1、ISO/ASTM 51650:2013(E)Standard Practice forUse of a Cellulose Triacetate Dosimetry System1This standard is issued under the fixed designation ISO/ASTM 51650; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revision
2、.1. Scope1.1 This is a practice for using a cellulose triacetate (CTA)dosimetry system to measure absorbed dose in materialsirradiated by photons or electrons in terms of absorbed dose towater. The CTA dosimetry system is classified as a routinedosimetry system.1.2 The CTA dosimeter is classified as
3、 a type II dosimeteron the basis of the complex effect of influence quantities on itsresponse (see ASTM Practice E2628).1.3 This document is one of a set of standards that providesrecommendations for properly implementing dosimetry inradiation processing, and describes a means of achievingcompliance
4、 with the requirements of ASTM E2628 “Practicefor Dosimetry in Radiation Processing” for a CTA dosimetrysystem. It is intended to be read in conjunction with ASTME2628.1.4 This practice covers the use of CTA dosimetry systemsunder the following conditions:1.4.1 The absorbed dose range is 10 kGy to 3
5、00 kGy.1.4.2 The absorbed-dose rate range is 3 Gy/s to 41010Gy/s(1).21.4.3 The photon energy range is 0.1 to 50 MeV.1.4.4 The electron energy range is 0.2 to 50 MeV.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of th
6、e user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced documents2.1 ASTM Standards:3E170 Terminology Relating to Radiation Measurements andDosimetryE275 Practice for Describing and Measuring
7、Performance ofUltraviolet and Visible SpectrophotometersE2628 Practice for Dosimetry in Radiation ProcessingE2701 Guide for Performance Characterization of Dosim-eters and Dosimetry Systems for Use in Radiation Pro-cessing2.2 ISO/ASTM Standards:351261 Practice for Calibration of Routine Dosimetry Sy
8、s-tems for Radiation Processing51707 Guide for Estimating Uncertainties in Dosimetry forRadiation Processing2.3 International Commission on Radiation Units and Mea-surements (ICRU) Reports:4ICRU Report 85a Fundamental Quantities and Units forIonizing RadiationICRU Report 80 Dosimetry Systems for Use
9、 in RadiationProcessing2.4 Joint Committee for Guides in Metrology (JCGM)Reports:JCGM 100:2008, GUM 1995, with minor corrections,Evaluation of measurement data Guide to the Expres-sion of Uncertainty in Measurement5JCGM 200:2008, VIM, International vocabulary of metrol-ogy Basis and general concepts
10、 and associated terms63. Terminology3.1 Definitions:1This practice is under the jurisdiction of ASTM Committee E61 on RadiationProcessing and is the direct responsibility of Subcommittee E61.02 on DosimetrySystems, and is also under the jurisdiction of ISO/TC 85/WG 3.Current edition approved April 9
11、, 2013. Published June 2013. Originallypublished as ASTM E 165094 with title: Practice for Use of Cellulose AcetateDosimetry Systems. ASTM E 165094 was adopted by ISO in 1998 with theintermediate designation ISO 15570:1998(E). The present Third Edition of Inter-national Standard ISO/ASTM 51650:2013(
12、E) is a major revision of the SecondEdition of ISO/ASTM 51650:2005(E).2The boldface numbers in parentheses refer to the bibliography at the end of thisstandard.3For referenced ASTM and ISO/ASTM standards, visit the ASTM website,www.astm.org, or contact ASTM Customer Service at serviceastm.org. ForAn
13、nual Book of ASTM Standards volume information, refer to the standardsDocument Summary page on the ASTM website.4Available from the International Commission on Radiation Units andMeasurements, 7910 Woodmont Ave., suite 800, Bethesda, MD 20814, USA.5Document produced by Working Group 1 of the Joint C
14、ommittee for Guides inMetrology (JCGM/WG 1). Available free of charge at the BIPM website (http:/www.bipm.org).6Document produced by Working Group 2 of the Joint Committee for Guides inMetrology (JCGM/WG 2). Available free of charge at the BIPM website (http:/www.bipm.org). ISO/ASTM International 20
15、17 All rights reservedThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Techn
16、ical Barriers to Trade (TBT) Committee.13.1.1 absorbed-dose mappingmeasurement of absorbeddose within an irradiated product to produce a one-, two- orthree-dimensional distribution of absorbed dose, thus renderinga map of absorbed-dose values.3.1.1.1 DiscussionThe CTA dosimeter strip with appro-pria
17、te length provides the opportunity for high resolutionmeasurement of dose distribution, such as depth dose distribu-tion.3.1.2 absorbed-dose rate (D)absorbed dose in a materialper incremental time interval, i.e., the quotient of dD by dt.Also see E170. The SI unit is Gy s-1. (ICRU-60, 4.2.6)D5 dD/dt
18、 (1)3.1.2.1 Discussion(1) The absorbed-dose rate is oftenspecified in terms of its average value over longer timeintervals, for example, in units of Gymin-1or Gyh-1. (2) Ingamma industrial irradiators, dose rate may be significantlydifferent at different locations. (3) In electron-beam irradiatorswi
19、th pulsed or scanned beam, there are two types of dose rate:average value over several pulses (scans) and instantaneousvalue within a pulse (scan). These two values can be signifi-cantly different.3.1.3 calibration curveexpression of the relation betweenindication and corresponding measured quantity
20、 value.(VIM:2008)3.1.3.1 DiscussionIn radiation processing standards, theterm “dosimeter response” is generally used for “indication”.3.1.4 cellulose triacetate dosimeterpiece of CTAfilm that,during exposure to ionizing radiation, exhibits a quantifiablechange in specific net absorbance as a functio
21、n of absorbeddose.3.1.5 dosimeterdevice that, when irradiated, exhibits aquantifiable change that can be related to absorbed dose in agiven material using appropriate measurement instruments andprocedures.3.1.6 dosimeter batchquantity of dosimeters made from aspecific mass of material with uniform c
22、omposition, fabricatedin a single production run under controlled, consistentconditions, and having a unique identification code.3.1.7 dosimeter responsereproducible, quantifiable effectproduced in the dosimeter by ionizing radiation.3.1.7.1 DiscussionFor CTA dosimeters, the specific netabsorbance i
23、s the dosimeter response.3.1.8 dosimeter stockpart of a dosimeter batch held by theuser.3.1.9 measurement management systemset of interrelatedor interacting elements necessary to achieve metrologicalconfirmation and continual control of measurement processes.3.1.10 reference standard dosimetry syste
24、mdosimetrysystem, generally having the highest metrological qualityavailable at a given location or in a given organization, fromwhich measurements made there are derived.3.1.11 responsesee dosimeter response.3.1.12 routine dosimetry systemdosimetry system cali-brated against a reference standard do
25、simetry system and usedfor routine absorbed dose measurements, including dose map-ping and process monitoring.3.1.13 specific net absorbance (k)net absorbance, A,at a selected wavelength, , divided by the optical pathlength,d, through the dosimeter as follows:k 5A/d (2)3.1.14 Definitions of other te
26、rms used in this practice thatpertain to radiation measurement and dosimetry may be foundin ASTM Terminology E170. Definitions in E170 are compat-ible with ICRU Report 85a; that document, therefore, may beused as an alternative reference.4. Significance and use4.1 The CTA dosimetry system provides a
27、 means for mea-suring absorbed dose based on a change in optical absorbancein the CTA dosimeter following exposure to ionizing radiation(2, 3-10).4.2 CTAdosimetry systems are commonly used in industrialradiation processing, for example in the modification of poly-mers and sterilization of health car
28、e products.4.3 CTA dosimeter film is particularly useful in absorbeddose mapping because it is available in a strip format and ifmeasured using a strip measurement device, it can provide adose map with higher resolution than using discrete points.5. Overview5.1 CTA dosimeters are manufactured by cas
29、ting cellulosetriacetate with a plasticizer, triphenylphosphate, and solvents,for example, a methylene chloridemethanol mixture (2, 7).5.2 The commercially available dosimeter film is in theformat of 8 mm width and 100 m length rolled on a spool,which is described in the informative annex.5.3 Ionizi
30、ng radiation induces chemical reactions in CTAand the plasticizer, which create or enhance optical absorptionbands in the ultraviolet regions of the spectrum. Opticalabsorbance at appropriate wavelengths within these radiation-induced absorption bands is quantitatively related to theabsorbed dose. I
31、CRU Report 80 provides information on thescientific basis and historical development of the CTA dosim-etry systems in current use.5.4 The difference between the specific net absorbance ofun-irradiated and irradiated CTA dosimeter depends signifi-cantly on the analysis wavelength used to make the abs
32、orbancemeasurement. Typically, the manufacturer recommends theanalysis wavelength that optimizes sensitivity and post-irradiation stability. The analysis wavelengths recommendedfor some commonly used systems are given in Table A1.1.6. Influence quantities6.1 Factors other than absorbed dose which in
33、fluence thedosimeter response are referred to as influence quantities.These influence quantities include those related to the dosim-eter before, during, and after irradiation and those related to thedosimeter response measurements (see ASTM Guide E2701).Influence quantities affecting dosimeter respo
34、nse are discussedbelow.ISO/ASTM 51650:2013(E)2 ISO/ASTM International 2017 All rights reserved 6.2 Pre-Irradiation Conditions:6.2.1 Dosimeter Conditioning and PackagingThe dosim-eter may require conditioning and packaging, particularly forlow dose rate (gamma) irradiation. See 6.3.4.NOTE 1Conditioni
35、ng CTA film and packaging pieces of it in envi-ronmentally impermeable pouches under controlled relative humidityconditions will provide for the most consistent dosimeter response,however the film is often used with no packaging.6.2.2 Time Since ManufactureThe pre-irradiation absor-bance increases v
36、ery slowly with time and depends on theaccess to air (oxygen). The pre-irradiation absorbance of theouter layer(s) of a roll of CTA film may, therefore, increasemore than the inner layers; hence, it may be advisable todiscard the outer layer(s) of the film. Measure the pre-irradiation absorbance bef
37、ore using the dosimeter.Alternatively, compare the pre-irradiation absorbance to theaverage value noted at the time of calibration to determine ifthere is any significant change that should be taken intoaccount.NOTE 2The pre-irradiation absorbance to be used in the calculation ofspecific net absorba
38、nce will either be the value as measured beforeirradiation by the user, or a user-determined average pre-irradiationabsorbance.6.2.3 TemperatureAvoid exposure to temperatures outsidethe manufacturers recommended range to reduce the potentialfor adverse effects on dosimeter response.6.2.4 Relative Hu
39、midityThere is no known effect ondosimeter response.6.2.5 Exposure to LightThe dosimeter is insensitive tovisible light; however, exposure to UV light may have an effectand should be characterized. Exposure to UV prior to irradia-tion may increase the pre-irradiation absorbance of the film,and depen
40、ds on the intensity of the UV (11).6.3 Conditions During Irradiation:6.3.1 Irradiation TemperatureThe dosimeter response isaffected by temperature, particularly at low dose rates, and thiseffect shall be characterized (12, 11, 9, 10).6.3.2 Absorbed-Dose RateThe dosimeter response is af-fected by the
41、 absorbed-dose rate and this effect shall becharacterized (13, 14-4, 7-9).6.3.3 Dose FractionationThe dosimeter response is af-fected by dose fractionation and shall be characterized (14).6.3.4 Relative HumidityThe dosimeter response is af-fected by relative humidity, particularly at low dose rates
42、andrelative humidity extremes. This effect shall be characterized(12, 11, 4, 7, 9).6.3.5 Exposure to LightThe dosimeter is insensitive tovisible light, however, exposure to UV light may have an effectand should be characterized. Exposure to UVduring irradiationmay increase the optical absorbance of
43、the film, and likelydepends on the intensity of the UV (11).6.3.6 Radiation EnergyThere is no known effect on do-simeter response, however, the irradiation of 125 micron thickCTA film using electron energies below 300 keV can result ina dose gradient through the film.6.4 Post-Irradiation Conditions:
44、6.4.1 TimeThe dosimeter response varies with the timeinterval between radiation exposure and dosimeter measure-ment (12, 14, 11, 4, 10). This effect shall be characterized andthe measurement time standardized.NOTE 3The absorbance first decreases and then slowly increases withstorage time longer than
45、 fifteen minutes after high dose-rate electron beamirradiation. The dosimeter response will become more stable about twohours after irradiation. Therefore, it is recommended that the absorbanceof the dosimeter be measured at a constant time period, for example, twohours after irradiation (11, 4, 7).
46、6.4.2 TemperatureThe temperature of CTA film storageafter irradiation does have an effect and shall be characterized.The user may need to control the post-irradiation storagetemperature within a defined range (11).6.4.3 Conditioning TreatmentNo advantageous post-irradiation treatment has been found
47、(4).6.4.4 Relative HumidityThe rate of change of the post-irradiation absorbance may be affected by relative humidityand shall be characterized. The user may need to control thepost-irradiation storage relative humidity within a definedrange (12, 11, 7, 9).6.4.5 Exposure to LightThe dosimeter is ins
48、ensitive tovisible light, however, exposure to UV light may have an effectand should be characterized. Exposure to UV after irradiationmay increase the post-irradiation absorbance of the film, andlikely depends on the intensity of the UV (11).NOTE 4The post-irradiation absorbance of the film has bee
49、n shown tochange over longer storage periods (greater than 24 hours) and isdependent on the temperature and relative humidity during post-irradiation storage. The user should characterize longer term effects anddefine storage conditions if measurements will be made outside of the timeinterval used during calibration of the dosimetry system (see 6.4.1) (11, 9).6.5 Response Measurement Conditions:6.5.1 Exposure to LightThe dosimeter is insensitive tov
