1、BRITISH STANDARDBS ISO 12789-2:2008Reference radiation fields Simulated workplace neutron fields Part 2: Calibration fundamentals related to the basic quantitiesICS 17.240g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g
2、40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS ISO 12789-2:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 April 2008 BSI 2008ISBN 978 0 580 53407 2National forewordThis British Standard is the UK implementat
3、ion of ISO 12789-2:2008.The UK participation in its preparation was entrusted to Technical Committee NCE/2, Radiation protection and measurement.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the nece
4、ssary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsReference numberISO 12789-2:2008(E)INTERNATIONAL STANDARD ISO12789-2First edit
5、ion2008-03-01Reference radiation fields Simulated workplace neutron fields Part 2: Calibration fundamentals related to the basic quantities Champs de rayonnement de rfrence Champs de neutrons simulant ceux de postes de travail Partie 2: Concepts dtalonnage en relation avec les grandeurs fondamentale
6、s BS ISO 12789-2:2008ii iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Terms and definitions .1 3 List of symbols.4 4 Properties of simulated workplace neutron field facilities5 5 Characterization of simulated workplace neutron fields.5 6 Uncertainties 9 Annex A (normative) Conversion coeff
7、icients .12 Bibliography 14 BS ISO 12789-2:2008iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each
8、 member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Internationa
9、l Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards
10、 adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of
11、 patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 12789-2 was prepared by Technical Committee ISO/TC 85, Nuclear energy, Subcommittee SC 2, Radiation protection. ISO 12789 consists of the following parts, under the general title Reference radiation
12、fields Simulated workplace neutron fields: Part 1: Characteristics and methods of production Part 2: Calibration fundamentals related to the basic quantities BS ISO 12789-2:2008vIntroduction Neutron fields commonly encountered in radiation workplaces are, in most cases, quite different from routinel
13、y used calibration fields produced using standard radionuclide sources in low-scatter calibration facilities. The dose equivalent response of personal neutron dosemeters and neutron area survey meters depends upon the energy distributions of the neutron fields in which they are used, and, in the cas
14、e of personal dosemeters in particular, the angle of incidence of the neutrons. Calibrations of such devices in reference neutron fields as described in ISO 8529 (all parts) do not thus provide appropriate calibration factors in most cases. For this reason, several laboratories have developed simula
15、ted workplace neutron fields that are intended to simulate the characteristics of particular types of fields in which it is necessary to make personal dosemeter and area survey instrument measurements. These provide facilities in which the performance of these devices in workplace fields can be inve
16、stigate, and that, in some circumstances, can act as calibration facilities. Because workplace neutron fields depend upon the physical structure of each workplace, this part of ISO 12789 has been written to specify the methods of producing and characterizing simulated workplace neutron fields rather
17、 than standardizing reference fields as is the philosophy in the companion standard, ISO 8529 (all parts). This part of ISO 12789 is closely related to ISO 12789-1, which describes the facilities and methods currently used to produce simulated workplace neutron radiation fields. These fields have be
18、en constructed specifically to moderate source neutrons and include neutrons scattered from the surrounding structure and equipment for the simulation of workplace environments. This part of ISO 12789 describes the methods used to determine conventional values of the operational quantities character
19、izing the realistic workplace neutron fields. The operational quantities used in this part of ISO 12789 are ambient dose equivalent, H*(10), and personal dose equivalent, Hp(10). For reference radiation fields, it is recommended to determine their conventional values from the neutron fluence or flue
20、nce rate as a function of neutron energy and, for the case of Hp(10), the direction using the conversion coefficients listed in Annex A. In some cases, the use of conversion coefficients is not feasible for determining Hp(10), necessitating its direct calculation. At present, no simple methods exist
21、 to provide traceability of the operational quantities from a national standards institute to the simulated workplace neutron fields. The process of determining operational quantities from fluence described in this part of ISO 12789 introduces additional uncertainty. This part of ISO 12789 incorpora
22、tes accepted methods for determining the uncertainty associated with the values of the operational quantities and gives new information regarding the uncertainty associated with the inference of energy distributions of neutron fluence using accepted unfolding techniques. The uncertainties in determi
23、ning Hp(10) using information from the direction distribution of the neutron fluence can be large but, at present, the quantification of the uncertainty from this source is not addressed. BS ISO 12789-2:2008blank1Reference radiation fields Simulated workplace neutron fields Part 2: Calibration funda
24、mentals related to the basic quantities 1 Scope This part of ISO 12789 describes the characterization of simulated workplace neutron fields produced by methods described in ISO 12789-1. It specifies the procedures used for establishing the calibration conditions of radiation protection devices in ne
25、utron fields produced by these facilities, with particular emphasis on the scattered neutrons. The diversity of workplace neutron fields is such that several special facilities have been built in order to simulate them in the laboratory. In this part of ISO 12789, the neutron radiation field specifi
26、cations are classified by operational quantities. General methods for characterizing simulated workplace neutron fields are recommended. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 indication reading M quantity value provided by a measuri
27、ng instrument or a measuring system NOTE 1 An indication may be presented in visual or acoustic form or may be transferred to another device. An indication is often given by the position of a pointer on the display for analog outputs, a displayed or printed number for digital outputs, a code pattern
28、 for code outputs, or an assigned quantity value for material measures. NOTE 2 An indication and a corresponding value of the quantity being measured are not necessarily values of quantities of the same kind. ISO/IEC Guide 99:2007, 4.1 2.2 conventional quantity value conventional value of a quantity
29、 quantity value attributed by agreement to a quantity for a given purpose EXAMPLE 1 Standard acceleration of free fall (formerly called “standard acceleration due to gravity”) gn= 9,806 65 ms2. EXAMPLE 2 Conventional quantity value of the Josephson constant, KJ-90= 483 597,9 GHz V1. EXAMPLE 3 Conven
30、tional quantity value of given mass standard, m = 100,003 47 g. NOTE 1 The term “conventional true quantity value” is sometimes used for this concept, but its use is discouraged. BS ISO 12789-2:20082 NOTE 2 Sometimes a conventional quantity value is an estimate of a true quantity value. NOTE 3 A con
31、ventional quantity value is generally accepted as being associated with a suitably small measurement uncertainty, which might be zero. ISO/IEC Guide 99:2007, 2.12 2.3 neutron fluence quotient of dN by da, where dN is the number of neutrons incident on a sphere of cross-sectional area da, as given in
32、 Equation (1): ddNa = (1) NOTE The unit of the neutron fluence is metres to the negative 2 (m2). 2.4 neutron fluence rate quotient of d by dt, where d is the increment of neutron fluence in the time interval dt, as given in Equation (2): 2dddddNtat = (2) NOTE 1 The unit of neutron fluence rate is me
33、tres to the negative 2 times reciprocal seconds (m2s1). NOTE 2 This quantity is also termed neutron flux density. 2.5 energy distribution of the neutron fluence Equotient of d by dE, where d is the increment of neutron fluence in the energy interval between E and E + dE, as given in Equation (3): dd
34、EE = (3) NOTE The unit of the energy distribution of the neutron fluence is metres to the negative 2 times reciprocal joules (m2J1) 2.6 energy and direction distribution of the neutron fluence E,quotient of d by dE and d, where d is the increment of neutron fluence in the energy interval between E a
35、nd E + dE and the solid angle interval between and + d, as given in Equation (4): 2,dddEE= (4) NOTE The unit of the energy and direction distribution of the neutron fluence is metres to the negative 2 times reciprocal joules times reciprocal steradians (m2J1sr1). BS ISO 12789-2:200832.7 ambient dose
36、 equivalent at 10 mm depth (10) dose equivalent at a point in the radiation field that would be produced by the corresponding expanded and aligned field, in the ICRU sphere at a depth of 10 mm on the radius opposite the direction of the aligned field NOTE The unit of ambient dose equivalent is joule
37、s times reciprocal kilograms (J kg1) with the special name of sievert (Sv). 2.8 personal dose equivalent at 10 mm depth Hp(10) dose equivalent in soft tissue at a depth of 10 mm below a specified point on the body NOTE 1 The unit of personal dose equivalent is joules times reciprocal kilograms (J kg
38、1) with the special name of sievert (Sv). NOTE 2 In ICRU Report 4712, the ICRU considers the definition of the personal dose equivalent to include the dose equivalent at a depth, d, in a phantom having the composition of ICRU tissue. Then, Hp(10) for the calibration of personal dosemeters is the dos
39、e equivalent at a depth of 10 mm in a phantom composed of ICRU tissue, but of the size and shape of the phantom used for calibration (30 cm 30 cm 15 cm parallelepiped) and the conversion coefficients, hp,slab(10), are calculated for this configuration. 2.9 neutron fluence-to-dose-equivalent conversi
40、on coefficient hquotient of the neutron dose equivalent, H, by the neutron fluence, , at a point in the radiation field, as given in Equation (5): Hh= (5) NOTE Any statement of a fluence-to-dose-equivalent conversion coefficient requires a statement of the type of dose equivalent, e.g. ambient dose
41、equivalent hor personal dose equivalent hp,slab . 2.10 response R of a measuring instrument indication or reading divided by the conventional value of the quantity causing it NOTE The type of response should be specified, e.g., “fluence response”, as given in Equation (6): MR= (6) or “dose equivalen
42、t response”, as given in Equation (7): HMRH= (7) If M is a measurement of a rate, then the quantities fluence, , and dose equivalent, H, are replaced by fluence rate, , and dose equivalent rate, Hh(E) is the fluence-to-ambient-dose-equivalent conversion coefficient as a function of the neutron energ
43、y, E, given in Annex A. It is necessary to interpolate the energy for the tabulated coefficients, using a log-log four-point Lagrange interpolation technique. 5.4 Determination of Hp,slab(10) 5.4.1 General The determination of Hp,slab(10) requires knowledge of both the energy and the direction distr
44、ibution of the neutron fluence. These distributions should be determined in the presence of the phantom, which can disturb the incident neutron field. The method for determining the conventional value of Hp,slab(10) depends on the homogeneity of the radiation field and whether it is incident only on
45、 the phantom front face. Calculations and/or measurements are recommended in order to assess the degree of homogeneity, according to the required uncertainty level. Two methods are proposed, the first of which (see 5.4.2) is general and applicable to all neutron fields. The second (see 5.4.3) is app
46、licable to the special case of a uniform field (broad and parallel or superposition of a number of such fields) incident on the phantom front face. In this case, the conversion coefficients given in Annex A can be used. 5.4.2 Non-uniform neutron fields The neutron source and the irradiation geometry
47、 shall be simulated by transport calculations. The energy distributions of the neutron and photon fluences are determined at the point at which the quantity is defined, i.e. at 10 mm depth inside the ICRU slab. For example, using the kerma approximation and the LET-dependent quality factor of neutro
48、n-induced secondary charged particles, the operational quantity is calculated as indicated in Equation (10)6: nnnnntrp,slab n f()(1 )(10) ()()d dEEEgH QE kE E E=+(10)BS ISO 12789-2:20088 where Enis the energy distribution of the neutron fluence at the point at which the quantity is defined; Qnis the
49、 average quality factor for neutron-induced secondary charged particles7; kfis the kerma coefficient; Eis the energy fluence of the neutron-induced photons at the point at which the quantity is defined; tr/ is the photon mass energy transfer coefficient; g is the fraction on initial secondary electron energy that is radiated as bremsstrahlung radiation. 5.4.3 Uniform neutron fields For uniform irradiation conditions, i.e. in a broad, parallel neutron beam or in a field that can
