RADIATION RADIATION PHYSICSPHYSICS

Presentation Outline Presentation Outline

1-Discovery of X-rays 1-Discovery of X-rays 2-Overview of Atomic Structure2-Overview of Atomic Structure 3-Members and Properties of 3-Members and Properties of

the Electromagnetic the Electromagnetic Spectrum .Spectrum .

4-4- Properties of X-raysProperties of X-rays 5-Related Terminology5-Related Terminology

Discovery of X-rays

X-rays were discovered in 1895 by the physicist Wilhem Conrad Roentgen, who called them X-rays because their nature was at first unknown.

He was interested in the cathode tubes (stimulatedinternally by an electric volt and totally evacuated fro air) and decided to see what they could do.

He covered the cathode tube with a shield of blackcardboard and worked in a totally dark room.

• He saw a luminescent greenish faint glow coming from a fluorescent screen(a chemically-painted screen) placed on the table opposite the tube

He was even more amazed to find that when the rays passed through body parts, such as the hands, the bones beneath the skin became clearly visible on the screen.He recognized that these non-reflected,invisible,mysterious rays could penetrate solid objects and produce an image of them on sensitized plates

•He discovered then that certain invisible rays were emanating from the tube and penetrating the cardboard shield, and fell upon the luminescent screen, thus revealing their existence and making darkness visible.

First image taken by Roentgen for his

wife’s hands with a ring on her finger In early 1896, X-rays were

being utilized clinically in the United States for such things as bone fractures

and gun shot wounds.

Composition of matterComposition of matter:: - - Substance of which all physical things Substance of which all physical things

are madeare made - - Occupies space and has inertiaOccupies space and has inertia

- - Has mass and can exert force or be Has mass and can exert force or be acted upon by forceacted upon by force

- - Can exist in three forms: solid, liquid or Can exist in three forms: solid, liquid or gasgas

- - Divided into elements or compoundsDivided into elements or compounds::ElementsElements are accumulations of a single are accumulations of a single atom speciesatom speciesCompoundsCompounds are recurring arrangements are recurring arrangements of units of at least two different atomsof units of at least two different atoms

Atomic structureAtomic structure:: a. Central nucleus: (+ ve charged)a. Central nucleus: (+ ve charged)

- -Protons:Protons: carry the + ve charge carry the + ve charge

- -Neutrons:Neutrons: electrically neutral electrically neutral

b. Revolving electrons: ( - ve b. Revolving electrons: ( - ve charged)charged)

They revolve around the nucleus in paths They revolve around the nucleus in paths or shells designated letters from K to Qor shells designated letters from K to Q

NB:NB: An atom in its ground state is An atom in its ground state is electrically neutral containing equal electrically neutral containing equal numbers of protons and electronsnumbers of protons and electrons..

Atom (electrically neutral)

Atomic Number (Z) = # of protons

K-shell

L-shellprotons

neutrons

electronsM-shell

NB:NB: Atoms cannot be subdivided by Atoms cannot be subdivided by ordinary means but only broken ordinary means but only broken down into smaller sub-atomic down into smaller sub-atomic particles by high energy techniquesparticles by high energy techniques

Forces inside the nucleusForces inside the nucleus::

Atoms are present normally in a balanced Atoms are present normally in a balanced state due to equalization and balance state due to equalization and balance between two forcesbetween two forces::Electrostatic force:Electrostatic force: Force of attraction Force of attraction between + ve protons and between + ve protons and –– ve ve electronselectrons..Centrifugal force:Centrifugal force: Constant spinning Constant spinning motion of electrons at high speeds motion of electrons at high speeds around the nucleus pulling them awayaround the nucleus pulling them away

Binding energy:Binding energy: Energy required to Energy required to remove an electron from its orbitremove an electron from its orbit

Attraction between protons and electrons

Electrostatic Force

Centrifugal Force

Pulls electrons away from nucleus

Balance between electrostatic force and centrifugal force keeps electrons in orbit around nucleus

EF CF

Electrostatic force is the attraction between the positive protons and negative electrons. Electrons in the orbit closest to the nucleus (the K-shell) will have a greater electrostatic force than will electrons in orbits further from the nucleus .

Another term often used is binding energy; this basically represents the amount of energy required to overcome the electrostatic force to remove an electron from its orbit. For our purposes, electrostatic force and binding energy are the same. The higher the atomic number of an atom (more protons), the higher the electrostatic force will be for all electrons in that atom.

Ionization and Excitation:When energy strikes an atom, and is transferred to an orbital electron ionization or excitation may occur:

Ionization: The process by which an atom loses its neutrality and becomes an ion, either by addition of an electron (forming a –ve ion) or by removal of an electron (forming a +ve ion).To cause such ionization, sufficient energy is required to overcome the electrostatic force binding the electrons to the nucleus.

Excitation: If the transferred energy is not great enough to remove an orbital electron, it will raise the electron to a higher energy level within the atom. For the atom to return to its ground (stable state), the electron raised to a higher energy level is moved to an orbit at a lower energy level. In achieving this, energy must be lost and is given up in the form of electromagnetic radiation.

Ionization State

Ionization is the process of removing an electron from an electrically neutral atom to produce an ion pair. An ion is an atom or subatomic particle with a positive or negative

charge.

Ionization negative ion ) electron(

positive ion: atom with 3 protons, 2 electrons

X-ray enters atom and strikes electron, knocking it out of its orbit and creating two ions (ion pair). The ejected electron is the negative ion and the atom with a net positive charge is the positive ion.

Types of radiationTypes of radiation::

Radiation is the emission, Radiation is the emission, transmission and propagation of transmission and propagation of energy through space or matter in energy through space or matter in the form of particles or wavesthe form of particles or waves..

There are two types of radiationThere are two types of radiation::

A. Particulate or corpuscular A. Particulate or corpuscular radiationradiation

B. Electromagnetic radiationB. Electromagnetic radiation

A. Particulate RadiationA. Particulate Radiation::

**Consists of tiny sub-atomic particles that have mass, Consists of tiny sub-atomic particles that have mass, charge (except neutrons) and move at high speeds charge (except neutrons) and move at high speeds in straight linesin straight lines..

**They transmit kinetic energy by their extremely fast They transmit kinetic energy by their extremely fast moving and small massesmoving and small masses

* *They are given off from radium, uranium They are given off from radium, uranium radioisotopes or during atom splitting by high radioisotopes or during atom splitting by high energy techniquesenergy techniques . .

Examples of particulate radiationExamples of particulate radiation:: - - Alpha rays (from nucleus of heavy metals)Alpha rays (from nucleus of heavy metals)

- - Beta rays and cathode rays ( high speed electrons)Beta rays and cathode rays ( high speed electrons)

The movement of energy through space as a combination of electric and magnetic fields

B. Electromagnetic Radiation

Travel at the speed of light

(3 x 108 meters/second)(186,000 miles/second)

B. Electromagnetic B. Electromagnetic radiationradiation::

According to their energy and wavelength, they According to their energy and wavelength, they can be classified into ionizing and non-ionizing can be classified into ionizing and non-ionizing radiation. They can be arranged according to radiation. They can be arranged according to their wavelengththeir wavelength::

Ionizing Radiation:Ionizing Radiation: Non ionizing Non ionizing RadiationRadiation::

11 . .Cosmic rays 4. Ultraviolet raysCosmic rays 4. Ultraviolet rays

22 . .Gamma rays 5. Visible raysGamma rays 5. Visible rays

33 . .X-rays 6. Infra-red raysX-rays 6. Infra-red rays

77 . .Micro-wavesMicro-waves

88 . .Radio, radar and TV Radio, radar and TV waveswaves

Properties of electromagnetic Properties of electromagnetic radiationradiation::

11 . .Made of pure energy units called Made of pure energy units called photons or quantaphotons or quanta

22 . .They have no chargeThey have no charge

33 . .They have no mass or weightThey have no mass or weight

44 . .They propagate in the form of They propagate in the form of waveswaves

55 . .They are a combination of electric They are a combination of electric and magnetic fieldsand magnetic fields

66 . .They travel at the speed of lightThey travel at the speed of light

) )186,000186,000 miles/ secmiles/ sec( (

77 . .They differ in their properties and They differ in their properties and energies according to their wavelengths. energies according to their wavelengths. The shorter the wave length, the higher The shorter the wave length, the higher the energy; the higher the frequency the the energy; the higher the frequency the higher the energyhigher the energy..

wavelength wavelength λλ x frequency v = Speed of x frequency v = Speed of lightlight

meter x cycle/sec = 3 x 10 meter x cycle/sec = 3 x 10 meters/secmeters/sec

WLWL

Electromagnetic Spectrum

radio TV visible light

x-rays gamma rays

cosmic rays

Cosmic Gamma X-rays Visible Light

TV-wavesRadio-waves

Cosmic rays ------------------shortest w + highest frequency = highest penetration = least absorption

RadioWaves------------------ longest w + lowest frequency = lowest penetration = highest absorption

Wavelength x Frequency = Speed of light

F

W

W

ENERGY

Ability to penetrate

Shorter wavelength, higher energy

Higher frequency, higher energy

A

B

CHighest energy?

Highest energyShortest wavelengthHighest frequency

X-ray CharacteristicsX-ray Characteristics

High energy waves

No mass

No charge (neutral)

Travel at speed of light

Invisible

X-ray CharacteristicsX-ray Characteristics

Travel in straight line

Cannot be focused to a point

Differentially absorbed

Cause fluorescence

Harmful to living tissue

- - X-rays have X-rays have extremely short wave lengthsextremely short wave lengths

) )0.10.1- - 11 AA(◦(◦

- - The The efficiency of X-ray penetration and efficiency of X-ray penetration and absorptionabsorption depends on depends on::

a. Wavelength of the x-raysa. Wavelength of the x-rays::

The shorter the rays the higher penetration The shorter the rays the higher penetration powerpower

b. Frequency of the x-raysb. Frequency of the x-rays::

The higher frequency the higher the The higher frequency the higher the penetrationpenetration

c. Photon energy of the x-raysc. Photon energy of the x-rays::

The higher the energy the higher the The higher the energy the higher the penetrationpenetration

In addition toIn addition to::

d. The density of the radio-graphed d. The density of the radio-graphed objectobject::

The higher the density, the less penetrationThe higher the density, the less penetration

e. Atomic number of the objecte. Atomic number of the object::

The higher the atomic number, the less the The higher the atomic number, the less the penetrationpenetration

f. Thickness of the objectf. Thickness of the object::

The greater the thickness, the less the The greater the thickness, the less the penetrationpenetration

- - X-rays can X-rays can affect the photographic film affect the photographic film emulsionemulsion causing physical changes within causing physical changes within the emulsion (latent image) that cannot be the emulsion (latent image) that cannot be seen except after processingseen except after processing..

- - X-rays can X-rays can cause certain substances to cause certain substances to fluorescefluoresce or emit radiation of longer or emit radiation of longer wavelength in the form of visible lightwavelength in the form of visible light..

- - X-rays cause X-rays cause ionization of atomsionization of atoms with with the formation of ion pairs. In the human the formation of ion pairs. In the human body , these ion pairs cause several body , these ion pairs cause several harmful effectsharmful effects..

- - X-rays cause X-rays cause biological damagesbiological damages in the in the human body in the form of somatic and human body in the form of somatic and genetic effectsgenetic effects..

tubehead

control panel

support arms

X-ray Machine

X-ray Machine

a.Tube head and power supply i. Tube ii. Accessories

b. Support or adjusting arms

c. Control panel and timer

PID or(cone)

PID = position indicating device

X-ray Tube head

degrees

exposure time adjustment

Control Panel

Exposure Time

70 kVp 7 mA

Control Panel

PID or(cone)

PID = position indicating device

X-ray Tube head

degrees

X-ray Tube

Tube window

Focusing cup

Tungestenfilament

Focal spot upon tungesten target

Glass tube

Useful x-ray beam

Cathode (1,2) Anode (3,4)

Cupper headCupper arm

electrons

X-ray Tube Components

1

2

435

8

6

7

91. focusing cup 6. copper stem or head2. filament 7. leaded glass3. electron stream 8. x-rays4. vacuum 9. glass window5. target

Ionization State

Ionization is the process of removing an electron from an electrically neutral atom to produce an ion pair. An ion is an atom or subatomic particle with a positive or negative

charge.

Ionization negative ion ) electron(

positive ion: atom with 3 protons, 2 electrons

X-ray enters atom and strikes electron, knocking it out of its orbit and creating two ions (ion pair). The ejected electron is the negative ion and the atom with a net positive charge is the positive ion.

X-ray Tube

The tubeThe tube

Evacuated tube of glass with two Evacuated tube of glass with two poles (Cathode) & (Anode)poles (Cathode) & (Anode)

The tubeThe tube

Evacuated tube of glass with two Evacuated tube of glass with two poles (Cathode) & (Anode)poles (Cathode) & (Anode)

i. The tube

Evacuated tube of glass with two poles a. Cathode) & b. (Anode)

The x-ray tube is evacuated to prevent collision of the moving electrons with

gas molecules, which would significantly reduce their speed. This

also prevents oxidation and “burn-out" of the filament

The cathode in an x-ray tube consists of a filament and a focusing cup.

is the source of electrons within the x-ray tube.

It is a coil of tungsten wire about 0.2 cm in diameter and 1cm or less in length.

a. Cathode

1. The filament

A negatively charged concave reflector made of molybdenum. The focusing cup focuses the

electrons emitted by the heated filament into a narrow beam directed at a small rectangular

area on the anode called the focal spot.

2. Focusing cup

(molybdenum)

(tungsten)

Cathode

Focusing cup

Filament

x-section offilament

hotfilament

The hotter the filament gets, the greater the number of electrons that are released.

electrons

Thermionic EmissionRelease of electrons from hot filament when current flows after depressing exposure switch

b. Anode

The anode consists of a tungsten target embedded in a copper stem

The purpose of the target in an x-ray tube is to convert the kinetic energy of the electrons

generated from the filament into x-ray photons. In this process more than 99% of the electron kinetic

energy converted to heat.

The focal spot is the area on the target to which the focusing-cup directs the electrons from the filament

1 .Target

.

The tungsten target is typically embedded in a large block of copper to dissipate heat. Copper, a good

Thermal conductor, dissipates heat from the tungsten, thus reducing the risk of the target melting.

2. Copper stem or head

In addition, insulating oil between the glass envelope and the housing of the tube head carries heat away from

the copper stem. This type of anode is a stationary anode.

Tungsten

High atomic number (Target,filament) because it is most efficient in producing electrons.

• Transfers heat readily (Target) thus dissipating

heat into the copper stem.

• High melting point (Target, Filament)

• Can be drawn into fine wire (Filament)

(Filament and Target)

AnodeDental x-ray machines have stationary anode

Copper stem

Target

side view front view

Target

The smaller the focal spot (target), the sharper the image (teeth) will be.During x-ray production, a lot of heat is generated. If the target is too small, it will overheat and burn up.The target is inclined at an angle about 20 degrees to the central x-ray beam. This provides a larger actual focal spot for better heat dissipation and a minimal effective focal spot leading to increased image sharpness.

Line Focus Principle

Focal spot

Film

Line Focus Principle

Apparent (effective)focal spot size

Actual focal spot size

Target

Cathode (-)

Anode (+)

PID

Line Focus Principle

Apparent (effective) focal spot size (looking at target surface through PID)

Actual focal spot size(looking perpendicular to the target surface)

PID

The primary function of the power supply is to provide:

1. A current to heat the filament2. A potential difference between the cathode and

anode. These functions are accomplished by the use of

auto-transformers. a. Step-down transformer: connected to the

filament, reduces the voltage of the incoming alternating current from 220v to 8-12 volts.

b. Step-up transformer: connected to the copper stem, it raises the voltage from 8-12 v to 65-75kv

even 90kv

The power supply of the x-ray machine:

Autotransformer

Controls voltage between anode and cathode. It

serves as a step-up and step down transformer

Regulated by kVp selector

The glass tube, oil and transformers are surrounded by a metal housing which has a small aperature from

which the useful beam emerges and this metal housing is made from lead to prevent leakage of

radiation except for useful beam , it supports and protects the x-ray tube and oil. It is also a part of the

dissipating heat chain

Metal housing

Insulates the electrical components Cools the anode Filters the x-ray beam

oil

Step-up Trans

Step-down Trans

Oil in the X-ray Tubehead:

You cannot overexpose by holding the exposure switch down too long!

Allows current to flow to complete high and low voltage circuits.

Exposure Switch

Indicator light and sound

ii. Accessoriesii. Accessories

a. Filtersa. Filters

b. Collimatorb. Collimator

c. Conesc. Cones

Filtration

The process of removing low-energy x-rays from the x-ray beam

a. Filtersa. Filters:: It is a sheet of aluminum which absorbs x-It is a sheet of aluminum which absorbs x-

rays of long wave length having low rays of long wave length having low penetration powerpenetration power..TypesTypes::

11 . .Inherent filtration:Inherent filtration: Materials built Materials built within the pathway of the primary beam within the pathway of the primary beam from the focal spot to outside the tube. from the focal spot to outside the tube. They includeThey include::

- - Glass wall of the tubeGlass wall of the tube - - Insulating oil around the tubeInsulating oil around the tube

- - Metal housing around the tubeMetal housing around the tubeIt is determined by the manufacturer and It is determined by the manufacturer and is equivalent to 0.5 to 1 mm aluminumis equivalent to 0.5 to 1 mm aluminum

22 . .Added filtrationAdded filtration::

It is the addition of aluminum sheets to It is the addition of aluminum sheets to the machinethe machine..

33 . .Total filtrationTotal filtration:: It is the sum of inherent and total It is the sum of inherent and total

filtrationfiltration.. Equivalent to 1.5 mm aluminum in Equivalent to 1.5 mm aluminum in

machines up to 70 kvpmachines up to 70 kvp.. Equivalent to 2.5 mm aluminum in Equivalent to 2.5 mm aluminum in

machines higher than 70 kvpmachines higher than 70 kvp..

filter

PID

The aluminum filter is usually located in the end of the PID which attaches to the tubehead.

Inherent

Glass window of x-ray tube

Added(Aluminum filter)

Total

Total Filtration

Oil/Metal barrier

oil

70 kVp and above 2.5 mm aluminum equivalentBelow 70 kVp 1.5 mm aluminum equivalent

+ =

b. CollimationRegulates the size and/or shape of the x-ray beam

Function:

1. area exposed to x-ray (less

patient exposure)

2. scatter radiation (increases image quality)

collimated beam

collimator

target(x-ray source)

front views

Collimation

2.75 inches (7 cm) = maximum diameter of circular beam or maximum length of long side of rectangular beam at end of PID.

Collimation: Regulates the size and/or shape of the x-ray beam.

filter

Collimator

PID

TypesTypes::

11 . .Diaphragm collimatorDiaphragm collimator: A thick : A thick plate of lead with an apertureplate of lead with an aperture

22 . .Tubular collimator:Tubular collimator: A tube made A tube made of lead with one end in conjunction of lead with one end in conjunction to a diaphragm collimatorto a diaphragm collimator..

33 . .Rectangular collimator:Rectangular collimator: provides provides a beam of rectangular shapea beam of rectangular shape..

Diaphragm and rectangular collimators

Collimated film holder

c. Cone or ( Position c. Cone or ( Position Indicating Device)Indicating Device)

It is device used to fix the target-object It is device used to fix the target-object distance and indicate the point of entry of distance and indicate the point of entry of the x-ray beam. the x-ray beam. Classified according toClassified according to::

a. Shape:a. Shape: Cylindrical, rectangular and Cylindrical, rectangular and conicalconical

b. Length:b. Length: Short cone 8 inch and Long Short cone 8 inch and Long cone 16 inchcone 16 inch

c. Material:c. Material: Plastic, glass, metal or Plastic, glass, metal or combination of plastic cone with a thin combination of plastic cone with a thin lead lininglead lining..

Rectangular cone

Cylindrical cone

Its a device which controls the time of exposure and is calibrated in fractions of

seconds

Timer

1- Automatic or electronic timers

A. Direct or immediate timers:Press button just to activate the exposure but the

time is adjusted and will stop automatically even if we continue to press on the button

Associated with long cord to enable us to extend away from the field of radiation

B. Delayed timer:Provide an interval of 7-9 sec before the start of exposure so it provides us a period to get away

from the fields of exposure

Exposure is controlled manually; exposure will stop only if we stop pressing on the button.

Associated with long cord to enable us to extend away from the field of radiation

2. Manual timers

exposure button

oil

filterfilament

X-ray Machine Components

X-ray production

2. Activate low-voltage circuit to heat filament3. Activate high-voltage circuit to pull electrons across tube4. Electrons cross tube, strike target and produce x-rays1. Depress exposure button5. X-ray production stops when exposure time ends. Release exposure button

3

X-ray Production

Electron interactions with target atoms:

Less than 0.2% produce x-rays

While more than 99.8 % produce heat