Directly ionising radiation Flashcards
What are the main interactions for electrons?
Coulomb interactions:
collisional losses,
Bremsstrahlung interactions,
Cerenkov Radiation
What are the sources of coulomb interactions?
Elastic with orbital electrons or nuclei
Inelastic with orbital electrons
Radiative with nuclei
What is the impact parameter?
Measure of distance from incoming electron and nucleus = b
What is the process of collisional loses
b is large, the incident electron loses some energy to an electron on the atom. This energy excites the orbital electron. This can either lead to ionisation, a delta ray, through which the ejected electron causes more ionisation or the electron will fall back to its ground state releasing a photon of the same energy.
What energy is needed to produce a delta ray
Greater than 100eV
Collisional loses: What are the energy transferred, momentum gained, energy gained, energy loss along a path dl proportional to?
Energy transferred prop coulomb field of atomic electron
Momentum prop time of interaction 1/v
Energy gained prop 1/v^2 and 1/E
Energy loss along a path dl prop electron density of material
Collisional loses: What is dE/dl proportional to?
dE/dl prop e^2, 1/v^2, density, Z/A
Bremsstrahlung: What are acceleration, radiative energy loss, and emission proportional to?
Acceleration, f, prop Z/m
Radiative energy loss prop E
Emission prop (Z/m)^2
What is Cerenkov Radiation?
A ‘sonic boom’ for photons, when light is emitted in the visible spectrum as the phase velocity of the photons > c
What is the ratio of radiative losses to collisional losses?
EZ/800
What is the electron fluence?
phi = dN/da
What is the electron energy fluence
psi = dN/da . average energy
What is linear stopping power?
S=dE/dl, it is the rate of kinetic energy loss per unit path length of the particle. Consider energy deposited in the irradiated material
What is linear energy transfer?
Ldelta = (dE/dl)delta, the linear stopping power restricted to E of a delta ray = 100eV
What is the mass stopping power?
S/density = 1/density . dE/dl