MEDRADSC 2X03 - Lecture 2 - Interaction of Radiation with Molecules

what are the two main forms of radiation which contribute to human annual radiation doses?

naturally-occuring and man-made sources

what is considered to be the dominant man-made source of radiation?

radon & thoron, contributing 37% to exposure

X-ray transmission through matter is a(n) _____ function.

exponential

what does the transmission of an x-ray depend on?

mac, lac, density, thickness and intensity

what is considered to be the diagnostic range of x-rays?

10-150 keV

the photoelectric effect is strongly dependent on two factors, what are they and why?

energy of the incident photon and the Z of the material

photoelectric absorption occurs with ____-shell electrons.

inner

what are the predominant types of interactions involved in the diagnostic range of x-rays?

photoelectric absorption, compton scattering and coherent scattering

what are the products of photoelectric absorption?

an Auger electron or characteristic x-ray

what level of energy is required for coherent scattering to occur?

low energy

what level of energy is required for photoelectric absorption to occur?

energy must be slightly greater than or equal to the binding energy of the inner-shell electron

True or False: the resultant energy is equal to the incident energy of the photon in coherent scattering.

True

True or False: photoelectric absorption is often referred to as the "billiard ball" interaction, as the resultant characteristic x-rays or Auger electron are deflected from the original pathway of the incident photon.

False

compton scattering occurs by interacting with ____-shell electrons.

outer

what are the products of compton scattering?

a compton electron and a deflected photon with less energy than the incident photon

what are the two dominant interactions involved in radiation therapy?

pair production and photodisintegration

what level of energy does pair production require to occur?

1.022 meV

what are the products of pair production?

a negatron and a positron

what is the course of a positron after pair production has occured?

it can collide with an electron, which produces two photons that travel 180º opposite from each other with the energy 0.511 meV

what level of energy is required for photodisintegration to occur?

5-10 meV

what does photodisintegration result in?

a particle is ejected with the excess energy that was not absorbed by the nucleus of the atom, usually a neutron

what is similar between pair production and photodisintegration, in terms of their interaction?

they both interact with the nucleus of the atom