Ionising Radiation: Dose And Exposure Flashcards
What type of radiation is harmful
Ionizing radiation
What are the 3 different classifications of radiation
- Electromagnetic
- Particulate
- Ionizing and non-ionizing
Electromagnetic waves just like all waves are characterized by their
Amplitude (intensity of the wave)
Wavelength
Frequency
Speed
Speed for all electromagnetic waves is a coasted denoted by c, how do you find speed
For X rays, what unit is wavelength expressed in?
Nanometers (nm)
For X rays, what unit is frequency expressed in?
Hertz (Hz) = 1cycle/s = 1s^-1
Understanding how ionizing radiation (harmful) is absorbed is important because
It affects all uses of radiation in medicine
y-rays (gamma rays) are referred to as
Photons
What is a photon
A bundle or particle of radiation
What are the differences between light photons and y-ray photons
Their energy and frequency
How to find energy of a photon
E= h x f
Where h is Planck’s constant
F is frequency
What is Planck’s constant
6.626x10^-34 Js
What unit is used to denote photon energy
Electron volt (eV)
1J = How many electron-volt (eV)
6.241509 x 10^89 eV
In diagnostic radiology the only PARTICULATE RADIATION that needs to be considered is the
Electron
An electron has a rest mass and rest energy of?
Rest mass: 9.109 x 10^-31 kg
Rest energy: 511 keV
______ can be classified as ionizing and non ionizing
Radiation
Non ionizing radiation cannot ionize ____
Matter
When is electromagnetic radiation ionizing
When its frequency is HIGHER than the NEAR-ultraviolet region of the electromagnetic spectrum
When is electromagnetic radiation NON-ionizing
When electromagnetic radiation is with energy BELOW the FAR-ultraviolet region (visible light, infrared and radio frequency)
What is the atomic number
Number of protons
How to find atomic mass number
It’s the atomic number or (number of protons) + number of neutrons.
What can be said about the bohr’s atomic model
The different orbitals (or shells) have different names (K, L, M, N orbitals) and energy levels.
The further from the nucleus, the higher the energy.
Electrons can jump between orbitals, when this occurs, the electron takes on the energy of the orbital that it is in.
If an electron jumps from a higher energy orbital to a lower one, that energy is released in the form of a photon.
What are the three ways of interactions of photons (x-rays) with matter (bodies)
- Photoelectric. Absorption
- Compton scattering
- Pair production
In photoelectric absorption, a photon absorbed into the absorber (matter). What is step one of this process.
- Photon is absorbed by an inner shell electron
In photoelectric absorption, a photon absorbed into the absorber (matter). What is step one and two of this process.
- Photon is absorbed by an inner shell electron
- All photon energy is transferred from the photon to the electron so that the photon disappears
In photoelectric absorption, a photon absorbed into the absorber (matter). What is step 1, 2 and 3 of this process.
- Photon is absorbed by an inner shell electron
- All photon energy is transferred from the photon to the electron so that the photon disappears
- This electron is know called a photoelectron and is ejected, this leaves a vacancy
In photoelectric absorption, a photon absorbed into the absorber (matter). What is step 1, 2, 3, 4 of this process.
- Photon is absorbed by an inner shell electron
- All photon energy is transferred from the photon to the electron so that the photon disappears
- This electron is know called a photoelectron and is ejected, this leaves a vacancy
- To stabilize the atom, an outer shell electron fills the vacancy in the inner shell
In photoelectric absorption, a photon absorbed into the absorber (matter). What is step 1, 2, 3, 4 and 5 of this process.
- Photon is absorbed by an inner shell electron
- All photon energy is transferred from the photon to the electron so that the photon disappears
- This electron is know called a photoelectron and is ejected, this leaves a vacancy
- To stabilize the atom, an outer shell electron fills the vacancy in the inner shell
- Electron releases energy in the form of X-rays, also known as characteristic photon or characteristic radiation.
As we know each electron shell has a different energy level, those closest to the nucleus are lower in energy than those farther from the nucleus. In order to move between shells in step 4, an electron must absorb or release an amount of on energy. This is why when an electron drops to a lower-energy she, it releases energy in the form of X-rays
Photoelectric absorption is dominant for photon energies bellow ____
25 keV or 25000 eV
X-ray photon has a _____ energy
Fixed, because orbital electrons have fixed energies which correspond to the orbit they occupy
Why are X-ray photons, characteristic photons?
its energy is a characteristic of the absorbing material (I don’t get this)
List the first step of the Compton effect
- In Compton scattering, the photon transfers not all but only PART of its energy to sun OUTER shell electron
List the 2nd step of the Compton effect
- In Compton scattering, the photon transfers not all but only PART of its energy to sun OUTER shell electron
- The photon knocks the photoelectron/ electron out and looses some energy to it in the process
In the Compton effect, when does a photon lose its maximum amount of energy
When the collision is head on and the photon has its direction of travel reversed.
In the Compton effect, when does a photon lose a minimal amount of energy
If the collision is only a glancing one, the energy given to the recoil electron will be much less than during a head on collision
A single photon may undergo _____ collisions, losing energy on each occasion and eventually be absorbed by the ___ ___
Several, photoelectric effect
The loss of energy in Compton scattering depends on the ___ through which the photon is scattered
Angle
The Compton effect is the dominant effect for photon energies above ____ and up to ___
200 keV and up to 2 MeV
Between __ and __ both photoelectric and Compton effects can occur
60 keV and 90 keV
The probability of occurrence of photoelectric absorption ________ as the ENERGY of the incident photon DECREASES and the ATOMIC NUMBER of irradiated atoms _____. It also depends on the _____ ________ in the absorbing material
Increase, increase, chemical elements
Photoelectron absorption is dominant for photon energies bellow 25 keV
The likelihood of photoelectric absorption increases as the square of the atomic number. True or false?
False. It is the cube of the atomic number Z^3
Give an example of good absorbers of X-ray photons (photoelectric absorption)
Heavy metals like lead, Z= 82. That’s why lead lining is used to prevent objects from getting incident by X-rays as they absorb them.
In which part of X-ray beam is photoelectric absorption higher?
The one with the higher atomic number. Bone has the highest atomic number and density.
In the attenuation of an X-ray beam air is
Negligible (its black on image)
In the attenuation of an X-ray beam bone is
Significant due to high density (its thick and heavy, intensity is reduced)
In the attenuation of an X-ray beam soft tissue (muscle) is
Similar to water
Less dense than bone, allow most of x-ray to pass through and appears dark grey on film
Define attenuation
The reduction of intensity of an x ray beam as it traverses matter.
In the attenuation of an X-ray beam fat tissue is
Appears as shades of grey. Less dense bone.
In the attenuation of an X-ray beam of the lung
Weak attenuation due to density
Higher kVp ______ photoelectric effect leading to ____ image quality. WTF?
Reduces, better
COMPTON
COMPTON
COMPTON
How do the photoelectric and Compton effects help in X-ray imaging
Some Images reveal tissues, by both photoelectric absorption and the Compton scattering effects. In the following image the contrast is due to density and thickness differences. In most cases, photoelectric absorption effect plats the dominant role, thus contrast is affected more by chemical composition of materials and photon energy.
Mass of higher density = more visible
The absorption method of pair production only happens for
Very high-energy photons
Explain pair production
If the photon has sufficient energy then it can be absorbed by the atomic nucleus in the absorber and results in the production of an electron and a positron.
A case of energy being converted to mass is
Pair production
The mass of the electron and positron is such that ______ MeV is needed to produce
1.02
If the incident photon has more than 1.02 MEV of energy what happens?
The excess energy increases the velocity of the electron and positron
Positrons do not live very long… why is that?
Because if it meets an electron it combines with it to produce two photons of 0.51 MeV
WHAT ARE THE TWO KNOW PRODUCED PHOTONS FROM THE POSUTRON COMBINING WITH AN ELECTRON CALLED
ANNIHILATION RADIATION
Pair production is the dominant effect for photon energies ABOVE?
Above 5 MeV
Summarize this graph
Attenuation doesn’t only take place in the absorption processes but
In the inverse square law “attenuation (reduction of the intensity of a beam of photons)” as well
“If the radiation from a source can spread in all directions, then its intensity will fall off in inverse proportion to the distance squared” meaning
If you double the distance, you reduce the intensity exposure by a factor of 4
The intensity of radiation falls off as you move away from the
Source
Understand the image
The inverse spare law basically states that
Greater distance from source minimizes doze of radiation due to the decrease in intensity
