ANSI IEEE N42.15-1997 American National Standard Check Sources for and Verification of Liquid-Scintillation Counting Systems.pdf

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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 systemsAmerican National StandardAn American National Standard implies a consensus of those substantially concerned with its scopeand provisions

6、. An American National Standard is intended as a guide to aid the manufacturer, theconsumer, and the general public. The existence of an American National Standard does not in anyrespect preclude anyone, whether he has approved the standard or not, from manufacturing, market-ing, purchasing, or usin

7、g products, processes, or procedures not conforming to the standard. Amer-ican National Standards are subject to periodic reviews and users are cautioned to obtain the latesteditions.CAUTION NOTICE:This American National Standard may be revised or withdrawn at any time.The procedures of the American

8、 National Standards Institute require that action be taken to reaf-firm, revise, or withdraw this standard no later than five years from the date of publication. Purchas-ers of American National Standards may receive current information on all standards by calling orwriting the American National Sta

9、ndards Institute.Authorization to photocopy portions of any individual standard for internal or personal use isgranted by the Institute of Electrical and Electronics Engineers, Inc., provided that the appropriatefee is paid to Copyright Clearance Center. To arrange for payment of licensing fee, plea

10、se contactCopyright Clearance Center, Customer Service, 222 Rosewood Drive, Danvers, MA 01923 USA;(508) 750-8400. Permission to photocopy portions of any individual standard for educational class-room use can also be obtained through the Copyright Clearance Center.Copyright 1997 IEEE. All rights res

11、erved.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 the Accredited Standards Committee N42 on Radiation Instrumenta-tion. Committee N42 de

12、legated 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 standard as finally approved.This standard combines ANSI N42.15-1990, American Nationa

13、l 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 modifications. This standard wasapproved by N42 letter ballot on 28 January 1997.At the t

14、ime 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 Governmental Industrial HygienistsJesse LiebermanBicron/Harshaw CoJoseph C. BellianE

15、berline Instrument CoJames K. HeschEG used as subscript notation (e.g., ni).nNumber of measurements in a series.NTotal number of counts accumulated in an individual measurement.RNet count rate in an individual measurement in counts per minute.tCounting time in minutes.tcElapsed counting time for a s

16、hort-lived radionuclide expressed in the same units of time as the half-life.lRadioactivity decay constant.SComputed standard deviation of a measured distribution. An estimate of s.sTruestandard deviation for the measured distribution.Average of nmeasurements of Nas defined by Equation (1).c2Statist

17、ic 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 NANSIVERIFICATION OF LIQUID-SCINTILLATION COUNTING SYSTEMS N42.15-1997Copyright 1997 IEEE. All rights reserved.55. MaterialsThe recommen

18、dations for the 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 m

19、eet or exceed 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), s

20、hall be used 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-methylstyr

21、yl)-benzeneTheir 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

22、 vials, except 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

23、 gas such as 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-scintilla

24、tor solutes in 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

25、/L. The check source vial should be purged with inert gas before sealing. Tritiated toluene with anANSIN42.15-1997 AMERICAN NATIONAL STANDARD CHECK SOURCES FOR AND6Copyright 1997 IEEE. All rights reserved.activity of 1 105dpm to 3 105dpm (25 kBq) shall be contained in a Type II glass vial see IEC 60

26、582(1977-01).6.1.2 Carbon-14 check sourceThe carbon-14 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 scintillator is included, it shall be at a concentration of 0.010.5 g/L. The check source vial should be purged wi

27、th inert gas before sealing. Carbon-14 toluene with anactivity of 30 000 dpm to 150 000 dpm (0.53 kBq) shall be contained in 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 p

28、er 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 background 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

29、 flame-sealed check sources shall be dated when made and should be used no longer than 5 years aftersealing. (Check sources shall 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 re

30、commendations.7.2 Test procedures7.2.1 Frequency of testingThe user shall monitor instrument performance following installation, 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 tes

31、ts are given in 7.2.2. In addition, a quality-control program shall be estab-lished to monitor the day-to-day performance of 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 co

32、unting system and followingany of the events set forth in 7.2.1.a) Determination of the counting system efficiency (E) of thetype 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

33、of dispersion in the counting data by:1) The estimated standard deviation of the counting data, assuming it to be Poisson distributed2) Determination of the observed standard deviation SANSIVERIFICATION OF LIQUID-SCINTILLATION COUNTING SYSTEMS N42.15-1997Copyright 1997 IEEE. All rights reserved.73)

34、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 Efor the tritium check sourceUse a tritium check source of known activity A.Set the gain and discriminator levels (i.e., the tritium count-ing cha

35、nnel/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 maximum tritium efficiency for an unquenched check source shall begreater than

36、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 check source. (Failures of the check source are discussed in 8.7.)7.2.2.2 Co

37、unting 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 10 min measurements. If B exceeds40 counts per minute (0.67 Bq), the major sou

38、rces 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 Counting system efficiency and background counting rate for other radionuclides

39、Repeat 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 7.2.2.2.7.2.2.4 Counting system reproducibility7.2.2.4.1 Standard deviationA

40、 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 counterreproducibility. More detailed statistical treatments are given in NCRP Report 58-1985 B1

41、0, 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)whereNiis any individual measurement of a series of measurements.The scatter in these

42、 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 Poisson statistics, an estimate ofthe standard deviation for any given single

43、 observation is given by:N1n- Nii 1=n=s ANSIN42.15-1997 AMERICAN NATIONAL STANDARD CHECK SOURCES FOR AND8 Copyright 1997 IEEE. All rights reserved.(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 fr

44、om Equation (3) is much greater than 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) te

45、stStatistical tests, such as the c2test (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 prescr

46、ibedconfidence. 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 least ten replicate measurements shall be made, with N lyingbetween 50 000 counts and 500 000 counts. The test shall be performed with a ty

47、pe a) check source (see4.2), using a counting channel/region set according to the manufacturers recommendations. The computed c2value shall fall within the limits corresponding to probabilities of 0.05 and 0.95, respec-tively. If the system fails to meet this criterion in three consecutive trials, c

48、onsult with the manufacturer.7.2.3 Routine performance tests7.2.3.1 GeneralThe performance of the counting system shall be monitored on a daily basis during periods in which thecounter is in use. The tests shall be performed using flame-sealed check sources see 4.2, type a) and flame-sealed backgrou

49、nd check sources (see 4.3). The information that should be recorded is shown on the samplequality control record in Annex G. The data should also be recorded on control charts. If any instrumentoperating parameter is changed, a new control chart should be started.7.2.3.2 Check sourceThe flame-sealed check source shall be used throughout the useful life of the source, where useful life is aperiod not to exceed 5 years after sealing. The check source shall be counted at least once each day while thecounting system is in use, for a