Nuclear Physics Flashcards
What ideas does the equation E = mc^2 propose
1) Mass is a form of energy - the interaction of an electron-positron pair illustrates this idea well - the particles completely destroy each other and the entire mass of the particles is transformed into two gamma photons
2) Energy has mass - the change in mass of an object is related to the change in its energy. A moving ball has kinetic energy implying that its mass is greater than its rest mass.
How do unstable nuclei decay
By emitting either particles or photons
Explain nuclei decay using Einstein’s Mass-Energy Equation
Mass-energy is conserved
Energy is released in radioactive decay, there must be an accompanying decrease in mass.
Total mass of the parent particle/nucleus and the daughter nucleus must be less than the mass of the parent nucleus.
The decrease in mass is equivalent to the energy released.
What happens when positrons and electrons meet
They’re antiparticles they will annihilate each other.
Their entire mass is transformed into energy in the form of two identical gamma photons.
Minimum energy released = 2mc^2 - If interacting particles have kinetic energy, than the energy of each photon would be even greater
What happens in pair production
A single photon vanishes and its energy creates a particle and a corresponding antiparticle
What can be used to determine the mass of particles accurately
A mass spectrometer
How can nucleons be separated
By doing work to overcome the strong nuclear force, external energy must be supplied to make this happen. Since energy and mass are equivalent, the total mass of the separated nucleons must be greater than the mass of the nucleus
Define Mass Defect
Difference between the mass of the completely separated nucleons and the mass of the nucleus
Define the binding energy of a nucleus
Minimum energy required to completely separate a nucleus into its constituent protons and neutrons
Equation for binding energy of a nucleus
B.E = mass defect of nucleus x c^2
Whaen is a nucleus more stable
When it has a greater Binding energy per nucleon
What is induced fission
Uranium-235 absorbs slow neutrons, becoming unstable, and splitting up into two approximately equal halves plus fast neutrons.
What are slow neutrons also known as and why
Thermal neutrons because their mean kinetic energy is similar to the thermal energy of particles in the reactor core.
Why are neutrons used to split a Uranium-238 nuclei
U-238 Nuclei are more likely to capture the neutrons than to undergo fission.
Why are slow neutrons also known as thermal neutrons
Their mean KE is similar to the thermal energy of particles in the reactor core
