1. Radiation Physics II

2. X-rays
Weightless bundles of energy without an electrical charge that travel in waves with a specific frequency at the speed of light. X-ray photons interact with the materials they penetrate and cause ionization

3. X-Rays Properties Appearance Mass Charge Speed Wavelength
Path of travel

4. X-Rays Properties
Focusing capability: X-rays cannot be focused to a point and always diverge from a point
Penetrating power: X-rays can penetrate liquids, solids, and gases. The composition of the substance determines whether x-rays penetrate or pass through, or are absorbed
Absorption: X-rays are absorbed by matter; the absorption depends on the atomic structure of matter and the wavelength of the x-ray
Ionization capability
Fluorescence capability: X-rays can cause certain substances to fluoresce or emit radiation in longer wavelengths (e.g., visible light and ultraviolet light).
Effect on film
Effect on living tissues

5. The X-ray Machine Component
Control Panel
Extension Arm
Electrical connector (plug)
Tubehead

6. support arms
tubehead
control panel

7. support arms
control panel
tubehead

8. Control Panel
Exposure Time
exposure time
adjustment
70 kVp 7 mA

9. Control Panel

10. Tubehead
Metal housing, or the metal body of the tubehead that surrounds the x-ray tube and transformers and is filled with oil
Insulating oil, the oil surrounds the x-ray tube and transformers inside the tubehead; it prevents overheating by absorbing the heat created by the production of x-rays
Tubehead seal, or the aluminum
Permits the exit of x-rays from the tubehead
Seals the oil in the tubehead
Acts as a filter to the x-ray beam

11. Tubehead
Aluminum disks, 0.5-mm thick aluminum placed in the path of the x-ray beam; they filter out the non-penetrating, longer wavelength
Lead collimator (lead plate) with a central hole that fits
directly over the opening of the metal housing where the
x-rays exit; it restricts the size of the x-ray beam
Position-indicating device (PID), it is lead-lined cylinder that extends from the opening of the tubehead
X-ray tube, is the heart of the x-ray generating system
Transformer is a device that alters the voltage of incoming electricity

12. X-ray tube
Is the basic apparatus for generating x-rays, is composed of leaded-glass tube, cathode, and an anode

13. X-ray tube- leaded-glass tube
The glass tube is leaded to prevent x-rays from escaping in all directions
One central area of the leaded-glass tube has a “window” that permits the x-ray beam to exit the tube
The x-ray tube is evacuated to:
Prevent collision of the moving electrons with gas molecules, which would significantly reduce their speed
Prevents oxidation and "burnout" of the filament

14. X-ray tube- Cathode Filament
It is a coil of tungsten wire about 2 mm in diameter and 1 cm or less in length
It is mounted on two stiff wires that support it and carry the electric current
The filament produce electrons when heated

15. X-ray tube- Cathode Focusing Cup
The filament lies in a focusing cup, a negatively charged concave reflector made of molybdenum
The focusing cup focuses the electrons emitted by the filament into a narrow beam and directs the beam toward a small rectangular area on the anode called the focal spot
The electrons move in this direction because they are repelled by the negatively charged cathode and attracted to the positively charged anode

16. X-ray tube- Anode
Positive electrode, consists of a thin tungsten plate (target) embedded in a copper stem
A tungsten target serves as a focal spot and converts accelerated electrons into x-ray photons
The copper stem, which functions to dissipate the heat away from the tungsten target.

17. X-ray tube- Anode
The target is made of tungsten because it has a high atomic number, high melting point, and low vapor pressure at the working temperatures of an x-ray tube
The purpose of the target is to convert the kinetic energy of the electrons generated from the filament into x-ray photons

18. X-ray tube

19. Electricity and Electric Currents
Electricity is the energy that is used to make x-rays
Electrical energy consists of a flow of electrons through a conductor; this flow is known as the electric current
Amperage is the measurement of the number of electrons moving through a conductor. Current measured in amperes or milliamperes (mA)
Voltage is the measurement of electrical force that causes electrons to move from a negative pole to a positive one. Voltage is measured in volts or kilovolts (kV)
In the x-ray tube, the amperage can be increased or decreased by the milhiamperage (mA) adjustment on the control panel of the x-ray machine
The voltage of the x-ray tube current is controlled by the kilovoltage peak (kVp) adjustment on the control panel

20. Circuits
Low- voltage or filament circuit: the filament circuit uses 3 to 5 volts, regulates the flow of electrical current to the filament of the x-ray tube, and is controlled by the milliamperes settings
High-voltage circuit: the high-voltage circuit uses 65,000 to 100,000 volts, provides the high voltage required to accelerate electrons and to generate x-rays in the x-ray tube, and is controlled by the kilovoltage settings

21. Transformers
A transformer is a device that is used to either increase or decrease the voltage in an electrical circuit
In the production of dental x-rays, 3 transformers are used to adjust the electrical circuits: the step-down transformer, the step-up transformer, and the autotransformer

22. Transformers
The filament circuit uses 3 to 5 volts, a step-down transformer is used to decrease the voltage from the incoming 110 or 220 line voltage to the 3 to 5 volts required
The high-voltage circuit requires 65,000 to 100,000 volts and uses both a step-up transformer and an auto- transformer. A step-up transformer is used to increase the voltage from the incoming 110 or 220 line voltage to the 65,000 to 100,000 volts required. An auto- transformer serves as a voltage compensator that corrects for minor fluctuations in the current

23. kVp 3-5 volts 65-90 volts filament <110 volts 110 volts 65,000 to
kVp
3-5 volts
65-90 volts
filament
<110 volts
110 volts
65,000 to
90,000 volts

24. Production of Dental X-rays
Electricity from the wall outlet supplies the power to generate x-rays
2. The current is directed to the filament circuit and step-down transformer in the tubehead. The transformer reduces the 110 or 220 entering line voltage to 3 to 5 volts
3. The filament circuit uses the 3 to 5 volts to heat the tungsten filament in the cathode portion of the x-ray tube. Thermionic emission occurs; thermionic emission is the release of electrons from the tungsten filament when the electric current passes through it and heats it up. The outer shell electrons of the tungsten atom acquire enough energy to move away from the filament surface, and an electron cloud forms around the filament. The electrons stay in an electron cloud until the high-voltage circuit is activated

25. Thermionic Emission
Release of electrons from hot filament when current flows after depressing exposure switch
hot
filament
x-section of
filament
electrons
The hotter the filament gets, the greater the number of electrons that are released.

26. Production of Dental X-rays

27. Production of Dental X-rays
4. When the exposure button is pushed, the high-voltage circuit is activated. The electrons produced at the cathode are accelerated across the x-ray tube to the anode. The molybdenum cup in the cathode directs the electrons to the tungsten target in the anode
5. The electrons travel from the cathode to the anode. When the electrons strike the tungsten target, their energy of motion (kinetic energy) is converted to x-ray energy and heat. Less than 1% of the energy is converted to x-rays; the remaining 99% is lost as heat

28. Production of Dental X-rays
6. The heat produced during the production of x-rays is carried away from the copper stem and absorbed by the insulating oil in the tubehead. The x-rays produced are emitted from the target in all directions; however, the leaded-glass housing prevents the x-rays from escaping from the x-ray tube 7. The x-rays travel through the unleaded glass window, the tubehead seal, and the aluminum disks. The aluminum disks remove or filter the longer wavelength x-rays from the beam 8. Next, the size of the x-ray beam is restricted by the lead collimator. The x-ray beam then travels down the lead-lined PID and exits the tubehead at the opening of the PID

29. X-ray Production 3

30. Types of X-rays Produced
Not all x-rays produced in the x-ray tube are the same; x-rays differ in energy and wavelength
The energy and wavelength of x-rays varies based on how the electrons interact with the tungsten atoms in the anode. The kinetic energy of the electrons is converted to x-ray photons via one of two mechanisms: general (Bremsstrahiung) radiation OR characteristic radiation

31. General Radiation
General radiation is produced when an electron hits the nucleus of a tungsten atom or when an electron passes very close to the nucleus of a tungsten atom

33. + Bremsstrahlung X-ray Production
Bremsstrahlung X-ray Production
Electron slowed down by positive charge of nucelus; energy released in form of x-ray +
High-speed electron from filament enters tungsten atom
Electron continues on to other atoms until all of its energy is lost

34. + Bremsstrahlung X-ray Production Maximum energy+
High-speed electron from filament enters tungsten atom and strikes nucleus, losing all its energy and disappearing
The x-ray produced has energy equal to the energy of the high-speed electron; this is the maximum energy possible

35. Characteristic Radiation
Produced when a high- speed electron displaces an electron from an inner shell of a tungsten target atom and causes ionization of that atom
When this happens, another electron in an outer shell of the tungsten atom is quickly attracted to the void in the deficient inner shell. When the displaced electron is replaced by the outer-shell electron, a photon is emitted with an energy equivalent to the difference in the two orbital binding energies

36. Characteristic X-ray Production
Characteristic X-ray Production
Ejected electron leaves atom
vacancy M
High-speed electron with at least 70 keV of energy (must be more than the binding energy of k-shell Tungsten atom) strikes electron in the K shell L K
Recoil electron (with very little energy) exits atom

37. Characteristic X-ray Production
Characteristic X-ray Production
X-ray with 59 keV of energy produced. 70 (binding energy of K-shell electron) minus 11 (binding energy of L-shell electron) = 59.
Outer-shell electron
drops into vacant spot M L K

38. Characteristic Radiation