Topic 11: Nuclear Radiation Flashcards
What is the definition of binding energy?
Binding energy is the energy required to separate a nucleus into individual constituents (protons and neutrons).
How does binding energy change in either fission and fusion?
Total binding energy always increases as energy is always released during reaction.
Why is the mass of a nucleus always lower than the mass of the mass of its constituents?
The mass ‘lost’ is converted into energy and released. Known as mass deficit.
What is atomic mass unit?
Atomic mass unit is defined as 1/12 of the mass of a carbon-12 atom (1u = 1.661x10^27).
What is a mass defect?
When the mass of the constituents is greater than the mass of the nucleus.
Why does a mass defect occur?
A mass defect occurs because energy is required for nucleons to join together so the lost mass is converted into energy and released
What is nuclear fission?
Nuclear fission is the splitting of a large nucleus into 2 daughter nuclei.
When does nuclear fission usually occur?
In very large nuclei, which are unstable.
Why is energy released during fission?
because the Smaller daughter nuclei have a higher binding energy per nucleon.
What is nuclear fusion?
When two smaller nuclei join together forming one larger nucleus.
Why is enegy released during fusion?
Because the larger nucleus has a much higher binding energy per nucleon.
What is the binding energy per nucleon?
It is the binding energy of a nucleus divided by the number of nucleons in the nucleus.
How can you tell whether an element undergoes fission or fusion?
On the graph of Binding energy/nucleon over no of nucleons,
- the elements that undergo fusion have less nucleons than iron
- the elements that undergo fission have more nucleons than iron
What are the 2 conditions of nuclear fusion?
High Temperature
- Needed to overcome electrostatic repulsion between positively charged nuclei
High Density/Pressure
- Ensure nuclei are close together so increased rate of collision to maintain fusion reaction.
What is background radiation?
Background radiation is the level of ionising radiation present in the environment.
What is count rate?
No of decays recorded each second by GM tube
How to calculate corrected count rate?
- Calculate background radiation count
- Calculate total count
- Take away background count from total count
What is radiation?
Radiation is when an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable.
What can cause a nucleus to become unstable?
Unstable nuclei can be caused by
- too many neutrons
- too few neutrons
- too many nucleons (heavy)
- too much energy in the nucleus
How does a nucleus decay?
By radioactive decay.
This is when a nucleus decays by releasing energy/particles until it is in a stable form.
What are the 4 types of radiation?
Alpha - α - helium nucleus - 2 protons, 2 neutrons, +2 charge
Beta-minus - β, β- - electron
Beta-plus - β+ - positron
Gamma- Γ - short wavelength, high frequency EM wave
What are the properties of alpha radiation?
Alpha has a:
- strong ionising ability
- slow speed
- Absorbed by paper or few cm of air
What are the properties of a beta-minus?
Beta minus has a:
- Weak ionising ability
- Fast speed
- Absorbed by thin sheet of aluminium
What are the properties of a gamma?
Gamma particles are:
- EM wave
- Infinte range; follows inverse square law
- Weak ionising ability
- Absorbed by metrrs of concrete or inches of lead
List types of radiation from most ionising to least
Alpha
Beta
Gamma
List types of radiation from most penetrative to least
Gamm
Beta
Alpha
What is the nature of radioactive decay?
Random
-
Spontaneous
- Cannot influence when a nucleus will decay
What is the decay constant?
Probability of a nucleus decaying per unit time
ΔN/Δt = -λN
What is the half-life?
Time taken for the number of nuclei to halve
How can you determine half-life from graph?
- Measure t for sample size to half.
- Complete multiple times
- Work out average half life
Plot lnN₀ against time; straight line
Gradient is decay constant λ
Use λ to calculate half life
What is activity?
Activity is the number of nuclei that decay per second
A =λN
What is ionising radiation?
Ionising radiation removes electrons from atoms/molecules
What is not directly ionising but may still cause ionisation?
Presence of neutrons
Uncharged particles may not be directly ionising
Why is radioactive count repeated?
Radioactive is random process so count for fixed time will vary
Repeated measurements allow for mean to be calculated
What is the process of nuclear fusion? (2)
- Smaller mass nuclei come very close together
- So nuclei join and form a larger nucleus
Explain conditions required to bring about and maintain nuclear fusion in stars
Very high temperature
- as nuclei have positive charge leading to electrostatic force of repulsion
- High temp increases KE to help overcome electrostatic force of repulsion
Very high density
- So nuclei are close enough to fuse
- So collision rate is high to maintain fusion
