Radioactivity Flashcards
(68 cards)
1
Q
What particles are in the nucleus of an atom?
A
Protons and neutrons
2
Q
What particles are in the shells of an atom?
A
Electrons
3
Q
What is the unit for frequency of decay?
A
Becquerel (Bq), 1 (Bq) for 1 decay/sec
4
Q
What is the unit for distance in radioactivity?
A
centimetre (cm), normally however is (m)
5
Q
What is the unit for time in radioactivity?
A
hour (h), minute (min) but normally (s)
6
Q
What is the atomic (proton) number?
A
The number of protons in the nucleus of an atom. (bottom number)
7
Q
What is the mass (nucleon) number?
A
The total number of protons and neutrons in the nucleus of an atom. (Top number)
8
Q
What is an isotope?
A
Atoms of the same element that have an equal number of protons but a different number of neutrons.
9
Q
What are the three types of ionising radiation?
A
Alpha (α), Beta (β) and Gamma (γ)
10
Q
What is the relative charge of a proton?
A
+1
11
Q
What is the relative charge of an electron?
A
-1
12
Q
What is the relative charge of a neutron?
A
0
13
Q
What is the relative mass of a proton?
A
1
14
Q
What is the relative mass of a neutron?
A
1
15
Q
What is the relative mass of an electron?
A
1/1835
16
Q
What is alpha radiation?
A
-a helium nucleus (2 protons, 2 electrons) emitted from the nucleus
17
Q
What is beta minus radiation?
A
-an electron emitted from the nucleus
18
Q
What is gamma radiation?
A
-a high energy electromagnetic wave
19
Q
What are the two states a nucleus can be in?
A
stable or unstable
20
Q
What does an unstable nucleus do to become more stable?
A
It tries to become more stable by ejecting mass (α, β, or n) or energy (γ).
21
Q
What do we call atoms with unstable nuclei?
A
Radioactive
22
Q
What do we call atoms with unstable nuclei?
A
Decay
23
Q
Is the process of decay predictable?
A
No, decay is random, and you cannot predict when it will happen.
24
Q
What is the nature of alpha particles?
A
-Very ionising
-Low penetration (stopped by paper)
25
What is the nature of beta particles?
-Moderate ionisation
-Moderate penetration (stopped by a few mm of aluminium)
26
What is the nature of gamma rays?
-Not very ionising
-Very penetrating (stopped by a few cm of lead)
27
PRACTICAL: investigate the penetration powers of different types of radiation using either radioactive sources or stimulations
1. With no radioactive sources present, measure the background count for 2 minutes using the Geiger-Muller (GM) tube, counter + stop clock.
2. Set up the source 2 cm from the GM tube.
3. Record the counts detected from the source with no absorbing materials present for 5 minutes.
4. Place the paper between the ionising radiation source and the GM tube + record the count detected from the source for 2 minutes.
5. Repeat step 4 with aluminium + lead and record these values.
Note: It is important to measure the count for at least 2 minutes to collect an average value because the decay of unstable atoms is random.
28
Alpha emission equation
top: 4
bottom: 2
29
Beta emission equation
top: 0
bottom: -1
30
Gamma emission equation
top: 0
bottom: 0
31
Neutron emission equation
top: 1
bottom: 0
32
What can detect ionising radiation?
Photographic film or a Geiger-Müller detector.
33
How does a Geiger-Müller (GM) tube work?
- detects when the gas inside the chamber is ionised by radiation.
- each click/beep represents an incident of radiation, which could be gamma, beta, or alpha radiation.
34
What happens to photographic film when exposed to ionising radiation?
The film darkens, showing the presence of radiation.
35
What is background radiation?
Ionising radiation that comes from natural and man-made sources on Earth and from space.
36
What are the sources of background radiation from food and drink?
Radioactive isotopes (like K-40) decay over time.
37
How does nuclear power contribute to background radiation?
From power stations and bombs.
38
What medical activities contribute to background radiation?
X-rays, gamma-ray scans, cancer treatments, and sterilisation.
39
How does radon gas contribute to background radiation?
Produced by rocks containing small amounts of uranium.
40
How do cosmic rays contribute to background radiation?
Radiation from space, produced in stars (including the sun)
41
What happens to the activity of a radioactive source over time?
The activity of a radioactive source decreases over a period of time.
42
Half-life
-the time taken for half the undecayed nuclei to decay
-the time take for the activity to half its original value
43
How do you calculate half-life?
Half-life = time taken for activity to half its original value.
To find the number of undecayed nuclei in a sample:
1. State the start number
2. Go forward a half life, halving the sample size
3. Repeat until the target time has passed
44
Irradiation
-When someone is exposed to alpha/beta/gamma from a nearby source
-Once the person moves away irradation stops
45
Contamination
-When someone gets particles of a radioactive source on their person or inside their body
-They will continue to be exposed to radiation until the material has all decayed or it has been removed
46
What are the uses of radioactivity in industry?
-Smoke detectors
-Thickness monitoring
47
What are the uses of radioactivity in medicine?
-Sterilisation of equipment
-Diagnosis and treatment
48
Industrial use: Smoke detectors
- Use long half-life alpha emitters.
- Alpha particles create a current in the alarm.
- Smoke absorbs alpha particles, dropping the current and triggering the alarm.
49
Industrial use: Thickness monitoring
- Use long half-life beta emitters.
- Source & receiver placed on either side of a metal sheet during production.
- Changes in detected beta particles indicate thickness variation, prompting adjustments.
50
Medical use: Sterilisation of Equipment
- Gamma emitters kill bacteria or parasites.
- Can sterilise through protective packaging to prevent contamination.
51
Medical use: Diagnosis and treatment
Short half-life gamma emitters (e.g., technetium-99m) act as tracers.
-> Concentrate in specific body parts for diagnosis.
-> Half-life is balanced to allow procedures but avoid prolonged radioactivity.
Gamma emitters (e.g., cobalt-60) deliver high doses to destroy tumours.
52
What are the dangers of ionising radiations?
- Ions in DNA can cause
- Can result in cell damage & death (radiation sickness & radiation burns)
- Exposure to radiation can destroy living cell membranes by ionisation
- Causing the cells to die, or damage the DNA which causes cell mutations that could lead to cancer
53
What are the safety measures for when exposed to radiation?
- Minimising the time of exposure to radiation, keeping as big as a distance from the source as possible & using shielding against radiation (such as protective clothing made from dense materials such as lead)
- Radioactive waste from nuclear reactors must be disposed of carefully, usually by burying it in sealed drums deep underground & remotely handling it after it has been thoroughly cooled
54
What is radioactive decay?
The process in which an unstable nucleus loses energy by emitting ionising particles & radiation
55
Nuclear fission
- In nuclear fission, large nuclei break up to form smaller nuclei & release energy
- Fission reactions are used in the nuclear power stations & submarines
56
Nuclear fusion
- In nuclear fusion, 2 small nuclei fuse to form a larger nucleus
- Fusion reactions release energy inside stars
- It is currently unable to process on earth
57
How can a nucleus of U-235 be split by the process of fission?
Heavy nuclei (like Uranium-235) can be fissioned:
-> An incident neutron collided with the parent nucleus making it unstable
-> The nucleus splits (fission)
-> Energy is releases as kinetic energy of the fission products
58
59
Describe how a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei
- Neutrons released in fission can be absorbed by other nuclei
- These nuclei split (fission)
- Fission releases more neutrons
- Neutrons released in fission can be absorbed by other nuclei.. and so on.
- This is called a chain reaction
60
Neutrons in fission
- Neutrons are released in a chain reaction
- Slower neutrons are needed for fission
61
What if the role played by a moderator in the fission process
Graphite core around the reactor is a moderator:
- Neutrons in the moderator are slowed down
- Increasing the rate of fission
62
What if the role played by the control rods in the fission process?
- Control rods absorb neutrons
- Control rods can be moved in and out of the reactor
- This makes more or fewer neutrons available
- Increases or decreases the rate of fission
63
What is the told me of shielding around a nuclear reactor?
- Reactor vessels are made of steel & surrounded by a layer of concrete about 5 metres thick
- This prevents any radiation escaping, even neutrons
64
Explain the difference between nuclear fusion and nuclear fission
Fusion is the process of small nuclei being forced together to form a heavier nucleus.
- This is the energy source for stars.
- Fusion cannot happen at low temperatures and pressures.
- Fusion is very difficult to make a practical and economic fusion power station.
Fission is the process of a nucleus splitting into two smaller nuclei after absorbing neutrons, which releases more neutrons.
- This is the energy source for nuclear power stations.
- Fission can happen at low temperatures and pressures.
65
What is nuclear fusion?
1. Fusion is when 2 smaller particles join to form a larger one.
2. More massive particles are less massive than the sum of the smaller parts.
3. This mass becomes energy, which is released in fusion.
4. Fusion is the energy source for stars.
66
Why does nuclear fusion not happen at low temperatures & pressures?
Electrostatic repulsion of protons
- Positive charges will repel each other- this called electrostatic repulsion
- The faster the particles are, the closer they will get to each other before repelling
67
What conditions does fusion need to occur?
- Very high pressure
- Very high temperature
- Very high kinetic energy
-> Needed to overcome electrostatic repulsion
-> The more these increase the rate of collisions, which increases the rate of fusion
68
Why is it important to measure the background count for at least 2 mins when investigating the penetration powers of different types of radiation?
It is important to measure the count for at least 2 minutes to collect an average value because the decay of unstable atoms is random.
