ELECTROMAGNETIC SPECTRUM &

PROPERTIES OF X RAYS

CONTENTS: Basic definitions Electromagnetic spectrum Wave therapy Quantum Theory Types of radiation comprising ES Properties of X rays References

: Energy is defined as ability to do

work. There are different types of energy: KINECTIC ENERGY: it is energy

produced by virtue of movement. POTENTIAL ENERGY: produced by

virtue of its position ex: coiled spring. HEAT ENERGY: it is movement of

molecules and atoms of any material.

The level of heat is indicated by temperature.

ELECTRICAL ENERGY: it is measured by multiplying the electric charge being moved by electrical force.

CHEMICAL ENERGY: it is that energy locked up in the chemical compounds and released under certain circumstances eg explosives

NUCLEAR ENERGY: it is that energy that is locked up in the heart of the nucleus of an atom also called, atomic energy.

RADIATION ENERGY: it is that energy which is released during the process of ionization or excitation of an atom.

RADIATION: it is defined as the emission and propagation of energy through space or substances in form of waves or particles.

RADIOACTIVITY: it is the process by which certain unstable atoms or elements undergo spontaneous disintegration or decay, in an effort to attain a more balanced nuclear state.

ELECTRO MAGNETIC SPECTRUM:

X rays belong to a group of radiation known as electromagnetic radiation.

Electromagnetic radiation is the transport of energy through space as a combination of electric and magnetic fields.

Electromagnetic radiation is produced by a charged particle being accelerated.

The converse is also true, that is, a charge being accelerated will emit EM radiation.

EM radiation is made up of an electric and a magnetic field that mutually supports each other.

Wave concept of electromagnetic radiation:

EM radiation propagates in the form of waves.

They may be compared to waves travelling down a stretched rope when one end is moved up and down in a rhythmic motion.

EM radiation do not need any medium and can propagate in vacuum.

Waves of all type have an associated wavelength and frequency.

The distance between the two successive crests or troughs is the wave length and is denoted by λ (Greek letter lambda, the initial for length).

The number of waves passing through a particular point in a unit time is the frequency, denoted by “ν” (the Greek letter “nu”, the initial for number.

If each wave has a length λ, and ν waves pass a given point in unit time, the velocity of the wave is given by:

V= λ × ν EM radiations travel with the velocity of

light ie 186,000 miles per second. Therefore c= λ × ν c is velocity of light

c= λ × ν Because all types of radiation have

the same velocity, frequency of the radiation must be inversely proportional to the wavelength.

All types of radiation in the spectrum differ basically in the wavelength.

The various parts of the spectrum are named according to the manner in which the type of radiation is generated or detected.

There is considerable overlap in the wavelengths of various members of the spectrum.

CLINICAL SIGNIFICANCE:

X-rays are considered useful when their energy level is matched to the task of interest

Of the total amount of x-rays produced, only x-rays of certain energy levels are useful to diagnostic image production, these x-rays fall into the diagnostic energy range

X-rays used in dentistry have a wavelength of 0.1 to 0.5Å

Particle concept of EM radiation:

Short EM waves, such as X rays, may react with matter as if they were particle rather than waves.

These particles are actually discrete bundles of energy and each of these bundles of energy is calles a quantum or photon.

The amount of energy carried by each photon or quantum depends on frequency of the radiation.

If the frequency is doubled, the energy of the photons is doubled.

The actual amount of energy can be calculated by multiplying its frequency by a constant.

E= hν ( h= Planck’s Constant) The constant has been determined

experimentally to be 4.13 × 10-18 KeV sec and is called the Planck’s Constant

In SI unit it is 6.62 ×10-34 Joules sec.

The particle concept is used to describe the interactions between radiation and matter.

TYPES OF RADIATION COMPRISING EMS

The EM spectrum is the ENTIRE range of EM waves in order of increasing frequency and decreasing wavelength.

HERTZIAN WAVES: these waves are used by high altitude transmission satellites, and have wavelength of 1016 to 1013 Å.

COMMUNICATION OR RADIO WAVES

These waves can pass through most materials except that of great bulk. Wavelength varies from 1013 to 108 Å.

USES: MEDICINE: radiowaves are used to

transmit the pattern of the heartbeat through a monitor.

OTHERS: to convey information from one place to another through media(air, space).

MICROWAVES OR SHORTWAVES DIATHERMY

Wavelength: 3×10-2m to 3×10-4 , these overlap the wavelength of communication waves on one end and infrared on other end.

USES: Transmit information to satellite. Mobile phones. Microwave ovens. These waves can penetrate tissues

and cause moisturized molecules in cell to vibrate resulting in internal friction and increase in temperature of affected cell.

THERAPEUTIC USES: In ophthalmology. In selected cases of cancer therapy. In oral surgery, to reduce

postoperative swelling and trismus arising from traumatic procedures.

INFRARED WAVES: The name infrared means “below the

red”. These have wavelength ranging from

40,000 to 1,00,000 Å These occupy the part of spectrum

with a frequency less than that of visible light and greater than that of radio waves.

These were discovered in 1800 by Sir William Herschel.

USES: To study cloud structure. The temperature of a distant object

can be determined by analysis of infrared radiation from the object.

Radiometers operating in the infrared range serve as the basis for many instruments, including heat seeking devices in missiles and devices for spotting and photographic persons in the dark or fog.

Medical uses include technique of thermal imaging of thermography.

In dentistry: it is used for tooth vitality testing, surgical diathermy, altering properties of dental materials like waxes, gutta percha and for curing acrylic.

VISIBLE LIGHT: Wavelength ranges from 4,000 to 7700Å. The range of colour is often called

“VIBGYOR”, with red having the longest wavelength and violet having shortest wavelength.

Red, orange, yellow, green, blue, indigo, violet.

USES: In optical fibers. In dentistry it is used in dental

photography and operative field illumination.

ULTRAVIOLET LIGHT: Wavelength ranges from 1,000 to

2,000Å. These rays have slight penetrating

power and can penetrate live tissues for a depth of few mm and cause biological effects like:

Photo erythema Photo pigmentation Photo chemical cornification of skin

and skin carcinoma (malignant dermal changes).

Bactericidal effect. Aging of skin. Eyes are sensitive to UV rays which

can cause cataract or keratitis. Is an agent in the production of

vitamin D.

The UV rays can be divided into 3 categories:

Between 200 and 290 nm, short or germicidal UV rays or UVC, these can cause genetic mutations, altered reproductive cycles and cell death.

Between 290 and 320 middle or erythemal UV rays or UVB, these can cause skin erythema and are commercially available as sun or mercury vapor lamps.

Between 320 and 380 nm , long or black light UV rays or UVA, on its own it is not damaging but when used with sensitizing chemicals, it can cause extensive biological damage.

USES: Photography In dentistry: Disclose plaque Photo polymerization of composite

used for: Fissure sealing Splinting teeth Placing pontic in temporary bridge

work Restoring teeth

X RAYS: Four types: Grenz or super soft X rays: 1-2 Å,

mainly used to treat superficial lesions

Soft X rays: 1-0.5 Å, used in contact therapy.

Medium: 0.5-0.1 Å, mainly used in diagnostic and superficial therapy.

Hard X rays: 0.1 Å , mainly used for deep X ray therapy.

Other uses of X rays: Its properties of fluorescence is used

in medicine for fluoroscopic examination and intensifying screens in extra oral radiography.

Radiography and monitoring film badges.

To sterilize commercial items in bulk.

GAMMA RAYS: They are high powered X rays,

having wave length of 0.001 Å. These are EM radiations, but there

source is from radioactive decay process.

They have shorter wavelength and greater penetrating power and are used in treatment of tumors ex: Radon needles or seeds that are implanted at the tumor site, percutaneous radiotantalum wire implants.

COSMIC RAYS: These have the shortest wavelength

of 0.0001 Å. They played a critical role in the

scientific study of atomic nucleus and its components.

LASER: Light amplification by stimulated

emission of radiation is a device which can operate in infrared, visible or UV region of the spectrum and which amplifies electromagnetic waves by stimulated emission of radiation.

When atoms or molecules absorb energy they can emit light spontaneously or they can be stimulated to do so by a light wave.

If a body of atoms is raised to excited state by pumping, then an incident light wave will simulate photon emission and net amplification of the incident light beam results.

The output is extremely powerful and mobilizes intense heat at close range to emit photons at an infinitely greater rate than would spontaneously.

LASER light has four characteristics that distinguish it from light produced by other sources. These are:

Laser light is highly directional and travels in a narrow beam, the sides of which stay almost parallel.

Lasers produces coherent light, that is it has only one frequency.

It is of one single color. It is very bright, powerful with very high

intensity.

Laser concentrates and amplifies the light to a given concentrated beam of energy which can melt metals and drill holes in them.

It can be used to make very accurate measurement of distance, perform delicate surgical procedure involving the eye.

They have replaced many conventional techniques which have lead to shorter period of treatment.

It has also reduced blood loss due to its ability to seal blood vessels, less post operative infection and the fact that difficult, often inaccessible regions of the body can be reached more easily.

In dentistry two types of lasers are used:

Soft tissue laser (800-900 nm): eg. Argon, CO2.

Hard tissue laser (2500-3000nm): eg Er: YAG dental laser.

Dental Applications: Surgical excision of benign tumors

and small soft tissue growths (eg: epulis)

Frenectomy Nerve regeneration Cavity detection. OCT Low intensity lasers to reduce pain Treatment of TMJ for reduction of

pain and inflammation.

For ulcerative lesions. Oral biopsies Tooth sensitivity Melanin pigmented gingiva For etching Cutting and contouring of oral

osseous structures. Apicectomy.

Properties of X rays: X rays are weightless packages of pure

energy that are without electrical charge and that travel in waves along a straight line with a specific frequency or speed.

The properties of X rays can be classified into:

Physical Chemical Biological physiochemical

PHYSICAL PROPERTIES:

Wavelength 10-0.01 Å. They travel through space in a wave

motion. In free space they travel in a straight

line. They travel in speed of light (186000

miles per second).

As they travel through space, they can produce an electric field at right angle to their path of propagation and a magnetic field to right angle to electric field.

They are invisible to eye and can not be seen, heard or smelt.

They can not be focused by a lens. They can not be reflected, refracted or deflected

by a magnet or electric field as they do not possess any charge.

They do not require any medium for propagation.

They are pure energy, no mass and they transfer energy from place to place in the form of quanta (photon)

In free space they obey the inverse square law, which states that for a point source of radiation the intensity (I) at any given place varies inversely as the square of distance from the source to the place at which intensity is being considered.

I∞i/d2 or I =k/d2

K is a constant.

X rays are produced by collision of electrons by tungsten atoms.

Collision can be of two types: Continuous spectra (general

radiation, Bremsstrahlung Radiation, Braking Radiation)

Characteristic spectrum or line spectrum

CONTINIOUS SPECTRA (GENERAL RADIATION, BREMSSTRAHLUNG RADIATION, BRAKING

RADIATION):

Also called as brems, white, or general radiation.

Derived from two German words: bremse- ‘brake’ & strahl- ‘ray’

Called as ‘braking radiation’ as the radiation is produced by ‘braking’ or deceleration of high speed electrons.

A cathode electron that completely avoids the orbital electrons may come sufficiently close to the nucleus to come under its influence.

CONTINIOUS SPECTRA (GENERAL RADIATION, BREMSSTRAHLUNG RADIATION, BRAKING

RADIATION):

The incoming electron penetrates the outer electron shell and passes close to the nucleus of the tungsten atom.The incoming electron is slowed down and deflected by the nucleus with a large loss of energy, which is emitted in the form of X rays.The amount of deceleration and degree of deflection determines the amount of energy lost by the bombarding electron and hence the energy of the resultant emitted photon has a wide range of spectrum of energies and therefore called CONTINIOUS SPECTRUM.

CHARACTERISTIC RADIATION:

The incoming electron collides with an inner shell tungsten electron, displacing it to outer shell (excitation), or displacing it from the atom (ionization), with a large loss of energy and subsequently the orbiting tungsten electros rearrange themselves to return the atom to neutral or ground state.

This involves electron jumps which results in the emission of X ray photons with a specific energy called CHARACTERISTIC SPECTRUM.

Generation of photons with a wide range of photon energies (continuous spectrum)

This is due to : a) Continuously varying voltage

difference between target & filament

b) Most electrons participate in many interactions before losing their energy

X rays can penetrate various objects and degree of penetration depends upon:

Quality (penetration power), is defined as the energy carried by the X ray beam.

Quality is determined by KV, milli amperage, distance between the target and the object, time of exposure, filtration and target material.

Property of attenuation, absorption, scatter when passing through matter the intensity of radiation is reduced (attenuation) both because radiation energy is taken up by the material (absorption) and some is deflected from the original path to travel in a new direction(scattering).

Components of the body arranged in order of their power to absorb X rays, starting from lowest value:

Air Fat Soft tissue, blood, body fluids Medullary bone Cancellous bone Cortical bone Dentin and cementum Enamel

INTERACTION WITH MATTER:

When x-ray photons arrive at patient:a. Some x-rays are merely scattered with no

loss of energyb. Some x-ray photons are absorbed

completely in the patient (total loss of energy), &

c. Some x-ray photons pass through the patient without interacting with the tissue atoms

d. Some x-ray photons are scattered after loss of some energy

In the case of diagnostic X ray beam there are three mechanisms by which these processes take place:

Coherent scattering Photoelectric effect Compton scattering

COHERENT SCATTERING (elastic, classical, unmodified, Thomson, Rayleigh ):

It is a process by which radiation is deflected without losing energy.

X rays when passing close to an atom causes the bound electrons to vibrate momentarily at a frequency equal to that of incident photons.

The incident photon then ceases to exit.The vibration causes the electron to radiate energy in the form of another X ray photon of the same frequency and energy as that in the incident beam.Usually the secondary photon emitted is at an angle to the path of incidental X ray.

Contributes to 8% of the total no. of interactions.

Is of little importance in radiography as the it involves low energy x-rays.

At energy levels employed in diagnostic radiology, the effect of coherent scattering is negligible in production of fog.

This property is used to investigate internal molecular structure of materials by method of X ray diffraction, called X ray crystallography.

PHOTOELECTRIC EFFECT:

It is a process of interaction of the incident photon ant the bound electron leading to emission of characteristic radiation.It occurs when an incident photon collides with a bound electron in the atom of the absorbing medium.The incident photon ceases to exit and its energy helps to eject a bound electron from its shell to become a recoil electron or a photo electron.

The kinetic energy imparted to the recoil electron is equal to the energy of the incident photon minus that required to overcome the electron binding energy.The orbital vacancy caused by the electron reshuffle and the neutrality is obtained by attracting an electron from outside.During this rearrangement characteristic radiation is emitted.

In diagnostic radiography the characteristic radiation generated is of no significance as the X ray photons which are absorbed by the patient are of low energy.

COMPTON SCATTERING (inelastic, modified, incoherent): :

Or inelastic scattering is an interaction of photons with free or loosely bound outer shell electron.

The photon gives some of its energy to the electron and it, itself continues in a new direction, but with reduced energy and hence with increased wavelength.The ejected outer shell electron is called compton or recoil electron.

If scattered through a small angle, very small amount of energy is lost to the outer electron.

The recoil electrons further ionizing interactions with the tissues, and gradually lose energy along their tracts by causing secondary radiations and consequent biological damage.

This creates a serious problem as photons that are scattered at narrow angles have an excellent chance of reaching the film & producing film fog.

Contributes to 62% of the x-ray scattering.

Due to their energy, rays can emit photoelectrons from metals, when allowed to fall on them.

HEATING EFFECT: the production of heat is due to slowing down of the primary electrons, it also arises as an end product of the chemical reactions induced by radiation.

FLUORESCENCE: when X rays fall upon certain material, visible light is emitted called fluorescence.

IONIZATION: this is a process of converting atoms into ions.

CHEMICAL PROPERTIES: The outer electron of the atoms play

an important role in chemical combinations and therefore any disturbance in the outer electron configuration of an atom brings about chemical changes.

X rays induces color changes in several substances:

Methylene blue gets bleached Sodium platinocyanide which is apple

green turns to darker shades then light brown and finally dark brown.

Brings about molecular changes in biological molecules.

Organic compound gets oxidized to carbon dioxide with release of hydrogen.

Water in organic substances undergo oxidation and reduction reactions when irradiated.

X rays can cause oxidation of ferrous sulphate to ferric sulphate and this is used as a method of measuring X ray dosage (Frickle dosimeter).

X rays can cause destruction of the fermentation power of enzymes, which are vital substances for metabolism of cells of all living materials.

BIOLOGICAL PROPERTIES: When X rays are incident on an atom,

one of the reaction it produces is excitation. this property is used in:

Treatment of malignant lesions. Germicidal or bactericidal effect and

are used for sterilization and preservation of food.

Effects can be of two types: Somatic effect Genetic effect

SOMATIC EFFECT: The effect is cumulative and depends

upon the type of tissues and intensity of the radiation.

It may range from simple sun burn to severe dermatitis.

GENETIC EFFECT: This is due to radiation induced

mutation of genes and chromosomes. These are usually seen in off springs

of irradiated parents. The fetus is more sensitive to

radiation in early stages of development.

PHYSIOCHEMICAL PROPERTIES:

PHOTOGRAPHIC EFFECT: Photographic film when exposed to X

rays and developed will turn black. This blackening is known as film

density.

USES OF X RAYS: RADIOLOGY: Diagnostic use in dentistry and medicine. Medico legal cases. RADIOTHERAPY: Used to destroy malignant cells and cure

skin disease. RADIOBIOLOGY: Alteration of cells and tissues for

experimental purpose. CRYSTALLOGRAPHY

In industries Photochemistry.

REFERENCES Oral Radiology Principles and

Interpretation, 2nd Edition, Gaoz and White. Oral Radiology, Principles and

Interpretation, 4th Edition, White and Pharooh.

Christinsen’s Introduction to the Physics of Diagnostic Radiology, 3rd Edition, by Currary T.S., J.E. Dowdry, R.C. Murry.

Eric Whaites: Essential of Radiology and Radiography, 2nd Edition.