Radiographic TestingX-rays and Gamma raysElectromagnetic radiationof very short wavelength-10nm=100Aoand below &Of very high energy - KV and MeV

Unlike other members of electromagnetic radiation they are capable of penetrating and ionising the mater

Physical identity of X-rays and gamma rays are same. They differ only in their origin

X-rays are extranuclear Gamma rays nuclear in origin

Properties of X-rays and gamma rays1.St.line propagation: nondeflectability: invisibility2. Penetrability- high energy3. Attenuation I = Io e - t

As the radiation penetrates the matter, the intensity is getting reduced as given by the above expression

I0

I1Intensity is getting reduced

4. Differential attenuation If there are variations in the material, naturally, the attenuations will differ.

I1 I2 I1 I3 I1

Crack Inclusion

The properties 1,2,3 & 4 are responsible for the information of inside of the specimen which can be obtained from outcoming radiation. X-Rays are invisible - Information is not readily available

 6. Ionisation X-rays and gamma rays are ionising in nature, meaning they are capable of removing the electron from the matter. Ionisation leads to photographic effect in photographic films.

Fluorescence effect is the basis for fluoroscopy and photographic effect is used in film radiography 1. Photographic effect (Film radiography) 2. Fluorescence effect (Fluoroscopy or RTR)

Excitation and ionisation are responsible for recording the image information

5. Excitation X-rays and gamma rays are capable of exciting the electrons in the atom to higher energy levels. Excitation of electrons in some material leads to fluorescence, emission of light.

Penetration, St.line propagation,absorption and differential absorption are responsible for shadow image formation

Recording mediums

X- rays and gamma rays are invisible. Detectors or recording mediums are used to to see X-ray or gamma ray images

Photographic effect 

More X-rays Less X-rays Film

More ionization Less ionizationMore darkening Less darkening Shadow image

Fluoresence effectMore Xrays Less Xrays

More light Less light visible image Fl.screen

The recording mediums allow the invisible X-ray image visible

On development

Principle of radiography testingX-rays and Gamma rays are allowed to penetrate the material. They are absorbed as they penetrate the material. They are differentially absorbed when there is variation in material. 

As a result of differential absorption, different intensities are coming out the specimen carrying information about the variations. As these are invisible, they are allowed to fall on a recording medium to form a shadow image or silhouette image

The recording mediums are1.Photographic film(Film Radiography) (-ve image)2.Fluorescent screen(Fluoroscopy or RTR)(+ve image)

Film Radiography

Top view of developed film

X-ray film

The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.

= more exposure

= less exposure

The film darkness (density) will vary with the amount of radiation reaching the film through the test object.

Medicinal X-rays – Max.50KV- compared to 100 KV and above in industrial radiography

Applications of Radiographic Testing

Other applications:1. Correctness of assembly2. Connections in PCB and chips 3. Baggage checking in airports by security & customs

Baggage checking by Fluoroscopy/Real Time Radiography

Radiographic Images

RT is very good for volumetric defects like shrinkage, inclusion, porosity etc. Crack sensitivity is not good- laminations ??

                     

Appearance of inclusions in film radiography

Both are steel welds and film radiography. The left side inclusion appears dark and the other inclusion appears light – why?

In both the welds if the inclusions are same & identical,what is your comment on the two images

Do the doctors ever take radiograph of the abdomen – to look for any growth or variation Do they ever take the radiograph of brain to find the tumor (skull can be radiographed)

Radiograph of FRP fibre reinforced plastic – can it show the fibres & distribution and orientation of fibres .Differential attenuation is the basis of radiography and only when a large variation in attenuation between two different portions, a satisfactory image is obtained

A large inclusion in steel weld cannot show up, if the attenuation of the inclusion and steel material are one and the same

Differential attenuation is more when the defect is parallelel

X-ray GenerationWhen fast moving electrons are suddenly decelerated, X-rays are produced. The kinetic energy acquired is converted into X-ray photon energy The spectrum of X-rays generated in X-ray tube is continuous or white X-rays superimposed with characteristic X-rays, K α, Kβ etc.. Conventional X-ray tubes can produce X-rays energy upto 600 KV (100KV) High energy sources

There are applications for very much higher energy and penetrating power in the range of 1 Mev –25 Mev in industrial radiography. Basically they consist a source of electrons and a means of producing high electric field to accelerate the electrons. As in the case of X-ray tubes, they strike the target and high energy X-rays are produced. Betatron, linear accerators and Van de Graff generators are some of high energy sources

RadiographyThe radiation used in radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation can come from an X-ray generator or a radioactive source.

High Electrical Potential

Electrons-+

X-ray Generator or Radioactive Source Creates

Radiation

Exposure Recording Device

Radiation Penetrate the Sample

Typical X-ray Machines and Their Applications Maximum voltage- kV

Applications and Approximate Thickness Limits

50 Thin sections of most metals; moderate thickness of graphite and beryllium; small electronic components; wood, plastics etc

150 5 inch aluminum or equivalent 1-inch steel or equivalent - 11/2-inch steel or equivalent

300 3 inch steel or equivalent - 4 inch steel or equivalent.

400 31/2-inch steel or equivalent 41/2-inch steel or equivalent

1000 5-inch steel or equivalent.. 8-inch steel or equivalent

2000 8 inch steel or equivalent 8 to 25 MeV 16 -inch steel or equivalent.

20-inch steel or equivalent.

Thickness limitation

In d u str ia l G a m m a -R a y S o u r c e s a n d T h e ir A p p lic a t io n s (p r a c t ic a l th ic k n e ss r a n g e ) S o u r c e A p p lic a t io n s a n d

A p p r o x im a te P r a c t ic a l T h ic k n e s s L im its

T h u liu m 1 7 0 P la s t ic s , w o o d , lig h t a llo y s . 1 /2 - in c h s te e l o r e q u iv a le n t

Ir id iu m 1 9 2 0 .5 - to 3 1 /2 - in c h s te e l o r e q u iv a le n t

C e s iu m 1 3 7 0 .7 5 to 4 - in c h s te e l o r e q u iv a le n t

C o b a lt 6 0 11 /2 - to 9 - in c h s te e l o r e q .

1. 17 & 1. 33 M e v

900KV

Av. 600KV

Thickness ranges for common isotope sources

Natural Radioactivity  Elements with Atomic number more than 88, the nucleus with very high mass becomes unstable and by disintegrating or decaying, nucleus becomes stable. The disintegration or decay mechanisms, or processes are emission of alpha, beta and gamma radiation

1.Alpha is +vely charged and beta is –ve2. Nondeflectability of gamma rays

Artificial radioactivity

Definitions –Isotope, Isobar, Radioactivity –natural

Isotopes – Atoms of the same element having different atomic masses –eg Examples Co 59 and Co 60 Z Nc A

27Co 59 27 Co 60

Other examples

Same atomic No. but different atomic masses -

What leads to this variation or the origin of isotopes

1H1 1H2 1H3

RT-Basics-6 (contd)

Isobars:Atoms with same atomic mass and different atomic number. Mother and daughter nucleus of radioactive isotopes

27Co 60 and 28 Ni 60 

Artificially produced radioactive Isotopes Certain elements can be converted into radioactive isotopes by neutron bombardment. They are unstable because of the extra neutron and undergo changes resulting in emission of gamma rays.In entire radiography only artificially produced radioactive isotopes are used and never naturally occurring radioactive elements.

Gamma ray sources: (artificial isotopes- Co60,Ir192, Cs137) Artificial isotopes can be obtained either as fission product or due to fussion Cs135 is fission product (U(235) Co60 and Ir.192 are fusion product with Neutron bombardment

Normal elements like Co, Ir are exposed to neutron bombardment in nuclear reactors. Small pellets of Co, Ir are taken in Al cylinders and subjected to neutron bombardment.

Co 59 + n = Co 60 + gamma (neutron in gamma out)

27 C0 60

beta decay 28 Ni 60 *   1.17Mev 1.33 Mev 28 Ni 60

Isomeric transition

A = N a f (1-e – 0.693 t/T ) A = activity N - no of atoms in sample f - neutron flux ( )a - is the cross section in sq.cmt - time of neutron bombardmentT - the half life of the product

.0011 .01 1010.1

.01

0.1

1

CAESIUM 137

.0011 .01 1010.1

.01

0.1

1

IRIDIUM 192

.0011 .01 1010.1

.01

0.1

1

COBALT 60

Gamma ray spectrum

Compared to X-rays – continuous super imposed with characteristic X-raysGamma rays are discreet and discontinuous

Interaction of X-rays and Gamma rays with matter

When X-rays and gamma rays pass through the matter the intensity of primary radiation decreases as given by the attenuation equation.   I = I o . e - t (transparencies)

This is due to the various interaction processes the radiation undergoes with the matter. The two main processes of attenauation are 1) absorption and 2) scattering. Put together the various interaction processes are 1. Rayleigh scattering (coherent scattering)2. Photoelectric effect3. Compton scattering (incoherent cattering)4. Pair production

As a result of interaction processes X-ray and gamma ray photons are partly absorbed and partly scattered leading to reduction in transmitted radiation Absorption process – photoelectric effectScattering process - Rayleigh and Comton scattering

Higher the energy lower the attenuation coefficient what is the meaning

Interaction processes are less and radiation penetrates without getting affectedHigh energy X-rays penetrate more !!!

Summary and final result or impact on radiographic testing

Scattered radiation ( )Primary radiation Secondary radiation Particle radiation ( )Total attenuation coefficient is sum individual attenuation coefficients

μT = σ RS + σ PE + σ CS + σPP

μT = C ρ Z3

E3 More μT or less μT for radiographic image ?What is the disadvantage: EgMore E or less E : Xray and gamma rays

Radiation units

Energy – quality of radiation –ev,kv. MevIntensity – quantity-ma mts- Ci mtsSource strength of gamma ray sourcesDisintegrations /secBq – SI unit – 1 dpsCi – CGS unit – 3.7 x 10 10 dps

Other units are Exposure doseRadiation absorbed dose Radiation equivalent man

If one follows chronology and evolution, the units can be easily understood and differentiated

Basis for these units These units exposure dose, radiation absorbed dose and radiation equivalent man are indicative of the effect the radiation is going bring about in air, all materials and man respectively. The effect is due to both energy and intensity. However for one kind of radiation, it may be directly related intensity or amount and hence they are taken to be roughly intensity unitsExposure dose: (Roentgen)R is defined as the quantity of radiation that will produce 10 9 ion pairs in 1 cc of air at NTP. Or that will produce 1 esu in dry air at NTP. 1 R if it is fully absorbed will produce an amount of ionisation equivalent to 83 ergs of energy/gm of air. ( mR) This unit is applicable to X-rays and gamma rays only and only to air

Radiation Absorbed Dose (Rad) Limitation of Roentgen To cover all materials and all radiations Rad :It is the amount of radiation energy imparted to matter /unit of mass of irradiated material. 1 Rad represents 100 ergs of energy/gm of material at the place of exposure. R = 83 ergs/gm – airR = 97 ergs/gm – animal tissues R is approximately equal to Rad in these cases. For other materials there may differer much Problem with this unit ?One Rad of alpha radiation can cause more damage to human cells compared to one Rad of X-ray and gamma rays. Or in otherwords bilogical effectiveness of different radiations are different. (LET)

Radiation Biological effectiveness(RBE) Weighing factor/quality factorThe relative biological effectiveness of different radiations are   X-ray and gamma rays = 1 Beta particle = 1 Neutrons = 10 Alpha particles = 20

So to differentiate the effect of various radiations on human beings the unit rem - radiation equivalent man has been introduced.-Rem The Rem is defined as the quantity of ionising

radiation of any type which when when absorbed in biological system results in the same biological effect as one unit of absorbed dose in form of low LET (linear energy transfer) radiation.   R e m = Rad X RBE.

SI unit and comparison with old unit

  Old unit SI unit

Exposure Dose

Roentgen109 ion pairs in air83 ergs/gm

coulombs/kg  1R=2.58x10-4 C/kg

Radiation absorbed dose

Rad100 ergs/gm

Gray1 J/kg = 100rad

Radiation equivalent man

rem Sievert1 Sievert = 100rem 

Dose rate = R/hr, mR/hr etc

Some more useful unitsSpecific gamma ray constant –Specific emissionThe exposure dose rate of 1 Ci Co source at 1 mtre is a specific vale and is known Specific gamma ray constant RHM(Roentgen/hour at 1 mtreRHM of Co is 1.32 R/hr at 1 mtreRHM of Ir is 0.5 R/hr at mtre

Specific Activity is   Ci /gm determines the size of the source for same activity-high spcific activity source is smaller for the same activity-significance

Inverse Square law

I1 /I2 = d 22/ d 2

1

Basic imaging considerations Subject Contrasta)Image contrast Radiographic contrast Film Contrast Geometric unsharpnessb) Image Definition Image Sharpness Inherent unsharpness c)Distortion of image : Graininess 

Image quality

Definition (sharpness, acuity) Ability to distinguish two close points

Contrast Difference in film density (blackness) between two points

Measured by image quality indicator (penetrameter)

Quality Definition Contrast

To obtain a good radiograph Reduce the unsharpnesses to the minimum Select the conditions for high contrast Ensure radiation beam parallel to the orientation defect to reduce distortion

Assess the quality of the radiograph by using Image Quality Indicators Artificial details Penetrameters (penny)

Sensitivity of the radiograph is ascertained using the above. In radiography the sensitivity is so defined that a lower sensitivity is higher quality radiograph and the other way. In RT standards specify a sensitivity of 2% or less.

Definitions of contrast and definition

Radiograph is a shadow image – an image filled with light and dark regions. Then what is contrast and definitionContrast is darkness (photographic density) variation between the image and background or other portions.Definition or sharpness is darkness variation between the boundary and adjacent portion

Example

Differentiate between contrast and definition-the variables that influence contrast and definition

In review, it is entirely possible to have radiographs with the following qualities:

• Low contrast and poor definition • High contrast and poor definition • Low contrast and good definition • High contrast and good definition One must bear in mind that radiographic

contrast and detail are not dependent upon the same set of factors. If definition in a radiograph is originally lacking, then attempts to manipulate radiographic contrast will have no effect on the amount of definition present in that radiograph. 

Radiographic contrast

Radiographic contrast or image contrast is photographic density difference between the image and the background. This comprises of both subject contrast and film contrast

Photographic density:Opacity: measure of “darkness” or “lightness”Film transmittance:the ability of a film to pass light

light that passes through the film at PTtotal light incident on film at P

1log( ) logD OT

D = log Io

It

Density: the common logarithm of film opacityExampleMeasurement

Structure of film

X-ray film : characteristics of X-ray film as compared to photographic film: coating of emulsion on both sides and also thickness of emulsion is considerably greater than ordinary photographic film. An emulsion of AgBr on Cellulose acetate or polyester easeType of films and their characteristics

The film construction is essentially  a.transparent base- for the photosensitive emulsionb.emulsion (photosensitive AgBr dispersed in gelatin)c. bonding layer between base and the emulsiond. antiabrasive layer to protect the emulsion from S scratches etcs

Structure of film ( contd )

This acts as the support for all important emulsion layer which is responsible for image formation. This layer is transparent and is blue tinted for easy identification by the human eyes. Thickness of the layer is 0.001 in.Cellulose nitrate - used earlier - explosive -discordedCelllulose acetate - used for some time -now disposedPolyester or plastic - versatile - many good propertiesPresently widely used including for automatic processing Emulsion layer:This part of the film is responsible for image formation. This layer consists of dispersion of light (photo) sensitive AgBr grains (AgBr Crystals) in the trasparent gelatin layer.Emulsion thickness is 0.025 mmThe AgBr grain or crystal size varies between 0.2 mto 1.0 mThis variation in the grain size leads to various types of films like high speed and low speed and also high contrast and low contrast films.In other words, the entire classification of films by manufacturers are based on the variation of grain sizes that leads to various classes of radiograph.

Structure of radiographic film 

Type and class Speed of the film

Grain size Contrast  Definition

NDT 45 Cl ID2

Very slow

Ultra fine grain

Very high contrast

While sharpness

NDT 55 Cl IID4

Slow very fine grain

High contrast

is mainly determined

NDT 65 Cl IIID7

Medium Medium grain Medium contrast

by geometric

NDT 70 Cl IVD10. in No in contrast

High speed

Coarse grain Low contrast

arrangementfilm also contributes to definition.

Structure of film

Film contrast (continued)

logDE

γ= 2.3 m x S

fine grain Type of film1. Film property – m - High contrast coarse grain Low contrast

2. Photographic density S Higher the density higher will be the contrast Normally doubling of S doubles the contrast Normally in ind.radiography, we have S= 2-3 1.8 - 4.0 and 2.0 - 4.0 (as per standard-Why? above 4 not preferred ?Limitations of viewing conditions and above 5 no increase in contrast 3. Processing condition ie the developing time ASM Hand book

Ug=F t / D where t is thickness when object is placed on the filmUg = F t / SFD-t where SFD is source to

film distance

Pneumbral shadowBlurring extension of the image

Distortion of image due to direction of beam

X-ray beam parallel-no distortion –good image X-ray beam at angle- distortion – not satisfactory

Depending upon the defect (orientation) X-ray beam need be directed. Different configurations of weld different exposures to cover all features

Laminations and radiographic testing

Distortion of image due to direction of beam

X-ray beam parallel-no distortion –good image X-ray beam at angle- distortion – not satisfactory

Depending upon the defect (orientation) X-ray beam need be directed. Different configurations of weld different exposures to cover all features

Laminations and radiographic testing

Porosity shows up irrespective of direction of radiation.Lack of side wall fusion needs a definite direction of radiation to be shown

Image quality factors

Variables that be controlled

Assessment of quality of the radiograph Image quality indicators (IQI) or penetrameters

High Contrast Good definition Least Distortion Less graininess

K V (energy) mA (Current) mts (Time) FFD OFD Focal Spot size Type of Film Density of film Processing condition Use of screens Orientation of X-rays

Artificial details placed on the specimen and radiographed. The smallest detail that is seen in the radiograph is indicative of the quality of the image and not the size of the defect that can be seen

Image quality indicators: Two types of penetrameters or image quality

indicators are mainly used to determine the quality of the radiographic image.

Penetrameter material and the specimen need be one and the same

These are placed on the specimen and radiographed

Radiograph gives the image of the specimen superimposed with the image of penetramenter. The image of penetrameter gives an indication about the quality of the image.

Penetrameter sensitivity is indicative of only the quality of the image and it shall not be related to the size of the defect that can be detected. This is because the penetrameter orientation is ideal with respect to absorption and the actual defect orientation is not known.

A sensitivity of 2% or less is required as per standards 

ASTM plaque type penetrameters:

 Metal plaques of various thicknesses containing holes of diameters of 1T, 2 T and 4 T. Plaque of 2% of the thickness of the specimen is placed and radiographed. In the radiograph  1.the outline of the gives the contrast sensitivity and the2.perceptible holes gives the definition sensitivity and both put together gives the overall sensitivity. Fig.    

The quality levels are 2 - 1T and 2 - 2 T and 2 - 4T depending upon the visibility of the outline of the plaque and smallest perceptible hole. These level can be converted to DIN penetrameter sensitivity by the use of the following equation and the equation also facilitates use any penetrameter in the case the suitable one is not available.

Equivalent penetrameter sensittivity = 1/x X (T h/2) where x is the specimen thickness T is the thickness of plaque (inch) and h is the hole dia. (inches)

Personnel safety and radiation protection

X-rays and gamma rays bring about ionisation and excitation in living cells causing damage to the human body. The damage is of two types namely Somatic and Genetic. Somatic effects relate to injuries to the cells which are concerned with maintenance of body functions say cells in blood and bone marrow 

Genetic effects relate to the cells in the genes and chromosomes which are responsible for passing genetic characteristics to the subsequent generation.

Living with radiation

Background radiation

Background radiation

Natural Background 0.006 mR/hr Coal Burning Power Plant 0.165 mR/yr X-rays from TV set (1 inch) 0.500 mR/hr Airplane ride (39,000 ft.) 0.500 mR/hr Nuclear Power Plant (normal operation at plant boundary)

0.600 mR/yr

Weapons Fallout ~1 mR/yr Building materials (concrete) 3 mR/yr Drinking Water 5mRem/yr Cosmic Radiation (sea level) 26 mRem/yr Radionuclides in the body (ie potassium)

39 mRem/yr

Average annual total 360 millirem/year

Maximum allowable limits

The following are the exposure limits as per I C R P.

Radiation workers above 18 years - 0.05 Sv 5 Rem / year

Trainees below 18 years - 0.015 Sv 1.5 Rem/year

General public above 18 years - 0.005 Sv 0.5 Rem/year

The whole body dose of 0.05 Sv is usually interpolated as 1 mSv = 0.001 Sv/week (1mSv = 100 mRem) and to 25 micro Sv/hr ( 2.5 mRem/hr) (no Banking concept)

Dose limits for individual organs and tissues (other than lens of the eye)/year

RADIOGRAPHIC RADIOGRAPHIC TECHNIQUESTECHNIQUES

FILM SCREEN COMBINATION

SWSI

S1 S2

SWSISWSI

15° S1 - F1

S2 - F2

10° - 15° OFFSET TOPENETRATE THE ROOT

F1

TWO INDIVIDUAL EXPOSURES ON TWO SEPARATE FILMS

sIQI

IQI

IQIFILM

SOURCE INSIDE FILM OUTSIDESWSI“ PANAROMIC EXPOSURE ”

S

IQI

FILM

SWSISWSI

SOURCE INSIDEFILM OUTSIDE

SFILM

SOURCE OUTSIDEFILM INSIDE

SWSISWSI

FILM

S

DWSIDWSI

DWSI FOR LARGE CS JOINTS,CROSS COUNTRY PIPE LINES, SOURCE OUTSIDE, FILM OUTSIDE, IQI ON FILM SIDEMIN. SFD > OD OF PIPE

WELD IS SEGMENTED TO COVERTHE ENTIRE GRITH + OVERLAP.

FILM

DWDIDWDI PIPES<3½” ODOD/ID RATIO LESS THAN 2

TWO EXPOSURES AT 90° APART TO COVER COMPLETE VOLUME OF WELD

ELLIPTICAL IMAGE

PIPE OD < 3½”OD/ID> 2.No. OF SHOTS REQD.

1.7 X OD/ID( To the Next Highest integer)

Not Covered in Two Exposures At 90° Apart.

DWDI SUPERIMPOSEDDWDI SUPERIMPOSED

Double Wall superImposed Image interpreted for Both sides of Welds

SOURCE SIDESOURCE SIDEFILM SIDE IMAGES -FILM SIDE IMAGES -OVERLAPEDOVERLAPED