Nuclear Flashcards
What is Rutherford’s scattering experiment?
Alpha particles are fired at thin Gold sheets in a vacuum. They were fired onto a fluorescent screen where they could be detected with a microscope.
What does the graph of radioactive decay look like?
Exponential
What model of the atom was produced from Rutherford’s experiment?
The nuclear model
What model of the atom did they believe before the Rutherford scattering experiment?
Thomson’s plum pudding model
What were the results of the scattering experiment?
It was found that although most particles were deflected by a small amount, some were deflected by angles so large that they bounced back. This proved the existence of the nucleus
What were the conclusions from the experiment?
The atom has a very small positively charged nucleus .
The nucleus contains nearly all the mass of the atom
The atom is mostly empty space
What is an alpha particle?
They are nuclei of helium atoms
What are the properties of alpha particles?
They are strongly ionising
Only travel a few centimetres in air and can be stopped by paper or skin
How are alpha particles deflected in magnetic fields and electric fields?
slightly deflected in strong fields as they have very low kinetic energy
What are Beta particles?
Beta particles are fast-moving electrons (just slower than the speed of light) from the nucleus
What are the properties of beta particles?
Not as ionising as alpha particles and they can travel about a metre in air
They can be stopped by aluminium foil
How are beta particles deflected in electric and magnetic fields?
They are deflected by large angles
What are gamma rays?
photons or electromagnetic waves from the nucleus
What are some properties of gamma radiation?
They have an infinite range (follows inverse square law)
The least ionising of all radiation
Can be absorbed by several metres of concrete or several inches of lead
how are gamma rays deflected in electric and magnet fields?
They are not deflected because they are not charged.
What are some natural sources of radiation?
Radon gas, cosmic rays, rocks
What are some sources of background radiation?
Radon gas, cosmic rays, rocks and artificial sources
What law does the intensity of gamma radiation follow?
The inverse-square law
Why is ionising radiation dangerous?
because ions are produced in our bodies which damage cells and the functions of enzymes are changed. This can lead to cell damage and mutations which can cause cancer
What is the unit of a dose of radiation?
gray (Gy)
What is radiation?
Where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to come become stable
How should radioactive sources be safely handled?
Kept in lead lined boxes and locked away
Only used for short periods of time
Kept at long distances from our bodies
Use long handled tongs to move the source
What is the nature of radioactive decay?
Spontaneous and random
Is the decay of one radioactive particle independent of others?
Yes completely
What is the decay constant?
The probability of one nucleus decaying per unit time
Define activity?
The activity of a radioactive source is the number of decays per second
Define half life
One half life is the time taken for half of a radioactive sample of nuclei to decay
What is radiotherapy?
A beam of gamma rays is directed at the tumour while rotating as to not give healthy tissues a high dose. This damages the cancerous cells
What are daughter nuclei?
The product of radioactive decay
What is A?
mass number
What is Z?
Atomic number
Which particles in the graph of stability, decay with Beta decay?
The ones to the left
What is N?
Neutron number
Define a metastable state
When an atom or a nucleus exists for an extended time other than the system’s state of least energy
When a nucleus decays, what state is it in?
An excited state
How does a nuclei enter a metastable state?
Sometimes when a nucleus excites then decays, its de-excitation process is hindered leading the nucleus to remain in a metastable state for a period
What is the mass defect?
The mass of the nucleus is slightly smaller than the mass of the individual constituents.
What binding energy?
The energy required to overcome the bonds between the nucleons
how do you calculate binding energy?
mass defect x c^2
How do you calculate the average binding energy per nucleon?
total binding energy / number of nucleons
How can binding energy show a nuclei is stable?
The higher the binding energy per nucleon, the more stable
What does the mass difference between the original nuclei and products correspond to?
The amount of energy released
What is fusion?
The process by which smaller light nuclei join together, form a new nucleus and release energy. It can only occur in small nuclei at very high temperatures
What conditions are required for fusion?
A very high temperature
High density
What is fission?
When a nucleus splits into two or more smaller parts, releasing energy. Only occurs in very large nuclei which are unstable
Does nuclear power use fission or fusion?
Fission
How do fission reactions generate power?
Fission reactions generate power by when a neutron is captured by a uranium nucleus and these become unstable and split into smaller pieces releasing energy in the form of heat. It also releases more neutrons
What is the role of a moderator in a nuclear reactor?
To slow the neutrons down as they pass through
How do moderators slow down neutrons?
by using elastic collisions between the nuclei of the moderator atoms and the fission neutrons.
Why do moderators slow down neutrons?
Fission can only occur when the neutrons are slow
What materials are moderators made of? Why?
Water- inexpensive and unreactive
Graphite
What is the role of control rods in a nuclear reactor?
They control the rate of reactions in the reactor.
How do control rods control the rate of reactions?
by absorbing neutrons.
What are control rods normally made of?
Boron
cadmium
What is the role of the coolant in a nuclear reactor?
to prevent it from overheating
What does the coolant do?
They are fluids that absorb heat from the reactor and transfer this heat away to drive turbines that generate the electricity
What are coolants normally made of?
Water- high specific heat capacity
molten salt
Gas e.g. helium
What is nuclear waste?
Produced from nuclear power stations and is handled remotely sometimes using robotic machinery
How is nuclear waste stored?
Underground in cement or steel containers, fuel rods are stored underwater then mixed with molten glass and then solidified in steel containers
How can radiation be used in the production of a material?
e.g. the production of aluminium foil
In the production of aluminium foil a beta source is placed on one side of the material, while a detector is placed on the other. If the material becomes too thick, less beta radiation will pass through the foil, therefore the reading on the detector decreases causing the rollers to move closer together, meanwhile if the material becomes too thin, the reading will increase causing the rollers to move
apart.
Same process for alpha radiation and paper and gamma and steel sheets
What are some ways gamma radiation can be used in medicine?
As a detector with gamma cameras
To sterilise equipment as it will kill any bacteria present
radiation therapy to kill cancerous cells
How do you find the corrected count rate?
Measure background radiation first then subtract it from the total count rate.
Corrected rate=Total-background
Why can the decay constant only be used for a large sample?
because it is a statistical model for the number of decays so the larger the sample, the more accurate
What is carbon dating?
By measuring the amount of carbon-14 and comparing it to the initial amount, you can approximately work out how old something is as the percentage of carbon-14 is basically equal in all living things
How are nuclei held together?
With the strong nuclear force
Name 4 reasons why a nucleus might become unstable?
It has too many neutrons- decays through beta-minus emission
It has too many protons- decays through beta-plus emission or electron capture
Has too many nucleons- decays through alpha emission
Has too much energy- decays through gamma emission. Usually occurs after a different type of decay as the nucleus becomes excited and has too much energy
Why does the number of nucleons not increase uniformly beyond around 20 of each?
Because the more protons there are, the greater the electromagnetic force of repulsion is than the strong nuclear force keeping them together therefore more neutrons are needed to increase the distance between protons in order to decrease the magnitude of the electromagnetic force
Why is Technetium-99 ideal for medical diagnosis’?
Because it is a pure gamma emitter and has a half life of 6 hours which is long enough for tests but short enough to limit exposure
Describe the change in kinetic energy as a particle moves towards a charged particle
For a positive atom, It will experience an electrostatic force of repulsion and slow down as its kinetic energy is converted to electric potential energy. The point at which the particle stops and has no kinetic energy is its distance of closest approach
Define electric potential
potential energy per unit charge of a positive charge
Why is using electric potential not the best method for finding the nuclear radius?
Because t is always and overestimate
Which is the best method for finding nuclear radius?
electron diffraction as electrons are leptons meaning they will not interact with nucleons in the nucleus through the strong nuclear force so this would be a far better estimate
How does electron diffraction work?
The electrons are accelerated to very high speeds so that their De Broglie wavelength is around
10^-15 m, and are directed a very thin film of material in front of a screen causing them to diffract through the gaps between nuclei and form a diffraction pattern.
In the nuclear radius equation, what does A represent?
Nucleon number
How is nuclear mass and energy related?
They are completely interchangeable and are related by E=mc²
What can happen to nuclei smaller than iron?
They can undergo fusion
What can happen to nuclei larger than iron?
They can undergo fission
What are the benefits of nuclear fission?
It is used in power plants to create electricity without the emission of greenhouse gases
What are the negatives of nuclear fission?
Produces daughter nuclei that are radioactive that need to be stored safely for thousands of years and there is always risks of meltdowns
How can fission be induced?
By firing a thermal neutron(Thermal because they have low energy) into a uranium nucleus causing it to be very unstable. It then undergoes fission and produces another neutron. This then causes a chain reaction where each fission reaction causes at least one more
Define critical mass
The minimum mass of fuel required to maintain a steady chain reaction
What is the fuel in nuclear reactors?
Enriched uranium
What surrounds the nuclear reactor?
very thick concrete
How does a nuclear reactor shut down in an emergency?
The control rods are dropped into the reactor core completely to stop fission reactions as soon as possible as they absorb all free neutrons in the core
