RADIOGRAPHIC

REFRESHER COURSE

TRAINING PROGRAM

DEVELPED FOR: SHELL PETROLEUM DEVELOPMENTCOMPANY OF NIGERIA

BY

LUMLEY TERRY

RADIOGRAPHIC

REFRESHER COURSE

TRAINING PROGRAM

DEVELOPED FOR: SHELL DEVELOPMENT

COMPANY OF NIGERIA

BY

T. W. LUMLEY (DMB-TNK)

ONE DAY RADIOGRAPHIC REFRESHER COURSE

1.0 BASIC PRINCIPLES OF FILM RADIOGRAPHY

1.1 Film radiography is carried out using X-ray or Gamma ray sources.

1.1.1 X-rays or Gamma rays pass through the object to be radiographed and record a latent image on a radiographic film positioned on the opposite side

1.1.2 The quality and amount of radiation reaching the film will be largely determined by the object thickness and density, eg. a crack in a weld increases the amount of radiation effect on the film due to a reduction in thickness.

1.1.3 For the purposes of the course limitations in time, we will concern ourselves solely with Gamma-radiography as generally used on site.

1.1.4 In consideration of 1.1.2, you should be aware that a radiographic test method relies on having a correct orientation in order to successfully detect a defect as is the case with all other N.D.E methods wit the sole exception of dye penetrant testing therefore consider two dimensional defects such as laminations fine cracks and lack of side wall fusion which may become ‘invisible’ using radiographic testing methods due to the defects orientation to the beam which can result in little or no discernible radiation absorption difference, resulting in no trace of the defect being evident on the processed radiograph whereas the same defects can be easily seen on a C.R.T. employing the normal ultrasonic testing methods.

Gamma Ray Source

Fig. 2

Angle probe 0• probe

L.O.S.W.F.

LAMINATION

L.O.S.W.F.

21 FILM

Fig. 1

In conclusion, it should also be sad that gamma or X-ray techniques are more sensitive methods for the detection of weld cap porosity L.P.O. and most three dimensional defects, with M.P.I. D.P.I. Eddy current etc being most superior in the detection of surface breaking defects therefore all NDE methods compliment each other.

Note: Where on fig.1, defect No. 1 ma be ‘invisible’ due to the radiation beams orientation, defects No.2. would be clearly seen as even though identical to No. 1 in dimension and nature, the orientation of defect No. 2 would give a far greater cross sectional change through its longest axis resulting in a greater radiation absorption.

1.1.5 When the film containing the ‘Hidden’ or latent image is processed a negative is produced, and when viewed, the thin areas of an object will be darker than the thicker areas therefore most detected weld defects will show up dark in relation to the surrounding areas, exceptions are excess weld metal, spatter, copper or tungsten inclusions.

2.0 RADIOGRAPHIC QUALITY

2.1 An overall assessment of radiographic quality technique is made by the use of image quality indicators (IQIs), the more wires visible the better the sensitivity.

Sensitivity Formulae:

Thickness of thickest wire visible x 100 Material thickness = % Sensitivity

2.1.1 The density of an image on a radiograph i.e. its degree of blackness is also measured to specification requirements.

2.1.2 The contrast is the degree f difference between density fields on a radiograph.

2.1.3 The definition is the degree of sharpness at the boundaries of density fields.

3.0 PROPERTIES OF X AND GAMMA RAYS

1) They cannot be detected by the human senses2) They have adverse effects on body tissue and blood3) They penetrate matter4) They travel in straight lines5) They are part of the electromagnetic spectrum6) They travel at the speed of light7) They obey the inverse square law8) They can be scattered9) They effect photographic emulsion10) They make certain materials fluorescence11) They may be refracted, diffracted and polarised12) They ionise gases

4.0 GAMMA RAY GENERATION

A radioactive material spontaneously emits corpuscular and electro-magnetic energy the gamma radiation is a by-product produced from the disintegration of the radioactive isotope.

4.1 For industrial radiography it is more practical to consider Gigabecquerels (Gbq) and curies where Giga = 109

1 Gigabecquerel = 109 Becquerels37 Gigabecquerel = 1 Curie

A ten curie source strength = 370 Gbq.

5.0 CHARACTERISTICS OF GAMMA RAY SOURCES

Source Half Life OutputGamma Ray

Energies MEV

Approx-X-ray Equi-valent KV

Possible Range in

Steel

Optimum Range in

SteelCobalt 60 5.26 Yrs 1.32 1.17-1.133 1000-2000 50-200mm 75-100mmCaesium

1342.1 Yrs 0.87 0.48-1.37 800 25-100mm 45-75mm

Caesium137

30 Yrs 0.33 0.66 750 25-100mm 45-75mm

Iridium192

74.4 Days 0.48 0.29-0.61 500 6 – 90mm 20-45mm

Ytterbium169

31 Days 0.125 0.053-0.309 200 Up–17mm 1 – 15mm

Thulium170

127 Days 0.0025 0.084 180 Up–12mm 10mm

6.0 HALF VALUE THICKNESS (HVT) OR HALF VALUE LAYER (HVL)

The halve value thickness of a material such as lead concrete, steel, may be used as a guide for determining the thickness of material needed to reduce the radiation levels to half of the original intensity.

When using Iridium 192, the thickness of lead needed to reduce the radiation level to half is 5.5mm, steel – 13mm, concrete – 43mm.

When using Cobalt 60, the thickness of lead needed to reduce the radiation level to half is approximately 11-12mm, steel –20mm, steel – 20mm and concrete – 63mm.

Because safe distances are not always available, the materials as described may be used in reducing or shielding the radiation beams intensity. In this regard for gamma radiography, a purpose made shielding device known as a collimator is used which effectively absorbs harmful radiation whilst its window allows the beam to penetrate the test item unhindered, radiation beam control collimation can also be used for X-ray equipment.

7.0 THE INVERSE SQUARE LAW

7.1 The inverse square law states that “At twice the distance from the source, the same radiation covers four times, the are but the intensity of radiation is four times less, at four times, the distance from the source the same radiation covers sixteen times the area but the intensity of the radiation is sixteen times less etc”.

7.1.1 Therefore when considering exposure times, the greater the SFC the greater the exposure time needed to obtain a given density.

7.1.2 The inverse squares law can be shown mathematically in relation to radiation intensity.

Therefore When I = IntensityD = Distance

I1 = D2²I2 = D1²

7.1.3 The following formulae based on the inverse square law can be used to determine new exposures when the S.F.D. changes.

Where E = ExposureD = Distance

E1 = D1²E2 = D2²

(E1) (D2²) New Exposure = Old Exposure x New Distance²

Old Distance² (D1²).

Note: O x ONew Exposure CalculationN N

O x NSafe Distance CalculationN O

7.1.4 Using the inverse square law formulae, we can further transpose safe working distances using the following formulae adaptations using IR 192.

1) Old Units:Activity x Output x 1000

.75 mR/hr

Eg.

10 Curie x .5 x 100 .75 mR/hr

= Distance = 81.6 Meters.

2) New Units:GBq x Output

7.5 µSV/hr

370 GBq x 130

7.5

= Distance = 80 Meters

3) Rough Calculation

10 Curies x26

Distance = 82 Meters

8.0 RADIOGRAPHIC TECHINIQUES

8.1 There are a number of techniques which may be used for establishing a radiographic techniques which is best suited for a given test specimen at hand, as follows.

8.1.1 S.W.S.I. (Panoramic) Source centered inside, Film outside

This technique may be performed either using an automated ‘crawler’ which basically comprises a centred isotope affixed to a motorised carriage which is controlled as on a newly constructed pipelines of substantial length externally by a radiographic specialist using a slave isotope or commander grader to control the movement and action sequences of the internally positioned ‘crawler. The panoramic method technique may also be utilised using conventional projection type equipment as normally seen on site for open ended pipe/flange weldments etc, providing the minimum S.F.D. requirements can be met regarding ‘Penumbra’.

8.1.2 D.W.S.I. Source outside, Film outside (contact)

This technique is most commonly applied to all pipe welds where the use of the panoramic technique is not possible or practicable, or above 90mm diameter. Normally three to four exposures for the same weld test are required using this method, dependent on the pipe diameter/thickness.

The isotope is projected to a front guide tube which is offset to approximately 85º from the weld face and film to eliminate the possibility of superimposing the top and bottom of the weld on the same exposure in comparison to the panoramic technique, the double wall single image technique when considering for example, a 24” diameter weld test, the time taken will be considerably longer due to the beam having to penetrate both wall thickness and of course the distance is effectively doubled giving a 4.1 ratio increase in exposure time needed and three times the amount of exposures needed to cover the welds circumferential length.

8.1.3 S.W.S.I. Source outside, Film inside

This technique is used mainly on plate testing such as oil holding tanks etc. it may also be used on larger diameter pipes where internal access is permitted in order to reduce the (S.F.D.) ‘source to film distance’ which in turn will reduce exposure times necessary, again consider the inverse square law where the distance is inversely proportional to the square of the distance. The required number of exposures required for a given diameter are given in for example BS. 2910 specification.

Note: The smaller the diameter using this technique, the more exposures needed due to curvature and thickness resulting in fade off (1.1).

8.1.4 D.W.S.I. Film outside, Source Outside

This double wall double image technique is normally applied to pipes/fittings 90mm diameter or below. Unlike the other techniques, the film cassettes are not bent around the pipe circumference but are held flat and offset to the weld to record an elliptical image, the isotope is positioned offset at least on fifth of the S.F.D. distance. A minimum of two-three exposures are required giving either four or six elliptical images for radiograph interpretation, the number of exposures required to fully cover the circumference of the weld is dependent on the contractual specification used.

Note: On smaller bore pipework, it may be permitted by specification or client for the radiation to be passed through the weld centre giving a superimposing source/film side image on the radiograph with both these techniques, the normal rule is that the S.F.D. should be ten times the diameter of the pipe to meet penumbral requirements.

8.1.5 Furthermore, specialised radiographic techniques are not available such as the Parallax, Stereoscopic, Real Time Methods, etc.

9.0 PENUMBRA OR GEOMETRIC UNSHARPNESS

9.1.1 This is the unsharpness as recorded on a radiograph caused by geometry of the radiation beam in relation to the object being radiographed and the film penumbra always existing and borders all density fields the dimensions of the source size, Object to Film Distance (O.F.D.) and Source Film Distance (S.F.D.) all effect penumbra. To reduce penumbral effect, we must consider the following:

1) The source size should be as small as possible2) O.F.D. should be as small as possible3) S.F.D. should be as long as practicable.

9.1.2 Penumbra size can be calculated from the following formulae

Penumbra = Source size x O.F.D. FFD - OFD

9.1.3 The (O.F.D.) is normally considered to be the thickness of the specimen or pipe diameter for 2” and below.

The normal maximum for penumbra = 0.25mm.

Eg. ug = 1.5 x 25 700 - 25

ug = 37.5 675

ug = .055mm

10.0 FILMS

There are many different manufacturers of radiographic film, i.e. Kodak, Agfa, Dupont, Fuji, etc. The make of film RTD Quality Services (Nig) currently uses Agfa, the grade of film used may vary relative to quality and practicability needed in any given circumstance.

Silver halides impregnated into a films emulsion vary in size for films of different speeds and are given a film factor for example a very fine grained film such as Agfa Gevaert D4 will take approximately three times more exposure time needed to achieve the same density using film speed D7.

IMAGE

a) POINT SOURCE b) SMALL FOCAL SPOT c) LARGE FOCAL SPOT

FILM

PENUMBRA UMBRA

Object

A fine grained film such as D7 is said to be a ‘fast film’ with film type D4 being classified as being a slow film. We can draw a comparison from film used in everyday photography where the D7 would compare with a A.S.A. 300 with D4 comparing with A.S.A. 100.

Therefore, the slower finer grained film will give sharper definition but will take three times as long to produce than a ‘fast film’.

10.1.1 SANDWICH TECHNIQUES

A practical use for films of different speeds can be demonstrated when double loading a film cassette with for example, a D4 and D7 film for a test item comparing of thick and thin sections which then may be radiographed in one exposure achieving acceptable density levels.

11.0 FILM DEVELOPMENT

Film processing can be carried out manually or by using an automatic film processor. Manual processing methods are carried out in a darkroom under ‘safe light’ a normal processing sequence being as follows:

1) Development - 4 to 5 minutes2) Stop both approximately 20 seconds3) Fixing tank – for twice the clearing time approximately 4 minutes4) Running or static wash – approximately 25 minutes5) Wetting agent tank i.e. photo flo – 2 to 3 seconds6) Drying cabinet or free hanging.

12.0 TYPICAL SITE R.T. VISIT

12.1 Arrangement should be made by the radiographic subcontractor crew that all relevant persons/authorities have knowledge of their intended site visit.

12.1.1 The R.T. crew should determine through the Engineer/Inspector whether any work location hazards exist by way of work permit(s).

12.1.2 R.T. crew should make equipment checks, and have in their possession the company’s rad safety handbook and contingency plan.

12.1.3 R.T. crew should posses rad monitoring equipment such as a monitor T.L.D. (film badge) and Q.F.E. (pen dosimeter).

12.1.4 The R.T. crew vehicle should display radiation warning signs when an isotope is located within the vehile.

12.1.5 R.T. crew should be observed to be in control of the intended radiation zone and ensure that non-classified personnel have vacated the test zone area.

12.1.6 R.T. crew can be observed to be using shielding/collimation for absorption of gamma radiation emission.

12.1.7 R.T. crew should erect barriers, warning signs etc which should be the internationally recognised colours, black and yellow.

12.1.8 R.T. crew should monitor/patrol the barriers to assess radiation levels as the barriers and ensure non-entry by unclassified personnel, maximum rad level to be 7.5 sv/hr or .75 mR/hr.

12.1.9 R.T. crew can be observed to monitor radiation levels present pre/post exposures.

12.1.10 R.T. crew must remove all signs, barriers etc when leaving site, ad lodge any permit issued.

12.1.11 Knowledge of R.T. crew departure should be notified to the Engineer/Inspector responsible at the site.

Note: Classified Personnel = 25 sv/hr “ “ = 2.5 mR/hrUnclassified Personnel = 7.5 sv/hr “ “ = .75 mR/hr

13.0 RADIATION EFFECTS ON HUMAN

Ionising radiation are undetectable by the human senses which make them particularly dangerous, they can cause injury to human tissue and organs. Cells in the body which divide are very sensitive to radiation damage: The production of red blood cells in bone marrow is particularly effected. Excessive doses either acute or chronic can cause injury to the persons involved, somatic effects such as leukaemia etc. and in extreme cases death, the damage done to yourself may also effect your future family (genetic effects).

Probable effects of an acute radiation dose to the whole body is as follows:

MSV DOES PROBABLE EFFECT1) 0-250 No obvious injury2) 250-500 Possible blood changes no serious injury3) 500-1000 Blood cell changes some injury but no disability4) 1000-2000 Injury and possible disability5) 2000-4000 Injury and disability plus possible death6) 4000-6000 50% fatality7) > 6000 Fatal – certain death.

13.1 It can be seen that working with radiation involves specialist knowledge requirements by the personnel performing radiography and even though a radiographic crew on site is a common place event you should always be aware of ‘safety first’ for yourself and others who may be responsible to you and may not have your knowledge of the subject.

13.2 A controlled radiation zone area means literally that, therefore any admission to such a zone must only take place with the responsible radiographer’s permission only.

13.3 Finally, be aware that any problems relative to a radiographic visit i.e. equipment malfunction etc, is adequately catered for by the R.T. subcontractors personnel by way of contingency plans as required by law, which if ever necessary are actioned by the R.T. crew company R.P.S./R.P.A. etc.

APPENDIX 1

A number of accidents have occurred in industrial radiography in the course of time. These accidents were the result of a number of different causes, but the common denominator was the failure to follow established safety procedures, and the failure to make adequate radiation survey.

In the hope that individuals will learn from the mistakes of users, the US Nuclear Regulator Commission requires that radiographers receive instructions in the case histories of radiography accidents. This section of the handbook describes summaries of selected radiography accidents. These cases have been selected because they highlight errors which are not uncommon. We hope that by understanding summaries of these accidents, and the results, you may be less likely to make the same errors.

CASE 1 A radiographer retracted a 27 Curie cobalt source until he felt it a tighten and stop. He assumed that the source had returned to fully shielded position within the exposure device and did not take a physical radiation survey. He then proceeded to disconnect the source guide tube from the exposure device, on the removal of the source guide tube, the radiographer recognised that the source extended approximately two inches out of the exposure device. He attempted to push the source into the device with his hand, but was unsuccessful. He then retreated to the control crank and was able to retract the source.

The radiographer’s film badge indicated a dose equivalent of 760m rem. However, the film badge was partially shielded during the incident. A re-enactment of the incident indicated that the dose equivalent to the radiographer’s hand was 574 rem.

The principal cause of the incident was the failure to make a survey after retracting the source. The radiographer showed a lack of judgement by attempting to force the source into a shielded position with his hand, which further increased his dose.

CASE 2 Two radiographers were performing pipeline radiography with a 40 Curie iridium source. The source assembly became detached from the driving cable and remained exposed in the guide tube for a 6 hours. During this period, the radiographers continued to radiograph pipeline welds.

The accident was discovered when the film was processed and proved to be over exposed. The radiographers pocket dosimeters were check and found to be off scale, no radiation surveys were made because the survey meter was left at the site office.

Film badge indicated whole body does equivalent for the two radiographers to be 21 rem and 15 rem respectively. The senior radiographer had slight swelling of the right hand after seven days with some discomfort in the fingers, blistering of the palm occurred in two weeks. Treatment of the hand continued for six months during which time the injury showed continued regression, at eighteen months, the right forth finger was slightly atrophied with the decrease ability to flex.

The principal case of the incident was the performance of radiography without the availability of an operable radiation survey meter.

CASE 3 During a radiographic operation, a 48 Curie source assembly became stuck

in the source guide tube. While the radiographer attempted to retract the source, it became disconnected from the driving cable. The radiographer with the help of his supervisor, removed the source from the guide tube, and manually returned the source to a shielded position.

A re-enactment of the incident indicated that the supervisor received a whole body dose equivalent of 3 rem and 1500 rem tone hand. The radiographer suffered severe radiation burns to the exposed hand.

The principal cause of the incident was the failure to follow appropriate emergency procedures when the abnormal occurrence was recognised.

CASE 4 After completion of a radiographic operation using a 90 Curie iridium source, the radiographer surveyed the exposure device and source guide tube and assured that the source was in the proper shielded position. However, he did not lock the exposure device after the survey, he picked up the exposure device with the controls and source guide tubes attached, and moved the device to another location. In the course of moving the device, the crank of the control unit caught on an obstruction and caused the source to be moved to an unshielded position.

The film badge which was worn in the shirt pocket approximately three fee from the source, indicated 8.8 rem. The estimated dose equivalent to the thigh, which was closer to the source, was 7 rem.

The principal cause of the incident was the failure to lock the exposure device at the completion of the operation. The radiographer could have minimised his dose by observing his survey meter while moving the exposure device.

CASE 5 A radiographer was performing radiogrpahy with an 80 Curie iridium source. At the conclusion of the exposure, he retracted the source into the exposure device with survey meter and noted normal radiation levels. He did not survey the exit port area of the device.

He then disconnected the source guide tube from the exposure device and attempted to install the storage plug. When the storage plug could not be properly installed, he recognised that the source was not fully retracted into the device.

A re-enactment of the incident that the radiographer received a whole body dose equivalent of 3 rem, 45 rem to the left hand and 600 rem to the right hand.

The principal cause of the incident was the failure to make a complete radiation survey of all sides of the exposure device at the completion of the operation.

CASE 6 While performing radiography with a 78 Curie iridium source, the radiographer recognised that the source did not retract to the shielded position in the exposure device. Further investigation revealed that the source assembly had become disconnected from the driving cable. The radiographer disconnected the source guide tube extracted the source assembly, reattached it to the driving cable, and retracted the source.

By the eleventh day following the incident, redness, swelling and tenderness of the palm and finger tips had developed. About the sixteenth day, blisters appeared, in approximately one month, the involved areas healed but the skin remained thin, atrophic and sensitive. The symptoms still persisted one year after the event.

A re-enactment of the incident that the radiographer received a whole body dose equivalent of approximately 50 rem and 1500 rem to the hand.

The principal cause of the incident was the failure to follow the appropriate safety procedures once an emergency situation has been recognised.

CASE 7 A radiographer was returning a 32 Curie iridium source after a source exchange. In the course of preparing the source changer for shipment, the radiographer moved the source from the shielded position in the source changer to an exposing position. He did not make a radiation survey prior to shipping the package. The exposed source was discovered upon receipt at the source manufacture facility after the source had been transported on two aeroplanes and through three airports.

The maximum estimated dose equivalent to airpot handlers were: Airport A – 10.4 rem; Airport B – 26 rem; Airport C – 134.4 rem.

Estimated maximum dose equivalents to passengers could have been 10.6 rem on the first plane and 6.8 rem on the second plane.

The principal cause of the incident was the failure to properly package the source for shipment and the failure to make a radiation survey prior to shipping the package.

CASE 8 A radiographer was using a 14 Curie iridium source to perform radiography on a construction platform approximately on half mile offshore. The radiographer failed to connect the source guide tube to the exposure device. Upon exposure, the source went over the side of the platform. Due to the weight of the driving cable and the ocean currents, the entire drive cable wit the source assembly attached sank to the bottom in forty feet of water.

In an attempt to retrieve the source, a specially designed radiation detector for use at that depth was built. Using this detector and with special communication equipment, police divers attempted to locate the source assembly and drive cable. However, due to poor visibility, it was not successful.

The next approach was to lower a grab attached to a crane and attempt to grapple the drive cable. This worked on the first try. The source was brought to the platform and placed into a shielded position. The maximum dose equivalent received by any individual was 20 m rem.

Although the incident did not involve any radiation over exposure, the source retrieval required five days intensive work by a large number of people at considerable cost.

APPENDIX 2

FACTORS AFFECTING IMAGE QUALITY

Affected By: Affected By: Affected By: Affected By:

A Absorption diffe-rences in speci-

A Type of film A Focal-spot size A Type of film

B

men (thickness, composition, density).

Radiation

B Degree of deve-lopemnt (type of developer;

B Source-film distnace

B Type of screen

wavelength time and tempe-rature of deve-

C Specimen-film distnace

C Radiation wave length

C Scattered radiation

Reduced by:

lopment; activi- ty of developer;degree of agita-tion). D Abruptness of D Development

1 Marks and diaphragms

C Densitythickness changes in specimen

2

3

Filters

Lead screens

D Type of screens (fluorescent vsLead or none)

E Screen-film contact

4 Potter-Bucky diaphragms

F Motion of specimen

DENSITY

Expressed as D, is the degree of blackness on the film. B.G.C. requires a density of D = 2.5 on the pipewall.

API 1104 requires a density of D = 2.0 on the pipewall and D = 1.8 on the weld metal.

These are minimum densities.

RADIOGRAPHICCONTRAST

RADIOGRAPHICIMAGE QUALITY

DEFINITION

SubjectContrast

FilmContrast

GeometricFactors

Film GraininessScreen Mottle Factors

The B.G.C. also states that the viewing box should have sufficient light intensity to enable the interoperation of films with a density of D = 3.5.

Density is measured by a Densitometer, and is defined by Hurter and Driffield as:-

D = log Io when Io is the original intensity of lightIt (e.g. from the viewing box), and It is the intensity of light transmitted through the film viz:-

Assuming that the Io was 1000 units of light intensity (log of 1000 is log 3) and that of It was 10 (log of 10 is log 1( then log 3 minus log 1 = 2, therefore D = 2.

Similarly, if Io was 10,000 units and It 10 units then log 4 minus log 1 =3 therefore D = 3.

Factors Affecting Density

1. Exposure : The grater the exposure, the higher the density

2. Development time: The longer the time, the higher the density

3. Temperature : The higher the temperature, the higher the density and vice versa.

CONTRAST

Film contrast is an inherent characterisitic of the film and will never vary for that particular film. Film contrast is the difference in densities between any two areas of the film.

Io It

film

APPENDIX 3

RADIOGRAPHY GLOSSRY OF TERMS

ABSORPTION

The reduction in intensity of a beam of radiation during its passage through matter, the three primary causes being photo-electric absorption, absorption due to scattered and absorption due to pair production.

ACTIVITY

The number of disintegrations per unit time taking place in a radioactive specimen (see ‘curie’).

ADQUATE SHIELDING

Shielding of any form, including air or open space, which reduces the radiation dose rate at the boundary, averaged over any one minute, to levels defined as acceptable in the statutory regulations issued by the Ministry of Labour.

ARTEFACT

A spurious indication on a radiograph caused by faults in the manufacture, handling or processing of a film.

BACK SCATTER

That part of the scattered X – or gamma radiation which is emitted at any angle of more than 90º in relation to the direction of the incident beam.

BARIUM CONCRETE

Concrete containing a high proportion of barium compounds used for protection purposes. Similarly for barium bricks, plaster, etc.

BEAM ANGLE

1. The angle of divergence of the beam of radiation in any given plane passing through the focus.

2. The angle between the central axis of the radiation beam and the plane of the film.

CASSETTE

A light-tight container for holding a radiographic film, paper or plate or without screens during exposure, the front face of which is relatively transparent to X- or gamma rays.

CHARACTERISTIC CURVE

A curve showing the relation between the common logarithm of exposure (frequency expressed in the arbitrary units) and the photographic density.

CHARACTERISTIC RADIATION

X- radiation consisting of discrete wavelengths which are characteristic of the emitting material.

CLEARING TIME

The time required for the first stage of fixing during which the whiteness of the film disappears.

COLLIMATION

The limiting of a beam of radiation to a near parallel beam.

CONSTANT-POTENTIAL CIRCUIT

A circuit which is so arranged to apply and maintain a substantially constant potential across an X-ray tube.

CONTAINER, GAMMA-RAY SOURCE

A device for housing radioisotope and giving a required degree of protection against radiation. (This may take the form of an exposure container or storage container).

CONTRAST

The relative brightness of two adjacent areas on an illuminated radiograph or fluorescent screen image.

RADIOGRAPHIC CONTRAST

Contrast on a radiograph. (This may be measured as the density difference between an image and the background).

FILM CONTRAST

See ‘gradient’.

DECAY CURVE

The strength of a radioactive source, measured in curies, plotted against time. (For convenience, the curve is usually plotted on a log-linear basis).

DEFINITION

The sharpness of delineation of image details in a radiograph, photographic reproduction or fluorescent screen image. Generally used qualitatively.

DENSITOMETER

An instrument for measuring light transmitted and/or reflection density of film, plat or paper.

DENSITY, PHOTOGRAPHIC

The common logarithm of the ratio of incident to the transmitted luminous flux. The value of the density depends on the method of measurement. Two extremes are in general use namely, total diffuse density and specular density.

DEVELOPMENT

The conversion of a latent image into a visible image.

DEFFRACTION MOTTLE

A superimposed mottle on an image due to diffraction of incident radiation, and results from certain combinations of wavelength of that radiation, and the size and orientation of the grains of the material through which it has passed.

DOSEMETER

An instrument for measuring quantities of radiation.

DOSE RATE

The rate at which radiation is delivered. Note: The term has a slightly different meaning in relation to health physics.

DOSE RATE METER

An instrument for measuring radiation dose rate.

EXPOSURE CHART

A chart indicating the radiographic exposure appropriate for different thickness of a specified material.

FIML BADGE

A film contained within a special holder which is worn by personnel to assess the radiation dose to which the wearer has been exposed.

FILM BASE

The transparent or translucent support for the photographic emulsion.

FILM PROCESSING

The operations necessary to transform a latent image into a permanent visible image.

FILM SPEED

A measure of the exposure required to produce a given density on a photograph emulsion under any given set of conditions.

FILM VIEWER

Equipment incorporating a suitable area of illumination for viewing radiographs.

FILTER

Material interposed in the path of radiation in order to reduce selectively the intensity of radiation of a certain range of wavelengths or energies.

FILTRATION, INHERENT

The filtration of an X-ray beam by any parts of the tube or shield, including insulating and cooling fluids, through which it must pass.

FIXING

The chemical removal of silver halides from an emulsion after development.

FLASH RADIOGRPAHY

Radiogrpahy in which the exposure time is extremely short for the purpose of examining transient effects.

FLAW SENSITIVITY

The minimum size of defect which can be found under specified conditions. (This should not be confused with image quality indicator sensitivity).

FLUORESCENT SCREENS

A suitably mounted layer of material which fluoresces in the visible region of the spectrum under the action of X-rays for other ionising radiation.

FLUOROGRAPHY

Photography of a fluoroscopic image.

FLUOROSCOPY

The production of a visual image on a fluorescent screen (eg. X-rays) and its use for the examination of materials by direct viewing.

FOCUS SIZEFOCAL SPOT SIZE

The apparent dimensions as viewed along the X-ray tube beam axis, of that portion of the target from which X-rays are emitted.

FOCUS-TO-FILM DISTANCE

The distance from the focal spot of an X-ray tube to a film set up for radiographic exposure. Abbreviation – F.F.D.

FOG

A general term used to denote any increase in the optical density of a processed film caused by anything other than the direct action of image forming radiation. It can be any of the forms defined below.

CHEMICAL FOG

Fog arising from unwanted chemical reactions during processing of a film.

EXPOSURE FOG

Fog arising from any unwanted exposure of a film to ionising radiation or light, at any time between manufacture and final fixing. INHERENT FOG

The formation of a latent image in some of the grains of a photographic material during storage.

PHOTOGRAPHIC FOG

Fog arising solely from the properties of an emulsion and the processing conditions, i.e. the total effect of inherent fog and chemical fog.

FULL WAVE RECTIFICATION

Rectification which allows current to flow through an X-ray tube during each half-cycle of an alternating supply.

GAMMA-RAYS

Electromagnetic radiation emitted by radioactive nuclei.

GAMMA-RAY SOURCE

A quantity of matter emitting gamma-radiation suitable for radiography.

GAMMA-RADIOGRAPHY

The slop of a characteristic curve at a specified density. Symbol Gb). Note: The term ‘gamma’ is used for the slope of the approximately straight portion of the curve.

GRADIENT

A visual effect due to the random distribution of the silver grains in the emulsion layer.

GRAIN SIZE

The average size of the silver halide particles in a photographic emulsion.

HALF LIFE

The time in which the strength of a radioactive source decays to half its value.

HALF-VALUE THICKNESS

The thickness of a specified substance which, when introduced into the path of a given beam of radiation reduces its intensity to one half. It may be used as an indication of the quality of the beam or the opacity of the substance.

HALF-WAVE RECTIFICATION

Rectification which allows current to flow through an X-ray tube only during alternate half-cycles of an alternating supply.

‘HARD’ RADIATION

A term used to describe qualitatively the more penetrating types of X-rays.

HADENER

A substance (eg. Potassium alum, chrome alum or formalin) used to harden the gelatine in the emulsion, commonly added to the fixing bath. IMAGE QUALITY INDICATORPENETRAMETER

A device used for judging, from the appearance of its image in a radiograph, the overall quality of that radiograph.

IMAGE QULAITY INDICATORSENSITIVITY

The smallest change in image quality indicator thickness which can be detected in a radiograph, expressed as a percentage of the subject thickness, the subject being assumed to be of specified homogeneous material. (It should not be confused with ‘flaw sensitivity’).

INTENSIFYING FACTOR

The ratio of the exposure time required intensifying screens to that when screens are used, other conditions being the same.

INTENSIFING SCREEN

A layer of material which, when placed in close contact with a photographic emulsion, adds to the radiographic effect of the incident radiation by reducing exposure time. Two kinds of screen in common use are:

1. Salt Screen

An intensifying screen consisting of a material, such as calcium tungstate, which fluoresces in the visible or ultraviolet region of the spectrum under the action of X-rays or the other ionising radiation.

2. Metal Screen

An intensifying screen of metal foil, usually lead, which emits secondary radiation under the action of X-rays or other ionising radiation.

LATENT IMAGE

An invisible image produced in a recording medium by exposure to radiation and capable of being converted into a visible image by development.

LATITUDE

Of an emulsion. The range in exposure corresponding to the useful density range of an emulsion.

LOCALISING CONECOLLIMATING CONE

A cone which limits the divergence of a beam of radiation.

MASKING

The application of material which limits the area of irradiation to the region undergoing radiographic examination.

NON-SCREEN FILM

X-ray film designed for use with or without metal screens, but not intended for use with salt screens.

OVER-DEVELOPMENT

Development which is greater than that required to produce the optimum results in a particular radiograph. It may arise from development for too long a time, or at too high a temperature, and may give rise to excessive graininess fog and lack of contrast.

PANORAMIC EXPOSURE

An arrangement of simultaneous exposures from a single course.

PENUMBRA

Blurring at the edges of a radiograph image resulting from the fact that the radiation source is of finite dimensions.

PHOTOGRAPHIC EMULSION

A dispersion of photo-sensitive material, such as silver halide grains, in a medium such as gelatine.

PRESSURE MARK

A mark produced by pressure on or crinkling of the film which after developing results n areas of either increased or decreased density. See ‘artefact’.

PRMARY RADIATION

Radiation which is incident on the absorber and continues unaltered in energy and in direction after passing through the absorber.

QUALITY

Of a beam of ionising radiation. The penetrating power of the beam. From a heterogeneous X-ray beam it is commonly measured in terms of half-value thickness.

RADIOGRAPH

A photographic image produced by a beam of penetrating ionising radiation after passing through a material.

RADIOGRAPHIC EXPOSURE

The subjection of a recording medium to radiation for the purpose of producing a latent image. radiographic exposure is commonly expressed in terms of milliampere seconds or mallicurie hours.

RADIOGRAPHY

The production of radiographs.

RADIOLOGY

The science and application of X-rays, gamma-rays and other penetrating ionising radiation’s.

RECIPROCITY LAW

A law which states that, all other conditions remaining constant, the time of exposure required to produce a given photographic density is inversely proportional to the intensity of the radiation.

REPLENISHER

A modified form of the original developer which, when added to partially exhausted developer, restores its effectiveness.

RESOLUTIONGE

The smallest distance between recognisable images on a film or screen. It may be expressed as the number of lines per millimeter which can be seen as discrete images.

RETICULATION

A net-like structure appearing in an emulsion as a result of buckling of the gelatine film due to differences in temperature between the processing baths, or rinsing water.

REVERSAL

A complete or partial reversal of he tones of a radiograph.

SAFELIGHT

A source of filtered light of colour or waveband chosen to give insignificant fogging of a particular film type at intensity levels necessary for handling and processing films in a dark room.

SCATTED RADIATION

Radiation different in direction from the primary radiation.

SCREEN-TYPE FILM

X-ray film designed for use with salt screens, which has a high sensitivity to the fluorescent light emitted by such screens under the action of X-rays and gamma-rays.

SECONDARY RADIATION

Radiation different in quality from the primary radiation.

‘SOFT’ X-RAYS

A term used to describe qualitatively the less penetrating types of X-rays.

SOLIRIZATION

The diminution on photographic density produced by exposure additional to that required to give maximum density on development. This may result in reversal.

SOURCE

The radioactive material from which primary radiation is emitted. Of ‘target’.

SOURCE SIZE

The apparent dimensions as viewed along the beam axis of that porting of the source from which ionising radiation’s are emitted.

SOURCE-TO-FILM DISTANCE

The distance from a source of primary radiation to a film set up for a radiographic exposure. Abbreviation S.F.D.

SPECIFIC ATIVITY

The activity per unit mass of a source.

STEP WEDGE

A block of material in the form of a series of steps used for the preparation of exposure charts.

STOP BATH

An acid bath to arrest development and to neutralise alkalin developer in an emulsion before transfer to the fixing bath.

TARGET

The area on the surface of the anode of an X-ray tube on which the electron stream impinges and from which the primary beam of X-rays is emitted.

TOMOGRAPHY

The radiography of a predetermined layer of a material. In one method the X-ray tube and film are moved simultaneously in opposite directions about a pivotal point in the plane of the layer.

TUBE CURRENT

The current passing between the cathode and anode during the operation of an X-ray tube.

TUBE DIAPHRAGM

A device, normally fixed to a tube shield or head, to limit the extent of the emergent X-ray beam.

TUBE HEAD

A type of tube shielded, which in addition to the X-ray tube may contain part of the high voltage generator.

TUBE SHIELD

The housing of an X-ray tube which normally provides protection against electric shock and affords a degree of protection against radiation.

TUBE WINDOW

The window in the X-ray tube through which radiation pass. (Materials have different absorption properties, and thus some ‘windows’ are designed by their material, eg. ‘beryllium window’).

UNDER-DEVELOPMENT

Development which is less than that required to produce the optimum results in a particular radiograph. It may arise from development for too short a time, or at too low a temperature, or from the use of exhausted developer.

UNSHARPNESS

Image blurring resulting in loss of definition. This may be due to:

1. Film Unsharpness

Image spread caused by electron or light scatter through the emulsion grains.

2. Geometric Unsharpness

Unsharpness caused by penumbra.

3. Movement Unsharpness

Unsharpness caused by unco-ordinated relative movement between radiation source, object and film during an exposure.

4. Screen Unsharpness

Unsharpness caused by the use of intensifying screens or fluorescent viewing screen. It may result from the scatter of light by the crystals of the fluorescent layer of poor contact between screens and film.

USEFUL DENSITY RANGE

The range of photographic density which is adequate for he required recognition of image details.

X-RADIATION

Electromagnetic radiation resulting from extra nuclear loss of energy of charged particles (eg. Electrons) and having shorter wavelength than ultra-violet radiation.

X-RAY FILM

A film base which is coated (usually on both sides) with an emulsion designed for use with X-rays and gamma-rays.

X-RAY PAPER

White paper coated on one side with emulsion, which is suitable for some purposes as an alternative to X-ray film.