Nuclear Physics and Energy Flashcards
Weak Nuclear Force
The weak force is responsible for radioactive decay and neutrino interactions. It has a
very short range. It is very weak. The weak force causes Beta-decay ie. the conversion
of a neutron into a proton, an electron and an antineutrino
Atomic Mass Unit
An atomic mass unit (amu, u, or Da) is a unit of measurement that is used to measure
the mass of atoms. The atomic mass unit is equal to the 1⁄12 of the mass of the
carbon-12
Binding Energy
The binding energy of the nucleus is the work that must be done to separate the nucleus into its constituent neutrons and protons
Mass Defect
the difference between the mass of the separated nucleons (protons & neutrons) and the mass of the nucleus
Mass Defect & Binding Energy
When a nucleus is formed, the protons & neutrons lose potential energy due to the strong force (in the same way that an object on the floor has less GPE than an object on the table)
Similarly, to pull a nucleus apart you have to do work against the strong force increasing the potential energy of the protons and neutrons (in the same way you have to do work to raise an object from the Earth’s surface).
The binding energy is therefore the energy that has to be put in to break a nucleus apart, or given out when a nucleus is formed. Note that this is consistent with the idea of chemical bonds: energy is given out when
bonds are formed, and energy it required to break bonds.
The mass defect is the mass difference observed due to the binding energy.
The higher the binding energy (and mass defect) the more stable a nucleus is
Binding energy per nucleon
The binding energy per nucleon (proton & neutron) is the average work done per nucleon to remove all the nucleons from a nucleus
Therefore the binding energy per nucleon is a measure of how stable a nucleus is
Nuclearfission
Nuclearfissionis a process in nuclear physics in which the nucleus of an atom splits into two or more smaller nuclei asfissionproducts, and usually some by-product particles
Nuclear Fusion
Nuclear fusion is the joining of two atomic nuclei to form a larger one.
Nuclear fusion requires incredibly high temperature and pressure to occur. It is the process by which energy is released in stars.
Fission of Uranium-235
A single neutron is absorbed by a Large U-235 nucleus
The nuclei is now more unstable, and so it splits into two smaller nuclei
and some spare neutrons
Induced fission
Splitting of a nucleus into two smaller nuclei brought about by bombardment with neutrons
Thermal Nuclear Reactor
Steel pressure vessel is called the reactor core
Water in the reactor core acts as a moderator and coolant
Steam is used to drive turbines, and hence generate electricity
A fission chain reaction releases a lot of heat energy from a small mass of U-235 and Pu-239
Enriched uranium fuel rods contained 2-3% of the fissile Uranium-235 isotope
Heat is used to turn water in to steam to turn a turbine which turns a generator, just like a coal power station
Neutrons go between the fuel rods to keep the fission chain reaction going in all the rods in the reactor
Control rods can be lowered in between the fuel rods to absorb some of the neutrons so that fission is controlled
Coolant
Used to remove energy from the reactor core
Typically transferred to another coolant loop because the primary coolant takes on short term radioactivity from the core
Most nuclear power plants use water as the coolant but other materials from metal and gas have been used
Moderator
Convert high energy fission neutrons into low energy thermal neutrons that are much more likely to cause U-235 to fission. KE is transferred from the fission neutron to the moderator atoms through repeated collisions
Ideally, moderators have a nuclear mass similar to the neutron, low neutron absorption and a high scattering cross section
Fusion
Joining of two atomic nuclei to form a larger one
Requires incredibly high temperature and pressure to occur
Deuterium-tritium reactions
One atom of deuterium and one atom of tritium combine to form a helium-4 atom and a neutron. Most of the energy released is in the form of the high-energy neutron
