X-ray production

x-ray tube window

Is the area of the glass or metal enclosure, approximately 5 cm2 , that is thin and through which the useful beam of x-rays is emitted.

Useful beam

X-rays emitted through the window

Leakage radiation

X-rays that escape through the tube housing

100 Mr/hr

Leakage radiation should not exceed ___mR/hr at 1 meter when operated at maximum condition

Cathode

Negative side of the x-ray tube

Filament and focusing cup

The cathode is the negative side of the x-ray tube and contains two primary parts:

Filament

Usually approximately 2 mm in diameter and 1 or 2 cm long

2 mm, 1 or 2 cm

Usually approximately __ mm in diameter and _ or _ cm long

Thoriated tungsten

Filaments are usually made of __

3410 degrees C

Tungsten melting point

Thermionic emission

When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are "boiled off" and ejected from the filament

Focusing cup

Focuses the electrons toward the target

Space charge

Is a concept in which excess electric charge is treated s a continuum of charge distributed over a region of space (either a volume or an area) rather than distinct point-like charges

Anode

Positive side of the x-ray tube: it conducts electricity and radiates heat and contains the target.

Electrical conductor, mechanical support, thermal dissipation

Functions of anode assembly

Target

Area of the anode struck by the electrons from the cathode

Focal spot

actual x-ray source

small focal spot

used when better spatial resolution is required. Ranges from. 0.1 to 1 mm

0.1 to 1 mm

Small focal spots range from

Large focal spot

used when large body parts are imaged and when other techniques that produce high heat are required

Stationary Anode

Are used in dental x-ray imaging systems, some portable imaging systems, and other-purpose units in which high tube current and power are not required.

Rotating anode

Capable of producing high intensity x-ray beam. Heat capacity can be further improved by increasing the speed of anode rotation

3400 rpm and 10,000 rpm

Rotating anode rpm

Stationary anode, rotating anode

Types of Anode

Stationary anode tubes

The target consists of a tungsten alloy embedded in the copper anode. About 4 mm^2

Rotating anode tubes

the entire rotating disc is the target. About 3159 mm^2

Induction motor

The rotating anode is powered by an electromagnetic _______.

Stator and rotor

An induction motor is consist of 2 parts

Atomic number, thermal conductivity, high melting point

Tungsten is the material of choice for the target for general radiography for three main reasons:

Molybdenum or Rhodium Targets

Special x-ray tubes for mammography have _____ or _____ targets principally because of their low atomic numbers and low K characteristics x-ray energy

Alloying tungsten (usually with rhenium)

Mammographic X-ray tubes: ________ ( usually with _____) gives it added mechanical strength to withstand the stresses of high speed rotation

Molybdenum and graphite

Mammographic X-ray tubes: _____ and _____ have lower mass density than tungsten, thus allowing the target to easily rotate

42, 19 keV

Mo - atomic numbers: __ ; K-shell electron binding energy: __ keV

45, 23keV

Rh - atomic numbers: __ ; K-shell electron binding energy: __ keV

Line focus principle

Results in an effective focal spot size much less than the actual focal spot size

Line focus principle

allows high anode heating with small effective focal spots. as the target angle decreases, so does the focal spot size

GOETZE principle

Line focus principle is also known as

5 to 20 degrees

Diagnostic x-ray tubes have target angles that vary from approximately __to __ degrees

Heel effect

The smaller the anode angle, the larger is the ___________

Cathode side

Radiation intensity is greater on the _______ of the x-ray field

Off-focus radiation

Electrons bounce off the focal spot and then land on other areas of the target, causing x-rays to be produced from outside of the focal spot.

Kinetic energy

energy of motion

Projectile electrons

Electrons traveling from cathode to anode

Projectile electrons

______ interacts with orbital electron of the target atom

99%

Approximately ___% of kinetic energy of projectile electrons is converted to heat

1%

Only approximately ___% of projectile electrons is converted to x-ray

Independent

The efficiency of x-ray production is (dependent or independent) of the tube current

Directly Proportional

Efficiency of x-ray production and kVp relationship

Characteristic radiation

Are emitted when an outer-shell electron fills an inner-shell void

15%

At 100 kVp, approximately ___% of the x-ray beam is characteristic

Bremsstrahlung radiation

Are produced when a projectile electron is slowed by the electric field of a target atom nucleus.

Bremsstrahlung radiation

"Slowed down radiation"

To brake

"Bremsen-"

Radiation

"Strahlung"

"Braking radiation" or "deceleration radiation"

Bremsstrahlung meaning

Wilhelm Conrad Roentgen

discovered x-rays

November 8, 1895

When were x-rays discovered?