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1、BRITISH STANDARD BS ISO 11929-4:2001 Determination of the detection limit and decision threshold for ionizing radiation measurements Part 4: Fundamentals and application to measurements by use of linear-scale analogue ratemeters, without the influence of sample treatment ICS 17.240 NO COPYING WITHOU
2、T BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 11929-4:2001 This British Standard, having been prepared under the direction of the Engineering Sector Committee, was published unde
3、r the authority of the Standards Committee and comes into effect on 15 August 2001 BSI 08-2001 ISBN 0 580 37368 1 National foreword This British Standard reproduces verbatim ISO 11929-4:2001 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Techn
4、ical Committee NCE/2, Health physics instrumentation, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may
5、 be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British S
6、tandards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals fo
7、r change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 10, an inside back cover and
8、 a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARD IS
9、O 11929-4 First edition 2001-06-01 Reference number ISO 11929-4:2001(E) Determination of the detection limit and decision threshold for ionizing radiation measurements Part 4: Fundamentals and application to measurements by use of linear-scale analogue ratemeters, without the influence of sample tre
10、atment Dtermination de la limite de dtection et du seuil de dcision des mesurages des rayonnements ionisants Partie 4: Principes fondamentaux et leur application aux mesurages raliss laide dictomtres analogiques chelle linaire, sans linfluence du traitement dchantillon Licensed Copy: sheffieldun she
11、ffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 11929-4:2001(E) iii ContentsPage 1Scope .1 2Terms and definitions 1 3Symbols 2 4Statistical values and confid
12、ence interval .3 5Application of this part of ISO 11929 5 6Figures and tables 6 Annex AExample of application of this part of ISO 119298 Bibliography.10 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 11929-4:2001(E) iv Foreword ISO (the
13、 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 member body interested in a subject for which a technical committe
14、e 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 International Electrotechnical Commission (IEC) on all matters of electrotechni
15、cal standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval
16、by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this part of ISO 11929 may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. InternationalStandardISO 11929-4waspre
17、paredbyTechnicalCommitteeISO/TC 85,Nuclearenergy, Subcommittee SC 2,Radiation protection. ISO 11929 consists of the following parts, under the general titleDetermination of the detection limit and decision threshold for ionizing radiation measurements: Part 1: Fundamentals and application to countin
18、g measurements without the influence of sample treatment Part 2: Fundamentals and application to counting measurements with the influence of sample treatment Part 3: Fundamentals and application to counting measurements by high resolution gamma spectrometry, without the influence of sample treatment
19、 Part 4: Fundamentals and applications to measurements by use of linear-scale analogue ratemeters, without the influence of sample treatment Part 5: Fundamentals and applications to measurements of aerosols or gaseous or liquid effluents while running Annex A of this part of ISO 11929 is for informa
20、tion only. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 11929-4:2001(E) v Introduction ISO 11929 gives basic information on the statistical principles for determination of the detection limit and decision threshold (and directives for
21、 specification of the confidence interval) for nuclear radiation measurements based on the principles defined by Altschuler and Pasternack 1, Nicholson8, Currie4. This part of ISO 11929 applies to linear-scale analogue pulse-rate measurements as they are frequently used in the routine monitoring of
22、clothes, hands, feet, body, surfaces, air filters, working places, desks and other flat materials, wipe-test papers, and other contamination checks in stationary use of equipment and sources. For scanning of surfaces, this measurement can be used when the detector is moved slowly enough for the surf
23、ace to be measured to remain under the detector area for twice the time constant of the integrating circuit in the equipment. ISO 11929-1 and ISO 11929-2 deal with integral counting measurements with or without consideration of the sample treatment. Specific problems which occur in case of spectrome
24、tric measurements or continuous monitoring of radioactive effluents are covered in ISO 11929-3 and ISO 11929-5. This part of ISO 11929 deals with ionizing radiation measurements in which events, in particular pulses, are measured using linear-scale analogue ratemeters, without considering the influe
25、nce of a sample treatment. It considers exclusively the random character of radioactive decay and of pulse-rate counting by use of a linear-scale analogue ratemeter, and ignores other influences (e.g. due to sample treatment, weighting, enrichment, or instability of the equipment). It is based on th
26、e assumption that the product of pulse rate and time constant of the meter is sufficient to permit approximation of the real pulse/time distribution by a normal standard distribution, and that dead- time losses are negligible. Wherever activities or specific activities are to be determined, it is as
27、sumed that the factors for the conversion of pulse rates into activities or specific activities have been determined with sufficient accuracy to ignore the influence of their uncertainty in the measurement. This part of ISO 11929 should not be used for ratemeters with cyclic digital counters. In thi
28、s case, ISO 11929-1 should be applied. For this purpose, Bayesian statistical methods are used to specify values of statistics characterized by the following given error probabilities. The decision threshold, which allows a decision to be made for each measurement with a given probability of error a
29、s to whether the registered pulses include a contribution by the sample. The detection limit, which specifies the minimum sample contribution which can be detected with a given probability of error using the measuring procedure in question. This consequently allows a decision to be made as to whethe
30、r a measuring method checked using this part of ISO 11929 satisfies certain requirements and is consequently suitable for the given purpose of measurement. The confidence limits, which define a confidence interval of the measurand with a given probability if the measured value exceeds the decision t
31、hreshold. NOTEThe difference between using the decision threshold and using the detection limit is that measured values are to be compared with the decision threshold while the detection limit is to be compared with the guideline value. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48
32、 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARDISO 11929-4:2001(E) 1 Determination of the detection limit and decision threshold for ionizing radiation measurements Part 4: F
33、undamentals and application to measurements by use of linear- scale analogue ratemeters, without the influence of sample treatment 1Scope This part of ISO 11929 specifies suitable statistical values which allow an assessment of the detection capabilities in ionizing radiation measurements, without t
34、he influence of sample treatment, using linear-scale analogue ratemeters. For this purpose, statistical methods are used to specify statistical values characterizing given probabilities of error. 2Terms and definitions For the purposes of this part of ISO 11929, the following terms and definitions a
35、pply. 2.1 linear-scale analogue rate-meter electronic device whose output increases suddenly with every incoming pulse, and decreases with a given time constant until the next pulse arrives NOTEThe pulses should be of equal electrical charge, and the time constant should be independent of the pulse
36、rate. 2.2 measuring method use of a linear-scale analogue ratemeter for pulse-rate measurements under specified conditions 2.3 decision threshold critical value of a statistical test for the decision between the null hypothesisand the alternative hypothesis NOTEIt should be the valuewhich, when exce
37、eded by the determined value, is taken to indicate that the null hypothesis should be rejected. The statistical test should be designed such that the probability of wrongly rejecting the null hypothesis (error of the first kind) is equal to a valuewhich is fixed prior to commencement of the measurem
38、ent. 2.4 detection limit smallest differenceassociated with the statistical test concerned for the decision between the null hypothesisand the alternative hypothesisand having the following characteristic: if in reality , the probability of wrongly not rejecting the null hypothesis(error of the seco
39、nd kind) shall be at most equal to a valuewhich is fixed prior to commencement of the measurement 2.5 confidence interval interval forto be specified for the measured value obtained for NOTEThis interval includes the true value ofin at leastof all cases. s= 0 s 0 R n Rn n= s 0 s= 0s 0 n n s= 0 nRn n
40、(1 ) 100 % Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ISO 11929-4:2001(E) 2 2.6 sample whole amount or an aliquot of a material, the content of radioactive nuclides of which has to be determined by ionizing radiation measurement 2.7 bac
41、kground effect measured counting rate without radioactivity of interest in the sample NOTEThis covers radiation caused by external sources and detector noise. 2.8 gross effect measured counting rate from the sample (sample contribution) and the background radiation 2.9 net effect ?sample contributio
42、n? gross effect minus the background effect 2.10 guideline value value which corresponds to scientific, legal or other requirements for which the measuring procedure is intended to assess, for example, as activity, specific activity, surface activity, or dose rate 3Symbols Ratemeter output without s
43、ample (background pulse rate) Expectation value of Ratemeter output with sample (gross effect pulse rate) Expectation value of Net counting rate (difference between gross and background pulse rate), Expectation value of Decision threshold for the net counting rate Detection limit for the expectation
44、 value of the net counting rate Squared standard deviation Expectation value of Error of the first kind; the probabilitiy of rejecting the null hypothesisfor the alternative hypothesis when the null hypothesis is true Error of the second kind; the probability of accepting the null hypothesisagainst
45、the alternative hypothesiswhen the null hypothesis is false Confidence level of the confidence interval for Time constant of the ratemeter R0 0R0 RsRn sRs RnRn= Rs R0 nRn R n Rn n Rn s2 2s2 s= 0 s 0 s= 0 s 0 1 n Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 03:42:48 GMT+00:00 2006, Uncontro
46、lled Copy, (c) BSI ISO 11929-4:2001(E) 3 Time constant for background measurement Time constant for sample measurement ,Quantiles of the standard normal distribution (see Table 2) 4Statistical values and confidence interval 4.1Principles 4.1.1General aspects The definition of the statistical values
47、for decision threshold, detection limit and confidence interval are based on the squared standard deviation of the measured results. They are dependent on the squared standard deviation caused by counting statistics. Measurement equipment instability normally can be neglected because usually it is s
48、mall compared with the other influences. The contribution of counting statistics can be calculated by the Poisson equation in combination with the Campbell theorem 2. 4.1.2Model If device instabilities are neglected, the following model may be applied: The pulse rate measured without a sample, is ca
49、used by background radiation (external sources and activity in detector and shielding). The gross pulse rate, measured with a sample is the sum of background counting rate and sample radiation (net counting rate): It is assumed that, for a constant radioactive emission rate and a given time constant, both the number of pulses counted in a measurement of the gross effect, as well as in an independent measurement of the background effect, follow a Poisson distribution. Theref
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