SP6: Radioactivity Flashcards

1
Q

SP6a
1) Describe the structure of an atom (in terms of nucleus and electrons).
2) State where most of the mass of an atom is found.
3) State the sizes of atoms and small molecules.

A

1) The protons and neutrons make up a central nucleus and the electrons orbit the nucleus.
2) Most of the mass is found in the nucleus.
3) The typical size of an atom is 1 x 10 to the power of -10 metres or 0.1 nanometres (nm)

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2
Q

SP6a
Describe how and why our model of the atom has changed over time, including the plum pudding model and the Rutherford’s experiment.

A

Democritus: he stated that atoms are particles that cannot be broken down.
John Dalton: he state that atoms were different types of solid spheres.
JJ Thompson: he created the plum pudding model. The atom consisted of a positive ball with negative electrons scattered inside it.
Ernest Rutherford: He did an experiment to test the plum pudding model. He directed a beam of alpha particles at a very thin gold leaf suspended in a vacuum. Most of the alpha particles did pass straight through the foil, but a small number of alpha particles were deflected by large angles as they passed through the foil, and a very small number of alpha particles came straight back off the foil.
Rutherford had discovered the nuclear atom, a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.
Neil Bohr: he discovered that electrons orbited the nucleus on electron shells.

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3
Q

SP6b
1) State what is meant by an isotope.
2) Represent isotopes using symbols.
3) Explain how atoms of different elements are different (in terms of numbers of electrons and protons).

A

1) Isotopes are forms of an element that have the same number of protons but different numbers of neutrons.
2) On atomic symbols the mass number (big/ top number) will change while the atomic number (small/ bottom number) remains the same.
3) Atoms of different elements have different numbers of protons, electrons and neutrons. Atoms of the same element will have the same number of protons and electrons but different neutrons.

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4
Q

SP6b
1) Recall the charges and relative masses of the three subatomic particles.
2) Explain why all atoms have no overall charge.
3) What is a nucleon number?

A

1) Protons: +1 charge and relative mass of 1
Neutrons: 0 charge and relative mass of 1
Electrons: -1 charge and relative mass of almost 0
2) Every atom has no overall charge (neutral). This is because they contain equal numbers of positive protons and negative electrons. These opposite charges cancel each other out making the atom neutral.
3) A nucleon number is another name for the mass number of an atom.

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5
Q

SP6c
1) Describe where electrons are found inside atoms (in terms of shells).
2) Describe when electrons can change orbit.
3) Recall what an ion is.

A

1) Electrons in atoms occupy energy levels, also called electron shells, outside the nucleus. Different shells can hold different maximum numbers of electrons. The electrons in an atom occupy the lowest available energy level first. This is the shell nearest the nucleus.
2) An electron can move into a high energy level and further away from the nucleus by absorbing electromagnetic radiation. An electron can move into a lower energy level and closer to the nucleus by emitting electromagnetic radiation.
3) An ion is an atom or group of atoms with a positive or negative charge, that has lost or gained electrons in order to have a full outer shell.

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6
Q

SP6c
1) Describe how ionisation occurs.
2) Explain the Bohr model of the atom, and explain the energy levels of the orbits

A

1) The electrical charge of an atom can be changed by ionisation. If an atom loses electrons, then it will turn into a positive ion, and if an atom gains electrons will turn into a negative ions.
2) The Bohr model of an atom has a small, positively charged central nucleus and electrons orbiting in at specific fixed distances from the nucleus. As you get further away from the nucleus, the energy levels (electrons shell orbits) get closer together. So electrons falling to an energy level closer to the nucleus will have a greater change in energy than one that is further away from the nucleus. This means that they release electromagnetic radiation with a higher energy, and so a higher frequency is released when an electron falls to the energy level closer to the nucleus.

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7
Q

SP6d
1) Explain what background radiation is.
2) Describe how radiation measurements need to be corrected for background radiation.
3) List some sources of background radiation.
4) How can a graph be used to estimate the count rate of the background radiation?

A

1) Background radiation is ionising radiation that is always in the environment. It comes from space and naturally radioactive substances in the environment.
2) When scientist measure the radioactivity of a source, they need to measure the background radiation first by taking several reading and finding the mean. This mean value is then subtracted from the measurement of the radioactive source.
3) Sources of background radiation include:
- Radon gas: produced by rocks that contain small amount of uranium.
- Cosmic rays: high-energy, charged particles that streams out of stars
- Hospital treatments (eg. X-rays and cancer treatments)
- Fallout from nuclear weapons (Fallout is the radioactive particles that fall to earth as a result of a nuclear explosion.)
4) The count rate of background radiation is when the count rate on the graph plateaus.

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8
Q

SP6d
1) Describe how photographic film can be used to detect radioactivity.
2) Describe how a Geiger-Müller tube works
3) Describe how the amount of radioactivity can be measured (in terms of the darkness of photographic film or by attaching a counter to a GM tube).

A

1) Radioactivity can be measured using photographic film, which becomes darker and darker as more radiation reaches it. However, the film has to be developed in order to measure the amount of radiation (the dose).
2) The radioactivity of a source can be measured using a Geiger-Müller (GM) tube. Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow.
3) A GM tube can be connected to a counter, to count the pulses of current, or the GM tube may give a click each time radiation is detected. The count rate is the number of clicks per second or minute.
The darker the photographic film, the more radiation it has been exposed to.

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9
Q

SP6e
1) Recall the relative masses and relative electric charges of protons, neutrons, electrons and positrons.
2) List five types of radiation that are emitted in random processes from unstable nuclei, and what type of radiation is it?
3) State the three types of ionising radiation emitted by radioactive decay

A

1) Proton: mass = 1, electrical charge = +1
Neutron: mass = 1, electrical charge = 0
Electron: mass = almost 0, electrical charge = -1
Positron: mass = almost 0, electrical charge = +1
2) Alpha, beta +, beta -, gamma, neutron. The five types of radiation are ionising radiation.
3) Alpha, beta and gamma radiation

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10
Q

SP6e
1) Describe what alpha and beta particles are
2) Describe the nature of gamma radiation

A

1) An alpha particle is also a Helium-4 nucleus, so it is written as ⁴₂He (as seen in the periodic table) and is also sometimes written as ⁴₂α.
A beta particle (β) is a fast moving electron or positron, it has a very small mass. An electron has a -1 charge and a positron has a +1 charge.
2) Gamma ray (γ) is a high-energy electromagnetic wave. Gamma rays are caused by changes within the nucleus. They are part of the electromagnetic spectrum and so travel at the speed of light. They have no mass and no charge.

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11
Q

SP6e
1) Compare the penetrating abilities of alpha, beta and gamma radiation
2) Compare the ionisation abilities and the range of alpha, beta and gamma radiation

A

1) Alpha particles are absorbed by paper. Beta particles can travel through paper, but it is absorbed by aluminium. Gamma rays are highly penetrating, and can travel through paper and aluminium. It is absorbed by lead.
2) Alpha particles have a range of a few cm because they are highly ionising, beta particles are ionising and have a range of a few metres, gamma particles have a range of a few kilometres because they are weakly ionising.

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12
Q

SP6f
1) Describe the process of β– decay.
2) Describe the process of β+ decay.
3) Explain how the proton and mass numbers are affected by different kinds of radioactive decay.

A

1) During a β– decay, a neutron changes into a proton and an electron. The electron is ejected from the atom. This type of decay is written as 0 mass number, -1 atomic number, and the symbol ‘e’ in a nuclear equation.
2) In a of β+ decay, a proton becomes a neutron and a positron. The positron is ejected from the atom. This type of decay is written as 0 mass number, +1 atomic number, and the symbol ‘e’ in a nuclear equation.
3) In β- decay, the atomic number increases by 1, but there is no change to the mass number.
In β+ decay, the atomic number decreases by 1 but the mass number does not change.
In alpha decay, the atomic number decreases by 2 and the mass number decreases by 4.
In gamma decay, neither the atomic number nor the mass number changes.
In neutron decay, the atomic number does not change, but the mass number decreases by 1.

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13
Q

SP6f
1) Describe what happens during nuclear rearrangement after radioactive decay.
2) How do you balance nuclear equations for mass and charge.

A

1) When the radioactive decay is emitted, the nucleus loses energy, and the subatomic particles in the nucleus are rearranged.
2) On the left hand side of the arrow, write the formula for the atom before the radioactive decay. On the right hand side of the arrow, write the formula of the atom after radioactive decay, + sign, then the formula of the decay that it emitted.

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14
Q

SP6g
1) Describe how the activity of a substance changes over time.
2) State how half-life can be used to describe the changing activity of a substance.
3) Recall the unit of activity.
4) How does the half life correspond with how unstable the isotope is?

A

1) Radioactive decay is a random process. It is not possible to say which particular nucleus will decay next but given that there are so many of them, it is possible to say that a certain number will decay in a certain time.
2) Half-life is the time it takes for half of the unstable nuclei in a sample to decay, or for the activity of the sample to halve or the count rate to half.
3) The activity of a sample is measured in bequerels (Bq).
4) The shorter the half life, the more unstable the isotope is. Therefore, it will have more activity because the shorter the half life, the more nuclei that will decay per second.

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15
Q

SP6g
1) Describe how half-life can be used to work out how much of a substance will decay in a certain time.
2) How do you calculate the half life of a sample?
3) Why is the estimate of activity less likely to be accurate after a longer period of time?
4) Describe what the count rate of radioactive decay will be like

A

1) First find the number of nuclei remaining after the specified number of half lives, then subtract this from the initial number of nuclei to find how much of the substance will decay. For example, to calculate the number of decays after 2 half lives, if the initial sample contains 400 nuclei, after 2 half lives, there is 200 undecayed nuclei remaining. 800 - 200 = 600 decayed nuclei.
2) You need to find the time it take for the count rate to half.
When using a graph: if the initial count rate is 60cps, half of this is 30cps, and you need to see how many seconds 30cps corresponds to on the graph. The number of seconds is the half life.
When given the time: For example, the initial activity is 8800 Bq, and after 6 hours the activity is 1100 Bq. It takes 3 half lives to get from 8800 to 1100. 6 hours is 3 half lives, so 2 hours is 1 half life.
3) Radioactive decay is random, and the effect of randomness on the results will be greater for lower activities. Therefore, a single reading of the count rate does not necessarily indicate that the count rate will not increase again.
4) The process of radioactive decay is unpredictable and occurs randomly. Therefore, the count rate would not be constant, and there will be variations with each reading.

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16
Q

SP6h
1) Describe how radioactivity is used in smoke alarms.
2) Describe how radioactivity is used in irradiating food.
3) Describe how radioactivity is used in sterilising equipment.

A

1) An isotope of americium which emits alpha particles is used in smoke alarms. Alpha radiation ionises the air and this allows a small current to flow between two electrodes. Alpha is weakly penetrating so smoke stops it, the current drops and the alarm goes off.
2) Food can be irradiated with gamma rays to kill bacteria. This makes it safer to eat and the food can stay fresh for longer.
3) Gamma radiation kills microbes and can be used to sterilize medical instruments; the instruments are sealed into bags. Using radiation instead of hot water to sterilise equipment means that plastic equipment isn’t exposed to high temperatures that could damage or melt it. Gamma is most suited to this because it is the most penetrating out of all the types of radiation, it is penetrating enough to irradiate all sides of the instruments, and instruments can be sterilised without removing the packaging.

17
Q

SP6h
1) Describe how radioactivity is used in tracing and thickness gauging.
2) State the medical use of radioactivity

A

1) Radioactive isotopes can be used as tracers. A gamma source added to water is used to detect leaks in water pipes that are underground. When there is a leak, water flows into the surrounding earth. A Geiger-Müller tube following the path of the pipe will detect higher levels of radiation where there is a leak.
In a paper rolling mill, the thickness of the paper is monitored by how much beta radiation is received at the detector. The thicker the paper, the lower the count rate the detector records.
2) Radioactivity can be used to help diagnose cancer using tracers in the body. It can also be used to treat cancer.

18
Q

SP6i
1) Describe the hazards of ionising radiation in terms of tissue damage and possible mutations
2) Explain how the dangers of ionising radiation depend on the half-life.
3) Explain the precautions taken to reduce the risks from radiation and ensure the safety of patients exposed to radiation, and link these to the half-lives of the sources used.

A

1) A large amount of radiation can cause tissue damage such as reddened skin (radiation burns). Small amounts of ionising radiation over long periods of tine can damage the DNA inside a cell. This damage is called a mutation. Some mutations can cause the cell to malfunction and may cause cancer.
2) If an isotope has a short half-life, the nuclei will decay very quickly. This means that the isotope will emit a lot of radiation in a short amount of time. If only a small amount of the isotope is used, having a short half-life can be advantageous, as the material will quickly lose its radioactivity. If a large amount is used, however, the levels of radiation emitted could make handling the isotope extremely dangerous.
If an isotope has a long half-life then a sample of it will decay slowly. Although it may not emit a lot of radiation, it will remain radioactive for a very long time. Sources with long half-life values present 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.
3) Patients are protected by:
- Using the smallest possible dose
- Using a source with a short half life
- Minimise the time that the patient is exposed to the radioactive source.

19
Q

SP6i
1) Explain the precautions taken to reduce the risks from radiation and protect people who work with radiation.
2) Describe the differences between contamination and irradiation effects.
3) Compare the hazards of contamination and irradiation

A

1) To protect from irradiation:
- Shield the source
- Increase the distance from the source
- Minimise the time spent in the presence of the source.
To protect from contamination:
- Wear gloves
- Handle the source using tongs
- Wear a protective suit or mask
2) Irradiation is when a person is exposed to alpha, beta or gamma radiation from nearby radioactive materials. The irradiation stops when the person moves away.
Contamination is when the person gets particles of the radioactive material on their skin or inside their body. They will be exposed to radiation as the unstable isotopes in the material decay.
3) Irradiation:
- Being irradiated does not make the person radioactive
- It can cause damage to skin
- Radiation can penetrate the body if it has a long range (gamma radiation) and cause damage to tissues or organs. However, alpha and beta particles cannot penetrate the body.
Contamination:
- Contamination will expose the person to more radioactive particles, and the person my accidentally inject (eat) some
- Or if the ionising radiation particles get into the air, the person could breathe them in
- The radioactive source will decay while inside the person’s body, which can cause a lot of damage
- If the radiation is highly ionising (eg. alpha decay), it can be very dangerous.
- So contamination is more dangerous of irradiation

20
Q

SP6j
1) Explain how tumours are treated with radiation applied internally.
2) Explain how tumours are treated radiation applied externally.
3) Explain the use of radioactive tracers in diagnosis.

A

1) Internal radiotherapy uses a beta emitter such as iodine-131 placed inside the body, within or very close to a tumour. Beta radiation is used when treating tumours internally. This is because it is ionising enough to pass through the casing of the implant and kill the cells of the tumour, but will also have a short enough range that damage to healthy cells is limited.
2) Most radiation is external radiotherapy, which uses beams of gamma rays, X-rays protons directed at the tumour from outside the body. Gamma radiation is able to pass through the body and get to delicate organs, which is why the patient and nurses need to be protected. The gamma radiation is carefully focussed on the tumour, to reduce damage to healthy cells and sometimes shielding is placed on other parts of the body. The radiotherapy machines are kept in room that are specially shielded, to protect other patients and staff in the hospital.
3) A tracer is a radioactive isotope that can be used to track the movement of substances, like blood, around the body.
The isotope is injected into the patient, where it would bind to the substance it is tracking. The isotope would then decay, emitting gamma radiation that could be detected outside the body. If there is the substance present, lots of radiation will be emitted from the area where the substance is present.

21
Q

SP6j
1) Explain the use of PET scanners in diagnosis.
2) Explain why isotopes used in PET scanners have to be produced nearby.
3) Explain why alpha emitters are not used in medical imaging
4) What makes a medical tracer suitable for use?

A

1) PET scans use a positron emitter as the radioactive tracers. The positrons emitted by the tracer will react with electrons in the patient’s body and produce gamma rays which can be detected outside the body. Multiple detections can build up a picture of the movement of the tracer inside the body.
2) Isotopes used in PET scanners have to be produced nearby. The isotopes have short half-lives, so if the source had to travel a long distance, its activity would drop to a low level which would mean it couldn’t be used for a PET scan.
3) Alpha radiation is highly ionising and so cause damage inside the body. It would not be detectable outside the body, as it hasn’t got a long range, so it cannot penetrate body tissue. Therefore, alpha emitters are not used for medical imaging.
4) - It releases radioactive decay that is penetrative enough to be detected outside the body.
- It does not release highly ionising radiation (eg. alpha radiation), which would be dangerous inside the body.
- It has a half life that is long enough to still emit radiation once it is in the patient, so it can be traced, and a diagnosis can be made. However, the half life should not be too long, or the substance will remain radioactive for a long time and be dangerous.

22
Q

SP6k
1) Describe some advantages of using nuclear power to generate electricity.
2) Describe some disadvantages of using nuclear power to generate electricity.
3) Evaluate the use of nuclear power to generate electricity.

A

1) Advantages:
- It is a relatively safe method for generating electricity
- It can generate a lot of energy from a small amount of fuel compared to other energy resources
- It provides a reliable supply of energy
- Fuel reserves will last a long time
- Nuclear power doesn’t produce carbon dioxide, which contribute to global warming
- It provides employment/jobs
2) Disadvantages:
- Some nuclear waste has a very long half-life so its hard to dispose of, and expensive to dispose
- The nuclear waste can cause mutations in cells and lead to cancer
- The cost of building a nuclear power plant is high
- There is a small risk of a nuclear accident, that can pollute large areas
- It is expensive to build nuclear power stations, and expensive to decommission (dismantle safely) a nuclear power station at the end of its lifetime
3) - Nuclear reactions can be a source of energy
- Uranium is a non-renewable fuel, but it is estimated that supplies will last much longer than other non-renewables, such as oil.
- It is expensive to dispose of nuclear waste. Also, it is very expensive to decommission (dismantle safely) a power station at the end of its life, because parts of the power station become radioactive as it is used.
- Sometimes nuclear accidents occur, such as small leaks of radioactive materials, and reactor explosions. These have serious consequences for many people.

23
Q

SP6k
Describe the three types of nuclear reactions

A

Radioactive decay: the radiation emitted by the unstable nuclei transfers energy.
Nuclear fission: large nuclei (such as uranium-235) break up into smaller nuclei and release energy. Fission reactions are used in nuclear power stations.
Nuclear fusion: two small nuclei join together (fuse) to for a larger nucleus. Fusion reactions release energy inside the Sun.

24
Q

SP6l
1) Describe the products of the fission of U-235
2) Describe what a chain reaction is
3) Explain how a chain reaction is controlled in a nuclear power station

A

1) The isotope splits into two daughter nuclei, and energy and two or three neutrons are released. The products of the nuclear fission are radioactive.
2) A chain reaction is when the neutrons released by nuclear fission are absorbed by other nuclei, causing more fission.
3) Neutrons, which are released in a chain reaction, can only be absorbed (to cause fission) if they are slow-moving, thermal neutrons. The moderator (a graphite core) in a nuclear power station slows down the neutrons until they have thermal energies and can be absorbed. Control rods are movable rods (they can be moved in and out) which are used to control the speed of the chain reaction. They absorb some neutrons so that there is a steady rate of fission. They can increase or reduce the number of neutrons available for fission.

25
Q

SP6l
1) Describe how the thermal energy from a chain reaction is converted to electrical energy.
2) Explain nuclear fission

A

1) The reactor is surrounded by a coolant (often water). The thermal energy released from the process is used to heat up the coolant, and turn it into steam. The steam turns turbines that are connected to an electricity generator.
2) A nucleus absorbs a slow-moving thermal neutron, which makes it more unstable. The unstable nucleus undergoes fission - it splits into two lighter elements (daughter nuclei). Energy is also released, along with two or three neutrons. These products are radioactive. These neutrons can be absorbed by other nuclei, causing more fission, which is a chain reaction.

26
Q

SP6m
1) Describe what happens in nuclear fusion.
2) Explain the difference between nuclear fusion and nuclear fission.

A

1) Nuclear fusion is when two light nuclei fuse together to create a larger nucleus. This releases energy. The total mass of the nuclei before nuclear fusion is greater than the total mass of the nuclei after nuclear fusion. The energy released from nuclear fusion is due to a difference in the mass of the nuclei before (greater) and after (smaller).
2) Nuclear fusion is the fusion of light nuclei to make heavier nuclei to release a lot of energy. However, it only happens inside stars due to the high temperatures and pressures required for it to happen. Nuclear fission is when large, unstable nuclei split into two smaller nuclei. This produces a lot of energy, but not as much as nuclear fusion. Nuclear fission is used in power plants to generate electricity.

27
Q

SP6m
1) Explain why high temperatures and pressures are needed to make fusion happen, and why it is difficult to make a practical and economic fusion power station.
2) What is nuclear fusion the energy source for?

A

1) For fusion to occur, two nuclei need to collide and fuse together. All nuclei have a positive charge, so there is electrostatic repulsion between them. High temperature and pressures are needed to overcome this and bring the nuclei close enough together that they can fuse. Lots of energy is needed to create these conditions - more than is released by fusion. Because the experimental fusion reactors currently use more energy than they produce, it is difficult to make a practical and economic fusion power station.
2) Nuclear fusion is the energy source for stars.