Nuclear Physics Flashcards
What is equation between mass and energy
E=mc^2
What is the mass defect Δm
Mass defect is the loss in mass due to the release in energy in assembling the nucleus from the individual nucleons
BE = Δmc^2
- Binding energy is the energy released when the nucleus is formed from its separate protons and neutrons.
What is binding energy per nucleon
BE/A = Δmc^2/A
What is the variation of binding energy per nucleon with nucleon number
- Avg BEpN is about 8 MeV
- Max BEpN is 8.8 for 58Fe as it one of the most stable nucleides. The greater the BEpN, the larger the energy released to form nucleus, greater the stability
- Nuclei with high mass number undergo fission
- nuclei with low mass number undergo fusion
- Smaller values of binding energy per nucleon for higher an lower masses imply that nuclear fission and fusion are potential sources of energy
What is nuclear fission
It is the disintegration of a heavy nucleus into two lighter nuclei of comparable mass with the emission of neutrons and release of energy
What is nuclear fusion
It occurs when 2 light nuclei combine to form a single more massive nucleus, leading to the release of an enormous amount of energy.
What is radioactivity
It is the spontaneous and random emission of radiation from a radioactive source when an unstable nucleus disintegrated to acquire a more stable state
What is spontaneous
It means the process is unaffected by any external factors such as temperature or pressure
What is random emission
It mean it is impossible to predict which nucleus will decay next, but each has the same constant probability of decay per unit time. The probability of decay follows the law of statistics.
What are α-particles
They re doubly positively charged helium nucleus consisting of 2 protons and 2 neutrons. It is emitted with discrete energy. This emission results in a new atom with a mass number smaller by 4 and an atomic number smaller by 2 than the original atom.
What are β-particles
It is a high speed electron originating from the nucleus through nuclear transformation in which a neutron changes into a proton and an electron. It occurs for nuclides with too high a neutron proton ratio.
Does not change nucleon number but atomic number larger by 1
What are γ-rays
It is a high frequency em photon of discrete energy spectrum. It is emitted when a radioactive nuclide in its excited state returns to ground state. It often follows another decay process such as alpha or beta emission which has left the daughter nucleus on an excited state.
How was the existence of neutrinos predicted
- β-particles are emitted with a continuous range of energy
- Unexpected as deviated from the laws of conservation of energy and momentum
- 3rd particle must be present to carry away missing energy and momentum
- named neutrino (ν)
What affects nuclear stability
- Depends on the competition btw the attractive strong nuclear force btw nucleons and repulsive electric force btw protons
- Attractive nuclear force 100 time stronger than coulomb for but very short rang while coulomb force inversely proportional to the square of separation
- for light nucleus N = Z approx
- for heavy nucleus, N to Z ratio increases as extra neutrons needed to increase attractive nuclear force
- Beyond Z=82 no stable nucleus
What is activity A of a radioactive substance
It is the number of disintegrations per unit time
A = -dN/dt = λN
- λ is the decay constant - N is the number of radioactive nuclei
