as 2177 1 1994 non destructive testing radiography of weld

radiography of weld

Title AS 2177.1-1994 Non-destructive testing - Radiography of welded butt joints in metal Methods of test Licensee Licensed to SAIPEM (SPCM) on 11 Sep 2002 Conditions of use This is a licensed electronic copy of a document where copyright is owned or managed by Standards Australia International Your licence is a single user licence and the document may not be stored, transferred or otherwise distributed on a network You may also make one paper copy of this document if required Web Check-up AS 2177.1—1994 Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Australian Standard® Non-destructive testing— Radiography of welded butt joints in metal Part 1: Methods of test This Australian Standard was prepared by Committee MT/7, Non-destructive Testing of Metals and Materials It was approved on behalf of the Council of Standards Australia on 14 June 1994 and published on 22 August 1994 The following interests are represented on Committee MT/7: Australian Institute for Non-Destructive Testing Australian Nuclear Science and Technology Organization Australian Pipeline Industry Association AUSTROADS Bureau of Steel Manufacturers of Australia Department of Defence Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Electricity Supply Association of Australia Metal Trades Industry Association of Australia National Association of Testing Authorities, Australia Railways of Australia Committee Society of Automotive Engineers—Australasia Welding Technology Institute of Australia WorkCover Authority of N.S.W Additional interests participating in preparation of Standard: Non-destructive testing service organizations Royal Melbourne Institute of Technology Review of Australian Standards To keep abreast of progress in industry, Australi an Standards are subject to periodic review and are kept up to date by the issue of amendments or new editi ons as necessary It is important therefore that Standards users ensure that they are in possession of the latest editi on, and any amendments thereto Full detail s of all Australi an Standards and related publications will be found in the Standards Australi a Catalogue of Publications; this information is supplemented each month by the magazine ‘The Australi an Standard’, which subscribing members receive, and which gives details of new publications, new editi ons and amendments, and of withdrawn Standards Suggesti ons for improvements to Australian Standards, addressed to the head offi ce of Standards Australi a, are welcomed Noti fi cati on of any inaccuracy or ambiguity found in an Australian Standard should be made without delay in order that the matter may be investigated and appropriate action taken This Standard was issued in draft form for comment as DR 91258 AS 2177.1—1994 Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Australian Standard® Non-destructive testing— Radiography of welded butt joints in metal Part 1: Methods of test First publi shed in part as AS B164 — 1965 AS B230 fi rst publi shed 1967 AS B237 fi rst publi shed 1967 AS B164 — 1965, AS B230— 1967 and AS B237 — 1967 revised, amalgamated and redesignated AS 2177.1 — 1978 Second editi on 1981 Thir d editi on 1994 PUBLISHED BY STANDARDS AUSTRALIA (STANDARDS ASSOCIATION OF AUSTRALIA) THE CRESCENT, HOMEBUSH, NSW 2140 ISBN 7262 9105 AS 2177.1 — 1994 PREFACE This Standard was prepared by the Standards Australia Committee on Non-destructive Testing of Metals and Materials to supersede AS 2177.1 — 1981, Radiography of welded butt joints in metal, Part 1: Methods of test The second Standard in the series is AS 2177.2—1982, Radiography of welded butt joints in metal, Part 2: Image quality indicators (IQI) and recommendations for their use In this edition, cognizance was taken of the following International Standard during the revision of the clauses on gamma-ray sources, radiographic density and film coverage: ISO 1106/3 Recommended practice for radiographic examination of fusion welded joints —Part 3: Fusion welded circumferential joints in steel pipes of up to 50 mm wall thickness This edition also contains a new Appendix which gives guidance on the use of the Standard Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited This Standard does not cover methods which employ non-film imaging techniques These techniques will be considered at the next revision of the Standard The use of non-film imaging techniques for the radiographic examination of welded joints is now permitted by the ASME Boiler and Pressure Vessel Code The term ‘informative’ has been used in this Standard to define the application of the appendices An ‘informative’ appendix is not an integral part of a Standard and is included for information and guidance only © Copyri ght STANDARDS AUSTRALIA Users of Standards are reminded that copyri ght subsists in all Standards Austr alia publi cati ons and software Except where the Copyri ght Act all ows and except where provided for below no publi cati ons or soft ware produced by Standards Australi a may be reproduced, stored in a retr ieval system in any form or transmitt ed by any means without prior permission in writ ing from Standards Australi a Permission may be condit ional on an appropri ate royalt y payment Requests for permission and information on commercial software royalt ies should be directed to the head offi ce of Standards Austr alia Standards Austr alia wil l permit up to 10 percent of the technical content pages of a Standard to be copied for use exclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Austr alia Standards Austr alia wil l also permit the inclusion of its copyri ght material in computer soft ware programs for no royalty payment provided such programs are used exclusively in-house by the creators of the programs Care should be taken to ensure that material used is fr om the curr ent edit ion of the Standard and that it is updated whenever the Standard is amended or revised The number and date of the Standard should therefore be clearly identif ied The use of materi al in print form or in computer software programs to be used commercially, with or without payment, or in commercial contracts is subject to the payment of a royalty This policy may be vari ed by Standards Austr alia at any ti me AS 2177.1 — 1994 CONTENTS Page FOREWORD Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited SECTION SCOPE AND GENERAL 1.1 SCOPE 1.2 REFERENCED DOCUMENTS 1.3 DEFINITIONS 1.4 TEST METHOD DESIGNATION 1.5 SAFETY PRECAUTIONS 1.6 QUALIFICATION OF PERSONNEL 6 6 7 SECTION EQUIPMENT AND ACCESSORIES 2.1 GENERAL 2.2 X-RAY EQUIPMENT 2.3 GAMMA-RAY SOURCES 2.4 INTENSIFYING SCREENS 2.5 CASSETTES 2.6 FILTERS 2.7 IMAGE QUALITY INDICATORS 2.8 FILMS 10 2.9 FILM PROCESSING FACILITIES 10 2.10 VIEWING FACILITIES 10 SECTION TEST METHOD REQUIREMENTS 3.1 GENERAL 3.2 SURFACE PREPARATION 3.3 PLACEMENT OF IMAGE QUALITY INDICATORS 3.4 GEOMETRIC UNSHARPNESS 3.5 RADIOGRAPHIC DENSITY 3.6 FILM COVERAGE 3.7 BACK-SCATTER PROTECTION 3.8 RADIOGRAPHIC IDENTIFICATION 3.9 RECOMMENDED TUBE VOLTAGES 3.10 FILM LOCATION 3.11 MASKING 3.12 RADIOGRAPHIC PROCEDURAL REQUIREMENTS 3.13 PROCESSING OF RADIOGRAPHS 3.14 VIEWING OF RADIOGRAPHS 3.15 STORAGE OF RADIOGRAPHS 11 11 11 12 12 12 16 16 17 17 18 18 20 20 21 SECTION PRESENTATION OF TEST DATA 4.1 SCOPE OF SECTION 4.2 RECORD OF TEST 4.3 TEST REPORT 22 22 22 AS 2177.1 — 1994 Page Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited APPENDICES A PURCHASING GUIDELINES B GUIDANCE FOR THE USE OF THIS STANDARD C RADIOGRAPHIC EQUIVALENCE FACTORS 24 26 41 AS 2177.1 — 1994 FOREWORD In the methods described in this Standard, the photographic film is generally placed parallel to and in contact with one surface of the weld The source of ionizing radiation is located on the remote side of the weld and at a calculated distance from it For hollow products the radiation may be required to penetrate both walls of the product Radiographic sensitivity is affected by parameters which include radiation energy (kilovolt or isotope spectrum), the film/screen combination, scattered radiation control, and exposure geometry (source-to-film distance and effective source size) Although the highest radiographic sensitivity is usually achieved using X-rays, their use is limited by the thickness of the workpiece Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited For the radiography of hollow components, either single-wall or double-wall methods are used Although the radiographic sensitivity obtained when using single-wall methods is generally superior to that obtained when using double-wall methods, other factors such as diameter, thickness and accessibility may influence the choice of method AS 2177.1 — 1994 STANDARDS AUSTRALIA Australian Standard Non-destructive testing—Radiography of welded butt joints in metal Part 1: Methods of test S E C T I O N S CO P E A N D G E NE R A L 1.1 SCOPE This Standard sets out methods and requirements for X-ray and gamma-ray radiographic testing of welded butt joints in metal products It does not cover neutron radiography and does not specify the permissible defect levels used for the acceptance/rejection criteria of welds The individual methods of test and the permissible defect levels should be specified in the relevant product or application Standard NOTES: Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Advice and recommendations on information to be supplied by the purchaser at the time of enquiry or order are contained in Appendix A Guidance and general information which should assist the users of this Standard is contained in Appendix B 1.2 REFERENCED DOCUMENTS The following documents are referred to in this Standard: AS 1929 Non-destructive testing—Glossary of terms 2177 Radiography of welded butt joints in metal 2177.2 Part 2: Image quality indicators (IQI) and recommendations for their use 2243 Safety in laboratories 2243.4 Part 4: Ionizing radiations 3669 Non-destructive testing —Qualification and registration of personnel — Aerospace 3998 Non-destructive testing —Qualification and certification of personnel — General engineering Z5 Z5.2 Glossary of metal welding terms and definitions Part 2: Terminology of and abbreviations for fusion weld imperfections as revealed by radiography BS 1384 Photographic density measurements ASTM E 1165 Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging 1.3 DEFINITIONS For the purpose of this Standard, the terms and definitions given in AS 1929 apply 1.4 TEST METHOD DESIGNATION Radiographic methods are designated in the following manner: (a) By prefix letters ‘XR’ or ‘GR’ to identify the radiation source, i.e X-ray or gamma-ray COPYRIGHT (b) AS 2177.1 — 1994 By a number 1, or to indicate the film type, as follows: (i) Type 1: Very fine grain, very high contrast, low speed (ii) Type 2: Fine grain, high contrast, medium speed (iii) Type 3: Medium grain, medium contrast, high speed (c) By a solidus (/) followed by one or two letters to indicate whether testing is required through a single plate or wall (S), or through a double wall (DW), and in the latter case, by the addition of another letter to indicate whether a single image of the weld (S) or a double image of the weld (D) is required Examples of designation : XR1/S, XR2/DWS, GR3/DWD 1.5 SAFETY PRECAUTIONS Prolonged exposure of any part of the human body to ionizing radiation can be injurious Adequate precautions shall be taken to protect testing personnel and any other persons in the vicinity, when X-ray equipment or radioactive sources are being used Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited NOTE: The use of radioactive substances and irradiating apparatus is controlled by various statutory regulations Reference should be made to the ‘Code of Practice for the Safe Use of Industrial Radiography Equipment (1989)—Radiation Health Series No 31’, issued by the National Health and Medical Research Council Reference should also be made to AS 2243.4 for ionizing radiation safety precautions 1.6 QUALIFICATION OF PERSONNEL Personnel who perform radiographic testing to this Standard should have recognized qualifications in the specific area of test NOTE: The Australian Standards for personnel qualification are AS 3669 and AS 3998 COPYRIGHT 27 AS 2177.1 — 1994 The effect of increasing the tube voltage is to shorten the wavelength and to increase the penetrating power of the X-rays produced The influence of this increase in penetrating power on radiographic contrast can be illustrated by the following example: Example A sample made of steel 26 mm thick containing a mm machined step is X-rayed using 100 kV, 200 kV and 400 kV radiation exposures The increase in the transmitted radiation reaching the film through the 25 mm section, due to the step, will be as follows: (a) For 100 kV 45% (b) For 200 kV 12% (c) For 400 kV 6% The greater differences in transmitted radiation between the adjacent 25 mm and 26 mm sections will produce correspondingly greater differences in film density Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Thus, lower X-ray tube voltages will produce better radiographic contrast resulting in improved IQI and discontinuity sensitivity, but will require increased exposure times as the tube voltage is reduced As a general principle, therefore, exposure should be carried out at the lowest tube voltage consistent with a reasonable exposure time In practice, the tube voltage and hence the exposure time, is chosen to achieve the required sensitivity It should be noted that this principle requires modification for radiation at voltages of MV and above B4 SELECTION OF RADIOGRAPHIC TECHNIQUE The choice of a suitable radiographic technique for a given application is based on the requirement to reveal all discontinuities which are considered unacceptable by the construction code or product Standard In practice, this objective may be difficult to quantify Thus the chosen radiographic technique will always be a compromise between radiographic quality and such economic factors as the number of exposure shots and the exposure time A considerable degree of variation in radiographic quality will result from each of the six test method groups specified in this Standard as well as between individual method designations Variation in any of a number of test parameters will affect both the sensitivity obtained and the time taken to carry out the test This is demonstrated by the following example: Example (a) Film densities may vary from 1.7 to over 3.5 Higher film densities will give better contrast and hence better sensitivity (b) The source-to-film distances specified in Figure 3.4 and Clause 3.10.2 are the minimum values Increasing these values will improve definition and hence sensitivity (c) Recommended maximum tube voltages are specified in Figure 3.3 for method XR1, and in Clause 3.9 for other methods Table 2.1 gives the approximate minimum thicknesses of steel for the various isotope sources If X-ray tube voltages used are lower than the maximum values specified and steel thicknesses are greater than the minimum values required for isotope sources, subject contrast and sensitivity will be improved Thus it may be possible to obtain the same or improved IQI and discontinuity sensitivity using test parameters which have been optimized in this manner, than by using the minimum test parameters of a nominally more sensitive method For example, method XR2 when used with higher film density, increased source-to-film distance and reduced tube voltage, may provide a more sensitive technique than method XR1 carried out to the minimum requirements COPYRIGHT AS 2177.1 — 1994 28 The use of very fine grain film (Type 1) will optimize detail definition and increase the probability of detection of fine discontinuities, especially when using gamma radiation Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited B5 EFFECT OF VARIABLES ON RADIOGRAPHIC CONTRAST Various radiation intensities transmitted by a test piece are rendered as different photographic intensities in a radiograph Differences in density from one area to another constitute radiographic contrast, which in turn depends upon both subject contrast and film contrast Whereas subject contrast is the difference in radiation intensity between adjacent areas in a test piece arising from differences in attenuation characteristics of those areas, film contrast refers to the property of a film to record differences in density in relation to intensity of radiation Film contrast depends on the gradient of the characteristic curve at a given density If necessary, film manufacturers should be consulted for characteristic curves of their films The ability of a radiograph to reveal the presence of any discontinuities is influenced by many variables; the effects of changes in some of these variables is shown in Figure B1 B6 PRECAUTIONS AGAINST SCATTERED RADIATION B6.1 General Scattered radiation is produced when a beam of X-rays or gamma-rays interacts with the object (workpiece) or its surroundings, materials of low atomic number being particularly affected As the intensity of the primary beam is reduced by scattering and absorption processes, the intensity of scatter, which is oriented in all directions, increases Scattered radiation is less penetrating than the primary beam, and is produced as follows: (a) Within the workpiece being radiographed (b) By re-irradiation from nearby objects, e.g cassettes, walls, the work bench and from other parts of the object not exposed to the radiation beam Scatter lowers the contrast and definition of the image by producing a general background of radiation which prevents the formation of a coherent image On occasions, spurious shadow images also can be formed B6.2 Procedures to reduce scatter Scattered radiation may be reduced by taking the following precautions: (a) Use masks or diaphragms to ensure that the primary beam is restricted to the test area (b) Use a diaphragm or collimator to prevent scatter from nearby objects or parts of the object outside the test area (c) Use a mask of lead sheet, or other absorbing material, to shield parts of the cassette or film not covered by the object (d) Correctly position lead filters or screens as follows: (i) Between the object and the film It may be necessary to increase the thickness of this front lead screen or add a supplementary lead screen (ii) Between the object and the source NOTES: These arrangements preferentially reduce the softer radiation in X-ray potentials of up to 400 kV and are beneficial particularly where the edges of an object are required to be shown Where the shape of the object is such that there is little filtration of the primary beam, a large amount of scatter will be produced in the cassette and film, and will spread sideways causing a degradation of the image of adjacent areas (see Figure B2) COPYRIGHT 29 AS 2177.1 — 1994 Where the edges of the object are in close contact with the film, it is preferable to position the filter between the workpiece and the film or inside the cassette to absorb radiation scattered by the film and by the directly irradiated part of the cassette (see Figure B2) (iii) By using mm to mm thick lead shielding behind the cassette to reduce scatter from the floors, walls and surrounding objects Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Higher-energy radiation may also be used to reduce scatter, as the direction of the resulting scattered radiation will be more closely aligned with the primary beam FIGURE B1 EFFECT OF VARIABLES ON RADIOGRAPHIC CONTRAST COPYRIGHT Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited AS 2177.1 — 1994 30 FIGURE B2 TECHNIQUES TO REDUCE SCATTER B7 EFFECTS OF SURFACE FINISH The quality of a radiograph (its ability to display a discontinuity) is dependent on many factors such as film type, radiation energy, source size, source-to-object distance, object thickness and film processing For thin sections of welded material, the thinner the parent plate the greater is the effect of weld reinforcement on the radiograph, i.e its height, smoothness and degree of penetration of the weld bead In general, the height of the weld bead, if maintained within the specified code limits, should produce a radiograph of sufficient quality to reveal any discontinuity above a certain size, dependent on the technique However, where the surface is left excessively rough by coarse grinding, or where there is excessive ripple or cratering, there is a possibility that discontinuities can be masked, thus making interpretation of the radiograph difficult COPYRIGHT 31 AS 2177.1 — 1994 Usually it is the planar type of discontinuity, the type which is most harmful, which is masked by surface effects Such planar discontinuities include lack of side-wall fusion, fusion zone cracking and root discontinuities Method XR1 requires that the dressing of weld reinforcements be carried out where radiographic images of surface irregularities mask or confuse the viewing of the image of a discontinuity In other methods, the Standard requires that where there is any uncertainty in the interpretation of a radiograph due to surface features, the weld reinforcement is to be dressed and another radiograph taken B8 FILM DENSITY AND SCREENS B8.1 Film density Photographic (radiographic) density is the quantitative measurement of film darkening When a photographic (radiographic) film is held up to the light it can be seen to be comprised of varied areas of opacity, dependent on local density of the emulsion Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited Opacity is usually expressed as follows: Density is expressed as the logarithm of the opacity as follows: Thus, Opacity Density 10 100 000 10 000 In a radiograph, the various intensities transmitted by the specimen are rendered as different densities in the image The density differences between adjacent areas constitute radiographic contrast Any detail within the image is visible by reason of the contrast between it and its background Such density differences are due to the following factors: (a) The variation in intensity of the X-ray beam as it passes through the sample, traversing areas of high or low attenuation (b) The gradient of the film which depends on the region of the sensitometric curve on which exposures fall The steeper the slope of the curve in this region, the greater is the visibility of areas of unequal X-ray intensity This is shown in detail by a typical sensitometric curve (see Figure B3) In Figure B3, the upper and lower intensity limits of exposures A and B represent those exposures obtained under thinner and thicker sections of the specimen, where a discontinuity is present For exposure B, the total amount of radiation is greater, hence the film will be blackened to a greater density Because of the higher gradient of the curve in this region, a density difference of 2.0 will be obtained, whereas exposure A, on the lower gradient portion, only produces a density difference of 0.5 COPYRIGHT AS 2177.1 — 1994 32 Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited The ability of a radiographic film to amplify the subject contrast is of the utmost importance, otherwise many small discontinuities would not be detected It is important, therefore, that the exposure is chosen so that the (nominally) straight-line portion of the characteristic curve is used FIGURE B3 A TYPICAL SENSITOMETRIC CURVE B8.2 Fluorometallic screens In present-day radiography, it is sometimes necessary to use long exposures to obtain high-quality radiographs This implies an increase in costs which is not always justified In addition, the films used require relatively long processing times, even though automatic processing may be used In summation, conventional radiography fails to meet the requirements of some modern inspection procedures An example is the installation of off-shore pipelines A fast but efficient way of quality control of the welds is required and must be undertaken even while the pipes are being lowered into the sea The conventional methods involving the use of the slower fine-grained films with lead screens are not suitable as their exposure and processing times are far too long The relatively high silver content of these films prevents the processing times from being lowered COPYRIGHT 33 AS 2177.1 — 1994 Considerable improvement in this direction has been achieved by the development of fluorometallic screens which consist of a layer of calcium tungstate with a phosphor which emits blue/ultraviolet light This material is coated onto lead (or any other heavy metal foil) and mounted on a supporting base Unlike conventional lead screens, which rely on the emission of secondary X-rays and electrons for an intensification factor of up to three, fluorometallic screens used in conjunction with rapid cycle or similar types of film are 10 to 20 times faster for X-radiation, relative to similar techniques employing Type film When used with gamma-radiation, say from 192Ir, the system is about five times faster Fluorometallic screens may be used with a conventional screen film resulting in a lower intensification factor of approximately two Licensed to SAIPEM (SPCM) on 11 Sep 2002 Single user licence only Storage, distribution or use on network prohibited The relative speed is dependent on both the energy and the intensity of the incident radiation Although the ‘reciprocity law’ is approximately maintained when these screens are used with Type films, results show that the speed of rapid cycle films (RCF) varies with the intensity of the radiation Using wire IQIs, tests have shown that conventional techniques based on Type film show an improvement of one wire compared with RCF/fluorometallic screen methods The image produced by X-rays in conjunction with an RCF film/fluorometallic screen combination lies somewhere between the results obtained using XR2 and GR2 methods B9 VIEWING OF WET RADIOGRAPHS Wet radiographs should be viewed only to ascertain the following: (a) Adequacy of exposure, and the presence of processing and film defects (b) The presence of high contrast discontinuities The interpretation of radiographs should be carried out only when the film is dry, under conditions which best favour the proper assessment of the details in a radiograph Effects such as streaking due to water drainage and increased back-light reflections from wet film surfaces can reduce viewing acuity and lead to misinterpretation of a radiograph B10 FACTORS CONTROLLING SOURCE-TO-FILM DISTANCE B10.1 General The source-to-film distance should be chosen following consideration of related factors including image definition, film grain, exposure time and the length of film to be irradiated Factors which affect image definition are discussed in Paragraphs B10.2 to B10.5 B10.2 Inherent unsharpness (U i) is a function of secondary electron scattering acting on the silver halide in the film emulsion, causing a blurring of the edges of the image Inherent unsharpness is sometimes referred to as film unsharpness, U f The inherent unsharpness is affected by the radiation energy and the intensifying screens used The influence of the film type is also a factor of lesser importance For X-ray potentials up to 420 kV, the inherent unsharpness is less than that produced by gamma-rays from such radioisotope sources as 60 Co and 192Ir For X-rays with energies below 100 keV, without screens, U i is generally quoted as 0.05 mm, while above 100 keV, with screens, the figure increases to 0.15 mm at 400 keV For gamma-rays with 0.1 mm screens, the figures normally used for Ui are 0.17 mm for Ir and 0.35 mm for 60 Co 192 Typical values of Ui for different values of kV, and for gamma-ray sources are given in Table B1 COPYRIGHT AS 2177.1 — 1994 34 TABLE B1 TYPICAL VALUES OF INHERENT UNSHARPNESS (Ui) X-ray potential, kV and gamma-ray source Inherent unsharpness, Ui mm