P2.5 Nuclear fission and nuclear fusion Flashcards
What are sub-atomic particles?
Protons,neutrons and electrons
What are nucleons?
The particles found in the nucleus
What is the atomic number of an element?
The amount of protons it has
What is another name for the mass number?
Nucleon number
What is the nucleon number?
The total number of protons and neutrons in the nucleus
What are isotopes?
The same element with a different number of neutrons but the same number of electrons
What is an ion?
An atom that has lost or gained an electron/s
How does an unstable nucleus become more stable?
It decays by losing energy when certain types of ionising radiation are emitted from the nucleus
What are the three types of ionising radiation?
- alpha particles
- beta particles
- gamma rays
Can you predict when a nucleus will decay?
No, it is a random process
What are the subatomic particles of an alpha particle, and what is its charge?
It contains two neutrons and two protons but no electrons, so it has a charge of +2
Why do alpha particles have a short penetration distance?
They lose energy quickly because they produce many ions when they are emitted from the nucleus at high speeds
Why do beta particles have a longer penetration distance than alpha particles?
They are less ionising than alpha particles and so can penetrate further into matter as they don’t lose energy as quickly
What speed to gamma rays travel at?
The speed of light
Do gamma rays have an electrical charge?
No
Why are gamma rays able to penetrate more substances than beta particles?
Gamma rays are ten times less ionising and so don’t lose as much energy
What materials can stop gamma rays?
Lead and many metres of concrete
What is the most ionising type of radiation?
Alpha particles
What type of radiation has the longest penetration distance?
Gamma
What are three types of nuclear reaction?
- radioactive decay
- nuclear fission
- nuclear fusion
What is nuclear fission?
When a large unstable nucleus splits into two smaller daughter cells
When does nuclear fission occur?
When a large unstable nucleus absorbs a neutron
What is the product of nuclear fission?
Two daughter cells and three neutrons
What two types of energy are released from nuclear fission?
Thermal and kinetic
What is an uncontrolled nuclear chain reaction?
When the neutrons released from fission are absorbed back into the daughter cell, making it unstable so that it splits and releases three neutrons which can get absorbed into another daughter cell, causing the reaction to happen again and again
How can a chain reaction be controlled?
Another material can be made to absorb some of the neutrons
What type of reaction is used in a nuclear reactor?
A controlled nuclear chain reaction
What is nuclear fusion?
The process of two small nuclei combining to make a larger one
What do nuclear reactors do?
Transform nuclear energy into thermal energy using fission
Where do nuclear reactors get nuclear energy from?
The nuclei of uranium and plutonium atoms
Where are control rods placed in the reactor core?
Between the fuel rods
How do you increase the rate of fission in a nuclear reactor?
You move the control rods out so that fewer neutrons are absorbed
What happens when the control rods are fully lowered in the reactor core?
The chain reaction stops and the reactor shuts down
Why is concrete shielding used in a nuclear reactor core?
To prevent radiation and stray neutrons from escaping
What does a moderator do?
Slow down the neutrons emitted from fission
How is thermal energy produced in a nuclear reactor transferred to electrical energy?
- thermal energy is transferred to a coolan which is pumped through a reactor
- the super-heated water is pumped through a “heat exchanger” which produces steam
- the steam drives a turbine, which turns a generator
- the generator transfers the kinetic energy to electrical energy
What is radioactive waste made up of?
Radioactive daughter nuclei and isotopes
What is the energy source of stars?
The fusion of hydrogen atoms combining to form helium
What is electrostatic repulsion?
A force that pushes apart two particles with the same charges
Why does fusion happen on the Sun?
The Sun has a very strong gravitational field, which creates very high densities of nuclei at its centre, which means nuclei are much more likely to collide
How can nuclei overcome electrostatic repulsion?
By travelling fast enough to collide
How can you increase the speed nuclei move at?
Increasing the temperature
Why is fusion power not being used?
It is difficult to sustain the high temperature required for fusion which means no experimental reactors have produced more energy than they have put in
