ANSI N42.15-1997 Performance Verification of Liquid-Scintillation Counting Systems《液体闪烁计数系统的性能检定》.pdf

1、The Institute of Electrical and Electronics Engineers, Inc.345 East 47th Street, New York, NY 10017-2394, USACopyright 1997 by the Institute of Electrical and Electronics Engineers, Inc.All rights reserved. Published 1997. Printed in the United States of America.ISBN 1-55937-970-7No part of this pub

2、lication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.ANSI N42.15-1997(R2004)American National Standard Check Sources for and Verification of Liquid- Scintillation Counting SystemsSponsorNational Committee on Rad

3、iation Instrumentation, N42Accredited by theAmerican National Standards InstituteSecretariatInstitute of Electrical and Electronics Engineers, Inc.Approved 29 September 1997Reaffirmed 2 December 2004American National Standards InstituteAbstract: Tests and procedures to ensure that a liquid-scintilla

4、tion counting system is producingreliable data are provided for designers and users. This standard does not cover the calculation ofsample activity for quenched unknown samples, sample preparation, efficiency correlation (quenchcorrection) procedures, or identification of unknown radionuclides.Keywo

5、rds: calculation of sample activity, liquid-scintillation counting systems, quenched unknownsamples, tests and procedures for liquid-scintillation counting systemsCopyright The Institute of Electrical and Electronics Engineers, Inc. Provided by IHS under license with IEEENot for ResaleNo reproductio

6、n or networking permitted without license from IHS-,-,-American National StandardAn American National Standard implies a consensus of those substantially concerned with its scopeand provisions. An American National Standard is intended as a guide to aid the manufacturer, theconsumer, and the general

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12、etworking permitted without license from IHS-,-,-Copyright 1997 IEEE. All rights reserved.iiiIntroduction(This introduction is not part of ANSI N42.151997, American National Standard Check Sources for and Verification ofLiquid Scintillation Counting Systems.)This standard is the responsibility of th

13、e Accredited Standards Committee N42 on Radiation Instrumenta-tion. Committee N42 delegated the development of this standard to its subcommittee N42.RM. Drafts werereviewed by Committee N42, Subcommittee N42.RM, and other interested parties, and the commentsreceived were utilized in producing the st

14、andard as finally approved.This standard combines ANSI N42.15-1990, American National Standard Verification of Liquid-Scintilla-tion Counting Systems, and ANSI N42.16-1986, American National Standard Specifications for SealedRadioactive Check Sources Used in Liquid-Scintillation Counters, with modif

15、ications. This standard wasapproved by N42 letter ballot on 28 January 1997.At the time it approved this standard, the Accredited Standards Committee on Radiation Instrumentation,N42, had the following members:Louis Costrell,ChairOrganization Represented Name of RepresentativeAmerican Conference of

16、Governmental Industrial HygienistsJesse LiebermanBicron/Harshaw CoJoseph C. BellianEberline Instrument CoJames K. HeschEG used as subscript notation (e.g., ni).n Number of measurements in a series.N Total number of counts accumulated in an individual measurement.R Net count rate in an individual mea

17、surement in counts per minute.t Counting time in minutes.tcElapsed counting time for a short-lived radionuclide expressed in the same units of time as the half-life.l Radioactivity decay constant.S Computed standard deviation of a measured distribution. An estimate of s.s True standard deviation for

18、 the measured distribution.Average of n measurements of N as defined by Equation (1).c2Statistic used to compare the observed variance of a distribution with a hypothetical variance; c2=S2/s2.X2Computed value of c2for a real distribution; see Equation (4).s N4 Copyright 1997 IEEE. All rights reserve

19、d.ANSIVERIFICATION OF LIQUID-SCINTILLATION COUNTING SYSTEMS N42.15-1997Copyright The Institute of Electrical and Electronics Engineers, Inc. Provided by IHS under license with IEEENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-5. MaterialsThe recommendations for t

20、he various sample components are based on the availability of the material andestablished criteria of purity as they relate to assay for radioactivity by liquid-scintillation counting.5.1 SolventAnalytical-grade toluene shall be used as the solvent for all check sources. Toluene shall meet or exceed

21、 thespecifications of B13 for purity and shall be of fossil origin. (As of this writing, all commercially availabletoluene is of fossil origin.) Requirements for toluene acceptance are listed in Annex E.5.2 Organic-scintillator solutesA primary scintillator, 2,5-diphenyloxazole (PPO), shall be used

22、in preparing check sources. The physicalproperties of this compound are listed in Annex A. One of the following secondary scintillators may beincluded in preparing check sources:a) 1,4-bis-2-(5-phenyloxazolyl)-benzeneb) 1,4-bis-2-(4-methyl-5-phenyloxazolyl)-benzenec) p-bis-(O-methylstyryl)-benzeneTh

23、eir physical properties are listed in Annexes B, C, and D, respectively. 5.3 Radioactive materialTritium-labeled and carbon-14-labeled toluene shall be used as radioactivity standard material.5.4 Sample containerThe sample container shall conform to IEC 60582 (1977-01) for Type II glass vials, excep

24、t for the overallheight, which shall not exceed the specified maximum. For small-vial counting systems, see 8.3. The glassshall be low-potassium, borosilicate glass. The sample shall be contained within the cylindrical portion ofthe vial.5.5 Purging gasThe purging gas shall be any inert gas such as

25、argon or nitrogen of at least 99.995% purity, containing nomore than 2 parts per million (ppm) oxygen and no more than 1 ppm water.6. Description of check sourcesA given set of check sources (e.g., tritium, carbon-14, background) should be made from the same solventand organic-scintillator solutes i

26、n the same concentration.6.1 Check sources6.1.1 Tritium check sourceThe tritium check source shall contain 15 mL 0.2 mL of toluene with a concentration of 5 g 1 g PPOper liter of toluene at 20 C. If a secondary organic scintillator is included, it shall be at a concentration of0.010.5 g/L. The check

27、 source vial should be purged with inert gas before sealing. Tritiated toluene with anCopyright 1997 IEEE. All rights reserved. 5ANSIN42.15-1997 AMERICAN NATIONAL STANDARD CHECK SOURCES FOR ANDCopyright The Institute of Electrical and Electronics Engineers, Inc. Provided by IHS under license with IE

28、EENot for ResaleNo reproduction or networking permitted without license from IHSactivity of 1 105dpm to 3 105dpm (25 kBq) shall be contained in a Type II glass vial see IEC 60582(1977-01).6.1.2 Carbon-14 check sourceThe carbon-14 check source shall contain 15 mL 0.2 mL of toluene with a concentratio

29、n of 5 g 1 g PPOper liter of toluene at 20 C. If a secondary scintillator is included, it shall be at a concentration of 0.010.5 g/L. The check source vial should be purged with inert gas before sealing. Carbon-14 toluene with anactivity of 30 000 dpm to 150 000 dpm (0.53 kBq) shall be contained in

30、a Type II glass vial see IEC 60582(1977-01).6.1.3 Background check sourceThe background check source shall contain 15 mL 0.2 mL of toluene with a concentration of 5 g 1 gPPO per liter of toluene at 20 C. If a secondary scintillator is included, it shall be at a concentration of 0.010.5 g/L. The back

31、ground check source shall be contained in a Type II glass vial and should be purged withinert gas before sealing see IEC 60582 (1977-01).6.2 Expiration date of check sourceAll flame-sealed check sources shall be dated when made and should be used no longer than 5 years aftersealing. (Check sources s

32、hall not be stored in direct sunlight or under fluorescent lights.)7. Operations and tests7.1 GeneralAll instruments shall be operated in conformance with the manufacturers recommendations.7.2 Test procedures7.2.1 Frequency of testingThe user shall monitor instrument performance following installati

33、on, service, replacement of sealed checksources, or any other circumstance that may affect the accuracy of the data obtained using the counter.Details of these performance tests are given in 7.2.2. In addition, a quality-control program shall be estab-lished to monitor the day-to-day performance of

34、the instrument. These routine performance tests are given in7.2.3.7.2.2 Initial performance testsThe following tests shall be performed by the user upon installation of the counting system and followingany of the events set forth in 7.2.1.a) Determination of the counting system efficiency (E) of the

35、 type a) check source (see 4.2)b) Determination of the counting rate (B) of a background check source in each counting channel thatis used under normal conditionsc) Estimation of dispersion in the counting data by:1) The estimated standard deviation of the counting data, assuming it to be Poisson di

36、stributed2) Determination of the observed standard deviation S6 Copyright 1997 IEEE. All rights reserved.-,-,-ANSIVERIFICATION OF LIQUID-SCINTILLATION COUNTING SYSTEMS N42.15-1997Copyright The Institute of Electrical and Electronics Engineers, Inc. Provided by IHS under license with IEEENot for Resa

37、leNo reproduction or networking permitted without license from IHS-,-,-3) Completion of a chi-squared (c2) test, or other test, to determine the reproducibility of themeasured sample count rate7.2.2.1 Counting system efficiency E for the tritium check sourceUse a tritium check source of known activi

38、ty A. Set the gain and discriminator levels (i.e., the tritium count-ing channel/region) according to the manufacturers recommendations. Accumulate approximately 105counts and compute the net sample count rate (R). Compute the counting efficiency as E = (R/A) 100.For a typically newer system, the ma

39、ximum tritium efficiency for an unquenched check source shall begreater than 63% when the tritium counting channel/region is set to encompass most of the tritium pulse-height spectrum. A slightly lower value would not be grounds for rejecting the instrument, since the effi-ciency also depends on the

40、 check source. (Failures of the check source are discussed in 8.7.)7.2.2.2 Counting system background in the tritium channelUsing the instrument settings described in 7.2.2.1, measure the background count rate (B). The backgroundcheck source is described in 3.2.3. Compute the background from these 1

41、0 min measurements. If B exceeds40 counts per minute (0.67 Bq), the major sources of the background counts should be identified. Some ofthe factors that may cause a high background are discussed in 8.8. If the cause of the high backgroundcannot be identified, consult with the manufacturer.7.2.2.3 Co

42、unting system efficiency and background counting rate for other radionuclidesRepeat the procedures in 7.2.2.1 and 7.2.2.2 with counting channels/regions and check sources appropriatefor the radionuclide selected. If tritium is not routinely used, another radionuclide can be substituted in7.2.2.1 and

43、 7.2.2.2.7.2.2.4 Counting system reproducibility7.2.2.4.1 Standard deviationA major measure of performance is that the counting system gives reproducible results. The statisticalconcepts presented in 7.2.2.4 are necessarily limited to those required to perform a basic test of the counterreproducibil

44、ity. More detailed statistical treatments are given in NCRP Report 58-1985 B10, Evans B4and NBS Handbook 91 B9.If a check source is counted n times, for equal counting times, the total number of counts Niaccumulated inthe ith interval will be distributed about some average value given by:(1)whereNii

45、s any individual measurement of a series of measurements.The scatter in these measured values, or, more precisely, the estimated standard deviation of this distribution, is a measure of the counting system reproducibility.Since the probability of radioactive decay events is distributed according to

46、Poisson statistics, an estimate ofthe standard deviation for any given single observation is given by:N1n- Nii 1=n=s Copyright 1997 IEEE. All rights reserved. 7ANSIN42.15-1997 AMERICAN NATIONAL STANDARD CHECK SOURCES FOR ANDCopyright The Institute of Electrical and Electronics Engineers, Inc. Provid

47、ed by IHS under license with IEEENot for ResaleNo reproduction or networking permitted without license from IHS(2)The standard deviation may also be predicted from the n replicate measurements as:(3)If the measured standard deviation (S) of the data as computed from Equation (3) is much greater than

48、 thatpredicted by Poisson statistics, of Equation (2), the user shall find the cause of the additional error in theexperiment. Perhaps, for example, the sample changer is not positioning the vial reproducibly in the count-ing chamber. 7.2.2.4.2 Chi-squared (c2) testStatistical tests, such as the c2t

49、est (see B4) are used to determine whether the system is operating withinallow-able limits. The value of c2computed from a sample distribution is given by:(4)If the X2value is within certain limits, the counter is said to be operating satisfactorily at some prescribedconfidence. An example of the use of the c2test is given in Annex F. To conform to this standard, a test, suchas the one shown there, shall be performed. At