Nuclear Radiation Flashcards
What two processes can cause electrons to change energy levels?
Excitation and Ionisation
What are the four scenarios in which an atom may become unstable?
- The atom having too many neutrons
- The atom having too few neutrons
- The atom having too much mass
- The atom having too much energy
How do unstable nuclei become more stable?
Unstable nuclei are radioactive, so emit radiation in order to become more stable.
The type of radiation they emit depends on what makes them unstable
What are the constituents of an alpha particle?
Two protons and two neutrons
What are the penetration capabilities of alpha radiation?
Alpha particles are weakly penetrating and so are stopped by a few centimetres of air or a sheet of paper
What does beta-minus radiation consist of?
High energy electrons
What does beta-plus radiation consist of?
High energy positrons
What are the penetration capabilities of beta-minus radiation?
Beta-minus radiation has medium penetrative capabilities and is stopped by a few mm of aluminium or around 1m of air
What are the penetration capabilities of beta-plus radiation?
Beta-plus radiation is almost instantaneously annihilated by electrons and so has virtually zero range
What is gamma radiation?
Gamma radiation is a form of high-energy electromagnetic radiation
What charge go gamma rays have?
Gamma rays are a form of EM radiation and so don’t have a charge
What type of radiation is most ionising?
Alpha
What type of radiation is most weakly ionising?
Gamma
What type of radiation travels the fastest and at what speed?
Gamma radiation travels at the speed of light - 3 x10^8 ms-1
Under what circumstance is alpha radiation emitted?
When a nucleus has too much mass
Under what circumstance is beta minus radiation emitted?
When a nucleus has too many neutrons
Under what circumstance is beta plus radiation emitted?
When a nucleus has too many protons
Under what circumstance is gamma radiation emitted?
When a nucleus has too much energy
What are the penetrative capabilities of gamma radiation?
Gamma radiation is highly penetrative but is absorbed by several inches of lead or several metres of concrete
Explain the process of beta-minus decay.
A neutron inside a nucleus splits into a proton and releases an electron and an electron neutrino
Explain the process of beta-plus decay.
A proton inside a nucleus splits into a neutron and releases a positron and an electron neutrino
How does the mass of a nucleus compare to the sum of the individual masses of its consitituents?
The mass of the individual constituents is higher than the mass of the nucleus
What is the name given to the difference in mass of a nucleus and its individual constituents?
Mass deficit / Mass defect
Explain why there is a mass defect in nuclei.
The mass defect is a result of some of the mass being converted into energy used to hold the nucleus together
What is the name for the value of energy required to hold a nucleus together?
Binding energy
How can the mass defect be used to calculate the binding energy of a nucleus?
Using E = mc^2
^ Einstein’s mass energy equation
Why isn’t it useful to compare binding energies for different nuclei?
Different nuclei have different numbers of nucleons
What is a more useful measure to compare the binding energies of different nuclei?
Binding energy per nucleon
State the equation used to calculate the binding energy per nucleon of a nucleus.
Binding energy / number of nucleons
What is the relationship between the stability of a nucleus and its binding energy per nucleon?
The more stable a nucleus is, the higher its binding energy per nucleon will be
What is the most stable nucleus?
Iron
Name two nuclear processes that can be used to generate electricity.
- Nuclear fusion
- Nuclear fission
What are the two types of fission?
- Spontaneous fission
- Induced fission
Explain the basic process of induced fission.
A large nucleus absorbs a thermal nuetron causing it to split into two smaller nuclei, releasing energy and at least one neutron
Explain the basic process of nuclear fusion.
Two smaller nuclei join together to form a larger one, and releases energy in the process
Why is nuclear fusion not currently a feasible method of energy production?
Nuclear fusion requires very high temperatures in order to overcome the electrostatic force between the nuclei. This makes it hard to contain and means more energy must be inputted to heat the nuclei than is generated
Where does nuclear fusion constantly take place?
In stars
What is binding energy?
The energy needed to separate all of the nucleons in a nucleus and its equivalent mass deficit
What is half life?
The average time it takes for the number of undecayed nuclei to halve
What is the equation for half life?
λ = ln(2) / t(1/2)
decay constant = ln(2) / half life
What are the decay equations?
N = N0 e^(−λt) -> Number of nuclei
A = A0 e^(−λt) -> Activity
What is the equation for activity?
decay constant x number of undecayed nuclei
A=λN
What is activity?
The number of nuclei that decay each second. Measured in Bq. It is proportional to the size of the sample
Why is it hard to use nuclear fusion as a source of energy?
Scientists have not successfully maintained a controlled nuclear fusion reaction. It is hard to force 2 positively charged, repelling protons to fuse together - the kinetic energy they need to overcome this repulsion requires millions of kelvin.
The reactrion would also need a very high density of protons for the reaction to be sustained
What are the dangers of beta decay?
Both inside and outside the body this has moderate ionisation so exposure should be minimised
What are the dangers of gamma radiation?
Only has minimal ionisation but cancer danger from long term exposure
But it is very penetrating so hard to absorb it
What is the most common fission reaction?
Uranium 235, if this nucleus is hit by a slow moving neutron, it could absorb it to form U-236 which is unstable and quickly breaks up. It will form 2 medium sized nuclei with a number of high speed neutrons
What is the decay constant?
Lambda, the probability that a given nucleus will decay each second. Units s^-1
Why don’t alpha particles travel very far?
Alpha particles are highly ionising and when it ionises an atom, it transfers some of the energy to the atom - since it quicjly ionises loads of atoms, alpha particles lose all its energy and so don’t tavel very far
What are the dangers of alpha radiaiton
Highly ionising inside the body
- can causes radiation posoning and cancer
- less dangerous outside the body as absorbed by the skin
give 5 sources of background radiation?
- Air
- Ground and Buildings
- Cosmic radiation
- Living things
- Man-made radiaiton
What is background radiation?
Background radiation is the low level radiation from natural sources that is always around us.
Usually between 0.2 - 0.5 counts per second
Why is lots of energy released by fusion?
A lot of energy is relseased during fusion because the new, heavier nuclei have much higher binding energies per nucleon. This process provides the energy to make stars shine
Explain the conditions required to bring about and maintain nuclear fusion.
Nuclear fusion requires a very high temperature and a very high density. A very high temp is eneded to provide enough energy to overcome the electrostatic repulsion between nuclei.
A very high density is needed to give a big enough collision rate to maintain the reaction
How do nuclear reactors work?
Using the process of nuclear fission, the kinetic energy given off drives the nuclear reactor. A moderator (graphite or water) slows down the emitted neutrons so they arrive at the next uranium fuel road at a slow speed to cause further fission reactions. To avoid a nuclear bomb there are control rods to absorb excess neutrons
Explain what happens in a proton-proton nuclear fusion reaction.
- First two protons can fuse if they overcome the electrostatic force between them
- One proton changes into a neutron in beta plus decay.
Another proton joins making a nucleus of He-3 - 2x He-3 nuclei fuse together and 2 protons break off leaving a He-4 nucleus
