2: Working With ☣️ Flashcards
What is the main difference between light and X-rays?
Energy
The most significant difference between alpha particle radiation and gamma radiation is that alpha particle have…
Mass
If radiation has sufficient energy to remove an electron from a neutral atom it is called ________ radiation.
Ionizing
Isotopes of an element do not have the same what?
Mass number
When charged particles give up part of their kinetic energy (or occasionally all) in the form of electromagnetic radiation, it is called…
Bremsstrahlung
The minimum energy of an incoming photon required for pair production is how many MeV?
1.02 MeV
The function of a photomultiplier tube is to convert _______ into _______.
Light into electrical pulses
What is the governing body that regulates the use of industrial X-ray equipment in Canada?
Health Canada
An X-ray tube can’t have more than how many mV flowing through it?
500
Where is the focal spot of the X-ray tube located?
Anode
What is the reason for keeping the focal spot of an X-ray tube small?
To increase image sharpness
The filament of the common “hot cathode” style X-ray tube is most often made of?
Tungsten
To overcome the repulsion between electrons, electrons are steered towards a common point on the target by means of a…
Focusing cup
The projected area of the target of an X-ray tube is called what?
Effective focal spot
The primary form of energy conversion when electrons strike a target in an X-ray tube results in the production of what?
Heat
A shorter wavelength does what to the penetrating power?
More penetration = more energy = shorter wavelength
Energy is directly proportional to what?
Frequency
Energy is indirectly proportional to what?
Wavelength
Ionizing does what to neutral atoms?
Causes them to lose electrons from their orbitals making them positively charged
Ionizing energy is the minimum energy required to do what?
Remove an electron from its shell
Which process of attenuation/ionization will repeat itself several times until the energy is low enough?
Compton scattering
What energy is required for pair production?
At or above 1.02 MeV
Which attenuation/ionization transducers it’s totally energy in the process?
Photoelectric process
A linear attenuations decrease is proportional to what?
The original intensity
How do you calculate the Roentgen Equivalence Man (REM)?
RAD x RBE
Radiation absorbed dose x radiation biological effects
Who are the scientists of radiography?
ICRP (international commission of radiation protection)
What does the ICRP recommend?
Dose limits and regulations… then CGSB will adopt them
How do you describe predicable effects?
Stochastic
Which survey meter uses a high voltage?
Geiger Muller
What does a TLD contain?
Thermoluminescent chips
What does an OSL contain?
Aluminum energy
What type of inert gas does a Geiger Muller contain?
Usually argon
What can produce DRD and PADs and why?
Electronic dosimeter because it has both the capabilities
What are the electrons called that are farthest from the nucleus?
Valence electrons
What do valence electrons control?
Conductivity (electrical & heat) and chemical & magnetic properties of the element
Where do radioactive transformations occur?
In the nucleus
If an atom could be seen, what would the diameter be?
1 millionth the diameter of a human hair
What are the 2 types of energy?
- Potential - stored but can be released
2. Kinetic - generated by motion
What can’t be created or destroyed, only changed in form?
Matter and energy
How can you describe a photon?
Energy without mass
What are some examples of non-ionizing radiation (4)?
- Heat
- Microwave
- Visible & infrared light
- Radio waves
How much more penetrating is cobalt compared to iridium?
2x
Energy isn’t an intensity of the radiation field produced by equipment, its actually what?
Penetrating ability of device
Is ionization a result of direct collision with the electron?
No because electromagnetic radiation has no mass
The does the photoelectric process take place?
In the inner shell of an electron
Where does the Compton effect take place?
Outer shell
Annihilation of the photon in pair production creates what?
2 charged particles: an electron (-1) and a positron (+1)
What does a value layer do?
Expresses the effectiveness of absorbing/shielding material
Who comes up with max permissible dose and effective dose limits?
International Commission on Radiological Protection (ICRP)
How much background radiation does a typical Canadian receive annually?
2 mSv (200 mrem)
What is the intent of the ICRP’s guidelines on exposure limits (2)?
- Prevent severe/over exposure
2. Limit prolonged exposures to acceptable levels
Exposure limits for a radiation worker per year, 5 year and special circumstance.
20 mSv (2 rem)/year 50 mSv (5 rem)/special circumstance 100 (10 rem)/5 years
What are 3 factors that affect radio sensitivity?
- Stage of cell division - immature cells more affected
- Cell activity - more active = more vulnerable
- Blood/food supply to cells - undernourished cells are less active = less vulnerable
What part of the body is most affected by radiation?
Blood and blood forming
What is primary function of red blood cells?
The hemoglobin they contain carry oxygen from respiratory organs to rest of body.
White blood cells play a role in scar tissue and…
Formation and promotion of antibodies - lack of will cause Leukopenia but too many will cause leukemia
What govern the quality and quantities of a radiation device?
kV = quality mA = quantity
Why must a “duty cycle” be adhered to?
Leads to overheating - insides will fry or it will shut off completely until it had cooled enough.
Collimators are generally used for what type of ray?
Gamma
For every 100 keV.. it will penetrate how much of steel?
1”
What is the main disadvantage of a passive dosimeter?
No direct reading capabilities
What type of X-ray tube is the most portable?
Bipolar Tube 150 kV to 450 kV
What type of X-ray tube can be positioned inside smaller openings and can produce a panoramic/circumferential exposure?
Unipolar tube
What are the 2 types of systems used to generate X-rays?
AC (alternating current) and CP (constant potential systems)
What are the 2 key point of AC?
- All the radiation isn’t useful so filters must be used to remove unwanted lower energy X-rays,
- Will result in longer wavelength radiation
What conversion happens in CP?
Tube rectifiers convert AC wall current into rectified AC that resembles DC
(More uniform mono-energetic radiation)
What type of beam does DC produce?
More uniform beam of harder/shorter wavelength X-rays
Valve tubes are specifically designed to do what?
Produce X-rays in short bursts/pulse (dependant on frequency of AC applied)
Describe the 3 types of transformers:
- Step Up: (high voltage) supplies tube power
- Step Down: powers filament in cathode
- Auto: control line volt supplied to tube equipment
What do rheostats do?
Controls filament heating current (and auto transformer controls high volt)
What are 3 ways rectification can be carried out?
- Use of valves & diodes
- Use of special rectification circuits
- Use of semi-conductor rectifiers
ALL take place after high volt secondary coil and anode
What are the 3 types of intensifying screens?
- Lead
- Fluorescent
- Fluorometallic
Not using a screen in your radiograph can result in a softer, grainier outline which can be referred to as what type of appearance?
Mottled
What are the intensification factors for the fluorescent screens?
Fluorescent: from 10-200
(Contrast & definition sucks)
Fluorometallic: 5-150
(Better quality/results from screens made of copper/steel)
Comes and diagrams generally used on what?
Smaller items not needing much radiation
What are the 2 tube essentials?
- Negative cathode containing high temp resistant tungsten filament
- Positive anode containing high density tungsten
What type of X-rays cause an electron in higher orbit to fall to lower levels thus giving off secondary X-ray photon?
Characteristic X-rays
Which element is usually the material of choice when operating X-ray tube at low voltages?
Beryllium (lightest solid, stable element)
What does the focusing cup contain?
Electrons that are “boiled off” of filament
What are the 3 main international standard organizations that recommend protection levels?
- International Commission on Radiological Protection* (ICRP) 1928
- International Atomic Energy Agency (IAEA) 1957
- International Commission on Radiation Units & Measurements (ICRU) 1925
When tube current is increased, what is affected?
Only intensity
When tube voltage is adjusted, what is affected?
Wavelength and intensity
Electron emission (from filament) is a function of what?
Temp via thermionic emission process
What is the Heel Effect?
Intensities in cathode see slight increase in intensity before steady decrease towards edge.
What 3 things are needed to achieve the highest level of definition/sharpness?
- Focal spot as close to point source as possible.
- Source to detector distance as great as practical
- Specimen to detector as small as practical
How are images stored in xeroradiography?
On selenium coated electro statically charged plate (using a developing powder that was applied to imaging paper)
What’s the difference between a radiograph and a photograph?
Radiograph = photo-negative Photograph = photo-positive
What is a radiographic film coated with?
An emulsion containing fine crystals/grains of radiation sensitive silver halide crystals (like silver bromide & chloride)
Lead screens are in direct contact with both sides of film for what range?
150 to 400 kV
Fluorometallic screens are often used in conjunction with what?
Fast speed films to greatly reduce exposure times
When using sources with energy ranges higher than 1 MeV, lead isn’t the best material for intensifying screens. What works better?
Copper/steel
