Lectue 1 Physics

8/3/2019 Lectue 1 Physics

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Radiation PhysicsyDr Khaled Allouba



Ionization:y An atom is neutral when the number of its protons is

equal to the number of its electrons

y

When the stable atom looses one or more of itselectrons it becomes a positive ion

y When the stable atom acquires or gain one or moreelectron it becomes a negative ion

y Process of losing or acquiring electrons by a stableatom is called Ionization



Radiation:y The process of transmission of energy through space and

matter

y It occurs either as: particulate radiation, or electromagneticradiation

y Particulate radiation consist of a nucleus or subatomicparticles moving at high velocity.

y Examples of particulate radiation is a alpha which is

made of a helium nucleus one proton , one neutron, Bbeta radiation electrons emitted from radioactive nuclei,Cathode rays are high speed electrons produced by amanufacturer device X ray tubes.



Basic terminology

Radiation: It is the process of emission ,propagation andtransmission of energy in the form of waves.

Radiology: science that deal with diagnosis ,therapeuticand research application of high energy radiation.

Roentgenology: science that deal with application of x rayon any field.

Radiograph: it is the image received on a dental film dueto passage of the x ray through an object or body.

Dental radiograph: A photographic image produced on film by the passage of x-rays through teeth and relatedstructures.

Dental radiography: The making of radiographs of the teeth

and adjacent structures by the exposure of film to x-rays.



Discovery of X-Rays

y Wilhelm Roentgen (1895)image from Wolfram Research

Bremsstrahlung Radiation

image from Cathode Ray Tube Site

Cathode ray tube



Wilhelm Conrad Roentgen discovered the x-ray on November 8,1895. Roentgen had experimented with the production of cathode rays(streams of electrons). He used a vacuum tube, an electrical current, and special screenscovered with a material that glowed (fluoresced) when exposed toradiation.

He made the following observations about cathode rays: the raysappeared as streams of colored light passing from one end of the tube to

the other, the rays caused fluorescent screens to glow.

Roentgen noticed a faint green glow coming from a nearby table.

Roentgen observed that the distance between the tube and thescreens was much greater than the distance cathode rays could travel. He realized that something from the tube was striking the screens

and causing the glow.



He replaced the fluorescent screens

with photographic plate.Roentgen proceeded to make thefirst radiograph of the human body; he placed his wife¶s hand

on a photographic plate andexposed it to the unknown raysfor 15 minutes.

When roentgen developed the photographic plate, the outline of

the bones in her hand could beseen.Roentgen named his discovery

x-rays



Composition of Matter

Matter:

Any thing that occupies space and has a mass and volume

Matter can exert a force or can be acted on by a force

Matter occurs either as solid , liquid or gas

Matter occurs either as an element or compounds

Atom is the basic unit of element



Composition of Matter

Atoms:

Niels Bohr model of atomic structure ³1913´: Atomicstructure is like the solar system

The nucleus is the center of the atom ³sun´

Electrons ³ planets´ revolve at high speed around thenucleus in different energy levels

Electrons are negatively charged

Protons are positively charges occupying the nucleus

Neutrons are non charged particles found in the nucleus



An atom is composed of electrons (with a negative charge),

protons (with a positive charge) and neutrons (no charge).

The protons and neutrons are found in the nucleus of the

atom and the electrons rotate (orbit) around the nucleus.

The number of electrons equals the number of protons in

an atom so that the atom has no net charge (electrically

neutral).

However, all the atoms in a given material will have the

same number of electrons and protons.



AtomThis atom has 7 protons and 7 neutrons in the nucleus. There

are 7 electrons orbiting around the nucleus.

protons

neutrons

electrons



The electrons are maintained in their orbits around the

nucleus by two opposing forces.:

The first of these, known as electrostatic force, is theattraction between the negative electrons and the positive

protons. This attraction causes the electrons to be pulled

toward the protons in the nucleus. In order to keep the

electrons from dropping into the nucleus,

The other force, known as centrifugal force, pulls the

electrons away. The balance between these two forces keeps

the electrons in orbit.



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.

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), thehigher the electrostatic force will be for all electrons in that

atom.



Centrifugal force pulls the electrons awayfrom the nucleus

Force needed to remove an electron from a certain energy

level should exceed the electrostatic force and is called

³electron binding force´ or Ionization energy



The balance between electrostatic force and centrifugal force

keeps the electrons in orbit around the nucleus

EF CF



Atomic Number (Z):

The number of protons in the nucleus of an atom.

Neutron number (N):

The number of the neutrons in the nucleus of an atom.

Atomic mass number (A):

Sum of the number of protons and neutrons in an atom

(A=Z+N).



Ground state:atoms are electrically neutral because the

number of positive charges(protons) is balanced by thenumber of negative charges (electrons).

If an electron is removed, the atom is no longer neutral, but

becomes positively charged and is referred to as a positive ion.The process of removing an electron from an atom and

forming ion pair is called ionization. Such ionization requires

sufficient energy to overcome the electrostatic force binding

the electrons to the nucleus.

When the stable atom acquires one or more electron it

becomes a negative ion.





If an electron is displaced from an inner shell to an outer shell (i.e. to a higher energy level), the atom remains neutral

but is in an excited state. This process is called excitation.

The unit of energy in the atomic system is the electron volt(eV), 1 eV= 1.6x 1019 joules.



Radiation is the transmission of energy through space and

matter. It may occur in two forms: particulate and

electromagnetic.

Radiation

Radioactivity

The process whereby certain unstable elements undergo

spontaneous degeneration in an effort to attain a more

balanced nuclear state. A substance is consideredradioactive if it gives off energy in the form of particles or

rays as a result of disintegration of atomic nuclei.



Ionizing Radiation

Radiation that is capable of producing ions by removing or

adding an electron to an atom.

Particulate radiation Electromagnetic radiation

Classified into two groups



Ionizing Radiation

Four types of particulate radiation are recognized:

1-Electrons:

Classified as Beta particles or cathode rays .

Beta particles: fast moving electrons emitted from thenucleus of radioactive atoms.

Cathode rays: streams of high speed electrons but

Originate in an x-ray tube.

I-Particulate radiation

-Tiny particles of matter that posses mass and travelIn straight lines and at high speed.

-Particulate radiation transmit kinetic energy by means of

their extremely fast-moving, small masses .



2-Alpha particles:

Are emitted from the nuclei of heavy metals and existAs two protons and neutrons without electrons.

3-Protons:

Are accelerated particles, especially hydrogen nuclei,

With a mass of 1 and a charge of 1.

4-Neutrons:

Are accelerated particles with a mass of 1 and no electrical

charge.



Relative penetrating ability of

ionizing radiation in tissue

Alpha

Beta

Gamma

Neutron

(Several layers of skin)

102-12





Electromagnetic Radiation

-Propagation of wave-like energy (without mass) through

space or matter.

-The energy that is propagated is accompanied by oscillating

electric and magnetic fields positioned at right angles to one

another hence the term electromagnetic.

-These radiations are manmade or occur naturally ;examples

include: Cosmic rays, X-ray, infrared light, ultraviolet,

radiowaves, radar waves, tv waves, visible light, microwavesand gamma rays, travel at the speed of light (186,000 miles per

second). They travel through space as both wave and particle.



Electromagnetic Radiation

Em. radiation is ionizing

when it has sufficient energy

to remove orbital electrons

from an atom.

Electromagnetic radiation can be classified as ionizing or non-ionizing.

Only high energy radiation are capable of ionization as

cosmic rays, gamma rays and x-rays.



Quantum Theory of Ionization Radiation

Em radiation propagate in the form of bundles of energy called photons or quanta.

These bundles of energy with no mass or wieght thatmove in straight line

Each photon has the velocity of light and carries aspecific amount of energy E measured in electron

volt units which is the ³energy of electromagneticradiation´.



.

Wave theory

This theory characterizes electromagneticradiation as waves and focus on the propertiesof:

-Velocity-Wavelength-Frequency



Velocity

Refers to the speed of the wave. All electromagnetic radiationstravel as waves or a continuous sequence of crests at the speed

of light (3 x 108 meters per second or 186,000 miles per

second) in a vacuum.

They have a wave length (), frequency() and velocity.

C= x



D

W

W

The wavelength (W) is the distance from the crest of one wave

to the crest of the next wave. It determines the energy and

penetrating power of the radiation, the shorter the wavelength

the higher the energy and ability to penetrate matter, it is

measured in nanometers for shortW and meters for longer W.

The frequency (F) is the number of waves in a given distance(D). If the distance between waves decreases (W becomes

shorter), the frequency will increase. The top wave above has a

shorter wavelength and a higher frequency than the wave below

it.

F = 3

F = 2



Frequency and wavelength are inversely related; if the

frequency of the wave is high, the wavelength will be short,

and if the frequency is low, the wavelength will be long.

The amount of energy an electromagnetic radiation possesses

depends on the wavelength and frequency.

Low frequency electromagnetic radiation will have

««««..



radio

waves

tv

waves

visible

light

x-rays gamma

rays

cosmic

rays

Which of the above examples of electromagnetic

radiation has the shortest wavelength?

Which of the above has the lowest frequency?

Cosmic rays

Radio waves



A

B

CWhich of the above x-rays has the highest energy?

A: It has the shortest wavelength, highest frequency



Spectrumy Electromagnetic Spectrum: The range of electromagnetic

waves when placed in order of increasing frequency

RADIO WAVES

MICROWAVES

INFRARED RAYS

VISIBLE LIGHT

ULTRAVIOLET RAYS

X-RAYS

GAMMA

RAYS



The energy of a wave of electromagnetic radiation

represents the ability to penetrate an object. The higher the

energy, the more easily the wave will pass through the

object. The shorter the wavelength, the greater the energywill be and the higher the frequency, the greater the energy

will be.

X-ray Energy



X-ray Characteristics

X-rays are high energy waves, with very short wavelengths,and travel at the speed of light.

X-rays have no mass (weight) and no charge (neutral).

Y

ou cannot see x-rays; they are invisible. X-rays travel in straight lines; they can not curve around a

corner.

An x-ray beam cannot be focused to a point; the x-ray beam

diverges (spreads out) as it travels toward and through the

patient. This is similar to a flashlight beam.



X-rays are differentially absorbed by the materials they passthrough. More dense materials (like an amalgam restoration)

will absorb more x-rays than less dense material (like skin

tissue). This characteristic allows us to see images on an x-ray

film. X-rays will cause certain materials to fluoresce (give off

light).We use this property with intensifying screens used in

extraoral radiography.

X-rays can be harmful to living tissue. Because of this, you

must keep the number of films taken to the minimum number

needed to make a proper diagnosis.

X-ray Characteristics (continued)



Characteristics of X rays:

y Invisible , odorless , colorless and weightless rays

y They can ionize matters

yThey propagate in space in form of waves

y They have very short wave length Angstroms

y Thy penetrate dark and opaque objects

y They interact with the radiographic film the same

way light interacts with the photographic filmy They can cause harmful effects on living tissues

somatic and genetic effects

X M hi



Tube

head

Extension

arms

controlpanel

X-ray Machine

X M hi



X-ray Machine

X-ray equipment has three basic components:

(1) Control panel, which is plugged into an electrical outlet

allows you to alter the duration of the x-ray beam

(exposure time) and, on some x-ray machines, the

intensity (energy) of the x-ray beam.(2) Extension arms, which allow for movement and

positioning of the tubehead

(3) X-ray tubehead, contains x-ray tube which produces the

x-rays.

3

1

2



X-ray Machine

Components

Control Panel X-ray

Tube head

110, 220 lineOn-off switch

Indicator light

Exposure

button

Control device:

(Time m A

&KVP selector )

Step-down

transformer

Step-up transformer

Autotransformer X-ray Tube

Oil



Control Panel



The control panel contains,

-On- off switch

-An indicator light

-Exposure button-Control devices (time, kilovoltage kVp and milliamperage

mA)

exposure time kVp control

mA control



PID(cone)

X-ray

Tubehead

degrees

The x-ray tubehead is attached to the extension arm sothat it can rotate up and down (vertically; measured in

degrees) and sideways (horizontally) to facilitate proper

alignment of the x-ray beam. The PID (Position

Indicating Device) is attached to the x-ray tubeheadwhere the x-ray beam exits and it identifies the location

of the x-ray beam. Some people refer to the PID as a

³cone´; the PID¶s on very old x-ray machines used to be

coneshaped.



Tubehead ComponentsThe x-ray tubehead is a tightly sealed heavy metal housing

that contains x-ray tube that produces x-ray.

It includes:

1-Metal housing : metal body of the tubehead that surrounds

the x-ray tube and transformers and filled with oil.

2-Insulating oil: surrounds the x-ray tube and transformers

inside it to prevent overheating.

3-Tubehead seal: or aluminum or leaded glass covering the

tubehead, it seals the oil and act as a filter to the x-ray beam.



4-X-ray tube: the heart of the x-ray generating system, willBe discussed later.

5-Transformers: device that alters the voltage of incoming

electricity.

6-Aluminum disks: or sheets of 0.5 mm aluminum that act

as a filter to the x-ray beam.

7-Lead collimator: lead plate with central hole that fits

directly over the opening of the metal housing , it restricts

the size of the x-ray beam.

Tubehead Components



Tubehead Components

8-Position indicating device or cone:

It extends from the opening of the metal housing of the

tubehead. It aims and shapes the x-ray beam.

PID(cone)

X-ray Tube

head



X-ray Tube

X-rays are produced in the x-ray tube, which is located in

the x-ray tubehead. X-rays are generated when electrons

from the filament cross the tube and interact with the

target. The two main components of the x-ray tube are the

cathode and the anode.

Glass vacuum tube in which all of the air has been removed



X-ray TubeMetal Housing

Insulating oil

Unleaded glass window

Tube head seal

Leaded glass

housing

Vacuum



Components parts of the x-ray tube

1- Leaded glass housing

2-Cathode

3-Anode



1-Leaded glass housingLeaded glass vacuum tube that prevents x-ray from escaping

In all directions except for on central area or window that

permit X-ray beam to exit the tube and direct it toward the

aluminum Disks, collimator and PID.



(tungsten)

2-CathodeFocusing

cup

Filament

The cathode is composed of a tungsten filament which is

centered in a focusing cup. Electrons are produced by the

filament (see next slide) and are focused on the target of the

anode where the x-rays are produced. The focusing cup has a

negative charge, like the electrons, and this helps direct theelectrons to the target (³focuses´ them; electrons can be

focused, x-rays cannot).

side view

(cross-section)

front view

(facing target)



Thermionic Emission

x-section

of

filament

hot

filament

When you depress the exposure button, electricity flows

through the filament in the cathode, causing it to get hot.The hot filament then releases electrons which surround

the filament (thermionic emission). The hotter the filament

gets, the greater the number of electrons that are released.

(Click to depress exposure button and heat filament).

electrons



3-Anode

Copper stem

Target

The anode in the x-ray tube is composed of a tungsten targetembedded in a copper stem. When electrons from the filament

enter the target and generate x-rays, a lot of heat is produced.

The copper helps to take some of the heat away from the target

so that it doesn¶t get too hot.

side view front view

Target



Characteristics of tungsten material:

1-high atomic number (Z=74)

2-high melting point (3370º C)

3-low vapor pressure at the working temperature4- Can be drawn into fine wire

5-Low thermal conductivity: so it is embedded in a copper

stem which is a good thermal conductor, dissipates heat from

the tungsten thus reducing the risk of target melting.



The sharpness (detail) of images seen on a radiograph isinfluenced by the size of the focal spot (area in the target

where x-rays are produced). The smaller the focal spot

(target), the sharper the image of the 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. In order

to get a small focal spot, while maintaining an adequately

large target , the line focus principle is used.

Line Focus Principle



Line Focus Principle

Apparent (effective)

focal spot size

Actual focal

spot size

Target

(Anode)Cathode

PID

The target is at an angle (not perpendicular) to the electron

beam from the filament (see above). Because of this angle, the

x-rays that exit through the PID ³appear´ to come from asmaller focal spot (see next slide). Even though the actual

focal spot (target) size is larger (to withstand heat buildup),

the smaller size of the apparent focal spot provides the sharper

image needed for a proper diagnosis.



1. Focusing cup: focuses electrons on target

2. Filament: releases electrons when heated3. Electron stream: electrons cross from filament to target during length

of exposure

4. Vacuum: no air or gases inside x-ray tube that might interact with

electrons crossing tube5. Target: x-rays produced when electrons strike target

6. Copper stem: helps remove heat from target

7. Leaded glass: Keeps x-rays from exiting tube in wrong direction

8. X-rays produced in target are emitted in all directions

9. Beryllium window: this non-leaded glass allows x-rays to passthrough. The PID would be located directly in line with this window.

X-ray Tube Components (continued)



X-ray Tube Components

1

2

43

5

8

6

7

9

1. focusing cup 6. copper stem

2. filament 7. leaded glass

3. electron stream 8. x-rays4. vacuum 9. beryllium window

5. target

(for description, see next slide)



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Lectue 1 Physics