Radioactivity & Particles Flashcards
(74 cards)
1
Q
Components of an atom
A
Protons, neutrons, electrons, electron shells
2
Q
Location, relative mass and relative charge of protons, neutrons and electrons
A
- protons = 1mu, +1, nucleus
- neutrons = 1mu, 0, nucleus
- electrons = 1/1836mu, electron shells
3
Q
How does an atom become an ion?
A
Electron loss or gain
4
Q
Which number is unique to each element?
A
Proton/atomic number
5
Q
Define atomic number
A
Number of protons in atom
6
Q
Define mass number
A
Total number of protons and neutrons
7
Q
Define isotope
A
An atom with the same number of protons but different number of neutrons
8
Q
What never changes in an isotope?
A
Atomic number
9
Q
Why do nuclei decay?
A
To become more stable, due to a variety of reasons :
- too many neutrons
- too big (too many protons + neutrons)
- too much energy
10
Q
What type of process is decay and why?
A
Decay is a random process ; we cannot predict which unstable nucleus in a radioactive isotope will decay or when that decay will occur
11
Q
What happens to unstable nuclei when they decay and why?
A
They give off radiation in the form of alpha, beta or gamma in order to release energy
12
Q
What makes radiation ionising?
A
They have enough energy to ionise atoms by stripping electrons off them when they interact
13
Q
Properties of alpha
A
- 2 protons + 2 neutrons
- charge = +2
- relative mass = 4
- ionising power = high bc they lose energy quickly + interact w/ atoms a lot due to size and energy
- penetrating power = low
- stopped/absorbed by = paper or card
- range in air = 2-3cm
14
Q
Properties of beta
A
- high energy electron
- charge = -1
- relative mass = 1/1836mu
- ionising power =moderate
- penetration = moderate
- stopped/absorbed by = thin aluminium foil
- range in air = around 1m
15
Q
Properties of gamma
A
- electromagnetic wave
- relative mass = almost 0
- charge = 0
- ionising power = low
- penetration = high
- stopped/absorbed by = thick lead + concrete but it’s hard to stop
- range in air = 1km+
16
Q
Alpha damaging and penetration
A
As it’s a big heavy particle, it loses a lot of its energy very quickly. This means that, whilst it does cause lots of damage, it cannot penetrate very far
17
Q
Beta damage and penetration
A
- small and excited electron that repels electrons off of their shells in atoms so has medium damage, less than alpha
- travels up to a meter in air so is more penetrating than alpha
18
Q
Gamma damage and penetration
A
- gamma is an electromagnetic wave (not a particle) with no charge and essentially no mass so doesn’t affect the atom as it passes through it
- it travels a few kilometres in air and isn’t easily stopped so it’s very penetrating
19
Q
Describe the investigation about penetration of different radiation
A
- measure background count for 5 mins using a GM tube
- place alpha near the GM tube and measure it’s counts for 5 mins
- test alpha penetration with paper, thin foil and lead
- repeat for each source of beta and gamma
- the GM tube reading should fall to background once paper and everything else is placed in front of alpha, aluminium foil and lead for beta and just lead for gamma
- gamma should partially drop when lead is placed as it is hard to stop
20
Q
What does the GM tube do?
A
Geiger-muller tube detects radiation
21
Q
What does the radioactive source do?
A
Emit radiation
22
Q
What does the counter do?
A
clicks and shows how many radioactive particles are detected each second by a GM tube. It measures counts per second (cps), not decays per second (becquerels).
23
Q
Define background radiation
A
Radiation that is ever present and cannot be removed
24
Q
What is the purpose of measuring over a long period of time?
A
As decay is random, a longer count period improve accuracy by reducing random error
25
Activity level is measured in…
Becquerels (Bq)
26
Range in air of alpha
A couple of centimetres
27
Range in air of beta
25cm-1m
28
Range in air of gamma
Km+
29
What happens to the nucleus in an alpha decay
2 protons + 2 neutrons are ejected from nucleus so atomic number decreases by 2 and mass number decreases by 4
30
What happens to the nucleus in a beta decay?
A high energy electron is ejected from the nucleus and a neutron has tuned into a proton , meaning that the atomic number increase by 1 and mass number stays the same
31
What happens to the nucleus when gamma passes through it?
Nothing - it is an electromagnetic wave not a particle so no particles are lost from the nucleus when gamma is emitted by it
32
What happens to the nucleus during a neutron decay?
Neutron(s) leave the nucleus meaning that the proton number is unchanged and the mass number decreases by however many neutrons are emitted
33
How is ionising radiation detected in a lab?
By a GM tube detects radiation
34
describe how the activity of a radioactive source can be tested using a Geiger-muller tube
- connect the Geiger-Müller (GM) tube to the counter
- use long-handled tongs to hold the radioactive source and increase distance between you and it
- measure background radiation first and subtract it from the total count
- place the source a set distance away from the GM tube and record counts for 60s and then divide the value by 60 to get activity in Bq
- take multiple measurements and take an average to reduce random errors + increase reliability + accuracy of results
35
What does the radiation badge do? How do they work?
- monitor exposure and warn if there are unsafe levels of radiation
- photographic film changes colour when exposed to different types of radiation
36
What percentage of background radiation sources are artificial and natural?
80% are natural and 20% are artificial
37
What are the sources of artificial background radiation?
- 17.5% medical
- 0.5% nuclear power + weapons testing
- 2% other
38
What are the sources of natural background radiation?
- 40% radon gas from the ground
- 15% buildings + ground
- 10% cosmic rays
- 15% humans + food + drink
39
What happens to number of undecayed nuclei of a radioactive source over time?
Decreases
40
What happens to decay rate over time?
Decreases
41
Definition of half life in terms of undecayed nuclei
The average amount of time taken for the number of undecayed nuclei in a radioactive sample to halve
42
Definition of half life in terms of activity levels rate
The average time taken for the activity rate (decays per second) to fall to half its original value
43
Irradiation
When something is exposed to the ionising radiation from a radioactive source. When the source is removed, the irradiation stops
44
Contamination
When the radioactive source gets into/ onto something so it’s being exposed continually
45
How do alpha emitter smoke detectors work?
- alpha emitter ionises air between charged plates that allow current to flow
- when detector senses current, the alarm doesn’t sound
- smoke enters the case and absorbs alpha = no ionsisation of air
- detector senses drop in current so the signal is sent for alarm to sound
46
Why is alpha suitable for smoke detectors? Why is a long HL required? Why can’t you dismantle an alpha emitter smoke detector?
- very ionising = effective ionisation of air + low penetrating power = can’t pass through the hard plastic case
- long HL = steady activity level + so doesn’t need replacement often
- dismantle = potential contamination by inhaling or ingesting accidentally
47
How is beta used in a foil factory?
If too much beta is detected, then the foil is too thin. If too little is detected, then it’s too thick
48
Why is beta good for foil factory usage? Why does it need a long HL?
- alpha has low penetration, so wouldn't penetrate foil regardless of thickness ∴ isn't useful
- gamma has vey high penetration, so would penetrate foil regardless of thickness ∴ isn't useful
- beta is suitable as it penetrates foil due to moderate penetration, but does this less as foil thickness increases ∴ allowing us to gauge the thickness of the foil and adjust roller pressure accordingly
49
How does gamma help in leaky pipe detection?
- gamma emitter is dissolved into water
- gamma radiation is detected on surface bc of high penetration
- higher levels of radiation = cracked pip as water is closer to surface
50
Why is gamma good for leaky pipe detection? Why does it need a short HL?
- weakly ionising = less danger posed + high penetration = more likely to pass through the ground
- short HL = quickly decays to a safe level by the time it reaches people’s homes
51
How is gamma used in sterilisation of surgical equipment?
- surgical equipment or food is sealed and remains sealed meaning that it is only irradiated
- gamma can kill unwanted bacteria and microorganisms
52
Why is gamma suitable for sterilisation of food and surgical equipment? Why is it safe to use these after?
- gamma can penetrate through package and kills bacteria
- Food and equipment has been irradiated not contaminated so it is not emitting radiation
53
How is gamma used in radiotherapy?
Gamma emitter is directed at cancerous cells repeatedly from multiple angles to ensure that healthy cells are not exposed
54
Why is gamma suitable for radiotherapy?
- it can penetrate through tissues to reach cancerous cells but is still not ionising so will not cause cell damage
- alpha would not penetrate and beta would be too ionising
55
What are the dangers of ionising radiation?
DNA is ionised which damages it and causes mutations and risks cancer. It can also kill cells
56
What are the three ways to limit exposure to ionising radiation?
- Increasing distance from radioactive source
- limiting exposure time and use of radioactivity detecting badges
- Shielding through the use of lead aprons for example
57
How does ionising radiation ionise a material?
Ionising radiation collides of atoms which become ionised because their electrons are stripped off causing the radiation to lose some of its energy
58
Why does alpha radiation have the strongest interaction with atoms in comparison to beta or gamma?
Alpha has the strongest interactions as it has the greatest charge of +2 in comparison to beta with minus one charge and gamma with no charge or or mass
59
Why is Alpha the most ionising?
Loses its energy at a faster rate as they lose more energy per interaction with other atoms in comparison to beta or Gamma
60
How are nuclear reactions used as a source of energy?
- thermal energy is released from nuclear reactions which can be used in power stations
- heat boils water into steam and the steam turns the turbine which turns the generator and generates electricity
61
what is nuclear fission?
the splitting of a large, unstable nucleus into two smaller nuclei
62
Describe the process of nuclear fission and how it can cause a chain reaction
- uranium-235 parent nucleus absorbs a neutron and becomes unstable
- it splits into two smaller daughter nuclei, releasing kinetic energy and 2–3 neutrons
- these emitted neutrons can be absorbed by other nearby uranium nuclei, causing more fission events
- each new fission releases more neutrons, which can trigger further reactions
- this repeating process is called a chain reaction
- if controlled (e.g. using control rods), the reaction is steady and safe (as in a nuclear reactor); if uncontrolled, it can become explosive (as in a nuclear bomb)
63
What happens when the control rods are removed from the reactor?
- control rods absorb neutrons to slow down or stop the chain reaction
- when a control rod is removed, fewer neutrons are absorbed
- this allows more neutrons to cause further fission reactions
- each fission produces fast-moving daughter nuclei and spare neutrons which carry kinetic energy
- kinetic energy of particles transferred to the surrounding material as heat
as the number of fission reactions increases, the total kinetic energy therefore the heat, increases rapidly
- causes exponential growth in energy output, which can become dangerous if uncontrolled
64
Nuclear fuel rod function
Rod containing radioactive material and allows spare neutrons to travel to neighbouring rods to continue fission events
65
Movable control rod function
- raised lowered into core to control the rate of chain reaction by absorbing excess neutrons without becoming unstable itself
- the lower in it is kept, the more neutrons absorbed, and the lesser the number of reactions occur
66
Graphite core/moderator
absorb some energy of neutrons so that they are more likely to cause fission in next rod
67
Coolant function
Transfer thermal energy to nearby boiler to drive turbines and generators to generate electricity
68
role of shielding around a nuclear reactor
- absorbs hazardous radiation, providing a safe environment around the reactor for workers
- made out of thick layers of steel and concrete that absorb the radioactive neutrons and daughter nuclei produced
69
what is nuclear fusion?
two light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy
70
why is it difficult to stop an area from being radioactive after it has been contaminated (e.g. nuclear bomb has been detonated)?
- long-half life = takes many years for activity of materials to fall to safe levels
- contamination means that it will continue to emit ionising radiation
- difficult to remove radioactive isotope as fallout range is often wide and quickly contaminates soil, water and buildings
- not possible to clean with humans as cell damage occurs quickly3
71
3 advantages and disadvantages of nuclear power stations
- A = no polluting gases produced
- A = very low fuel cost
- A = fuel is very energy dense
- D = waste is radioactive and hard to safely dispose of
- D = large-scale accidents can be catastrophic
- D = negative perception of nuclear power due to many accidents in past such as Chernobyl
72
explain the differences between nuclear fission and fusion
- fusion: Nuclei join together (e.g. hydrogen → helium). Occurs in stars. Produces a large amount of energy, stable larger nuclei, and requires very high temperatures and pressures.
- fission: Nuclei split (e.g. uranium → smaller nuclei). Occurs in nuclear reactors. Produces a large amount of energy, unstable smaller nuclei, and releases 2 or 3 neutrons. Requires thermal neutrons to induce fission.
73
what conditions does fusion require and why? where is the only known place where fusion is sustained?
- fusion can only be sustained in stars due to the high density and pressure they can maintain from the gravitational forces acting on their huge mass
- this forces particles closer together, causing them to heat up due to increased kinetic energy
- fusion requires very high heat and pressure to occur so that particles can overcome the very strong electrostatic repulsion to fuse together to produce larger particles
74
Cps versus Bq
- cps = counts per second - rate of detected radiation per second (1cps = 1 particle detected in one second)
- Bq = becquerels - the activity of the radioactive source (1Bq is one decay per second)
- CPS IS NOT EQUAL TO BQ UNLESS SYSTEM IS 100% EFFICIENT AND DETECTS EVERY DECAY
