
- 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
What radioactive isotopes are used as tracers and why?
- Isotopes that emit beta or gamma
- They can pass out of the body
- Short half lives to reduce radioactivity in patient
54
What is PET scanning used for?
- 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
How does PET scanning work?
- 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
What type of isotopes need to be used in PET scan and how are they sometimes made?
- 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
What effect can ionisation have on cells?
- 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
Why is it advised that patients don't get a PET scan too often and only when necessary?
- 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
During medical scanning using ionising radiation, in what ways are patient's exposure minimised?
- Given lowest possible doses of radiation
- Short exposure time
- May also wear lead shielding to protect areas not being treated
60
In what ways are the medical personnel's exposure to ionising radiation minimised when doing medical scanning?
- 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
How can internal radiation therapy be used to treat a tumour?
- 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
How can external radiation therapy be used to treat a tumour?
- High energy X-rays/gamma rays fired at tumour
| - Carefully focussed on tumour but some damage to normal cells
63
Why might internal radiation therapy be used to treat a tumour over external radiation therapy?
- 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
Why might external radiation therapy be used to treat a tumour over internal radiation therapy?
- Sessions only last 10 mins
| - Patient doesn't emit radiation after
65
What are the benefits of using radiation in medical physics?
- Often cures
- Even if doesn't cure, reduces suffering of patient close to death (treatment reducing suffering w/out cure is palliative care)
66
What are the drawbacks of using radiation in medical physics?
- 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
What are the ethical arguments around testing new medical techniques on people?
- 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?
