P7 - Radioactivity (Coming Up On March Mocks) Flashcards
Give an approximation for the radius of an atom.
1x10^−10 metres
What are the three subatomic constituents of an atom?
- Proton
- Neutron
- Electron
Where is most of the mass of an atom concentrated?
In the nucleus.
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
Describe the arrangement of protons, neutrons and electrons in an atom.
● The protons and neutrons are found in the atom’s nucleus
● The electrons are found in discrete energy levels around the nucleus
What type of charge does the nucleus of an atom have? Why?
● Positive charge
● The nucleus contains protons and neutrons
● Protons have a positive charge
● Neutrons have no charge
Give two ways that an atom’s electron arrangement can be changed.
- Absorbing electromagnetic radiation
- Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changes when it absorbs EM radiation.
● Electrons move further away from the nucleus
● They move to a higher energy level
Explain how an atom’s electron arrangement changes when it emits EM radiation.
● Electrons move closer to the nucleus
● They move to a lower energy level
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
● The number of protons is equal to the number of electrons
● Protons and electrons have equal and opposite charges, so charge cancels
What do all forms of the same element have in common?
They all have the same number of protons.
What is the name given to the number of protons in an atom?
Atomic Number
What is an atom’s mass number?
The total number of protons and neutrons in the atom.
What is an isotope of an atom?
An atom of an element that has a different number of neutrons, but the same number of protons.
How do atoms turn into positive ions?
● They lose one or more of their outer electrons
● Electrons are negatively charged, so the resultant charge of the atom is positive
What may lead to a scientific model being changed or replaced?
The discovery of new experimental evidence which doesn’t agree with the existing theory.
How did the plum-pudding model describe the atom?
A ball of positive charge, with negatively charged electrons distributed evenly throughout it.
Prior to the discovery of the electron what was believed about the atom?
The atom was believed to be indivisible - a big ball of nothing.
Which experiment led to the plum-pudding model being discarded?
Rutherford’s alpha-scattering experiment.
What is the name given to the currently accepted model of the atom?
The Bohr nuclear model
State the conclusions of the Alpha-Scattering experiment.
● Most of the mass of the atom is concentrated at the centre in the nucleus
● The nucleus is positively charged
What reinforces a scientific theory?
When experimental results agree with the hypothesised theoretical calculations and theories.
What did James Chadwick’s experiments on the atom prove?
The existence of neutrons.
Why do unstable nuclei give out radiation?
● Unstable nuclei undergo decay to become more stable
● As they release radiation their stability increases
What is the name of the process in which an unstable nucleus gives out radiation to become more stable?
Radioactive decay
Define the activity of an unstable nucleus.
Activity is the rate of decay of a source of unstable nuclei.
What is the unit of radioactive activity?
Becquerel (Bq)
What is count-rate?
The number of radioactive decays per second for a radioactive source.
Give an example of a detector that may be used to measure count-rate.
Geiger-Muller tube
State four types of nuclear radiation.
- Alpha particles
- Beta particles
- Gamma rays
- Neutrons
What are the constituents/properties of an alpha particle?
● Two protons and two neutrons (Helium - 4 He 2)
● It is the same as a helium nucleus
● In Nuclear equations, we represent alpha radiation via. Helium.
What is the range of an alpha particle through air?
A few centimetres (normally in the range of 2-10cm).
What will stop beta radiation from passing through a point?
● A thin sheet of aluminium
● Several metres of air
What will stop gamma radiation from passing through a point?
● Several centimetres of lead
● A few metres of concrete
Which type of radiation is most ionising?
Alpha radiation.
Which type of radiation is least ionising?
Gamma radiation.
State any changes to mass or charge that occur due to the emission of a gamma ray.
Both mass and charge remain unchanged.
Describe the nature of radioactive decay.
● Random
● It is impossible to predict which nuclei will decay and when (it is only by chance)
Define the half-life of a radioactive isotope.
● The time it takes for the number of unstable nuclei in a substance to halve
● The time it takes for the count rate from a sample to fall to half its initial level
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials.
What is irradiation?
● The process of exposing a material to nuclear radiation
● The material does not become radioactive
Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?
● To allow the findings to be independently checked
● This is known as peer review
Give 4 sources of background radiation.
- Rocks (i.e. granite, etc.)
- Cosmic rays from space
- Nuclear weapon testing
- Nuclear accidents
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations (half life etc.) are attempted.
What is the unit used to measure radiation dosage?
Sieverts (Sv).
How many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
Why might the radiation dosage that different people experience differ?
● Some occupations involve working with radiation
● Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
What factor determines how dangerous a particular radioactive isotope is?
The half-life of the isotope.
Why are isotopes with long half-lives particularly harmful?
● They remain radioactive for much longer periods of time
● They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
State two uses of nuclear radiation in the field of medicine.
- Examining of internal organs
- Controlling and destroying unwanted organisms/tumours, etc.
How is radiation used in sterilisation?
Gamma emitters are used to kill bacteria/parasites on equipment.
Explain the process of radiotherapy.
● Gamma emitters direct gamma rays at the cancerous cells
● The cancerous cells absorb the radiation and are killed
How are medical tracers chosen?
- They should have a short half life and decay into a stable isotope which can be excreted.
- They should only release gamma radiation since it is weakly ionising and can easily pass through body tissue without damaging it.
What is nuclear fission?
The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons).
Give an example of a fissionable isotope.
Uranium - 235
What usually needs to happen to induce fission?
● The unstable nuclei must absorb a neutron
HOWEVER
● Spontaneous fission (where no neutron absorption occurs) is rare, but can happen.
Alongside two smaller nuclei, what else is emitted in a fission reaction?
● Two or three neutrons
● Gamma rays
● Energy
What form of energy do all fission products have?
Kinetic energy.
What takes place during a chain reaction in a nuclear reactor?
● An unstable nucleus absorbs a neutron
● The nucleus undergoes fission and releases 2 or 3 further neutrons
● These induce more fission, which results in a chain reaction
What is the consequence of an uncontrolled chain reaction?
● The rate of fission events becomes to high and results in the production of too much energy
● This can lead to a nuclear explosion
What are the three main components of the core a nuclear reactor?
- Fuel rods
- Control rods
- Moderator
What is the role of the moderator in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause nuclear fission.
How is the chain reaction in a fission reactor kept under control?
● Control rods are positioned in between the fuel rods
● The rate of fission is controlled by moving these rods up and down
● The lower the rods are inserted, the slower the rate of fission (vice versa)
What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?
Fissile Nuclei
What is nuclear fusion?
The joining of two light nuclei to produce a heavier nuclei and release energy.
Name two isotopes of hydrogen which are commonly used in nuclear fusion.
Deuterium and Tritium
Which releases more energy, nuclear fission or nuclear fusion?
Nuclear fusion.
Explain the difficulty of generating energy through nuclear fusion.
Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.
Explain why nuclear fusion is currently not a viable way to produce energy on Earth.
With current equipment/techniques, the energy required is greater than the energy produced, resulting in energy net loss.
Write two difference between the radiation from uranium and the radiation from a lamp
The radiation from uranium consists from particles whereas radiation from the lamp consists of waves - this is infrared radiation which is an electromagnetic wave.
Write two differences between radioactive atoms compared with atoms in a lamp filament
Radioactive atoms have unstable nuclei ,whereas, the lamp in the filament have stable nuclei. The decay of the radioactive atom cannot be prevented whereas the atoms within the filament lamp stop emitting radiation when the lamp is turned off.
The radiation from a radioactive source is stopped by paper. Name the type of radiation that the source emits.
This is alpha radiation
The radiation from a different source goes through this paper. Name the type of radiation that this source emits.
This is beta or gamma radiation.
Name the type of radiation from radiative sources that is the most penetrating.
Gamma radiation
A Geiger muller counter clicks very rapidly when a certain substance is brought near it:
a. Describe the substance that the made the Geiger counter click
b. When the Geiger muller tube was near the substance, the counter clicked much less when a sheet of paper was placed between the substance and the tube. Explain why the counter clicked much less.
A. The substance emitting ionising radiation would cause the Geiger counter to click, this showing that the substance is radioactive.
B. The substance emitted alpha radiation in which was absorbed by the geiger muller tube, preventing most of the radiation emitted from the substance reaching the geiger muller tube.
Describe two differences between the nuclear model and the plum pudding model.
The the nuclear model of the atom all of the positive charge was concentrated within a nucleus whereas, in the plum pudding model positive charge was nuclear model and spread throughout the atom.
In the nuclear model of the atom the mass of the atom was concentrated within a nucleus where as in the plum pudding model this was spread out throughout the atom.
Explain why the alpha-particle scattering experiment lead to the acceptance of the nuclear model of the atom and the rejection of the plum pudding model.
The nuclear model of the atom showed why their was particle scattering at large angles where, where as in the plum pudding model this large-angle scattering shouldn’t be observed.
key points
› Isotopes of an element are atoms with the same number of protons but different numbers of neutrons, therefore have the same atomic number but different mass numbers.
During alpha decay:
> Nucleus looses 2 protons and 2 neutrons
> 2 protons and 2 neutrons emitted as an alpha particle
During beta decay:
> A neutron in the nucleus changes into a protons
> An electron is created in the nucleus and instantly emitted.
Explain why a radioactive source is stored in a lead-lined box.
To prevent radiation being emitted in to the environment, preventing radiation harming people and nearby objects.
Name the type of radiation from radioactive substances that it most easily absorbed.
Alpha radiation
Name the type or types of radiation from a radioactive source that are stopped by a thick aluminium plate.
Alpha and beta radiation
Name the type of radiation from a radioactive source that is:
A. uncharged
B. Positively charged
C. Negatively charged
A. Gamma radiation
B. Alpha radiation
C. Beta radiation
Name the type radiation from a radioactive source that:
A. Has the longest range in air
B. Has the greatest ionising power
A. Gamma radiation
B. Alpha radiation
Explain why ionising radiation is dangerous
It has the ability to knock electrons from atoms turning them into ions this ionisation damages cells and can be passed on in which causes cancer.
Explain how you would use a Geiger counter to find the range of radiation from a source of alpha radiation.
- Firstly, place the geiger muller tube in a holder so that it can be moved horizontally.
- Move the tube as close as possible to the radioactive source so that radiation is detected.
- Move the tube gradually away from source until count rate decreases significantly almost stopping, distance from the end of tube to source is range of alpha radiation.
Explain why gamma radiation is not suitable for monitoring the thickness of the metal foil.
Very little gamma radiation is absorbed by the foil, it would all pass straight through the foil therefore the thickness of the foil wouldn’t effect the detector reading.
Key points
> Alpha radiation is stopped by paper and has a range of a few centimetres in air, it consists of particles, each composed of two protons and two neutrons - it has the greatest ionising power.
Beta radiation is stopped by a thin sheet of metal and has a range of about one metre in air. It consists of fast-moving electrons emitted from the nucleus, it is less ionising than alpha radiation and more ionising than gamma radiation.
Gamma radiation is stopped by thick lead and has an unlimited range in air. It consists of electromagnetic radiation.
Alpha beta and gamma radiation ionise substances they pass through, ionisation in a living cell can damage or kill the cell.
Define the half-life of a radioactive substance.
The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
Key points
> Half-live of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
The count rate of a geiger counter caused by a radioactive source decreases as the activity of the source decreases.
The number of atoms of a radioactive isotope and the count rate both decreases by half every half-life.
The count rate after (n) half-lives = the initial count rate/2^n
Radiation from radioactive sources is used for different purposes, identity the type of radiation that you use and give a reason for your choice:
A. Obtaining an image of an internal organ
B. Finding out whether a kidney in a patient is blocked
A. Gamma radiation because this can be identified outside of the body.
B. Gamma radiation because a radioactive source would needed to be injected into to the organ to be imaged so this type of radiation needs to the least amount of damage whilst in the body, gamma radiation would be used because this has the least ionising power. The gamma radiation will pass through the tissue and can be detected using a gamma camera.
Give two sources of background radiation that can originate in the environment
- Food and Drink
- Radon Gas
Describe how nuclear radiation is used to destroy a tumour using a radioactive implant
- A small amount of a radioactive isotope is placed within the tumour
- radiation from the isotope destroys the cancer cells however the half-life of the radioactive isotope is not long enough to destroy any healthy cells surrounding the tumour in the process
- Also, the half-live of the radioactive isotope is short so that unstable nuclei decay before radiation destroys the other healthy cells.
State one type of radiation emitted by a radioactive implant
Gamma radiation
A. Explain why radioactive isotopes used in a kidney scan should have a half-life that is not too short and too long.
B. Evaluate whether this consideration is important for a temporary radioactive implant.
A. If the half-life of the radioactive isotope is too long the patient is exposed to ionising radiation unnecessary in which can damage healthy cells causing further health problems. If the half-life of the radioactive isotope is too short the radioactive isotope decays too much before the scan is complete.
B. If the half-life is too long the radioactive isotope will damage surrounding health cells, around the tumour. If the half-life is too short the radioactive isotope won’t destroy the tumour, and the radioactive isotope will decay before destroying the tumour.
Write down the ideal properties of a radioactive tracer
- Short half-life
- Has the least ionising power: non-toxic to the body
- Decays into a stable isotope
When a radioactive isotope is used explain why it is best to use a
radioactive isotope that decays into a stable isotope.
› Stable isotopes are not dangerous within the body compared to unstable isotopes that are are dangerous to the body because this emits ionising radiation.
Key points
> Radioactive isotopes are used in medicine for medical imaging, treatment of cancer and as tracers to monitor organs.
How useful a radioactive isotope is depends on:
its half-life
the type of radiation it gives out
For medical imaging with a radioactive isotope and for medical tracers, the half life should not be too long or too short.
A gamma beam or radioactive implant can destroy cancer cells in a tumour.
Natural uranium consists mainly or uranium-238. Uranium fuel is produced from natural uranium by increasing the proportion of uranium 235 in it.
a. Describe what happens to a uranium-235 nucleus when a neutron collides with and causes it to undergo nuclear fission.
b. Describe what happens to a uranium-238 nucleus when a neutron collides with it
a. The nucleus splits into two fragments and releases energy and two/three neutrons.
b. The nucleus absorbs the neutron without undergoing fission however forms an unstable nucleus in which goes through radioactive decay.
A nuclear reactor, describe the purpose of the control rods.
To absorb fission neutrons, and keep the chain reaction under control by maintaining an even rate of fission.
If the control rods in a nuclear reactor are pulled further into the reactor core, write and explain what would happen to the number of fission neutrons in the reactor.
More fission neutrons are absorbed so the number o fission neutrons within the reactor will decrease. This means that the amount of energy from nuclear fission would also decrease.
Explain why the core of a nuclear reactor is in a container made of thick steal and is surrounded by thick concrete walls.
The steal is used because this withstands very high temperature and pressure in the core, the thick concrete walls absorb ionising radiation that passes through the steal walls.
Key points
> Nuclear fission is the splitting of an atoms nucleus into two smaller nuclei and the release of two or three neutrons and energy
Induced fission occurs when a neutron is absorbed by a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits. Spontaneous fission occurs without a neutron being absorbed.
A chain reaction occurs in a nuclear reactor when each fission event causes further fission events.
In a nuclear reactor, control rods absorb fission neutrons to ensure that on average only one neutron per fission goes on to produce further fission.
Explain why the plasma of light nuclei in a fusion reactor needs to be very hot.
This is so that there is an enough kinetic energy to overcome the force of repulsion between the nuclei so that they fuse.
Explains why a fusion reactor needs more energy that it produces would not be much use.
This is because the energy input would be greater than the energy output therefore no energy would be produced overall.
Give two advantages and two disadvantages that a fusion reactor has compared with a fusion reactor
Advantages:
> Nuclear fusion fuel are easily available
> Fusion products are less reactive than nuclear fission products.
Disadvantages:
> Very large current needed to heat the plasma and start fusion
> Fission reactors produce far much more power than fusion products.
Key points
> Nuclear fusion is the process of forcing the nuclei of two atoms close enough together so that they form a single larger nucleus
Nuclear fusion can be brought about by making two light nuclei collide at a very high speed.
Energy is released when two light nuclei are fused together. Nuclear fusion in the sun’s core releases energy.
A fusion reactor needs to be at a very high temperature before nuclear fusion can take place.
The nuclei to be fused are difficult to contain.
Explain why radioactive waste needs to be stored:
a. Securely
b. For many years
a. This is because the radioactive waste propose a danger to people and the environment if this is released into the environment.
b. This is because radioactive waste contain radioactive isotopes with long half-lives
Explain why a source of alpha radiation is very dangerous inside the human body but not as dangerous outside it.
This is because alpha radiation has the greatest ionising power, this means that this is easily absorbed by tissues in the body and has the ability to turn atoms into ions harming cells, in which can cause cancer. Outside this is less dangerous because this has the least penetrating power.
In some locations, the biggest radiation hazard comes from radon gas that steeps up through the ground and into buildings.
A. Explain why radon gas is dangerous in the house.
B. Describe one way of making an existing house safe from radon gas.
A. This is because typically radon gas will be the biggest concentrated inside then outside. People could inhale the radiation hazard/breath this in which causes the lungs to be exposed comes from radon to radiation. This exposes people to be exposed to gas that steeps up
alpha radiation. Therefore the ionising affect in tissues in terms of damaging cells and causing cancer.
B. Pipes can be installed to pump radon gas out of the house before this reaches the ground, when doing so the top of the outlet pipe from the pump needs to be high up the outside of the house.
Suggest whether the UK government should replace existing nuclear reactors with new reactors, either fusion, fission or both. Answer this question by discussing the benefits and drawbacks of new fission and fusion reactions.
Benefits:
> No green house emissions
> large-scale generation of electricity compared with renewable supplies that take up much larger areas
Drawbacks:
> Long term-storage of radioactive waste is needed
> Possible escape of radioactive substances into the environment
Key points
> Radon gas is an alpha emitting isotope that seeps into house through the ground in some areas.
There are hundred of fission reactors safely used in the world. None of them is the same type as the Chernobyl reactor that exploded.
Nuclear waste contains may different radioactive isotopes that emit nuclear radiation for many years. The radiation is dangerous because it can cause cancer.
Nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future ) are removed from it.
