Nuclear physics Flashcards
(112 cards)
1
Q
What are atoms and what do they consist of?
A
Atoms are the building blocks of all matter
- They consist of a positively charged nucleus and negatively charged electrons in orbit around the nucleus
2
Q
What is an ion?
A
An ion is anelectricallychargedatom or group of atoms formed by the loss or gain of electrons.
3
Q
How can atoms form positive and negative ions?
A
Atoms can form positive ions when they lose an electron and form negative ions when they gain an electron
4
Q
What is Rutherford’s experiment?
A
They directed a beam of alpha particles (He2+ ions) at a thin gold foil suspended in a vacuum, expecting the alpha particles totravel throughthe gold foil and maybe change direction a small amount.
5
Q
What has the Rutherford model found evidence of?
A
- a verysmall nucleussurrounded bymostly empty space
- anucleuscontaining most of themassof the atom
- a nucleus that ispositively charged
6
Q
What are the results of Rutherford’s experiment?
A
- Most of the alpha particlespassed straight throughthe foil because the atom is mostlyempty space(A)
- Some of the alpha particlesdeflected by small anglesbut continued through the foil because the positive nucleus (which contains most of the mass)repelsthe positive α-particles (B)
- A few of the alpha particlesdeflected straight back from the gold foil because the nucleus is extremely small and dense
7
Q
Why is the gold foil suspended in a vacuum in Rutherford’s experiment?
A
The gold foil was suspended in a vacuum because alpha particles have a very short range in air and would quickly lose energy and be scattered by air molecules. Using a vacuum allows the alpha molecules to avoid collision with air molecules
8
Q
What is the nucleus composed of?
A
A nucleus is composed of:
- positively chargedprotons (+1)
- neutrally chargedneutrons (0)
Hence a nucleus has anoverall positivecharge
🌟 Protons and neutrons are the same mass while electrons (-1) are 1/1800 the mass of a proton
9
Q
What is the proton number?
A
Proton number is the number of protons in an atom Z
10
Q
What is the nucleon number?
A
Nucleon number is the total number of particles in the nucleus (neutrons + protons) A
11
Q
What is nuclide notation?
A
Atomic symbols are written in a specific notation calledZXAornuclidenotation
- The top number A represents thenucleonnumber
- The lower number Z represents theprotonnumber
12
Q
What are isotopes?
A
Isotopesare atoms of the same element that have an equal number of protons but a different number ofneutrons (same proton number, different nucleon number). An element may have more than one isotope
13
Q
Why are isotopes unstable?
A
- Isotopes tend to be more unstable due to their imbalance of protons and neutrons, meaning they’re more likely to decay
- Isotopes occur naturally, but some are rarer than others
14
Q
Relationship between proton number and relative charge
A
Nuclear charge = number of protons in the nucleus x relative charge of a proton
Ex: Atomic number of carbon is 6 and relative charge of proton is +1. The nuclear charge of carbon is +6
15
Q
Relationship between the nucleon number and the relative mass
A
Relative mass of an atom = number of protons and neutrons in the nucleus x relative charge of a proton or a neutron
Ex: An element of carbon has a nucleon number of 12. So the relative mass of carbon is 12 × 1 = 12
16
Q
Nuclear fission definition
A
Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei and releasing thermal energy
17
Q
Where does nuclear fission happen and what isotopes are used?
A
- Nuclear fission happens in the nuclear power station and nuclear bomb
- Isotopes of uranium (235 mainly) and plutonium (239 mainly) both undergo fission and are used as fuels in nuclear power stations
18
Q
Process of nuclear fission
A
- A heavy nucleus absorbs a neutron
- The nucleus becomes highly unstable
- The nucleus splits into two smaller nuclei called daughter nuclei and two or three neutrons are released
- The splitting releases a lot of energy in the form of gamma radiation and kinetic energy of the daughter nuclei
- A chain reaction is started where the emitted electrons go on to split other nuclei and so on
19
Q
What happens during nuclear fission?
A
During a fission reaction, energy is transferred fromnuclear energystore of the parent nucleus to the kinetic energy store of the reactants
20
Q
What happens to the mass during nuclear fission?
A
The mass of the products is slightly less than the mass of the original nucleus. This lost mass is converted into energy. Einstein’s famous equation is used for this: E=mc^2 (E=energy, m=mass, c=speed of light).
21
Q
How do nuclear power plants control nuclear fission?
A
Reactors use controlled chain reactions to produce energy, ensuring a stable and sustained release of power. To regulate the reaction, control rods are employed; these rods absorb neutrons, thereby controlling the rate of fission. Additionally, graphite serves as a moderator to slow down neutrons, which in turn helps to sustain the chain reaction by increasing the likelihood of fission events in the fuel without providing an extreme reaction
22
Q
What is nuclear fusion?
A
Nuclear fusion is the combining of two light nuclei to form a heavier nucleus and releasing thermal energy
23
Q
What is nuclear fusion used in?
A
Nuclear fusion is used to create energy in the stars and sun. In most stars, hydrogen nuclei (light nuclei) are fused together to form a helium nucleus (heavier nucleus) and massive amounts ofenergyis produced
24
Q
Why is nuclear fusion hard to reproduce on earth?
A
This process requires extremely high temperatures and pressures to maintain which is why it has been proven hard to reproduce on Earth
25
Process of nuclear fusion
1. Process begins with two light neutrons
2. For fusion to occur, the nuclei must come very close to each other, which requires extremely high temperatures (on the order of millions of degrees Celsius) and high pressures to overcome the electrostatic repulsion between the positively charged nuclei. At such high temperatures, the kinetic energy of the nuclei is sufficient to overcome the electrostatic repulsion (Coulomb barrier) between them, allowing them to come close enough for the strong nuclear force to take over and bind them together.
3. When the nuclei combine, they form a heavier nucleus and often release a neutron.
4. The mass of the resulting nucleus and the neutron is slightly less than the total mass of the original nuclei. This mass difference is converted into energy according to Einstein's equation: E=mc^2. The energy is released in the form of kinetic energy of the products and as radiation.
5. The products of the nuclei can also fuse together to create the heavier nucleus resulting in a chain reaction
26
What is nuclear fission and fusion?
Nuclear fission & fusion are nuclear reactions that change the nucleus of an atom to produce high amounts of energy from the energy stored in the nucleus of an atom
27
What is radiation?
Radiation is the emission of energy as electromagnetic waves or as moving subatomic particles: alpha particles, beta particles and gamma rays also called nuclear radiations
28
What is background radiation?
Background radiation is a small amount of radiation around us all the time because of radioactive materials in the environment
29
What are the two types of background radiation?
- Natural sources from radioactive elements that have always existed on Earth and in outer space (rocks, soil, air, building materials, food and drink, space)
- Man-made sources from human activity that adds to the amount of radiation humans are exposed to on Earth (medical equipment, waste from power stations)
30
What are the sources of background radiation?
Radon gas (50%)
Rocks and building materials (15%)
Medical eg X-rays (13%)
Food (11%)
Cosmic rays (10%)
Other (1%)
31
Radon gas (why contribute to background radiation)
- Radon gas is an alpha emitter
- Radon gas is particularly dangerous if it is inhaled into the lungs in large quantities
- The gas is tasteless, colourless and odourless, but it is not generally a health issue unless levels are significantly high
32
Rocks and building materials (why contribute to background radiation)
- Natural radioactivity can be found in building materials, including decorative rocks, stone and brick
- Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground. Uranium decays into radon gas
33
Radioactive material in food and drink (why contribute to background radiation)
- Naturally occurring radioactive elements can get into food and water since they are in contact with rocks and soil containing these elements
- Some foods contain higher amounts such as potassium-40 in bananas. However, the amount of radioactive material is minuscule and is not a cause for concern
34
Cosmic rays from space (why contribute to background radiation)
- The sun emits an enormous number of protons every second. Some of these enter the Earth’s atmosphere at high speeds, when they collide with molecules in the air, this leads to the production of gamma radiation
- Other sources of cosmic rays are supernovae and other high-energy cosmic events
35
Carbon-14 in biological material (why contribute to background radiation)
- All organic matter contains a tiny amount of carbon-14
- Living plants and animals constantly replace the supply of carbon in their systems hence the amount of carbon-14 in the system stays almost constant
36
What is ionising effect?
When unstable nuclei decay they give out ionising radiation. It causes atoms to gain or lost electric charge, forming ions, this is called an ionising effect
37
How is ionising nuclear radiation measured?
Ionising nuclear radiation can be measured using a detector connected to a counter. The detector uses count rate measured in counts/s or counts/minute
38
What is count rate and how does distance affect it?
- The count rate is the number of decays per second
- The count rate decreases the further the detector is from the source. This is because the radiation becomes more spread out the further away it is from the source
39
How can you determine a correct count rate?
Measurements of background radiation are used to determine a corrected count rate. This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present
40
What is the Geiger-muller tube?
The Geiger-Müller tube is the most common device used to measure and detect the count rate of radiation. Radiation entering a GM tube creates argon ions and electrons, which then causes more ionisation.
41
What happens every time the Geiger-muller tube absorbs radiation?
Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
- This makes a clicking sound and it displays the count rate on a screen
- The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing
42
What are other radiation detectors other than the Geiger-muller tube?
- Photographic film (often used in badges)
- Ionisation chambers
- Scintillation counters
- Spark counters
43
What is the emission from radiation from a nucleus?
The emission of radiation from a nucleus is spontaneous and random in direction
44
What does the random process of radioactive decay mean?
- There is an equal probability of any nucleus decaying so it cannot be known which particular nucleus will decay next
- It cannot be known at what time a particular nucleus will decay
- The rate of decay is unaffected by the surrounding conditions
- It is only possible to estimate the probability of a nuclei decaying in a given time period
45
Why are atomic nuclei unstable?
This is because of an imbalance in the forces in between the particles of the nucleus.
Either because the nucleus is too large or has too many protons to neutron ratio
46
Why is a nucleus that has too many protons or neutrons unstable?
The stability of a nucleus depends significantly on the neutron-to-proton ratio. Nuclei with a n/p ratio that is too high or too low tend to be unstable. If there are too many protons it causes the nucleus to be unstable due to the increased repulsive forces among protons (which are all positively charged) without sufficient neutrons to mediate these forces through the strong nuclear force.
47
Why is a large nucleus unstable?
As nuclei get larger (more protons and neutrons), the electrostatic repulsion between protons becomes more significant. This repulsive force can outweigh the attractive nuclear force holding the nucleus together, leading to instability. The forces keeping the protons and neutrons together in the nucleus will be weaker
48
How can unstable nuclei become more stable?
Unstable nuclei can emit radiation to become more stable. Radiation can be in the form of a high-energy particle or wave
49
What is alpha radiation?
When a helium nucleus is emitted. α2+ or He2+ Large particles
50
Alpha relative charge and mass compared to a proton
Charge: +2
Mass: 4
51
Speed of alpha particle
3x10^7 m/s (1/10 the speed of light)
52
What is ionising effect of alpha?
High. This is because it is heavy mass, low speed and high charge. +2 charge makes them highly ionizing. The strong electric field around the alpha particles attracts or repels electrons from atoms, causing ionization. High kinetic energy also contributes to their strong ionizing ability. They can cause significant ionization within a short range.
53
What is the relative penetrating effect of alpha?
Very short range - Can be stopped by a sheet of paper, skin or air around 5cm thick
54
What is alpha's deflection in electric and magnetic fields?
Slowly deflect towards the negative plate. Alpha particles are heavier than the other particles meaning that they deflect less even though it has higher charge, mass has a stronger influence than charge. In magnetic fields alpha particles follow the rule of positive conventional current so Fleming’s left-hand rule is used with the middle finger pointing in the direction of alpha particles
55
What is beta radiation?
When a high-speed electron is emitted from the nucleus. e-1 or β-1
56
Beta relative charge and mass compared to a proton
Charge: -1
Mass: 1/1800
57
Speed of beta particle
2.7x10^8 m/s (9/10 speed of light)
58
What is ionising effect of beta?
Moderate because it has low mass, higher speed and lower charge than alpha. Moderately ionizing because their lower kinetic energy and lower charge compared to alpha particles mean they ionize fewer atoms per unit distance traveled.
59
What is the relative penetrating effect of beta?
Moderate range (greater than alpha)
- Stopped by a few millimeters of aluminium or other metal around 5mm or by a few meters of air. This is because it has less ionising effect than alpha
60
What is beta's deflection in electric and magnetic fields?
The negative beta particles are lighter and quickly deflect towards the positive plate. Beta particles are shown in the direction opposite to the middle finger, as it represents electron flow, opposite of conventional current
61
What is gamma radiation?
Electromagnetic radiation/photons with very high frequency. γ
62
Relative charge and mass of gamma
Charge: 0
Mass: 0
63
Speed of gamma
3x10^8 m/s (speed of light)
64
What is ionising effect of gamma?
Low because it has no mass, no charge, and high speed. Due to their lack of mass and charge, they interact less frequently with matter, but they can penetrate deeper into materials.
65
Relative penetrating effect of gamma
High, very long range - Reduced by many centimeters of lead or thick concrete. They are only partially stopped by thick lead. This is because it has the weakest ionising effect compared to alpha and beta
66
What is gamma's deflection in electric and magnetic fields?
Not deflected by electric and magnetic fields, travels straight
67
What is radioactive decay?
Radioactive decay is a change in an unstable nucleus that can result in the emission of α-particles or β-particles and/or γ-radiation.
- This changes the nucleus into that of a different element until a stable element is formed. These changes are spontaneous and random
68
What is the initial nucleus and new nucleus called in radioactive decay?
The initial nucleus is often called the parent nucleus. The nucleus of the new element produced is often called the daughter nucleus. The daughter nucleus is a new element because it has a different proton and/or nucleon number than the original parent nucleus
69
Formula for radioactive decay
N=No(1/2)^n (new amount of nuclei=old amount of nuclei x 1/2 to the power of number of half lives)
70
What is alpha decay?
A heavy unstable nucleus breaks apart to release an alpha particle.
71
Why does alpha decay occur?
- This is often done when there are too many protons in the nucleus. Since like charges repel there will be too much repulsion
- To reduce the repulsion a helium nucleus is emitted. By emitting an alpha particle, the nucleus often becomes more stable because the heavy and large nucleus is reduced in size, lowering the repulsive forces among protons.
72
What is beta decay?
In beta decay, a neutron is converted into a proton and an electron. The proton remains in the nucleus while the electron is emitted as a beta particle
73
What does a neutron become when it splits?
neutron → proton + electron
74
What happens to the nuclide notation when alpha decay occurs?
When an atom undergoes α-decay, its nucleon number decreases by 4 and its proton number decreases by 2
75
What happens to the nuclide notation when beta decay occurs?
The emission increases the atomic number by 1 while the mass number remains unchanged
76
Why does beta decay occur?
This decay reduces the number of excess neutrons, moving the nucleus towards a more stable neutron-to-proton ratio increasing the stability of the nucleus
77
What is gamma decay?
In gamma emission, the nucleus releases energy in the form of gamma rays (high-energy photons) without changing the number of protons or neutrons.
78
Why does gamma decay occur?
- Gamma emission typically occurs after alpha or beta decay when the daughter nucleus is in an excited state and releases excess energy to reach a more stable state.
- This process makes the nucleus less energetic but does not change its structure because gamma radiation has no mass or charge
79
What is half life?
Half-life is the time taken for half the nuclei of that isotope in any sample to decay. It is a measure of the rate at which a radioactive substance decays.
80
Is the half life constant for specific isotopes?
The half-life is constant for a particular isotope
81
What is a decay curve?
A decay curve plots the activity of a sample over time, showing the exponential decrease in activity.
- The activity decreases by half in each half-life period from the previous half-life period.
82
What happens in a smoke detector?
Alpha particles are used in smoke detectors. The alpha radiation ionises the air within the detector, creating electrons and protons. These are attracted to the charged plates which causes the current to flow. The detector senses this current. When smoke enters the detector, it blocks the alpha radiation which reduces the ionising. This causes the current to decrease and if the current drops below a certain threshold it is interpreted as an indication of smoke and the alarm is triggered.
83
Why are alpha particles used in smoke detector?
- Alpha particles are used because they have low penetration and are easily absorbed by smoke particles. This makes them ideal for smoke detection because when smoke enters the detector, it disrupts the flow of alpha particles, triggering the alarm. Additionally, alpha particles are not highly penetrating and can be safely contained within the alarm device, posing minimal risk to humans.
- If beta and gamma were used, they would just pass through the smoke and the alarm wouldn’t go off
84
What isotopes are used in smoke detectors?
Isotopes with a long half-life are used for smoke detectors like for example Americium-241 so that they provide a long-lasting source for smoke alarms without requiring frequent replacement
85
Why is food irradiated?
Food can be irradiated to kill any microorganisms that are present on it. This makes the food last longer and reduces the risk of food-borne infections.
86
Why are gamma rays used for food irragiation and what isotopes are used?
- Gamma rays are used for this because gamma rays have high penetration power, allowing them to pass through food and kill bacteria, viruses, and parasites without making the food radioactive
- Isotopes with a relatively long half life are used to provide a stable and long-lasting source of gamma radiation, like cobalt-60
87
Why are gamma rays used for medical equipment steralisation?
Gamma radiation is widely used to sterilise medical equipment. Gamma rays can penetrate deeply into medical equipment, ensuring thorough sterilization of both the surfaces and internal components. It is also effective at killing all forms of microorganisms, including bacteria, viruses, and spores
88
What isotopes are used for medical equipment steralisation?
Isotopes with a relatively long half life are used to provide a stable and long-lasting source of gamma radiation, like cobalt-60 and cesium-137
89
Measuring and controlling thickness of items what radiation is used?
Beta radiation is most commonly used to measure the thickness of materials because it will be partially absorbed by most materials
- Alpha particles are used for thinner materials because they have a lower penetrating power and are absorbed by a thin sheet of aluminium
- Gamma radiation can be used for very thick materials because they have a higher penetrating power and are mostly absorbed by thick pieces of lead.
This works because if the material gets thicker more particles will be absorbed, meaning less will get through
90
What isotopes are used for measuring and controlling thickness of items?
Radiation used to measure the thickness of materials has a half-life of many years (10-20 years) so that the count rate remains relatively constant each day. Ex: Strontium-90
91
How are radioactive isotopes used as tracers?
Radioactive isotopes are used as tracers to help doctors identify diseased organs. The tracer is taken orally or injected. Its journey around the body can then be traced using a gamma camera to detect the emissions from a tracer to diagnose cancer and locate the tumour.
92
Why are gamma rays used for diagnosive imaging and why are isotopes with short half lives used?
- Gamma rays are used in diagnostic imaging (e.g., PET scans) to detect cancerous cells due to their ability to provide clear images of internal structures
- A short half-life is important for this because isotopes with short half-lives decay quickly, which means they remain radioactive for a shorter period. This minimizes the radiation exposure to the patient, reducing the potential for harmful effects. Ex: Technetium-99
93
How are radioactive isotopes used in radiotherapy?
Radiotherapy is the name given to the treatment of cancer using radiation. Radiation can kill living cells but some cells, such as bacteria and cancer cells, are more susceptible to radiation than others. Beams of gamma rays are directed at the cancerous tumour then gamma rays cause ionization within the cells, leading to damage in the DNA of the cancer cells. This damage prevents the cancer cells from dividing and growing, ultimately causing them to die.
94
Why are gamma rays used for radiotherapy?
Gamma rays are chosen for cancer treatment because they can penetrate the body, reaching the tumour. The beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour.
95
What isotopes are used for radiotherapy?
A moderately long half-life is used for this because a long half-life allows for a continuous and sustained release of radiation over a period of time, allowing for precise planning and consistent treatment dosages. Long-lived isotopes also reduce the need for frequent replacement of the radioactive sources, which can be cost-effective and logistically simpler.
96
How can radiation be dangerous?
Exposure to small doses of radiation is not damaging, but large doses are harmful to health. α-particles are less dangerous unless the source is ingested or inhaled. β- and γ-radiation can cause radiation burns, eye cataracts, and cancer
97
Effects of ionising nuclear radiations on living things
- Cell death
- Mutations
- Cancer
If the atoms that make up a DNA strand are ionised then the DNA strand can be damaged. If the DNA is damaged then the cell may die, or the DNA may be mutated when it reforms and if a mutated cell replicates itself then a tumour may develop (cause of cancer)
98
Symptoms of acute radiation exposure
- It can cause skin burns, similar to severe sunburn
- Radiation can reduce the amount of white blood cells in the body, making a person more susceptible to infections by lowering their immune system
99
Methods to minimise the risks associated with handling radioactive sources
- tore the sources in lead-lined boxes and keep them at a distance from people
- Minimise the amount of time you handle sources and return them to their boxes as soon as you have finished using them
- During use, keep yourself (and others) as far from the sources as possible.
- When handling the sources do so at arm’s length, using a pair of tongs
100
How is radioactive waste disposed of?
If an isotope has a long half-life then a sample of it will decay slowly which presents a risk of contamination for a much longer time. Radioactive waste with a long half life is buried underground to prevent it from being released into the environment
101
How radioactive materials are transported?
- Radioactive materials such as used nuclear fuel are transported in special containers called casks
- These casks can withstand extreme conditions such as fire, cold and being submerged in water
102
Safety precautions for all ionising radiation include:
- reducing exposure time
- increasing the distance between the source and living tissue
- using shielding to absorb radiation
103
Why does limiting the amount of time spent near a radioactive source reduce the amount of radiation dose received?
the amount of radiation exposure is directly proportional to the duration of exposure
- The amount of radiation received by a person is called the dose and is measured in sieverts (Sv)
- One sievert is a very big dose of radiation
- It would cause acute radiation poisoning
104
Why does increasing the distance of the radiation greatly reduce the size of the dose received?
if you are far from the source, your exposure would be much lower since the intensity of radiation decreases the further you are from the source of the radiation
105
Ways to increase the distance from the radiation
- Using tongs instead of your hand when handling a radioactive source can help with this
- Constructing nuclear power plants in remote areas increases their distance from people if there is a problem and burying nuclear waste far from places where people live also increases the distance from people
106
What is radiation shielding?
Radiation shielding is a barrier placed between a radiation source and a person or area to protect them. The purpose of shielding is to limit exposure to radiation at a certain location or time since barriers absorb the energy from radioactive sources.
107
What are radiation barriers made of?
Barriers are normally made of lead, water or concrete to stop gamma radiation
108
What happens when x-rays are taken to protect the radiologist?
the area around where the image is needed is shielded and the radiologist stands behind a barrier or leaves the room
109
What is used to detect leaks in pipes?
Gamma radiation. Gamma radiation is used because it's the most penetrating type of radiation and can easily pass through materials. Therefore, if the isotope emits gamma radiation, it will be able to penetrate the ground to surface for several meters, allowing the technician to detect higher radioactive count rates above the pipe where the leak is located
110
α-particles are more strongly ionising and have a shorter range in air than γ-rays.
Use your knowledge of the nature of these radiations to explain these differences
Alpha is a helium ion and is more ionising because it has a greater charge. α loses some energy with each collision causing the range to be short while γ is not charged and γ has few (successful) collisions (with electrons) so not very ionising/range
long
111
A radioactive source that emits α-particles is placed on the laboratory bench and the source
is gradually moved closer to the detector.
At first, the detector continues to register a low count rate sometimes slightly less than the
count rate registered without the source. The count rate suddenly increases to a very high
value when the source is very close to the detector.
Explain these changes in the count rate.
any three from:
low count rate due to background radiation only
slightly less reading due to random nature of radioactivity
very high reading due to α-particles OR emission from source
sudden increase of count rate at limit of range of α-particles
112
The technician sets up the same equipment in the same way every year. He notices
that the count rate registered by the detector every year is slightly smaller than it
was the previous year.
Suggest why this is so.
Radioactive decay of the source which limits the radiation the detector can detect. This decrease follows a predictable pattern based on the substance's half-life.
