Xray Interraction w/Matter Flashcards
What are the properties of X-ray/photons/EMR?
Pure energy, no mass, no charge, speed of light, waves
What is interacting with what?
X-ray photons interacting with the atoms that make up matter/human bodies.
What are the properties of atoms in the human?
Bohr atoms - solar system model/empty space
The big 4 - Hydrogen, carbon, nitrogen, oxygen
The Bohr atom
Like a miniature solar system
-nucleus at the center
-electrons in orbit
3D - mostly empty space
The 7 possible orbital rings:
K - innermost filled first L M N O P Q - outermost
Electron binding energy
The force that holds electrons in orbit.
- a balance of forces
- inertia of electrons
- magnetic attraction of (+) charged nucleus
Electron binding energy varies by:
Atomic number
Distance from the nucleus
As atomic number increases, binding energy
Increases
The human body is comprised of ? atomic number atoms
LOW
As distance from the nucleus increases binding energy
Decreases
Energy based ionizing radiation
Xray, gamma
Properties of energy based ionizing radiation
Bundles of pure energy No mass No charge Speed of light Waveform movement
Ionizing radiation
High energy, highly penetrating energy characterized by short wavelength and high frequency.
Includes x-radiation and gamma radiation (possess enough energy to ionize matter)
X-rays are emitted from
The electron shells of an atom
Gamma radiation is emitted from
The nucleus of a radioactive atom.
If given an X-ray and a gamma ray with equal energies
You would not be able to tell them apart
EMR interacts with
Objects whose size approximates its own wavelength
Visible light
Rods and cones within the human eye
Microwaves
Water molecules
Radio
Radio antenna
X-ray
Atoms
As wavelength decreases
Energy increases
As frequency increases
Energy increases
High energy EMR like X-ray possesses
Short wavelength and high frequency
The xraybeam is poly energetic
Waveform and energy values will vary within the polyenergetic beam up to the peak energy-KVP.
X-ray begins and ends with
Electrons
The wavelength of ray is
Very short
Approximately the size of atoms.
The primary X-ray beam is
Polyenergetic
A variety of wavelengths in beam
A variety of structures interacted with
Low energy X-rays
Relatively long wavelength
Moderate energy X-rays
Moderate wavelength
High energy X-rays
Relatively short wavelength
X-ray security scanners work by
Coherent/classical scattering
Compton interaction
Primary X-ray enters atom and collides with outer shell electron (low electron bind). X-ray easily overcomes the binding energy and electron ejected, the atom is ionized in the process. Incoming X-ray loses energy in collision, the energy is spent ejecting the outer shell electron. Incoming X-ray is redirected or scattered due to the collision.
In a Compton interaction the strength of the scattered X-ray is unpredictable and random but is exactly equal to
The strength of the original primary X-ray minus the energy lost in the collision.
When you think of scatter you should also think of
Compton and vice versa
Compton interactions are the primary source of
Scatter radiation
Photoelectric interaction
High energy X-rays collide with inner shell electron, primary X-ray dies in collision, it’s energy is transferred. Hole left in K shell causing characteristic cascade. The strength of the X-ray created us exactly equal to the difference in orbital ring change. X-ray too weak to exit patients body and absorbed.
When you think of photoelectric you should think of
Absorption and vice versa
Pair production
A very high energy photon approaches nucleus, photon influenced by nucleus to split into 2 particles. energy becomes matter - 1 normal charged electron and 1 abnormal (+) charged electron like particle (positron). + seeks - and they collide and annihilate each other, the energy contained by these particles is released. Matter becomes energy, these photons travel in opposite directions
Photodisintegration
Very very high energy photon enters nucles, photon energy is absorbed. Nucleus possesses an excess of energy, nuclear fragment is ejected.
Occurs at energy level far beyond the general medical image range.
When X-ray enters matter, one of 3 things will happen:
X-ray passes through matter without interaction
X-ray energy absorbed in matter due to interaction
X-ray energy redirected due to interaction with matter
Pass through X-ray and absorbed X-ray are
Good for the image, project the shadow of anatomy onto the image receptor
Redirection of X-ray is bad for the image
Scatter will degrade image quality and increase the exposure to all persons
Properties of X-ray
Bundles of pure energy No mass No charge Speed of light Waveform movement
Atoms that make up human tissue have properties:
Bohr atom (solar system arrangement)
Nucleus at center, electrons in orbit
Mostly empty space
EMR interacts with objects whose size approxiamtes
It’s own wavelength
Wavelength corresponds to
EMR energy
As EMR increases wavelength decreases
As EMR decreases wavelength increases
Yes
A primary X-ray beam is polyenergetic
It is comprised of photons with a variety of wavelengths
The beam wil. Interact with a variety of structures
Longer waves with entire atoms
Moderate atoms with outer shell orbits
Shorter wavelengths with inner shell orbits
Frequency
The number of waves or cycles per second (measured in hertz)
Wavelength
The distance between a point and a corresponding point on a wave (measured in meters).
Amplitude
The heighten the wave. From zero line to peak
Velocity
The speed of electromagnetic radiation.
Constant
Speed of light “c”
As frequency goes up wavelength
Goes down.
As frequency goes down wavelength goes up.
Ionization
To give an object charge (either positive or negative)
Ionizing radiation
Energy or matter based
Ionizes matter by disrupting normal atomic structure
X-ray ionizes matter by removing
Electrons from the orbital rings of atoms
EMR interacts with
Objects whose size approximates its own wavelength
Diagnostic medical X-ray energy range is
1kvp up to 150kvp
The wavelength of X-ray is measured in
Nanometers 10 to the -9 meters
Or
Angstroms 10 to the -10 meters
Classic/coherent/Thompson/Rayleigh interaction
Low energy photon approaches atom, energy absorbed by entire atom. Atom cannot hold excess energy, releases new (secondary) photon. Energy is exactly same as primary X-ray and proceeds isotropically.
Classical interaction
Excitation without ionization
Our job as techs
Minimize production of scatter - colimator
Minimize the impact of scatter on image - grid
Minimize the impact of scatter on people - shielding
Scatter is X-ray energy but adds
Density to the image
Contains no anatomical info
Adds fog or a veil of gray to the image, reducing image quality
