pcb radiation interactions

explain the principles of attenuation

Attenuation 衰减 of the x-ray beam occurs due to absorption and scattering of the x-rays.

What determines if an x-ray interacts or not?

X-ray energy, Material through which x-rays travel

If an x-ray interacts what type of interaction will occur?

absorption of scatter

what is Linear attenuation coefficient (μ)

the toal linear attenuation coefficient is the fraction of xray removed from the beam per unit thickness of the iradiated beam

what happens in photoelectric effect

incident xray photon collides with inner electron and xray is completely absorbed. if the xray energy is larger than the electron binding energy, the photo electron is ejected from the atom. the energy ejected electron is equal to the incident xray energy - electron binding energy. it is followed by xray emission.

how will be the probability of photoelectric effect be affected

increases strongly with increasing atomic number Z (of the absorbing material), decreases with increasing x-ray photon energy

what is compton scattering

the photon transfers some of its energy to the electron. The electron recoils and is ejected. The photon scatters off in a new direction with reduced energy and increased wavelength. This is an inelastic scattering process because the photon does not retain its original energy.

what does the compton scattering probability change with

increases with increasing atomic number Z and decreases with increasing photon energy

what is pair production

Incident x-ray passes close to the nucleus and interacts with the nuclear field, Absorption of x-ray, Energy converted to electron-positron pair

what is half-value-thickness

thickness of absorber required to reduce the intensity to 50% of the incident beam

what is tenth value thickness layer

thickness of absorber required to reduce the intensity to 10% of the incident beam

Explain the significance to radiotherapy of ‘linear’ and ‘mass’ attenuation coefficient

they determine dose deposition, beam penetration, and treatment planning accuracy

explain the term linear attenuation

the linear attenuation coefficient describes how quickly a photon beam loses intesnsity per unit distance in a material

explain the term mass attenuaiton coefficient

the mass attenuation coefficient (μ/ρ) describes attenuation per unit mass.

what is the equation for attenuation

Explain the mechanisms for interactions of electrons in matter

electrons are charged particles with mass and therefore interact differently to photons. they interact with the electric field of other charged particles like protons and orbital electrons. through the collisions the electrons may lose some of their kinetic energy and change direction of motion

Describe the concept of linear energy transfer (LET)

refers to the average energy deposited per unit length by a charged particle.

Describe the concept of a well defined range for electrons and other charged particles

they stop after a certain distance, it depends on incident electron energy, linear stopping power and energy lost per unit linear distance

describe the role of Bremsstrahlung in diagnostic imaging and radiotherapy

X-rays in a diagnostic x-ray unit are produced by Bremsstrahlung, X-rays are produced in a linear accelerator by the Bremsstrahlung process

inelastic collisions between incident electron and orbital electron can result in…

atomic ionisaiton, atomic excitation