Nuclear Fission And Fusion Flashcards
What is the structure and parts of an atom
3 parts, neutrons, protons and electrons. These are called sub atomic particles
Neutrons and protons are in the nucleus
Electrons are in electron shells that orbit the nucleus
Electrons have negative 1 charge and protons have +1 charge neutrons have no charge
Protons and neutrons have an atomic mass of 1 and electrons have almost 0
What is the atomic number
This is the number of protons in an element. All atoms from an element have the same amount of protons. This is also called the proton number
What is the mass number
This is the sum of protons and neutrons in an atom. This is also called the nucleon number.
Where is the atomic and nucleon numbers for an element found on the periodic table
On the left of the symbol. Top number is the mass number and bottom is atomic number. Atomic number is always smaller.
What are isotopes
Atoms from the same element (have the same number of protons) but have a different mass number as they have different amount of neutrons
What makes an atom an ion
Atoms usually have the same amount of electrons as they do protons to make them neutral (have no charge). If an atom gains or loses an electron/s , it becomes an ion
What is ionising radiation
Radiation with enough energy to cause atoms to lose electrons and become an ion.
What makes a substance radioactive
If they have an unstable nucleus
How do radioactive substances become more stable
They decay by releasing energy in Alpha particles , beta particles or gamma rays
Describe alpha particles. Atomic structure, penetration distance, rate of ionisation…
They consist of 2 protons and 2 neutrons and no electrons meaning they have a charge of +2. They are emitted from the new leurs st high speeds and produce many ions in a short distance. Every time they ionise an atom, they lose energy so they have a short penetration distance. They can be stopped by a few cm of air or few mm of paper.
Describe beta particles, structure, ionising rate, penetration distance…
They are electrons emitted from the unstable nucleus and are much less ionising than alpha particles so they don’t lose energy as fast so they can penetrate further. They can be stopped by a few mm of aluminium or even less lead
Describe gamma rays
They are electromagnetic waves and are very high frequency. They are emitted from unstable nuclei and are around 10x less ionising than beta particles. As they see waves they have no charge but travel at the speed of light. They are blocked by several M of concrete or a few cm of lead.
Apart from alpha beta particles and gamma rays, what else does radioactive decay release
Releases energy as alpha and beta particles are traveling fast so have lots of Kinetic energy and gamma rays have energy in the form of electromagnetic radiation.
Describe nuclear fission of barium 235 and goods and bands of it
When barium 235 absorbs a neutron, it splits into 2 daughter nuclei, barium 141 and krypton 92. As well as lots of energy and 3 more neutrons. These neutrons can then be absorbed by other barium 235 nuclei creating a chain reaction. If this is controlled, it can be used to make energy for homes, if not controlled a chain reaction can be triggered causing huge releases of energy and making an explosion.
What elements are usually used in nuclear reactors
Plutonium and uranium atoms, in nuclear reactors, the energy inside the nuclei of the particles is released
How does a nuclear reactor work
The fuel is mostly made of uranium and it is turned into pellets and inserted into several meter long fuel rods. These are placed into the core and the reaction with neutrons starts. This releases thermal energy.
How is nuclear fission controlled in a reactor
When nuclear fission occurs, 3 neutrons are released. These can then be absorbed by other radioactive nuclei and cause them to react. To control this, 2 of the neutrons have to be absorbed so the rate of fission doesn’t increase. This makes a controlled chain reaction. To absorb 2 neutrons, control rods inside the reactor core absorb the neutrons, these rods are placed between fuel rods. To increase the rate of fission, control rods can be raised so fewer neutrons are absorbed. To stop the reaction the control rods are completely lowered so all neutrons are absorbed.
What is and what is the purpose of a moderator in a reactor core
This is the material that fills the space between fuel rods and control rods. When fission takes place, the neutrons are emitted at very high speeds and need to be slowed so other nuclei are more likely to absorb them. The moderator is what slows down the neutrons.
How do nuclear reactors generate electricity
The thermal energy released is transferred to a coolant. The coolant is usually high pressure water and is pumped through the reactor. This heats the water to very high temperatures. The super heated water is pumped into a heat exchanger. In the heat exchanger are pipes with cool water, the thermal energy is transfers into the cool water making the high pressure water cool again and the water in the pipes become steam. This steam drives a turbine which turns a generator which transfers the kinetic energy into electricity.
What is radioactive waste
This is what builds up in nuclear reactors and is made up of radioactive isotopes formed when materials absorb the neutrons and daughter nuclei from the fission.
What is fusion
This is a way that energy can be made by combining small nuclei such as hydrogen to make larger nuclei such as helium. This process releases lots of energy and is the energy soude of stars.
What isotopes are used in fusion
Fusion uses hydrogen isotopes hydrogen-2 (Deuterium) and hydrogen-3 (Tritium) to make helium and energy by releasing a neutron.
Why is fusion so hard to recreate on earth
For fusion to occur, the hydrogen isotopes have to be forced together. They are both positively charged meaning they will repel though electrostatic repulsion. For them to fuse, they need to be within a million millionth of a millimetre together. It is harder on earth than on the sun as the sun has a very strong gravitational field which creates high densities of nuclei at its centre.
What conditions need to be met for fusion on earth (overcoming electrostatic repulsion.
If nuclei are travelling fast enough when they collide they can combine, this needs to be over 600km/s. The higher the temperature, the faster atoms move so the more likely they are to collide. On earth this temperature had to be 150000000C
