1、BRITISH STANDARD BS4094-2: 1971 Recommendation for Data on shielding from ionizing radiation Part 2: Shielding from X-radiationBS4094-2:1971 This recommendation, having been approved by the Nuclear Energy Industry Standards Committee, was published underthe authority of the Executive Board on 4 June
2、1971 BSI07-1999 The following BSI references relate to the work on this standard: Committee references NCE/2, NCE/2/2, NCE/2/2/2 Draft for comment66/18981 ISBN 580 06522 7 Co-operating organizations The Nuclear Energy Industry Standards Committee, under whose supervision this British Standard was pr
3、epared, consists of representatives from the following Government departments and scientific and industrial organizations: Association of Consulting Engineers British Electrical and Allied Manufacturers Association* British Insurance (Atomic Energy) Committee British Mechanical Engineering Confedera
4、tion Department of Employment and Productivity* Electricity Council, the Central Electricity Generating Board and the Area Boards in England andWales Institution of Chemical Engineers Institution of Electrical Engineers Institution of Mechanical Engineers Lloyds Register of Shipping Ministry of Tech
5、nology* Scientific Instrument Manufacturers Association of Great Britain* United Kingdom Atomic Energy Authority* The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee
6、entrusted with the preparation of this British Standard: Association of Shell Boilermakers Board of Trade British Institute of Radiology British Steel Industry Committee of Vice-Chancellors and Principals of the Universities of the United Kingdom Department of Education and Science Engineering Equip
7、ment Users Association Hospital Physicists Association Institute of Hospital Engineers Institute of Physics and the Physical Society Ministry of Defence, Army Department Ministry of Defence, Navy Department National Coal Board Non-Destructive Testing Society of Great Britain Radiological Protection
8、Service Society of Non-Destructive Examination Society of Radiological Protection Steel Castings Research and Trade Association Welding Institute Amendments issued since publication Amd. No. Date CommentsBS4094-2:1971 BSI 07-1999 i Contents Page Co-operating organizations Inside front cover Foreword
9、 iv Section 1. Introduction 1 General 1 2 X-rays10kV to500kV 2 3 X-rays500kV to35MV 3 Section 2. Data sheets and broad beam transmission graphs Appendix A Scattered radiation 45 Appendix B Leakage radiation 57 Appendix C Bremsstrahlung 60 Appendix D Secondary sources 70 Appendix E Design considerati
10、ons 79 Appendix F References 86 Appendix G Definitions 87 Figure 1 X-ray output4kV to50kV pulsating potential 6 Figure 2 X-ray output5kV to50kV constant potential 8 Figure 3 X-ray output50kV to200kV constant potential 10 Figure 4 X-ray output200kV to500kV constant potential 12 Figure 5 X-ray output0
11、.2MV to3MV constant potential 14 Figure 6 X-ray output2MV to35MV constant potential 16 Figure 7a Transmission of10kV to50kV constant potential X-rays through aluminium 16 Figure 7b Transmission of10kV to50kV constant potential X-rays through mild steel 19 Figure 7c Transmission of10kV to50kV constan
12、t potential X-rays through sheet glass 20 Figure 7d Transmission of10kV to50kV constant potential X-rays through Perspex 21 Figure 7e Transmission of10kV to50kV constant potential X-rays through wood 22 Figure 7f Transmission of20kV to50kV constant potential X-rays through brass 23 Figure 7g Transmi
13、ssion of20kV to40kV X-rays through lead (shown in tabular form only) 24 Figure 8 Transmission of50kV to300kV pulsating potential X-rays through concrete 26 Figure 9 Transmission of50kV to200kV pulsating potential X-rays through lead 28 Figure 10 Transmission of250kV and300kV pulsating potential X-ra
14、ys through lead 30 Figure 11 Transmission of50kV to200kV constant potential X-rays through lead 32 Figure 12 Transmission of250kV to400kV constant potential X-rays through lead 34 Figure 13 Transmission of300kV and400kV constant potential X-rays through concrete 36 Figure 14 Transmission of0.5MV to3
15、.0MV constant potential X-rays through concrete 38 Figure 15 Transmission of0.5 MV to2.0MV constant potential X-rays through lead 40BS4094-2:1971 ii BSI 07-1999 Page Figure 16 Transmission of4MV to38MV constant potential X-rays through concrete 42 Figure 17 Variation of percentage scatter with irrad
16、iated area for moderate energy X-rays 50 Figure 18 Variation of percentage scatter with energy for: Figure 18a Building materials 52 Figure 18b Metals 53 Figure 18c Low atomic number materials 54 Figure 19 Scattering patterns of X-ray and gamma ray beams normally incident on a concrete shield 56 Fig
17、ure 20 Diagram of hooded anode tube and housing 57 Figure 21 Transmission of 3 H bremsstrahlung through barriers of aluminium and steel 63 Figure 22 Transmission of 147 Pm/Al bremsstrahlung through lead and iron 65 Figure 23 Transmission of 85 Kr/C bremsstrahlung through a lead barrier 67 Figure 24
18、Transmission of 90 Sr and 90 Y/Al bremsstrahlung through a lead barrier 69 Figure 25 Neutron production cross section for gold 76 Figure 26a Photoneutron production from a semi-infinite electron target 76 Figure 26b Photoneutron production from an X-ray target and bremsstrahlung beam stopper 76 Figu
19、re 27 Neutron yield from targets as in Figure 26a and Figure 26b 77 Figure 28 Neutron yield from targets irradiated with18MeV and22MeV bremsstrahlung 78 Figure 29a and Figure 29b Lead shield abutments with concrete shield 81 Figure 30 Abutments of a shield on a floor 81 Figure 31 Fixing lead sheet t
20、o an existing wall 81 Figure 32 Packed screw in lead shield 82 Figure 33 Shield box for pipe or cable run 83 Figure 34 Examples of joint in shield panels 83 Figure 35 Typical design of sliding door used with250kV pX-ray set 84 Figure 36 Illustration of thick door in form of removable stepped plug 85
21、 Figure 37 Lead glass window for a high energy unit 86 Table 1 Lead equivalents of various materials for narrow-beam pulsating potential X-rays 44 Table 2 Exposure rates outside an open-topped room as fraction of beam output (40 primary beam pointed directly upward; target height80cm) 46 Table 3 Exp
22、osure rates outside an open-topped room as fraction of beam output (40 primary beam pointed directly downward; target height200cm) 46BS4094-2:1971 BSI 07-1999 iii Page Table 4 Factors by whichTable 3 values must be multiplied for different wall heights 47 Table 5 Energy of scattered X-rays 48 Table
23、6 Half-value thicknesses and tenth-value thicknesses for heavily filtered radiation 58 Table 7 Total spectral distribution of bremsstrahlung produced in lead for a range of primary beta energies 61 Table 8 Threshold photon energy for photoneutron production 70 Table 9 Half-lives and activities of nu
24、clei produced by (r, n) reaction 71 Table 10 Activation of targets by fast neutrons 73BS4094-2:1971 iv BSI 07-1999 Foreword This recommendation makes reference to the following British Standard: BS4094, Recommendation for data on shielding from ionizing radiation Part1:Shielding from gamma radiation
25、. Part1 of this recommendation, dealing with shielding from gamma radiation, was published in1966. Part2 of the recommendation is to provide data adequate for the calculation of shielding barriers against X-radiation. The data presented have been chosen with the radiation shielding problems of indus
26、try in mind. Most of the material has been drawn from existing sources although a certain amount has been measured or calculated specially. It is not possible to provide a compendium to cover all possible contingencies, but data are provided to allow for calculations to be made for a wide range of m
27、aterials and geometry likely to be encountered, and it is envisaged that additional data will be added from time to time. Provision of data alone is not sufficient to permit the calculation of the required barriers and the methods of calculation which are necessary are given in the text together wit
28、h examples. Section 1 of this part deals with the calculation of barriers against the primary X-ray beam, and Section 2 provides the data which permit the calculation to be carried out. Appendix A and Appendix B are concerned, respectively, with the calculation of the secondary barriers which are re
29、quired against scattered, and against leakage radiation. Appendix C gives methods and data for the calculation of barriers against bremsstrahlung radiation, arising from electron beams or beta particles from radionuclides. Appendix D gives guidance on the secondary hazards associated with high energ
30、y X-ray generators, namely, the production of neutrons, noxious gases and radiation arising from the activation of materials, radiation damage and the fire risk. Appendix E gives guidance on the design of shielded rooms. Where possible, methods have been simplified to allow calculations to be made b
31、y designers who do not have any specialist knowledge of radiation shielding. This recommendation does not attempt to define maximum permissible dose nor does it make any recommendations as to exposure rates for design purposes. Such matters are outside the scope of this recommendation as they are, i
32、n many cases, subject to legislation or various codes of practice. Exposure rates are quoted in roentgens per hour (R/h), roentgens per mA minute (R/mA min) or milliroentgen per hour (mR/h). Calculations may be required in millirads in air per hour. Although the millirad is a slightly larger unit th
33、an the milliroentgen, calculations giving the required answer in milliroentgens rather than millirads will be acceptable for protection purposes. However, it is to be noted that inAppendix D reference is made to secondary sources of radiation, where it is necessary to refer to the appropriate units
34、for exposure rate or dose. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pag
35、es This document comprises a front cover, an inside front cover, pagesi toiv, pages1to88 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4094-2:1971 BSI 07-1999 1
36、 Section 1. Introduction 1 General This section of the recommendation presents the collected data required for the estimation of shielding against a primary X-ray beam. Graphs of the variation of exposure rate for a range of kilovoltage (kV) and filtration are given; such data may be used when accur
37、ate measurement of exposure rate is not possible. The transmission data are given for lead and concrete shields since they are the commonest materials encountered, and in addition some limited guidance is given on the equivalent shielding in other materials. The information given in this section may
38、 be used with confidence for design purposes, when due allowance is made for any limitation in the data or methods to which references are made in appropriate parts of the text. The methods of calculation are illustrated with a number of examples. Where guidance on the measurement of X-ray intensity
39、 or further information on health precautions is required, advice may be obtained from the Radiological Protection Service (1)at Sutton or from one of their Regional Centres in Birmingham, Glasgow, Leeds and Manchester, or from the Advisory and Information Unit of the Department of Employment (2) .
40、The problems of scattered radiation, leakage radiation and bremsstrahlung are dealt with in the appendices. Definitions of terms used in this recommendation are given (Appendix G) and a list of references included (Appendix F) so that the original papers from which the data was compiled may be consu
41、lted. The main difficulty in shielding against X-rays arises from the use of experimental data which does not cover the entire field of X-ray usage, so that designers have sometimes to rely upon interpolation or on their own measurements. It is usual to describe an X-ray beam in terms of a) The kilo
42、voltage (kV) on the tube, which may be given as constant potential kV cpor as the peak voltage kV p . X-rays excited by direct-current potentials usually give a harder spectrum than pulsating (peak) potential sets and for the same potential the direct current set may require more shielding. b) The t
43、ube current (mA). c) The tube filtration. This is made up of two parts, the inherent filtration of the tube and any added filter, the latter normally being the greater. d) Target material. For a given tube voltage, if a target of higher atomic number is used the X-ray output is increased and the wav
44、elength of the line spectrum is reduced. The X-ray data have been considered in two energy bands, those generated below500kV and those above500kV. The main reason for this split is that the treatment of scattered radiation in these two energy bands is different, as is shown inAppendix A. This also c
45、onforms roughly with the change in type of X-ray generator from a conventional X-ray set to the more complex Linacs and Betatrons. To assess a shielding requirement it is necessary to know the exposure rate; this information may be given by the manufacturer but it is advisable to use measured values
46、 provided these have been obtained with a properly calibrated instrument in carefully controlled conditions. If it is not possible to obtain a precise measure of the exposure-rate thenFigure 1 toFigure 6 should be used. In certain circumstances it may be possible to relate the permitted exposure-rat
47、e to the type of area outside the shield wall, making different allowances, for example, for a corridor, a store room or a working area. This procedure may lead to a saving in shield thickness. Knowing the exposure-rate at a given point it can then be determined at any other point from the inverse s
48、quare law. For instance, an exposure-rate of y R/h at a distance of d cm from the tube target becomesy(d/d) 2at a distance of d cm. The output is directly proportional to the current nA) and increases with kV as can be seen inFigure 1 toFigure 6.BS4094-2:1971 2 BSI 07-1999 Departures from the invers
49、e square law occur if air absorption becomes significant. The following data (3)may be used as a rough guide to the percentage reduction in beam intensity due to air absorption. The transmission curves are given for broad beam conditions for filtrations which are considered to be those most likely to be encountered for each range of kV. As the atenuation is dependent on the spectral distribution of the X-rays care must be taken in interpolating for filtratio
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