Radiation Flashcards
Half life
Time for activity to half
What happens to a neutron that is incident on the moderator.
A neutron loses energy when it collides with the hydrogen particles causing it to slow down
What happens to a neutron that is incident on a control rod
It is absorbed to control the reaction
Describe the process of fission
Neutron absorbed and uranium-236 is formed. This causes the nucleus to split into small, daughter nuclei releasing several fast-moving neutrons.
The most dangerous source of waste in a nuclear power plant.
Products from the fission of uranium-235 and spent fuel rods
How is waste treated in a nuclear power plant
Waste is placed in cooling ponds. High level waste is vitrified and placed in concrete containers to be stored deep underground. This should all be done close to the plant.
Problems faced dealing with radioactive waste and potential solutions
The waste will be highly radioactive (for thousands of years) so must be placed in a geographically stable area.
Transporting waste is a risk to public so extra strong casing should be used or keep close to plant.
Waste should be remotely handled to avoid human contact.
Spontaneous reaction
Where no energy is supplied
Binding Energy
The amount of energy needed to separate the nucleus into its constituent protons and neutrons
Mass Defect
The difference between the mass of separated nucleons and the mass of the nucleus
Drawing a binding energy against mass number graph
Curve with a steep rise
A maximum between 8 and 10 MeV at between 50 and 60 nucleons
When can fusion occur?
When two smaller nuclei combine together to form a larger nucleus. The product nucleus (A < 50) has more binding energy per nucleus than the smaller nucleus. Fusion starts with two small nuclei on the left and moves to the right upwards towards the peak.
When can fission occur?
When larger nuclei split into two smaller, approximately equal fragments when bombarded by neutrons with the releases of two or three further neutrons and energy. If fission occurs, the smaller nuclei (A > 50) has more binding energy per nucleon than the original nucleus. Fission starts with a large nucleus on the right and moves to the left upwards towards the peak, The fragments are more stable than the original nucleus.
Critical Mass
The mass of material which will just allow a chain reaction to occur
When can a chain reaction occur?
If the rate of loss of neutrons is lower than the rate of production of neutrons.
How and why does the mass of a nucleus differ from the mass of its protons and neutrons when separated?
The mass of the nucleus is less because of the (binding) energy added to separate the nucleons.
Why does fusion require such high temperatures?
Nuclei need to be close together for the Strong Nuclear Force to be involved. But the electrostatic forces of repulsion try to prevent this from taking place. If the temperature is high then the nuclei have a high enough kinetic energy to overcome the repulsion.
Rutherfords experiment conditions
Alpha particles need to have the same speed
Evacuated container
Alpha source with long half life
Observations of Rutherford’s experiment
1 in 2000 alpha particles deflected
1 in 10000 deflected with at an angle more than 90 degrees
Conclusions of rutherfords experiment
Mass is concentrated towards the centre of the atom (nucleus)
The nucleus is positively charged
Energy of radiation
Alpha and gamma are constant, beta varies
When is gamma emitted
If a nucleus has excess energy after emitting an alpha or beta minus particle
Why do alpha emitters occur beyond z = 60
Too large to be stable because the strong nuclear force between the nucleons is unable to overcome the electrostatic force of repulsion between protons.
Why are beta minus emitters to the left of the stability belt?
They are neutron-rich. An electron is emitted from the nucleus along with an antineutrino. When a nucleus ejects a beta minus particle, one of the neutrons is changed into a proton.
Why are beta plus emitters to the right of the stability belt?
They are proton-rich, a proton changes into a neutron.
Thermal neutron
A slow moving neutron in thermal equilibrium with the moderator
