Rad-103: Ch 2 Fundamentals of Radiation Protection

what does production of x-ray require

rapidly moving stream of electron suddenly decelerating or stopping

what is thermionic emission and how does it occur

electrons being emitted when a negative electrode is heated

which electrode is a cathode

negative electrode

which electrode is anode

positive electrode

how are electrons stopped

rapidly move, and are attracted, to the anode

________________

what are the filaments in cathode

source of electron

coiled tungsten wire

focusing cup

what does source of electron create

thermionic emission

what is the size of coiled tungsten wire

large

small

what is a focusing cup

___________

what does focus cup do

focus stream of electrons from filament towards anode target

why are most x-ray dual focus tubes

contain two filaments

what is a focusing cup

contained made of nickel that nearly surrounds filament

what is anode composed of

molybdenum, copper, tungsten, graphite

why are specific materials for anode used

have thermal and conductive properties

what are the types of anode

stationary

rotating

what type of anodes are more common

rotating

when/where are stationary anodes used and why

dental offices due to use being limited/not as demanding

what is the speed at which rotating anodes operate

3000 - 10,000 RPM

why do anode tubes use tungsten as the target

has a high atomic number

efficient at producing x-ray

high melting point

what is atomic number of tungsten

74

melting point of tungsten

3400 C

6152 F

what does a rotating anode require to rotate

stator and rotor

what is a stator

electric motor that turns rotor at high speed

what is rotor composed of

copper

how is rotor connected to anode

via molybdenum stem

how much x-ray production is heat

99%

what can cause premature failure of rotating anode

buildup of heat in tube

what can prevent premature failure of rotating anode

effective dissipating of heat

how do modern tubes help cooling of rotating anode

tubes encased in oil

incorporate cooling fans

what does a target/focal tract of a rotating anode so

decelerates and stops electron

what is rotating anode target/focal tract made of

90% tungsten alloy

10% rhenium alloy

where is target/focal tract of rotating anode located

embedded in base of molybdenum and graphite

what is the target angle of the focal tract in a rotating anode

5 - 20 degrees

what happens after rotor is activated and exposure initated

kVp applied across tube to make cathode negative and anode positive → electrons repelled from cathode and attracted to anode → negative charged focus cup focuses electron into stream that travel across tube gap in tube current

what happens to kinetic energy of electrons that interacts with target in anode

converted into x-ray and heat

what is x-ray tube housing made of

metal or glass envelope

what material of tube housing is more commonly used

metal

what is advantage of metal envelope

reduces off focus radiation

what is tube housing lined with and why

lead shield to prevent leakage of radiation

what is permissible amount of maximum output of leakage from tube housing

100mR/h (1mGy_a/h) when 1m from source

what does x-ray circuit do

precisely control flow of electrons through x-ray system components

where are circuits integrated

layered circuit boards

how many voltage does x-ray produce

50,000 - 150,000 V

electrical power is expressed in

kilowatts (KW)

power maintenance formula

power (W) = amps (I) x volts (V)

what are the divisions of x-ray circuit

high voltage

low voltage

what is used as conductors in in circuits

copper wire

what division is part of primary circuit

high-voltage side

how does the primary circuit work

takes incoming voltage and increases it to kVp values during exposure

what value of V do most primary circuits use and why

440 to 480 V

it is more reliable that can be provided by the power utility

what do transfomers do

regulate voltage in x-ray system

what are transfomers

devices consisting of copper wire coiled around central core material of laminated steel plates

what does the input and output sides contain

primary coil

secondary coil

what determines whether a transformer is step up or step down

the ratio of windings between primary and secondary sides

what does transformer law determine

amount of induced voltage

formula for transfomer law

V_s / V_p = N_s / N_p

voltage induced on secondary coil / voltage coming on primary coil = number of turns on secondary coil / number of turns on primary coil

what can induce an electrical current

placing a varying magnetic field in close proximity to a closed-circuit conducting material

what happens in a transfomer

electrical current coming onto a set of coils on the input/primary side creates an electrical current and voltage in secondary coil windings aka output side

why is mutual induction termed that

both coils work together in mutual magnetic-electrical fashion to create a verting magnetic field around the primary side of transformer coil windings

what type of current is required for efficient operation of transformers in mutual induction

alternating electrical current

how does kilovoltage selection occur

through autotransformer

what does autotransformer determine

induced voltage going to the primary side of the high-tension transformer

what do transformer in x-ray system control

voltage values on secondary side

what is a step up transformer

efficient and large high voltage transformers without moving parts that produce little heat

what are step up transformers encased in and why

dielectric oil to absorb heat produced and prevent electrical shock when high voltages are produced

relationship between autotransformer and step up transformer

single coil autotransformer supplies induced voltage to primary windings of step-up and permits selection of kVp values

what does the degree of induced voltage created by transformer depend on

number of coiled windings that are electrically contacted as contact points

relationship between voltage and current is

inversely related

how does resistance to flow of electrical current occur

electrical circuits have moving electron charges as they travel along circuit pathways that inherently impede flow of negative electrons due to electron friction

how can resistive values be controlled

length, temperature, and type of conducting material

keep circuits as short as possible using low resistance material at safe temperatures

what are low resistance materials

copper, silver, gold

how are circuits cooled

whisper fans, ventilation panels in electronic cabinets

what happens when electrical circuits get too warm

system malfunctions

not perform as designed

how does milliamperage selection occur

using precise resistors which regulate amount of current passing through cathode filament during exposure

what are resistors designed to do

impede flow of currents flowing through them

what does internal structure of a resistor do and how

control electron flow by conductor material type and thickness

how is cathode filament controlled

by low-voltage side of circuit

what is typical filament amperage range when not making exposure

3 - 6 amps

what type of transformers do filament circuits use and why

low-voltage step-down due to filament circuits using

what state is step-down transformer kept in and why

stand-by state with voltage of 5 - 15 V and 3 - 5 amps to ke