Nuclear physics Flashcards
Einstein’s mass-energy equation
E= mc^2
Where m is the difference between the initial mass and the final mass, E is the change in energy and c is the speed of light
Mass is a form of energy
Annihilation
When particles and antiparticles meet they annihilate each other, their entire mass is transferred to energy, usually in the form of 2 photons
Pair production
The reverse of annihilation. Particle accelerators use this to simulate the early universe. Fast speeds simulate the early universe
Mass defect
The difference between the true mass of a nucleus and the total mass of the constituent nucleons. The true mass is lower than the mass of the nucleons. This mass defect can be considered as energy (E=mc^2) called binding energy
Binding energy
The energy required to completely separate a nucleus into its constituent protons and neutrons. Binding energy is always negative
Binding energy per nucleon
The greater the BE per nucleon, the more tightly bound the nucleons are
For A<56 (Up to Iron) BE per nucleon increases as A increases
For A>56 (above Iron) BE per nucleon decreases as A increases
Inducing fission
To induce fission, fuel(usually uranium) absorbs a slow neutron. This is called a thermal neutron because KE is similar to thermal energy of particles in reactor core
This makes the nucleus unstable, so it splits into two smaller nuclei and some neutrons
How is energy released in nuclear fission
Total mass of particles after fission is less than before. This corresponds to the energy released in the reaction. Total binding energy after fission is greater than before - the difference is released
Chain reaction
Neutrons released in fission reactions trigger further reactions. This only occurs if neutrons are slowed
Chain reactions must be controlled so that energy production doesn’t increase exponentially. Coolant is used to remove thermal energy produced
Moderator
Used to slow down fast neutrons produced. Water and carbon are good candidates as neutrons collide with protons and slow down
Water can be used as a moderator and a coolant
Control rods
Made of material whose nuclei readily absorbs readily absorb neutrons. This is used to slow down fission
Nuclear fusion
Nuclei have to be within a few fm to fuse so that short range strong nuclear force can attract them into a larger nucleus
Temperature and pressure must be very high to overcome repulsive electrostatic forces between nuclei
Use of fusion
Fusion occurs in stars
Fusion has not yet been used efficiently on Earth
