Research in Radiation Processing Dosimetry

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RESEARCH RADIATION I N PROCESSING DOSIMETRY

FINAL REPORT CO-ORDINATEE OFTH D RESEARCH PROGRAMME ON HIGH-DOSE STANDARDIZATION AND INTERCOMPARISON FOR INDUSTRIAL RADIATION PROCESSING ORGANIZEE TH Y DB INTERNATIONAL ATOMIC ENERGY AGENCY AND PROCEEDINGS OF THE FINAL RESEARCH CO-ORDINATION MEETING HEL MUNICHDN I , 8-11 NOVEMBER 1983

TECHNICAA L DOCUMENT ISSUEE TH Y DB INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1984

T RESEARC RADIATION HI N PROCESSING DOSIMETRY IAEA, VIENNA, 1984 IAEA-TECDOC-321

Printed by the IAEA in Austria December 1984 The IAEA does not maintain stocks of reports in this series. However, microfiche copies of these reports can be obtained from MicrofichS IM e Clearinghouse International Atomic Energy Agency Wagramerstrasse 5 P.O. Box 100 A-1400 Vienna, Austria prepaymenn o f Austriao t n Schillings 40.0 r agains0o IAEe on t A microfiche service coupon. PLEASE BE AWARE THAT ALL OF THE MISSING PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK CONTENTS

I. SUMMARY ...... 5

II. SCIENTIFIC REVIEW AND ACHIEVEMENTS ...... 13 1. Development of new dosimetry systems ...... 13 a) Alanine/ESR dosimetry b) Lyoluminescence dosimetry c) Thick radiochromic dye films d) Development of radiochromic dye film 2. Improvemen dosimetrf o t y systems ...... 6 1 . a) Method f calibratioso gamma-ran i y fields b) Sample production, data analysi precisiod san alanine th f no e dosimeter c) Glutamine lyoluminescence dosimeters d) Electrochemical potentiometry of ceric-cerous sulphate dosimeter e) Result improvemene th n so ethanol-chlorobenzene th f o t e oscillometric (ECB) dosimeter f) Packagin handlind gan f radiochromigo file mcdy dosimeters 3. Environmental effects ...... 20 a) Effec f temperaturo t e during irradiation ) b Effec f temperaturo t e during evaluation c) Effec f post-irradiatioo t n temperature d) Effect of humidity e) Effec f ligho t t 4. Dose intercomparison studies ...... :...... 24 a) High- and medium dose range ) b Low-dose range 5. Related activities ...... 6 2 .

III. SCIENTIFIC PAPERS ...... 9 2 .

Radiation process control, stud acceptancd yan f dosimetrieo c methods ...... 9 2 . B.B. Radak effece Th humiditf o t response dosimetrth X n H yo f eo y perspe radiatioo xt n ...... 1 6 . K.H. Chadwick Intercalibratio testind nan f blugo e cellophane cellulosetriacetatd -an emegarae filmth r fo s d dose range ...... 71 P. Gehringer, ProkschE. Environmental effects on the ethanol-monochlorobenzene dosimeter system before, during and after irradiation ...... 91 Kovâcs,A. lengerS V. Progress in alanine/ESR transfer dosimetry ...... 141 D.F. Regulla, U. Deffner, O. Schindewolf, A. Vogenauer, A. Wieser Dosimetr electror yfo n beam application ...... 9 15 . MillerA. Developmen techniqueR ES f o t frer sfo e radical dosimetr electron yi n beams ...... 7 18 . R.M. Uribe Radiochromic dye dosimetry using triphenylmethane leucocyanides in nylon or polyvinyl butyral ...... 9 20 . W.L McLaughlin, HumphreysJ.C

IV. LIS PARTICIPANTF TO S ...... 7 23 . I. SUMMARY

e co-ordinateTh d research programm high-dose th n o e e standardization and intercomparison for industrial radiation processing was initiated as one of the programmes of the Dosimetry SectioDivisioe th f o nLiff no e Science Marcn i s h 1978majoe Th .r objective f thio s s programme wer seleco t e t suitable dosimetry systems; to improve reliability of dosimeter and dosimetric techniques develoo t d w dosimetr;an ne p y e intersystemth r -fo s national dose assurance service to the radiation processing facilitie Memben i s r States.

In total researc7 , h contrac researc4 d an t h agreement holders from 10 countries particpated in this programme during the 5-year period (1978-1983). The results obtained under this programme were reviewed by the Committee for Contractual Scientific Services of the Agency in June 1980, which then decided to extend for 3 more years. o researcTw h co-ordination meetings were held, i.e Budapesn i . t (12-16 November Munic1979)n i d h,an (8-11 November 1983).

Sinc dose0 1 197e th 7intercompariso n studie differenn i s t dose ranges (low, medium and high) were performed with 19 laboratories in countrie4 1 internationa1 d an s l organization participating. Nine different dosimeter s listea s d below were tested.

Institutions participatin d dosimetran g y systems operater fo d intercomparison studies

Gesellschaf Strahlenr fü t d Umwelt-un - Alanine, Lithyum - forschung m.b.H., Munich, F.R. Germany borate

Atomic Energ Canadf o y a Ltd., Ceric-cerous Ottawa, Canada sulphate

Institute of Isotopes, Ethanol-chloro- Budapest, Hungary benzene, Fricke, Super Fricke

National Burea Standardsf o u , Radiochromic dye Washington, D.C., U.S.A. films Boris Kidric Institute of Radiochromic dye Nuclear Science, Belgrade, Yugoslavia liquid

Universit Aberdeef o y n Glutamine Aberdeen, Scotland, U.K.

Institute for Atomic Sciences Glutamine in Agriculture, Wageningen, The Netherlands

National Physical Laboratory, Teddington, U.K. Bhabha Atomic Research Centre, Bombay, India Comision Nacional de Energia Atomica, Buenos Aires, Argentina Ris;rf National Laboratory, Roskilde, Denmark Centre d'Etudes Nucléaire Saclaye d s , Gif-sur-Yvette, France Physikalisch-Technische Bundesanstalt, Braunschweig, F.R. Germany Australian Atomic Energy Commission, Sutherland, Australia Arbrook Products Ltd., Livingston, Scotland, U.K. American Hospital Supply Corporation Pasol ,E , U.S.A. Programa Preventive contra la Mosca del Méditerranée, Chiapas, Mexico Japan Atomic Energy Research Institute, Takasaki, Japan International Atomic Energy Agency, Dosimetry Laboratory, Austria

Major accomplishment co-ordinatee th f o s d research programme are listed as follows:

1. Selection of Alanine/ESR system as the reference transfer e internationath n i dosimete e us r l fo rdos e assurance service.

2. Selection of suitable back-up systems for use in special situations or in case of dispute (i.e., ethanol-chlorobenzene, ceric-cerous sulphate, glutamine/LL, radiochromic dye films).

. 3 Improvemen reliabilitf o t d developmenan y f techniqueo t f o s those dosimetry systems which were used in the intercomparison studies.

. 4 Determinatio effece th - d correctio un f an tno e th r fo n avoidable influence f environmentao s l factordose th e n o s evaluation (e.g., temperature, humidity, climate, light, instabilities).

. 5 Improvemen dosf o t e calibratio d intercomparisonan n procedures.

6. Design of standardized calibration apparatus and procedure. The scientific papers presented at the meeting (Munich) were accepted as the final report of the research contracts. The papers presented wer s listeea d below:

1. Environmental effects on the ethanol-monochlorobenzene dosimeter system before, durin d aftean g r irradiation, Stenger. ,V

2. Intercalibration and testing of blue cellophane and cellulose-triacetate films for the megarad dose range, Gehringer, P.

3. Organic lyoluminescence dosimetry: its mechanism and its applications, Ettinger, K.V. e effecTh humiditf o tresponse th . X dosimetr 4 H n o yf o e y Perspex to radiation, Chadwick, K.H.

5. Radiochromic dye dosimetry using triphenylmethane leucocyanides in nylon or polyvinyl butyràl, McLaughlin, W.L.

. 6 Radiation process control, stud d acceptancan y dosimetrif o e c methods, Radak. ,B

. 7 Developmen R techniqueES f o t r frefo se radical dosimetrn i y electron beams, Uribe, R.M. . 8 Dosimetr electror fo y n beam application, Miller. ,A

9. Progress in alanine transfer dosimetry, Regulla, D.F. and Deffner. ,U Research Contract Agreementd an s s

Title Name Period

I. Research Contract

1-1-1 Development of radiation dosimetry by Mallard, J.R. 01/08/1977 lyoluminescence in the region of high- (Ettinger, K.V.) 30/11/1980 doses relevan e need th f fooo o st d U.K. processin d sterilizatiogan medicaf no l materials and pharmaceuticals. (2045/RB)

1-1-2 Study of methods leading to improvement Ettinger, K.V. 15/12/1980 of reliability and extension of useful U.K. 30/11/1984 dose rang f freo e e radical dosimetry, with particular consideration of lyoluminescence technique. (2818/RB)

1-2-0 Intercalibratio d testinnan bluf o g e Gehringer. ,P 01/03/1979 cellophane- and cellulosetriacetate Austria 31/03/1983 megarae th film r dfo s dose range. (2333/RB)

1-3-1 Investigation of the radiochromic dye Miller, A. 01/08/1977 dosemeter under process conditions, Denmark 31/07/1981 including stability, precision, accuracy influence ,th dosf eo e rate, and the influence of the environment. (2051/RB)

1-3-2 Development of thin film dosimetry for Miller. ,A 01/08/1981 electron beam application. (2883/RB) Denmark 30/11/1983

1-4-1 Intercalibratio d testinnan f o g Radak, B. 15/12/1977 dosimetry system measurinr fo s g Yugoslavia 14/12/1979 large dose industrian i s l radiation processing. (2141/RB)

1-4-2 Compatibility and usefulness study Radak, B. 15/02/1980 of some dosemeter r radiatiofo s n Yugoslavia 14/02/1981 processing: Sterilizatio d polymean n r cross-linking. (2141/RB) higo t 1-4-hw dosLo 3 e rate transfef o r Radak. B , 15/05/1981 calibration of thin film dosemeters Yugoslavia 30/11/1983 for electron beam process control. (2141/RB)

1-5-1 Developmen precisioa f o t n free-radical Regulla, D.F, 15/12/1980 dosimeter based on amino acid detectors F.R. Germany 30/04/1984 and ESR readout for high-level photon and electron dosimetry. (2819/RB) Title Name Period

1-6-1 Investigation of different environ- Stenger, V. 01/06/1979 - mental effectmono-chloroe th n o s - Hungary benzene dosimeter systems after irradiation. (2389/RB)

1-7-1 Developmen R techniqueES f o t r fo s Uribe, R.M. 01/12/1981 free radical dosimetry in electron Mexico 30/04/1984 beams. (2968/RB)

II. Research Agreement

II-l-l The post irradiation stability of the Chadwick, K.H. 01/04/1978 clear perspex high level dosimetry Netherlands, 30/04/1981 system. (2180/CF) (CEC)

II-2-1 Environmental effect mailen o s d ceric- Chu, R.D.H. 01/10/1978 cerous dosimeters. (2192/CF) Canada 30/11/1979 II-3-1 Investigation of stability, temperature McLaughlin, W.L. 01/06/1978 dependenc humiditd ean y sensitivitf o y U.S.A. 31/05/1979 radiochromi dosimetere dy c s during irradiation and storage. (2177/CF)

II-3-2 Transition zone dosimetry. (2433/CF) McLaughlin, W.L. 15/09/1979 U.S.A. 14/09/1981

II-3-3 Tissue equivalent liquid systemr fo s McLaughlin, W.L. 15/02/1982 food druan dg processin d pestan g - U.S.A. 30/11/1983 control dosimetry. (3061/CF)

II-4-1 The development of lyoluminescence Fuite, K.J. 01/04/1978 technique for dose intercomparison Netherlands 30/04/1982 studies at high-dose level. (2179/CF)

II-5-1 Climatic influenc alaninn i e e dosimetry. Regulla, D.F. 01/11/1978 (2265/CF) F.R. Germany 31/10/1979

II-5-2 High-level photon and electron transfer Regulla, D.F. 01/11/1979 dosimetry with alanine. (2265/CF) F.R. Germany 31/10/1980 —\— ~r —T~ —r~ 1977 79 80 81 82 03 84 66 8? 88 89

World survey of International dose assurance II-Ü facilities service(gamma)

Dose interoomparison atudiea(H-M-L,ganuna) Pilot dose Pilot dose INTERNATIONAL DOUE (THS-205) assurance assurance (electron) ASSURANCE SERVICE (gamma) (ganun électron& a ) AÛM(l) AQM(2) AÛM(3)

HIGH-DOSE STANDARDIZATION à AOM(4) INTERCOMPARISON FOR INDUSTRIAL RADIATION PROCESSING Dose intercomparison studies DOSIMETHY AS QUALITY (electron) -CONTROL MEASURE IN RADIATION PROCESSING Seminar(l) Symposium Seminar(2)

Coordinated research programme(gamma) Coordinated research programme(electron)

RCM(gamma) RCM(gamma) RCM(electron)

AGM(l)iStandardizatio High-Dosd an n e Seminar (l) t High-Do se Dosimetry in Induati'ial Radiation Interoompariso r Industriafo n l Processing Radiation Processing :Dosimetr) (2 " n Radiatioi y n Processing Technology " (2)iDosimetry for High-Doses Employed TR3-2U5:Technical Report Series No.205» High-Dose Measurement in Industrial Radiation Processing in Industrial Radiation Processing " (3)«High-Dose Pilot Intercomparison 11 AG M- Advisor y Group Meeting :Dosimetr) (4 s Qualita y y Control HC M- Researc h coordination Meeting Measur n Radiatioi e n Processing Dose Intel-comparison Etudie - sGamm a (1977 - 1982)

Preliminary inter- 2nd high-dose inter- High-doae pilot High-doae research comparison, 20-50kQy, comparison, 5-lOOkGy atudy,5-100kGy(0.5- atudy,5-100kGy(0.5- High-Dose (0.5-10Mrud), lOMrad), lOMrad), Alanine Alanine Alanine Alanine 5-100kGy Ceric-coroua aulph. Ceric-ceroua aulph. Cerio-ceroua aulph. Cerio-ceroua aulph. (500krad- Radioohromio dy o Radioohromio dye Hadiochromio dye Radiochromie dy o lOMrad) Bthanol chlorobenz. Bthanol chlorobenz. Ethanol chlorobenz. Bthanol ohlorobenz. (4) (4) (4) Glutamine-ITAL(5) 9 irradiating laba. 11 irradiating labs 5 irradiating laba. 1 irradiating lab.

Preliminary inter- 2nd médium-dose comparison, l-5küy intercompariaon, Médium-Dose (0.1-0.5llrad), l-lOkGy(O.l-lMrad) 1-10kdy Alanino Alanine TLD,Lithium borate, ueric-ceroua aulph. (lOOkrad- Cerio-ooroui} aulph. fladioohromio dye Lod medium-doswan a IMrad) Radiochromic dye, Ethanol ohlorobenz. Low-dose pilot atudfl intercomparison, Bthanol chlorobena. (4) 0.01-3kOy(l-300kradj 0.01-10kGy(lkrad- (5) 11 irradiating laba, Alanine IWrad), 11 irradiating laba Hadioohromio dye Radioohromio dye Glutamine-lTAL/UA film, liquid Ethanol ohlorobenz. Preliminary inter- (4) 3 irradiating laba. Glutaroine-Ria//UA comparison. 0.01-3kGi (5) (l-300krad), 2 irradiating laba. Low-Doao Alanine 2nd low-dose inter- 0.01-3kGy Hadiocliroraio dye oompariaon,0.01- (Ikrad- film, liquid 3kGy(l-300krad), 3û01c) rad Bthanol chlorobenz. Radiochromic dyo Glutamine-ITAL/UA(6 liquid(l) 3 irradiating laba. 1 irradiating lab.

1977 1970 1980 1981 1982 IL SCIENTIFIC REVIE ACHIEVEMENTD WAN S

e scientificallTh y significant results achieve resula s a d t of these investigation e reviewear s d briefly.

. 1 Developmen w dosimetrne f to y systems

a) Alanine/ESR dosimetry

e suitabilitTh R analysiES f o y alaninf so usefua s a e l means of radiation dosimetry demonstrate U.S.Ae n 196th i d s n .2i ha been turned into a practical, versatile dosimetry method of metrological quality, owing to the work of the Gesellschaft für Strahlen- und Umweltforschung m.b.H. (GSF) solid state dosimetr yFederae grouth n i pl Republi Germanyf o c e Th . useable dose range is 1 to 5x10 Gy. Being based on the detection of free radicals in solid amino acid, ESR dosimetry measure bonde th s - breaking effec f ionizino t g radiation. e stabilitTh e freth e f radicalo y n thii s s organic solis i d excellent because of their steric properties and this is reflecte vera n yi d small signal change with different storage conditions. The readout method does not require any chemical manipulatio r indee nno y physica an d l contact with the sample. The samples have archival properties for dosimetry as the ESR analysis is non-destructive. The precision of readout can possibly be improved with the design of a more stable ESR spectrometer and with a cavity possessing a more uniform field distribution; hitherto achieved precision is better than 1.0%. The alanine system has the potential of being extende o lowey t d cG rw dosesfe a s ,a perhapw lo s a s and also may benefit from the development of a simplified readout equipment.

Long-term emphasis on the detector production, which is from pro-analysis material without the need of activators, has revealed excellent value f interspecimeo s n scatterin s wela g l

13 as of interbatch uniformity. The dosimeter samples designed and produced at GSF show excellent performance even under unusual environmental conditions.

b) Lyoluminescence dosimetry

Lyoluminescence dosimetry (LLD) was developed both at the Universit Aberdeenf o y Institute th , t U.K. a Atomir d fo e ,an c Science Agriculturn i s e (ITAL) Netherlandse ,th , under research contracts with IAEA, and was tried with both sugars (e.g., manose amind )an o acids (e.g., glutamine) considA . - erable effor botn i t h places went into constructin w typene g s of readout apparatus, investigating changes in the LL yields after a period of storage at various temperatures, studying the influence prevailinf o s g physical (temperature, dissolved gases) and chemical (pH, sensitizers) conditions during irradiatioe tim readoutf th o e t a d .nan Serious consider- ations were also given to the study of the physico-chemical basis and mechanisms of lyoluminescence which are now much better understood, than at the beginning of the programme.

LLD with mannose, with and without the addition of sensitizers, covers the range from a few Gy to approximately d witavailable an th h y G 0 e40 readout equipmen capabls i t f o e a precision of about 1-2%. It is, however, subject to thermal fading ,negligible b whic y hma r radiatiofo e n processing plant conditions wilt ,bu l seriously affece th t result mailea usef i ss a d d dosimeter. o knowThern s i ne method for correcting for this deficiency.

LLD with glutamine was tried in the high-dose range intercomparisons (>10 Gy), when adequate knowledge th f o e influenc environmentaf o e l factor s stilswa l lackings wa d ,an dropped, initially, frohigh-dose th m e sectio e proth -f no gramme.

LLD with glutamine in the low-dose range was more successful and as a result of the study of the factors mentioned above, both laboratories using this technique attained precisiod an n accuracy whic e highlhar y promisin r foofo gd irradiation applications.

14 At the moment LLD is operated by two laboratories National Laboratory and University of Aberdeen) but no commercial readout equipment or prepared dosimeter samples are yet available.

c) Thick radiochromic dye films

e radiochromin ordeI us o t r e filmsdy c , commercially available in large batches, as suitable dosimeters within the IAEA dose intercomparison studies recommendatioa , mads nwa e to produce thicke d thuran s more sensitive films e thickTh . - ness would thus be increased from the nominal 0.05 mm to cooperation i aboud undem m an guidance 1 tS th r NB n f witeo h the largest producer of radiochromic dye films. (Far West Technology Inc Golettan i . , Calif.). After several trials with nylon, halostyrenes, and vinyl film bases, the result of this project was the production of a polyvinyl butyral (PVB)-based film weigh y b wit % hexa(hydroxyethylf 5 ho t ) pararosanilin precursore e dy cyanide th e optica s Th ea . l quality, and mechanical properties and flexibility, proved 'to bese bf thosth eo t e being teste d nominaan d l thicknesses were 0.6 to 1.0 mm. Doses as low as about 50 Gy could be measured spectrophotometrically with these films, though the minimum limit proposed by the IAEA could not be attained (abou Gy)0 1 t e furthe.On r proble s thaopticae mwa th t l quality of these films was not as good as that of thin films, and showed somewhat cloudy surfaces in some specimens. One further attemp produco t t e thick radiochromi e filmdy cs ha s been made at the Physics Institute of the National Autonomous University of Mexico in order to use them for ESR dosimetry in electron beams, as previous studies using thin radiochromi e filmsdy c , wher ea relativel y smal R signalES s lwa obtained, showe e feasibilitth d f thio y s technique. Using similar formulations as those used to produce PVB-based thin films much better free-standing thicker films (1 to 2 mm) were cas n speciallo t y designed optically polished aluminium plates. Several combination precursore dy f o s d plastian s c matrices have been investigated, though the most suitable up to now seem to be those having leuco-cyanides of formyl violet or malachite green as the dye precursor in PVB or

15 pararosaniline cyanide in nylon. Some further investigations mus done b tn term i e usefuf o s l dose ranges, dose-rate dependence, and environmental effects in order to prove their applicability as a suitable dosimetry system for electrons at high dose d dose-ratesan s .

Developmen) d f radiochromio t file dy cm

Since 1978, unde rseriea researcf so h contracts wite th h IAERisd an A^ National Laboratory, Denmark, have conductea d successful programme of design and fabrication of new radiochromic dye thin film dosimeters. These studies have also involved the detailed testing of these dosimeters under radiation processing conditions. The stability, dose-rate dependence, and the effect of environmental factors on the precisio d accurac gamma-rae nan th f o y y dose estimates over the useable range of response (10 -10 Gy) have been investigated. Although several radiochromic dye film types were developed Rise th ,o type P-15 film, consistinf o g certain leuco-cyanide forms of triphenylmethane dyes in cast polyvinyl butyral plastic films (thickness ~ 50 ,urn) was the typ mosf o e t interes e IAEA th r possibl .fo y tb e us e

e resultTh f thio s s previoue wor e founth kar n i d s IAEA Technical Report Series No. 205 and in subsequent Riso National Laboratory reportIAEAe th .o t s Wor continuins i k g at Riso on the development of this system for use, also, in electron beam applications, the interest being in its high spatial resolution, its apparant ability to be easily calibrated and used at high dose-rates for reasonably accurate and precise dose interpretation, its ruggedness and its low cost. Effect f environmento s , light, "dose-rate, etc. f areo , course, matters to be reckoned with.

. 2 Improvemen dosimetrf o t y systems

Method) a f calibratioo s gamma-ran i n y fields

As a means of standardizing the gamma-ray irradiations and resulting value f absorbeo s d dos waten i er dosimete fo r r calibration, the National Physical Laboratory (NPL), U.K.,

16 devise calibratioa d n procedur dosimetea d ean r holder fo r all forms of dosimeter used in the intercomparison and pilot cell studies. This procedure involved the use of three NPL gamma-cell type sources providing three convenient dose-rates with dosimeter holders that fit interchangeably in thermo- stated positions in the gamma-ray fields. The dosimeter holders were designe o thas d t they provided approximate conditions of electron equilibrium, accurate temperature control, and an array of dosimeter locations in the holder that could be standardized in terms of absorbed dose rate in water by placement of standardized Fricke dosimeters at the location of each dosimeter to be calibrated. The individual groups of dosimetes were stored under controlled environmental conditions before and after irradiation to certain prescribed dose t specifiea s d temperatures.

b) Sample production, data analysis and precision of the alanine dosimeter

Within the framework of a research contract sponsored by the s achieveha IAEA F ,GS d remarkable precisio d reliabilitan n y L-alanine oth f e dosimeter, improvemento mainlt e du ye th f so ESR technique. This included improved sample preparation and the use of microprocessor assistance for evaluation of the ESR spectra (peak-to-peak measurement doublr o s e integrations of spectra to assess the free radical concentration); environmental or storage conditions have also been considered e improveith n R analysiES d s procedure.

c) Glutamine lyoluminescence dosimeters

Dosimetry with glutamine, whic s originallhwa y proposey b d the Universit Aberdeef o yt firs a s t nwa considere d unsuitable for mailed dosimetry applications, becaus f instabilito e y effects. A breakthrough was achieved at ITAL, by use of a special heat treatmen e sampleth f o ts after irradiation just before LL analysis. The resulting improvement in precision, which was investigated experimentally at both laboratories is not fully understood theoretically. The temperature during irradiation knowe needb ordeo n t i ns mako t r e suitable

17 correction r temperaturfo s e dependence e correctionTh . n i s the lower dose range (^10 kGy) are known, and they can be dosel al e sam sth t assume a ee lesb o st d e tha th kGy0 1 nn I . high-dose rang0 kGy>1 )( e these correction somewhae ar s t dependent on dose level as is also the case with alanine/ESR dosimetry. The effects of pH and dissolved gases in the solvent are known, and this knowledge is reflected in routine experimental procedures. The approach of the ITAL laboratory, involving N--saturated water, results in somewhat better precision than the other technique, which equilibrates the solvent with air n efforA . t toward developin readoua g t system wit n improvea h d metho handlinf o d glutamine th g e powder samples has also been made. An especially important improvement was afforded by standardization of the phosphor itself, i.e. availability of glutamine powder material having more homogeneous lyoluminescent properties. Significant improvements have not yet been achieved in the design of a routine instrument for LL readout. There is indeed need for a more sensitive instrument with a simple operating procedure, yet robust enough to be used in an industrial environment.

Electrochemica) d l potentiometr ceric-cerouf o y s sulphate dosimeter

Improved agreement between the dose interpretations of the ceric-cerous dosimeter (electrochemical potentiometry) and other dosimetric method recentls sha y been achieved undera research agreement with Atomic Energ Canadf o y a Ltd. Further improvement of the absorbed dose assessment by this method has been made by the AECL providing larger batches of ceric- cerous dosimeter ampoules, using standardized procedures and an improved electro-chemical potentiometric apparatus (supplie "Compu-Dose th AECy b ds a L e System") additionn I . , thorough studies were mad AECt a eenvironmentaf o L l effects, such as temperature dependence, on ceric-cerous dosimeter solutions.

Result) improvemene e th n ethanol-chlorobenzene o s th f o t e oscillometric (ECB) dosimeter

18 e dosTh e rang f oscillometrio e c evaluatio e irradiateth f no d mono-chlorobenzene dosimeter has been extended, thus making possible the use of the method for the absorbed dose control of some food irradiation processes as well as for most high-dose irradiations.

e lowe uppee Th 0 kradth r (4 rd dos y )dosan G e 0 elimi40 s i t 0 Mrad)oscillotitratow (5 ne y A .kG 0 limi50 s i tr readout instrument, havin mora g e sensitive readout capabilitys ,ha been introduce RADELKIe th y b d S Company, Budapest, Type w availableOK-302/1no s w ampouli ne d A ,an . e holdes rha also been developed for the oscillotitrator at the Institute of Isotopes of the Hungarian Academy of Sciences (INISO) and 3 this ampoule holder can be used for 5 cm as well as, for 3 m dosimetec 5 2. r ampoules ampoulw ne e eTh . holder gives considerably improved reproducibility of readings, and angular dependency of ampoule measurement has been eliminated by the new ring-type electrode system. By using an improved value of radiation chemical yield, G(C1 ) = 5,64 publishe, (10 ) co-workerDvornis . 0I eV hi y d b kan s in 1972, 198 d prove2an y internab d l intercmparison wite th h Fricke dosimeter syste INISt ma O (instea previousle th f o d y used G(C1~) = 5,05 (100 eV)'1), the ECB system shows relatively close agreement witIAEe th hA dose intercomparison results made durin pase th gt five years. Selectiof no improved glass dosimeter ampoules (within ^0.2 mm uncertainty in the ampoule dosimeter) has shown that appreciable improvement is achieved in the calibration curves and in the dose readings as well. The development and improve- e traditionath men f o t l conductivity evaluation methoy b d INISO makes possible the evaluation of the irradiated dosi- approximate meterth n i s e rang dosef MGy1 eo - s.y G fro 0 1 m e succesTh f thio s s development offer a ssyste m thas ha t essentiall variatioo n y responsf no e with moderate changen i s environmental conditions, one that is easy to use and is widely available.

19 Packagin) f handlind an g radiochromif o g e filcdy m dosimeters

In previous intercomparison studies using thin radiochromic dye filmss showwa t ni , that severe climatic conditions, such as those in tropical environments, adversely influence the dosimeter response. This effect gives rise to erroneous results in some situations of long-term storage. In order to look for possible reasons and to understand and correct the dosimeter response IAEe ,th A sponsore researca d h agreement with the U.S. National Bureau of Standards. Work by the Austrian Research Centre Seibersdor s alsfwa o sponsoreo t d study environmental effecte fildy m n o responses n thesI . e investigations it was determined that the main reasons for the erroneous result intercomparisone th n som i sf o e s were probably due to the large temperature and humidity changes during mailing, storage d irradiation,an attempn A . o t t avoid these effects included double-wrappin radioe th f -o g chromic dye film dosimeter assemblies with light-tight, well-sealed polyethylene pouches. Thoug adverse th h e environmental effects wer t completeleno y eliminatede th , later intercomparison results showed some improvemene th n i t case of irradiation and storage in hot-climate environments. A greater w beinefforno s gi t give produco t n e radiochromic dye films consistin f leso g s hydrophilic plastic matriced an s with temperature coefficients smaller and more established than those measurepresene th r tfo d film formulations under the IAEA sponsored work.

3. Environmental effects

Several environmental factors can affect the response of dosimeter systeme higth h t a sradiatio n doses use n radiatioi d n processing. In general, two categories of environmental variable e distinguishedb n ca e whic,on h canno e avoidetb r controlledo d , such as irradiation temperature, but which can be taken, at least to some extent, into account by using an appropriate correction factor e otheTh . r category canno correctee b t d forcant t bu ,a , least to some extent, be avoided or controlled, such as light exposur d relativan e e humidity.

20 Many environmental factors are inter-related, sometimes in a complicated way, such as moisture content and oxygen diffusion, so that in some cases it becomes virtually impossible to study the e e exclusioeffecfactoth on othersl o f t o ral f no ,

a) Effect of temperature during irradiation

In general, all dosimeter systems investigated have been foun havo t d responsa e e whic dependens i h n irradiatioo t n temperature. 1 Thiresearc s emphasize198 swa e th h y studb d y carried out at NPL which indicated irradiation temperature as a significant factor requiring correcton. Thibees ha sn confirmed in independent investigations of all the intercomparison systems except for the ethanol-chlorobenzene dosimeter, where no temperature dependence could be measured.

Most dosimeter systems sho wpositiva e temperatur- co e efficient with values varying from 0.3% to 7% per 10°C. The ceric-cerous sulphate dosimeter system has negative temperature coefficients having similar values at 2% per 10°C.

This variable is one of the most important factors affecting the accuracy of dose estimate in the type of dose assurance service envisaged by the IAEA. The temperature in radio- nuclide radiation facilitie n increasca s abouo t e t 50°C near the source, is difficult to determine and depends strongly on the geographical locatio processine th f no g facility. Fortu- nately, in most cases the correction factor required will not be very large.

b) Effect of temperature during evaluation

n effecA f temperaturo t e during evaluatio parametee th f no r measure provido t d e dose estimat s beeeha n foun r somfo de systems and careful control of this factor can improve the accuracy of dose estimation. This factor should normally be known but can be avoided by making measurements at constant temperature.

21 c) Effect of post-irradiation temperature

In the postal retrieval of dosimeter systems from all over the s impossiblworli t i d o controt e e conditionth l s thae th t system e exposear s prioo t d evaluationo t r e influencTh . f eo some environmental factoravoidee b n carefuy ca sb d l pack- aging, but the influence of temperature cannot be avoided. additionn I , littlo information r o e n abou average th t e post-irradiation temperature wil availablee lb n somI .e system radiatioe th s n induced signal fades with time after irradiation and the rate of fading is dependent on temperature. In some others the radiation induced signal has been found to increase with time after irradiation in a temperature dependent way. In the lyoluminescence of glutamine the effect of post-irradiation temperature can be avoided by heatin e sampleth g hour115°o 5 t s r sCfo just prio evalo t r - cellulose-triacetatuatione th n I . e system this sorf o t treatmen t successfuno s post-irradiatioe i tth s la n heat treatment in air does not stabilize the radiation induced response e ethanol-chlorobenzenTh . e syste bees mha n founo t d remain stable after irradiatio r lonfo ng period f timo st ea storage temperature 50°Co t p .su

Effec) d humiditf o t y

Storage of some dosimetry systems prior to irradiation at different level f relativo s e humidit s beeyha n founo t d affect the response of the systems to radiation, a. good example of this is the humidity dependence of the gamma-ray response of the blue cellophane system. This sort of effect is generally found in dosimeter systems basad on hydrophilic plastic films such as nylon-based radiochromic dye film, red Perspex, etc.

In some dosimeter dose-ratsa e effect, usually foun about a d t kGy/0 1 gamma-ran - i h 1 0. y irradiations bees ,ha n founo t d be dependent on the moisture content of the systems. To some extent this effect appears to be also dependent on the presence of oxygen, e.g. nylon-based radiochromic dye film, cellulose-triacetate film. It is important to note that

22 researc s showhha n that careful selectio f eitheo n r high moistur exclusioe th conten y b f oxyger no o t n during exposur elimatn ca e e these dose-rate effectscase f th o e n I . cellulose-triacetate fildose-rate th m e effec n onlca te b y eliminated by exposing the film in an inert gas atmosphere. n generaI rate f oxygeth lo e n diffusion into plastic films increases witmoisture th h e contenfilme th .f o t This i s illustrated by the more rapid fading of the radiation induced signa clean i l r Perspex wit higa h h moisture content.

It is very important to note that, although a dosimeter may be equilibrate desirea o t d d moisture conten y conditioninb t g under well defined humidity and temperature conditions, any consequent change in temperature will lead to a change in relative humidity and in the moisture content of the film. Thus even though dosimeters may be equilibrated and sealed at an optimal value of moisture content any consequent change in temperatur dosimetere th f o e r examplfo , e during irradiation, will alte moisture th r ey ma conten e fild th an m f to perhaps also alter the dosimeter response. This sort of effect would not occur in systems used in a dry state when a drying agent was included in the sealed dosimeter package. nylon-basee th n I d radiochromie th n i e fild dy cman cellulose-triacetate film the moisture content dependent dose-rat et bee effecno n s founha t dost a d e rates normally encountered in electron beam irradiations.

Experience has shown that the conditioning of thin film dosi- meteconstana o t s t moisture content leada significan o t s t improvemen precisionn i t .

Effec) e f ligho t t

Some dosimetry systems, such as the radiochromic dye film and liquids e ver,ar y sensitiv o ligh t ed mus an te protecte b t d from light exposure. Som emade b film en ca whics e lesar h s sensitive to light exposure.

The alanine and the ethanol-chlorobenzene dosimeters are both effected by post-irradiation exposure to intense near ultra

23 violet light although normal handlin daylighn i g t doet sno hav ea significan t effect.

Any errors in dosimetry arising as a result of light effects can, when recognized, easily be completely avoided.

4. Dose intercomparison studies

a) High- and medium dose range

- 1977 Preliminary intercomparison: 5 systems for 1-10 kGy, and 4 systems for 5 - 100 kGy

- 1978 Comprehensive intercomparison: 4 systems for 1-10 kGy, 4 systems for 5 - 100 kGy

Conclusion: Considerin e facth gt thae studth t y includeo tw d variables, namely, both dosimeter systems and irradiating laboratories the results were encouraging. The dose estimatio s generallnwa nominayf o withi% 10 l£ nj doses .

- 1980 High-dose pilot study 4 systems for 5 - 100 kGy

Irradiatio commerciat na l facilities under specified conditions in a fixed geometry in a phantom. Each issuing laboratory sent dosimeterestabliso t L NP o normalizina ht s g calibration entirelt no e stud Th s . ywa y conclusive, partly because of inability to take into account environmental influenc dosimeten eo r response. Consequentl yresearca h study was initiated.

- 1981 High-dose research study

e fouTh r dosimetry systeme 198th 0f studo s 2 wels a ys a l additional systems were irradiate L wite followinNP th ht a d g variables controlled: dose, dose-rate, irradiation temperature, post-irradiation storage temperatur d timee an e Th . experiment was based on a factorial design allowing all combinations of the influence factors to be subject to an analysi variancef o s .

24 The initial dose estimations were reported without knowledge of the environmental conditions. Revised estimates were given by the laboratories on the basis of information of these factors.

Conclusion e researcTh : h study showe importance th d e th f eo use of corrections for irradiation temperature for all systems studied, as well as the need for adequate sealing of solid system preveno t s n influencta humiditf o e d gasesan y .

b) Low-dose range

- 1980 Preliminary intercomparison 6 systems for 0,01 - 3 kGy

Conclusion: Not all systems proved useful for mailed dose intercomparison system3 t ,bu s showed promis werd ean e con- sequently further tested in in-plant irradiations.

- 1981 Low-dose range pilot intercomparison 5 systems for 0,01 - 3 kGy

e studTh y showe neee normalizatior th dfo d systee th f nmo calibration a commo o t s n referenc alst i od emphasizeean e th d neer propefo d r sealin f dosimetersgo .

e besTh t results were obtaine alanine th y db e dosimeter system.

These results demonstrated that alanine/ESR would providea single dosimeter system capable of operating correctly throughout bote low d th high-dosh -an e ranges, a-significant simplification for the dose assurance service.

- 1982 Low-and medium-dose intercompariso back-uf no p systems 5 systems for 0,01 - 10 kGy

NPL normalization was foreseen, but was not carried out.

Dosimetry systems used in the intercomparisons, see Table, page 11.

25 The successful operation of a reference service on a worldwide scale makes heavy demandperformance th n dosimetre o s th f o e y systems. They must have a high level of pre- and post-irradiation stability in order to be reliable over a period of some months d als,an o have freedo abilitme th fro r correco mo t y r fo t environmental effects. These intercomparisons have, for the first time, provided a series of tests of performance under realisti d referrean c d conditions.

It must be understood that the selection based on these criteria has led to the exclusion of systems otherwise acceptable under laboratory and facility conditions or under a more limited dose range.

. 5 Related activities

Several activities developing as a direct or indirect consequence of the co-ordinated research programme and the intercomparison exercise spositiva havd eha e interese effecth n o t t shown by many organizations in dosimetry in radiation processing. These activities can be classified under the broad heading of "technology transfer".

e mosTh t obvious direct exampl f thio e s technology transfes i r to be found at the Ris^ National Laboratory at Roskilde, Denmark, in September 1982. This training seminar was attended by 29 participants fro countries9 1 m experte th , s presented lecture d demonan s - stration aspectl al n f o thiso s s dosimetr particie y th fiel d an d- pants were encourage familiarizo t d e themselves with many different dosimetry systeme experimentath n i s l exercises e succesTh . f o s this training seminar has led to a recommendation that it be repeated in the near future.

A good example of the more indirect stimulation of radiation processing dosimetry is to be found in the fact that the requests from processor o standart s d laboratorie r calibratiofo s n controf o l dosimetry measurement e increasingar s numbee th , radiochromif o r c dye film dosimeters being sold commercially for processing dosimetry e ordeth f severao rf o w ilno s thousan monthr pe d d severa,an l

26 organizations scattered around the world are actively involved in establishin measuremene th g t equipmen d technologan t y necessaro t y be able to carry out dosimetry using the L-alanine/ESR system chosen for the IAEA dose assurance service.

One additional activity which deserves a mention here is the fact that the programme has led to several more informal bilateral exchange dosimetersf so , dosimetry systems, calibrationd an s intercomparisons.

27 Ill. SCIENTIFIC PAPERS

RADIATION PROCESS CONTROL, STUDY AND ACCEPTANCE OF DOSIMETRIC METHODS*

B.B. RADAK Laboratory of Solid State Physics and Radiation Chemistry, Boris Kidric Institut Nucleaf eo r Sciences, Vinca, Yugoslavia

Abstract

The methods of primary dosimetric standardization and the calibration of dosimetric monitors suitable for radiation process control were outlined in the form of a logical pattern in which they ar currenn n i industriaeo e tus l scal Yugoslavian i e e reliabilitTh . y of the process control of industrial sterilization of medical supplies for last four year s discussedswa e preparatorTh . ye th work r fo s intermittan electrof o e us t n beam cabln i s e industry were described.

I. REMARKS

The experimental part of this work was supported by the Interna- tional Atomic Energy Agency during past several"year e folth d - ha s lowing working titles:

- Intercalibratio d testinan n f dosimetrio g c system r measurinfo s g large dose n industriai s l processing. - Compatibility and usefulness study of some dose meters for radiation processing, sterilizatio d polymean n r crosslinking. - Low-to-high dose rats transfer of calibration of thin film dose meter r electrofo s n beam process control. By using the criteria and requirements for dose meter-controled radiation processing, mainl r industriafo y l sterilizatio d polymean n r treatment ,a numbe f dosimetrio r c system s beeha sn experimentally studied and intercompared. This work has brought about a complete expe-

Supported by IAEA under Research Contract No 2141

29 pimentai approacs establisheha d an h a systed f calibratioo m d crossan n - -checking, which has proved to be a useful and reliable tool in industrial application f radiatioo s n perforemd durin e pasth g t five years in Yugoslavia. The system is adaptable to changes, invovations, acceptance of new methods, i.e. those which could improve the confidence level of quality control or could simplify the experimental measurements. In the following sections the basic patterns are given, whereas the technical detail d soman s e tabulated result d procedurean s f practicao s l interes e Supplementse giveth ar t n i n .

II. CALIBRATION DEVICES AND PROCEDURES

Calibration measurements of different kinds were the main activi- tie thin i s s work r precis.Fo d accuratan e e calibratio o basitw n c conditions had to be met: (1) an adequate radiation source and irradiation geometry, and (2) a standardized reference dose meter. i (nominakC 0 1 e sourcla th Useactivity s s a edwa ) research radiation facility /1/, having a well characterized circular radiation field geometry, surroundin ga mechanicall m long)yc raise2 o sourc(1 C . d ro e The irradiation positions were fixed in an annular geometry around the _ source rod in a horizontal styrofrom plaque having a density of 15 mg cm These positions were cut in circular sectors in which holes for the dose meter samples were drilled at five fixed distances (plan view Fig.la, elevation view Fig.lb). The closest distance was 18 cm and the most distant one was at 40 cm from the source axis. These distances were o providt choses a e highes th eo s n t dose e approximatelb rat o et y five times higher than the lowest one, the positions in between providing lowese th thf to e dos4 factor d e an rate abouf 3 so e irradiatio , .Th 2 t n rig thus produce a singl n i d e irradiation time, five equally spaced absorbed doses thesn I . e irradiation hole e blacth s k polyethylene capsules (1.7 cm diameter, 7 cm high, 1 mm wall thickness) containing dose meter samples were inserted. 30 r liquiFo d dose meters standar l glasm 5 ds ampoule t snuglfi s y into the polyethylene capsules in the-rig. The ampoules were, without previous washing, wrapped in aluminum foil and baked at 400 C for 2 hours. After cooling the ampoules were unwrapped, filled with the dose meter solutio d flaman n e sealed, e Frick(excepth r e tfo solutio n whics wa h read immediately after relatively short irradiations). For irradiation of thin films with, radiocnromic?dyesv-. approximate conditions for electron equilibrium were made by sandwiching the films during irradiatio nm polyethylen m betwee 5 o tw n r Perspeo e x platesd ,an this sandwich was inserted into the polyethylene capsules in the rig so thae filth tm surface were perpendicula o radiat r l lines froe sourceth m . The red Perspex samples were placed similarly into the capsules without sandwiching, their plastic/aluminum sachets being compressed to fit the capsules. Serie f fivo s e dose metere calibrateb o t s d were usually placed inte positionth o d irradiatean 5 smeasurea o fror t 1 fo md d timee .Th dose for each sample was calculated from the irradiation time and the dose rate for the respective position as determined previously by standard Fricke (ferrous sulfate) dosimetry (see below). This comprised (as an assumption) that the dose meter was not dose rate dependent withi dose th ne rate rati f 1:5 o f les I . s than five samples were irradiated, glass ampoules with water (dummy samples) were placed inte th o unused positions. In orde o standardizt r e absorbeth e d dose e irradiatiorateth n i s n position rige th s n Fricki s e solution (10"2mo 1 T lFe 2+, 10~ 31 NaCmoI" ll in 0.4 mol 1~ ^SO^) was used. It has been established that the "age" e Frickth f o e solution doet plano s a ysignifican ts radia it rol n i e- tio n e absorbancchemicath e irradiatef i th , lf + o ye yielF df o dsolutio n is measured agains n unirradiatea t d one e dos.Th e meter solutios wa n

31 storre a volumetri n i d c flask, usualle dark th e absorbe n .Th i y d dos, D e was calculated from the relation /2/.

D(Gy) = 2.75 x 102 x AA

where aA Is theiabsorfaancy of the irradiated solution against the unirradiated"solutton e relatioTh t n comprises m opticac 1 : l path length, 2195 1 mol~1cm absorptivit , 1.02nm 44 solutio30 t ya n density, 25°C temperature. r checkinFo e rellabilitth g e currenth f o yt practice with Fricke solutio n intercomparisoa n f reading o ne sam th e f o sirradiate d samples * was made with National Physical Laboratory, Teddington, U.K. As can be seen froe Supplementh m below1 t e agreemen,th s vertwa l yal goor fo d five samples; slope of the 45° angle of the intercomparsion curve was 0.0994 and the correlation coefficient amounted to 0.9998.

III. RADIATION STERILIZATION PROCESS CONTROL

Responsibilities and organization of the process control in the routine operation of our industrial plant are reported elsewhere /3/. e presenIth n t studies somewhat more dosimetric aspect e consideredar s . Dose meters to be used for routine process control are calibrated as describe e previouth n i d s section. The e theyar n capabl r monitorinfo e g e absorbeth d dose administere e goodth so t dbein g sterilizee th n i d plant. Two different types of dose meters are used for this purpose; on a well-establishee d understooan d d system (cerium sulfate solution) which could theoreticall cross-checkede b y e othe th a thoroughl - rd ,an y calibrated routine dose meter (dyed plastic, radiochromic solutions, or ethanol chlorobenzene solutions) A .numbe f systemo r s have been studi-

The author is much indebted to Drs. S. El lis and P. Sharpe from Divi- sio Radiatioof n n Scienc Acousticsand e U.Kthe . of ,Nationa l Physical Laboratory for friendly cooperation.

32 d checkeean d d earlie n thii r s work /4/ e finding;th e brieflar s y tabulated below in Supplement 2. The systems which have been accepted for currenthin i se Laboratortus y shal mentionee b l d here. 4+ Cerium sulfate dose meter, consists of an aqueous solution of Ce ion together with Ce in 0.4 mol Itr ^USO, and is used in standard 5 ml ampoules. It has been suggested as a primary standard for the dose region from 103 to5 10 Gy since its radiation chemical yield, G(C3e +), e caob ntrace yielde d th bac f o primaro t sk y radiolytic products hydratee + th wate3 f o y b rdreduces i /5,6/electronse C o e t d.C , hydro+ 4 - gen atom hydroged an s n peroxide forme watern s i di + ,e C whil e th e being oxydized- back to Ce 4+ by OH radicals. This makes that the yield (per 100 eV absorbed) of Ce ion, G(Ce ), amounts to 2.3, which agrees with wha s knowi t n abou e mentionee valueth th t f o s d primary specief o s irradiated water. The prepared dose meter solution can therefore be checke calibrationy b d reasonablG(Ce e founs b i th o e) t f d i ; y close to 2.3 dose ,th e acceptee meteb n r userca fo d . e absorbeTh d dos measures i e a differenc s a d e (decreasee C f )o ion concentration befor d afteean r irradiatione us n ca r thie Fo . on s spectrophotometer at ^ = 320 nm and absorptivity of 5600 mo! 1 requiret i t bu cmelaboratn a s, " e dilution (1:100 f sample)o s before spectrophotometry because of the high absorbance of undiluted solution. An electrochemical potentiometric method /?/ has been however established that doe t requirno s e dilutions. With this metho e potentiath d l difference measure e platinuth n o d m electrodes inserte e unirradiath n i d - terd and irradiated solution is a measure of the absorbed dose. The advantag s thar i ethi fo t s measuremen e irradiateth t d solution froe th m ampoule is used directly, and with our own construction of a potentiometric cell, from a 5 ml ampoule at least 3 alicuots can be sampled (see Supplement 3 below).

33 During the plant operation we intercompared both methods of analy- e C formatiosif o s applyiny b n same g th thee o t dosm e meter samples used to monitor batches of goods being sterilized. Results are presented in Fig. 2 as normalized to the readings of red Perspex type 4043 E used as routine dose meter. Provided the nominal accuracy of red Perspex is about - 4 percent (see next Section), the agreement was sufficient to accept electrochemical potentiometry as an established practic r ceriufo e m sulfate dose meter solutions. During this work a number od details of practical interest has been worke t (preparatioou d d checkinnan f solutiono g , cell construction etc.); they are described in Supplemental 3 below. The Red Perspex dose meter was accepted as a routine monitor. The s use a wa larg( d l d Perspe batcel re e f o hw x r 404AERy b a 3E H guantity was purchased in 1978 and is stored at a temperature of about 5°C). The use of this type of dose meter is well established (net absorption per unit thickness at 640 nm) and shall not be considered here. It is, however, interesting to note that this dose meter, or in particular its batch "E", showed a better reproducibility than might be expected from some careful analysi f dato s a with another batch several years ago /8/. In Fig. 3 the calibration data taken over 4 years period are presented as an illustration of the reproducibility and usefulness. One should note that there were more recalibration measurements, since they are made regularly at least once a year. f intereso s e Icouli ton o nott w do sourc C ho efollo e th wdeca y with this dose meter, whose nominal accuracy limits are no better than percen5 t t date /9/ monitorinf Th .o a g absorbe dirradiae th dos n i e - e producon tio f o nt (syringes e take)ar n over yeae abouon r a tperiod . Th / ewer /3 dwel ey calculatekG l conveyee e timeth on f r o s pe rd from the experimental datpresented an a functioa s a d f timo n e (Fig. 4) .

34 The values fol1 owed the trend that was calculated on the basis of Co half life period (solid line).

Dose meters with radiochromic dyes. Substituted triphenylmethane leucocyanides in solution are radiochromic, i.e. strong coloration occurs whee solutioth n exposes i n o ionizint d g radiation (but also t o ultraviolet radiation and even daylight). They are used in two ways; as solidified solutions in the form of thin films /10J1/ and as Tiquid solution /12, 13/. The intensity of coloration (absorbance per unit thicknes r opticao s l length) versus absorbed dcs calibrates i e d spectrophotometrically for every new batch of solid or liquid dose meters. The samples should be protected against the action of UV or daylight, and thee handlear y d only under incandescent illuminatio laboratoryn i n .

Her e experienceeth s wite liquith h d solutions shal e describeb l d wherea e resultsth s with thin films shall tak ee lateplacth n ri e section on electron beams. For gamma rays the films were used primarily in the radiation sterilization plant during the commissioning measurement r dosfo se mapping, i.e e determinatio.th dose th e f distribuo n - tion withi e producth n x /14/bo t .

Becaus f problemo e s with sealing glass ampoules containin oxye th g - gen-saturated solution /14/, the accepted dose meter was 5 mmol l" pararosaniline cyanide (PCN), 15 mmol 1" nitrobenzene, 17 mmol }~ acetic acid in 2-methoxy ethanol, air-saturated. In the-dose range up to 10 kGy the dose-response curve slightly bends sublinearly (Fig.5), as reported before /12/, whereas in the lower region, up to about 1 kGy, a straight line is a good approximation (Fig.6). This dose meter has shown a good reproducibility in preparation. The solutions which were prepared during several years showed abou e samth te sensitivity (Table 1.).

This dose meter is in current use in the industrial sterilization plan r monitorinfo t g some short-term irradiations (lower absorbed dose)

35 and for mapping the absorbed dose distributions within the total load in the plant /14/.

Ethanol-chlorobenzene dose meter. The solution of chlorobenzene in ethanol, when exposed to radiation, yields HC1, the concentration whicf o bees ha hn take measura absorbee s th a n f eo d dose /15/r Fo . routine use in radiation processing the non-destructive fast method of oscillometric measurement /16/, based on the change of dielectric constant of the solution as a function of the HC1 concentration, ap- pearemore b eo t sattractiv e analytical method thae morth ne tradia- tional (and more accurate) titration of Cl~ ion /15/. Since the solution is stable for years, if not exposed to the direct sunlight, the ampoules are "memorizing" their values of absorbed dose. There is apparently no temperature .dependence of response. For these reasons they are usually kept in case of complaint or uncertainly sterilized goods. The dosimetric solution consists of ethanol containing 25 percent chlorobenzene, and approx. 4 percent of water and acetone. The ampoules containing this solutio e seale- e drawear nd la kepth an dn r i to r boratory closet. Usually ever w batcyne calibrates i h e numbeth s a rd of scale divisions of the pointer on a given sensitivity setting of the oscillotitrator (response) agains e absorbeth t d dose. Some ampoules from this calibration series are then kept for recalibration of the instrument before use. Ampoules must be checked for cylindrical symmetry and must not be tuched by bare hands. Besides the ease of measurements and "memorizing" the measured values, the advantage of this method is that the dose meters are easily produce y chemicaan n i d l laboratory. The method -was tested first by irradiating ethanol chlorobenzene dose meters froe Institutth m f Radiatioo e n Technique Technie th f o s-

36 * cal University, Lodz, Poland and sending them back for evaluation. e lineaTh r regressioe th f no analysiy e regiokG th 0 5 n i nso t fro 0 1 m nomina le dose th dose sd san foun e readin4 sampleb d1 e Lodzn th gi s , showe vera d y good -intercomparison agreemen 5 slop(4 t 0.955= m e , correlation coefficien 0.9986= r t , intercep 0.003)= b t . Testing was also done in the Vinca plant operation during sterilizatio a numbe f o nf batchero a batc( s h consiste f approxo d m 5 3 . goodsf o f syringe)o d needlesan s e result.Th s with ethanol-chlorobenzen e intercomparear e d wite potentiometrith h c reading f cerico s - -cerous system, the latter values taken as 1.00. As seen from Fig. 7 th emose deviationth t r parfo te withiar s 5 percent t n . Since th e accurac f oscillometryo beet no n s claime ha ybettee b o t dr tha3 nt percent, the ethanol-chlorobenzene üose meter is qualified as a reliable routine monito r radiatiofo r n processing. It shoul e noteb d d that the"errergy dependenc f responso e e .for both cerium sulfate and ethanol-chlorobenzene dose meters was reported /17/. The effect of this dependence expected in the degraded spectrum of gamma rays could hardly be noted in industrial radiation plants, because the contribution of this spectrum to the total absorbed dose is rather low.

IV. ELECTRON BEAM PROCESS CONTROL

In most electron beam processing, standardization of both electron- -faeam parameters and the absorbed dose as well as its distribution with- e irradiateith n d materia f majoo e rar linterest . Because relath f -o e tively short rang f penetratioo e f electrono n d higan s h dose ratese ,th

The author is friendly thankful to Dr. W.Bogus from the Technical Uni- versity of Lodz for this cooperation, and to Ors. V.Stenger and A.Kovacs froe Isotopth m e Institut Hungariae th f o e n Academ f Scienceso y , Budapest, Hungary.

37 choice of dosimetric systems, both for calibration and for monitoring, is generally more restricted than in the case of gamma radiation. e maith n On f o eobjective f thio s so establis t stud s ywa a path - tern of experimental methods to serve for standardization and process control at the 1.5 MeV 80 kW electron beam power dynamitron, the instal- latio f whico n s presentli h s finait l n e i ycablstag th t ea e factorS IK y Svetozarevo, Yugoslavia (UNDP Project YUG/78/007). r standardizatioFo electroe th f o n n beam parameters ,caloria - meter of the type similar to our earlier construction /18/ shall be used on line. This system is well established and does not need ex- tensive experimental checkin d studyan g . r absorbeFo d dose measurements within the_.irradiated material, thin film dose meters are for the present the only acceptable choice. Since the dose response of the thin1 films containing radiochromic dyes /9,19 bees /ha n e independenshowb o t ndose th e f to rate , they offere e advantageth d f simplo s e calibration calibratee .b The n yca d in a Co gamma field, at a lower dose rate, against a reliable reference dose dose-effece meterth d ,an t curve obtaine e directb n ca d- ly applicable in the high intensity electron beams as long as humidi- temperaturd tan y e effect correctee sar d for. Some more recent findings /4,20/ suggested thatat lower dose rate measurabla s e dose rate effect appears wit e filmth h s basen o d nylon. A typical diagram indicating this effect is given in Fig. 8. It illustrates what we found in a number of experiments; at very low dose somewha) rate ~ h sy t(belokG lowe5 0. w r respons obtainee b n ca e d par- ticularl e dosth ef i ymete maintaines i r t relativa d e humidity less than 50% e effec.Th t disappears practicall dose th e r ratefo y s higher t virtuallI . h yy doskG t exis tha5 no e 1. nt wite filmth h s based on polyvinyl butryrol (PVB s showa ) Fign i n wher9 . e datth e a wite th h dose rates ranging from 0.3 to 30 kGy h were collected (irradiations

38 were performed at the Boris Kidric Institute, Vinca, Yugoslavia, 1982, ant Instituta d f Isotopeso e , Budapest, Hungary, 1981). Calibrated thin PVB based films containing radiochromic leuco dye precursor hexahydroxyethyl pararosaniline cyanide, calibrates a d described in Section II, are adequate for measurements in the electron beams (nominal uncertainty limit percent)0 1 t salss i ot I .recognize d that this methoessencn i s i d e differential (sinc e unirradiateth e d blanks can have optical absorbancies themselves) and every point has to be measured with a number of samples in order to diminish deviations e cas th e f valuesradiochromi eo n th i f o s A . c liquids, these filme ar s also sensitiv V lighU d shoulo an t e d onl e handleb y d under incandescent, preferrably lower intensity, illumination. Some experienc s alsha e o been obtained wite thith hn film f bluo s e cellophane, a dose meter which is in routine use in radiation processin mann i g y place worln i s d (but als e wheron o e commercial suppliee ar s currently uncertain except perhaps in Japan /21/). In general dosimetry references /22/ a rather low accuracy is attributed to this system, and some more recent studies have attempted to explain it by the hydrophy- lic properties of cellophane /23/. Some other authors, however, have claimed that an accuracy ± 2 percent can be achieved with blue cellophane /24/. By investigatin a numbeg f differeno r t product e founsw d /25/ that mos f theo t m polariz e lighn effecth a et - ye t t no whic s ha h been reported for blue cellophane films. Therefore, if one uses a spectrophotometer for reading the films, two calibration curves can be obtained, as illustrated in Fig. 10. Each piece of film shows two different value f rotatei s d e abouanalyzin th e axi th f to s g light beam by 90°. This finding could possibly contribute to the explanation of relatively high scatterin f resulto g s obtained with blue cellophane. More detailed studie progresn d wili e publishe an b e l w ar s no s d soon /25/.

39 V. FUTURE TRENDS

Absolute calibration of thin film dose meters by using calorimetry and the "film stack" approach /18,26/ has been developed although not rigorously prove s yet a nappliet I . s essentiall o beamt y f accelerao s - ted charged particles. The basic idea is a calibration not based on the Fricke solutio d calibratio an o nsourceC a t shoul I .n i n d rathee rb e spot"th don n e ver,"o e th i.e yn i .bea m which wil e used monib l an d - tored in further work. The principle is similar to that applied for measuring absolute G values of liquid systems in high-intensity beams A bea . m segmen1111 t limite y coll-imatiob d d timinan n g (measure- pe d rio f timo r continuousd fo e r numbe,o f pulseo r d integratean s d pulse width r pulsefo s d beam absorbes )i d onc y totalleb y absorbing calorimeter body"an e totalld th the y b ny absorbing stac f doso k e meter films. e beaTh m spots e filmimageth sn o sare"the n analyze d integratean d d and the calibration values evaluated, in the way as described in Sup- plemen below4 t . Application of the fiber optics principle in the dosimetry with radiochromic dyes. Shortly afte e applicatioth r e light-guidth f o n e principle to solutions of radiochromic dyes, as a method of increasing the sensitivity /28/, commercial dose meters of this type appeared on the market /29/e producerTh . Wesr ,Fa t Technology, Inc. designed those dose meters for industrial applications of radiation, especial- r foolfo y d irradiation r experimentaOu . l stud f thio y s systes ha m showed that it can be applied from 0 to 2 kGy in the temperature range from 0 to 60°C, without limitations. It could even be applied up to 20 kGy if both irradiations and readings were made within 48 hours /30/ o ratN . e dependenc f responso e e rangs founth ewa n ei d from 1 to 104 Gy h"1.

40 developmene th wore n Th o k f spectrophotometrio t c analysi- op f o s tically guided absorption spectr f radiochromio a e solutiondy c n i s i s its final stage and is prepared for publication /31/. What has already been determine s thai dy usinb t e opticath g l wave-guide principln i e a spectrophotometer with the radiochromic dye solution as light trans- mitting liquid cor n increasea sensitivitn i e a facto y b ymorf ro e than 100 can be achieved, and in fact doses as small al 0.01 Gy can be measured with approximate uncertainty limits of ±10 per cent.

41 SUPPLEMENT 1 Intercomparison of the Readings of Irradiated Fricke Solutions

In positions 1 to 5 of the calibration rig at Vinca four series of samples were irradiated for the same period of time (5.0 minutes). Three series were measure Borit a d s Kidric Institute, Vinca, whereas th r analysise fo fourt L s senNP e result hwa o .Th t f readingo s d san their linear regression analysis are given in Table SI below.

Table SI. Afasorbancies (£A) of the Irradiated Solutions (normalize 25°Co t d )

??on~ BKI Vinea (x) NPL (y) Nominal - . - ~ - - Dose (Gy) ber>1 5er'^ ber'J 2SK Ser.4

1 15.4 0.688 0.668 0.663 0.673 0.669 2 12.3 0.539 0.538 0.534 0.537 0.539 3 9.8 0.430 0.428 0.437 0.428 0.434 4 6.3 0.275 0.278 0.272 0.275 0.280 5 3.4 0.151 0.151 0.148 0.150 0.149

y =• mx + b m = 0.994 b = 0.0043

0.999= v /S 8 s m r= x y where S x and S y____ are standard deviations = an t (N-2)/(1-rd 7 8 )= wher numbe- N e f correspondino r g points

42 SUPPLEMENT 2 Intercalibratio d Testinan n f Dosimetrio g c System r Measurinfo s g Large Doses in Industrial Radiation Processing

Dosimeter Methof o d Préparation Dose Nominal Remarks Measurement Range (kGy) Precision Limits Red Perspex Spectrophoto- Commercially 10-30 % 5 t Suitabl r shipmenfo e t withi days2 n - .Re metry 640 available check calibration every 6 months. Slight bleaching after irradiation. Radiochromic Spectrophoto- Commercially 5-50/60m 5n i 3% Suitable for precise dose mapping; Dye Films metry 605 and available 20-100/51m 0n mailing intercomparisons. Check calibra- m n 0 51 tion every 3-6 months. ÜV light and humidity sensitive (below 50 over 80%) Fades at temp over 60°C. Oxalic Acid Acidimétrie Prepared solution 15-1000 ± 8% Robust dosimeter. Aqueous titration poured into ampouled an s For i \0% accuracy no need for calibra- sealed tion. Ceric-Cerous Potent iometry Prepared solution 10-50 t 4% "Theoretical" dosimeter/traceable to Sulfate poured into ampoules basic values. Stabl kepf i e t away from Solution and sealed sunlight. Radiochromic Spectrophoto- Prepared solution 0.1-2.0 t 5% Each new batch needs calibration. Easy e SolutioDy n metry 550 nm poured into ampoules o handlt measurd an e f kepi e t away from (Pararosani- and sealed daylight. Irrad. temperature increases line cyanide) the yiel 0.5%/°y b d C Ethanol- Oscillometry Prepared solution 1-400 i Robust syste kepf i m t away from sun- -Chloro- poured into ampoules lignt. Stable and gives nondestructive -Benzene and sealed measurement. "Keeps the measured value" for years.

-t» W SUPPLEMEN3 T Cerium Sulfate Dose Meter Preparation, Checking, and Potentiometric Measurement

The ultimate dosimetric reaction in this dose meter (aqueous solution 4+ 1 of Ce ions in 0.4 mol I" H2S04) is

(S.3.1)

This net change is actually the consequence of reactions with the primary products of water radiolysis

4+ 3 1 + ce - e ———aq * Ce *H"= " (S.3.2.) x ' H + Ce4*———y Ce3+ + H+ (S.3.3.)

OH + Ce3+———* Ce4* + OH" (S.3.4.)

4+ 3+ H' 20+ 2Ce2 2 0 (S.3.6. »—-+ +* 2H 2Ce) +

e yiele C thereforTh f o d e amounto t s

3+ G(Ce 6)H + 2G= Q (eG ) H2U ^H - + 2 (S.3.6.)

Since 6g- = GQH = 2.8, GH =' 0.65 and GH Q = 0.8, one expects the net value G(Ce3+) ^2.25

Therefore a prepare f ,i d dostmetric solutio f ceriuo n m sulfata n i e gamma radiation field shows the G(Ce ) value between 2,25 and 2.30, the dose mete traceabls i r o independent e t established value f radiolysio s s of water and can be used as a primary reference system.

Preparation and checking the dosimetric solution. Since the solutions e rathear n rio sensitivf pur o e C e o impuritiet e 4+ d als an o daylightst o ,

44 e solutio addes th i o som t d o diminis e t neC h these effecte s th /2/ r .Fo absorbed dose region from 5 to 50 kGy good results are obtained with the solution where [Ce4J = [Ce3! = 10~2 mol l"1. The Ce + salts usually do not dissolve quantitatively even in 0.4 mol

1~ H2SO«. The easiest way to prepare the solution is therefore as recom- mended by Bjergbakke /2/, by weighing the double weight of Ce4 + and

reducin e halC e wit stoichiometrie on o gft th h c quantitn i Hf yo s 2 0(a 2 eq. S.3.5). Our experience showed that, upon long storage shelfth come n eo ,th - mercial Ce * salts are often partially changed (probably reduced to Ce ), and that simple weighing can be misleading (the error could amount to more tha percent)0 1 n e preparatio.Th dosimetrie th f o n c solution should therefore commence with checkin e C - qualite salte il th g th s ,a f yo lustrated by an example.

1 Ce(S04.0f o l 4g mo 4)4 2-4H0. l s dissolvem 20 wa 0 10 n i d s thewa n assumee e C b f o o t d 1 l mo 0 1 e Hth 2 S0d an 4 prepared aliquotl m 5 . f thto s s solution were then measured into five 50 ml volumetric flasks. To these flasks 0, 1, 2, 2 -1 3 and 4 ml of 5.3 x 10 mol 1 H202 solution (standardized by permangamometry that very day) were added, after which 1 they were Hfille2l~ S0 l 4

45 sale Onctrue th tth e n e i established quantit* e C f o yapproe ,th - priate double quantity for e.g. 2 liter solution is weighed, dissolved ~ e calculate^SO1 th l d mo .an 4 d0. i nstochiometri f o approx 1 5 1. . c addes i o reduct damoun O e halH f Ce^th ef o f to + ion e solutio.Th s i n then shaken occasionally during 5 to 6 hours to expel 1 oxygen, and then the flask is filled to the mark. After 7 to 10 days storage in the dark, the dose meter solution is pipetted into the ampoules which are then flame sealed and kept in the dark until use. The next checking of the dose meter is the determination of its value) G(Ce . Several ampoule irradiatee sar d with different dosed san measured spectrophotometrically after being diluted to 1:100. G(Ce +) is determined change froe slopth th mconcentratiof f eo o absorbee th s v n d dose. For routine dosimetry, potentiometry is used rather than spectrophotometry. The concentration cell (Fig. S.3.2) is in principle the same describes a r previouou n i Matthewy b dr so pape / s/? r /4/ thin .w I ne s e sintereversionth e us d ,t glashoweverno d o separatt sdi e ,w e unirradiated from irradiated solution. Now the container for unirradiated solution ended in a narrow neck into which a ptece of knotted fiberglass is pres- sed. This piece is easy to exchange which is of a great help by cleaning s onli e e measuremendeviceyl m th th needed5 r 1, Fo . o t , 1 ti.e . froa m ampoull m 5 e three sampletakee b fro. e measuren in nth m sca d potential difference betwee platinue th n m electrodes e absorbe,th d dos calcus i e - lates a d 9650 _____ D/kGy = G(Ce+Jx p ) x'antilog (AE/59.16\ )

where p is density of the solution (1.027), G(Ce3+) the 100 eV yield as measured during the checking of the solution, [Ce"'"f] and [Ce J the initial concentration e measureth E A dd an spotentia l differenc millivoltsn i e e Th . equation (S.3.7e programmeb n )ca d inty programmablan o e pocket calcula-

46 tor which has 40 or more program keystrokes. In Fig. S.3.3 the results of a calibration of AE vs the absorbed dose is presented. The solid line is a theoretical curv epredeterminee baseth n o d initiad dan G(C) + le concentration f eeriso cerou d an e s ione agreemenTh . f experimentato l results is this case is therefore a check per se, since it means also an agreement wit n independenha t quantity i.e. RT/nF thin whici ss i hcas e (n=1) .59.16mV molae constants th rga s ( i R temperature- ,T numbe- ,n molesf ro Fara- ,F - day constant).

SUPPLEMENT4 The "Film Stack" Calibration Metho r Thifo dn Film Dose Meters

The principle of the "Film Stack" method for caTibration of thin film dose meter rathes i s r simple .A collimate d radiation bea s incideni m n to a totally absorbing stack of film dose meter to be calibrated. An equal amount of radiation energy is measured by absorbing it fn a calorimeter same placeth e t placea d e ford intensit.Th an m f coloratioyo e th f o n beam spot is then analyzed throughout the depth of the stack and the absorbance compare calorimetrfcalle th o t d y measured energy. Assumin lineaa g r respons coloratiof eo e absorbeth o t n d doser ,fo the i-th film in the stack one can write

i A£ ' — s 4 1 ^I'K-OTT ' M i- ( - ' > where AA~- = average absorbance of the i-th film (JL. - radiation energy absorbed by the i-th spot pV.. - mass of the film under the spot K = calibration constant e relatee e b stac totaspotl - th th n al ab n lo kca i s t d r fo A A f o m su e Th sorbed energy as obtained by calorimetry (E calorim)

ZVi| Ai = EAEi = E Calorim (S.4.2)

47 Due to the inhomogenelty of the beam itself, and particularly due •to the scattering, the beam spot increases with the depth. The beam image, and therefore the dose distribution across the beam profile and particularly near the edge of the beam spot, ts not sharply defined. The cross sectio f beao n m image, however n everaga s ,ha e optical aBsorbance that can be averaged as follows

-7- _ jj dxdy i /; x y

which gives

Obviously, the main experimental problem is to find the Mi values as define. (S.4.3)eq y b de possibilitie .Th thio d so t sexperimentall y are considered in two typical examples.

a. Circular collimation In the case of an inhomogeneous beam with an axial symmetry, e.g. pulsed electron 'beafiela f o md emfsison (Febetron) accelerator ,cira - cular collimator fs centered at the beam axis. In a film stack such a beam will produc seriea e f circulaso r spots e diamete,th f whico r- in h creases with depth. Eq. (S.4.3) then has the form

R, R, n %(r)f ZTT ? rdr- ' ——————— =—^-7 A,(r r )rd (S.4.5)

. an(S.4.4eq d )

i 2Al caloriTE = A fr Crmrd ) (S.4.6)

48 where M-(r) absorbant- i-te hth f functioa fileo radiu s s a mit f so n (of the spot) R s - radius of the i-th spot thicknes- Al e i-ti hth f sfilo m - fil p m density

b. Rectangular collimation

case If scanneth no e d electron beams (e.g. accelerator r indussfo - trial applications) one may assume a relatively constant dose rate at t the position of irradiation throughout the complete beam scan. This per- mits another approach to the problem. Instead of a stack of films, one single film can be used if positioned obliquely in an appropriate material thick enough to absorb totally the electron beam energy as shown in Fig. S.4.1. One can see that 1 = x sin a, by which the conversion fro file e lengts measureth th m(a m f o h d froe positioth m n where film absorbere th absorbee stickf o th t o )t sou r thicknes e mades i th s s .A depth increase e absorberth n e fili s th e spo m,th n o tbroadens - il s ,a lustrated injFig. S.4.2. The same figure is then redrawn as a function of the true thickness, i.e. it Is contracted by 1 = X sine«, By assuming a linear broadenin spoe th t f wito g h depth average ,th M ove e f o erth whole rangs i e

l [ AA(1d ) ) al + (AYo ——————————————= M — (S.4.7) R (AYo + al) d!

where AYo is the minimum of the spot width and a its broadening coefficient; R is the maximum range of electrons. Since the absorbing volume file th m f amounto o (agait s n) a reducen si y b d R

Alft \ (AYo + al ) dl " S.4.8)

49 average th s wheri e Q thickneseAl e filme th th e equatio n ,th f i o s ) (4 n present case takes the form

E calorim = -|- AlQ AA(1) (AYo + al ) dl (S.4.9) o

Experimentally, this means that the aösorbance of the film is analy- d alon ze s length thes it gi nd ,presentean x sina) functioa = s 1 a d.( f o n The constan derives f ta d frospoe th mt image given functioa I s . na 1 f o n the case of undefened- edges of the spot, its optical density profile can be analyzed at right angles to the length at several places, the effective widths being thus approximated. This method has the advantage of saving time and the film dose meters.

REFERENCES

Draganid. I Rada. 1 B .d an k : 60"ThC C2k oe Radiatione th Uni f to Boris Kidric" Institute at VinCa", Bull. Inst. Nucl. Sei. Boris Kidrie, JJ3 7 (1962),7 . 2. Manual On Radiation Dosimetry (Holm N.W., Berry R.J. Eds.) Mar- Dekkerl Yoree w k,Ne ~ (1970). Markovic". V . 3 Radak. ,B Konstant!"novié. ,J Arandjelovic". ,M : "Ope- ratio Servica f no e Facilit r Industriafo y l Sterilization", Rad. Phys. 1/2 . 5 (1983)Chem.No 28 , , ,.22 4. B. B. Radak: "Evaluation of Several High-Level" Dosimetry Systems in Routine Use" in High-Dose Measurements in Industrial Radiation Processing" IAEA Tech. Rep. Serie . 205sNo , Vienn (1981)1 10 a . 5. A. 0, Alien: "The Radiation Chemistry of Water and Aqueous solutions Nostrann Va " Reinhold- d , Princeton J (1961),N . 6. I. G. Draganic" and Z. D. Draganic": "The Radiation Chemistry of Water" Academic Press, New York and Lonodn (1971). 7. R. W. Matthews: "Potentiometric Estimation of Megard Dose with the Ceric-Cerous System", Int. J. Appl. Rad. Isot., 23^, 179 (1972),

50 8. T. A. Olejnik: "Red 4034 Perspex Dosimetry in Industrial Radiation Sterilization Process Control", Rad. Phys. Chem. J£, No. 3-6, 431 (1979). Chadwick . H McLaughlin. Ehlerman. L E . K . . W A . d 9 . ,D an n , "Manual of Food Irradiation Dosimetry", Tech. Rep. Series No. 178, IAEA, Vienna (1977). McLaughlin. L 10. .W Miller. ,A . FidanS , . Pejterse,K Batsber. W d nan g Pedersen, "Radiochromic Plastic Film Accuratr fo s e Measurementf so Radiation Absorbed Dose and Dose Distributions", Radiation. Phys. Chem. JO, 119 (1977). 11. W. L. McLaughlin, J. C. Humphreys, H. Levine, A. Miller, B. B. Radak an. RativanichN d : "The Gamm y ResponsRa a f Radiochromieo e Dy c Film Different a s t Absorbed Dose Rates", Rad. Phys. Chem £ 987(1981).J . Kosanid. M 12. . NenadovidM .T . ,M Radak. B Markovi. M . ,B . ,V d an d W. L. McLaughlin: "Liquid Radiochromic Dye Dosimetry for Con- tinuous and Pulsed Radiation Fields Over a Wide Rlange of Energy Flux Densities", Int. J. Appl. Rad. and Isot., 28, 313 (1977). 13. N. Rativanich, B. B. Radak, A. Miller, R. M. Uribe and W. L. Mc- Laughlin: "Liquid Radiochrmic Dosimetry11-, Rad. Phys. Chem., ,18 1001 (1981). McLaughlin. Radak. L MarkoviB . M 14: . W B . , V d an d : "Dosimetrr yfo Commissionine th Versatila f o g e Irradiation Plant", Rad. Phys. Chem., J4, 449 (1979). 15. I. Dvornik, 1). Zee, F. Ranogajec: "The Ethanol-Chlorobenxzene Dosimeter as a New High-Level Dosimetry for Routine measurements" Food Irradiation (Proc. Symp. .Karslruhe 1966), IAEA Vienna 61 (1966). 16. FoldiakG . . Horvath,Zs Stenger. ,V : "Routine Dosimetr r Highfo y - -Activity Gamma-Irradiation Facilities", Dosimetr Agriculturen i y , Industry, Biology and Medicine, IAEA .Vienna, 367 (1973). 17. A. Miller and W. L. McLaughlin: "Calculation of the Energy Depen- denc f Dosimeteeo r Respons o Ionizinet g Photons", Appl . IntJ . . Radiât. Isot. 33, 1299 (1982). 18. Radak .B Hjortenber, E . Holm. W ,P . CalorimeteA N " : d an g r fo r Absolute Calibration of Thin Film Dosimeters in Electron Beams, Dosimetr Agriculturen i y , Industry, Biolog d Medicinean y , IAEA, Vienna, 318 (1973).

51 19. W. L. McLaughlin, J. C. Humphreys, B. B. Radak, A. Miller and T. A. Olejnik, "The Response of Plastic Dosimeters to Gamma Rays and Electron Higt sa h Absorbed Dose Rates", Radiation. Phys. Chen£ j u 533 (1979). . GehringerP . 20 . Eschweile,H . ProkschE d ran , "Dose-Rat Humidid ean - Effecty Gamma-Radiatioe t th n so n Respons Nylon-Basef eo d Radio- chromic Fiber Dosimeters", Int. J. Appl. Radiât. Isot., 3V.595 (1980). McLaughlin. L 21 . .W Miller. Urib. A M d . ,ean R : "Megaray Dosimetry Minitorinr fo Verf o g y Large Radiation Doses)" Radiât. Phys. Chem., 22, 333 (1983). Pikaev. K . A :. "Dosimetriy22 radiacionnov a i khimii", Nauka, Moscow (1975 Russiann )i . 23. P. Gehringer, E. Proksch and H. Eschweiler: "The Gamma-Radiation Respons f Blueo e Cellophane Films under Controlled Humidity Con- ditions", Int. J. Appl. Rad. Isot., 33, 27 (1982). Okuda. S . Fukuda. ,24 K OkabeTabat. . ,T S d aan : "Influence dy a f eo Film Dosimeter Inserted in a Solid on Electron'Behaviour and Dosi- metry", Nucl. Instrum. Methods, Phys. Res. 200 3 (1982),44 . 25. B. B. Radak and W. L. McLaughlin (prepared for publication). . MilleA . 26 r (see contributio o thint s Proceedings). 27. B. B. Radak, M. M. Kosanid, M. SeSid and W. L. McLaughlin: "A Calorimetric Approac e Calibratioth o t h f Liquio n d Dosimetern i s High-Intensity Electron Beams" Biomédical Dosimetry, IAEA, Vien- na(1975)3 ,63 . 28. S. Kronenberg, W. L. McLaughlin and C. R. Siebintritt: "Broad- -Range Dosimetry with Leuk e OpticaDy o l Waveguides", Nucl. Instrum. Methods, 190, 365 (1981). 29. K. C. Humpherys, N. 0. Wilde and A. D. Kanz: "An Opti-Chromic Dosi- metry Syste Radiatior fo m n Processin Food"f o g , (Transactionf so the 4-th Int. Conf. on Radiation Processing, Dubrovnik, Yugoslavia Markovid. - 1982V . Ed , ) Radiât. Phys. Chem. 2_2 . 3/5,No , 291(1983). 30. B. 8. Radak and W. L. McLaughlin: "The Gamma-Ray Response of 'Optichromic* Dosimeters", submitted for publication in Radiât. Phys., Chem. (1983). 31. B. B. Radak, W. L. McLaughlin and M. G. Simic (prepared for publication). 52 Tabl . Sensitivitie1 e N DosPC ee Meteth f o rs Solutions being prepared within a 3 years period

_ , Optical 1 Date path Sensitivity/Gy cm" - Dose Range/kGy length/cm

September Q>5 8>85 x 1Q-4 4 0. - 1

^f er 0.5 9.60 x IQ'4 1 - 1 0.

0 1. d an 5 9.60. °^ 010~x n g 4 1 - 1 0.

2 0. 9.56 10~x 4* 0.1 - 10

* e valuTh e calculated froe initiath m l linear part. /"^>^

so,'Co

(b) Fig. 1. Irradiatio f polystyreno g ri n positios eit foad - an mre n lative to the Co source at the Boris Kidric" Institute irradiation facility, (a) Horizontal cross section, (b) Vertical cross section..S and D denote the irradiate d dumman d y samples when only three - sampleir e ar s radiated.

53 1.05

enUl O ° AO iu 100-â- O A°OC.A A Ö A A * * O A S O O A A o O A A 00.95 c1e0 o in m < 1979 [ 1980 1981

Fig. 2. Intercomparison of cerium sulfate dose meters measured by spectrophotometry ( - o - ) and potentiometry ( - A - ).

10 ZO 30 40 50 ABSORBED DOSE, kGy

Fig. 3 . Calibratio d recalibratioan n d Perspenre datr xfo a 4034 E. Solid line - April 1978, - o - December 1978, - • - September 1980, - A - November 1982.

54 I I I I ! I I \ I 3O

•±5%

MONTHS

Fig. 4. Tren f the.conveyoo d r dwell tim termn i e f experimentalo s - ly monitored dose in kGy by red Perspex dose meters compared wite calculateth h d trend (solid line) basen o d decayo C the .

1.5

0.5

4 6 10 ABSORBED DOSE, kGy

Fig. 5. Calibration of 5 mrnol 1~ solution of pararosaniline cyanide in 2-methoxy ethanol. Absorbed dose range 0 to 10 kGy. Xma x = 550 nm. Optical path length 0.2 cm.

55 1.5

1.0

0.5

8 0. 6 0. 4 0. 0.2 1.0 1.2 ABSORBED DOSEy ,kG

Fig. 6. Calibration of 5 rranol 1" solution of pararosaniline cyanide in 2-methoxy ethanol. Absorbed dose range 0 to 1.0 Optica. nm 0 l55 par= kGyt m (valuelengtA .c 0 1. hs obtaine e higheth n i dr dose rang m cellec wit5 s 0. h normalized to 1.0 cm).

1.05 -O 00 UJ oo e o o o oo O OO 51'-°° o 0 O O OO O OO o o OO UJ o o g 0.95 O ffl

0.90 SEQUENCE OF BATCHES

Fig. 7. Intercompariso f ethanol-chlorofaenzeno n e (oscillometry) readings normalize ceric-cerouo t d s potentiometric dose readingroutine th r e resultefo .Th monitorine ar s f o g the industrial sterilization of single-use syringes and needles b.y 60C«o gamm' a rays.

56 20 40 ABSORBED DOSEv KC .

Fig. 8 . Calibratio thicm nn diagra0 k5 "FWT-60r fo m " nylon film containing hexahydroxyethyl pararosaniline cyanide. ; h y kG 5 1. - Absorbe-4 , h d y doskG e2 rates- • - : - o - 0.4 kGy h" . X _ = 510 nm. ITlamX v

I 40 80 120 ABSORBED DOSE, Fig. 9. Calibration diagram for 50 nm thick PVB based film containin lowea g r concentratio f hexadydroxyethyo n l pararosaniline cyanide. Dose rates rangino gt fro3 m0.

. nm 0 , X 60 ma" h = x y 30kG

57 1.0

< <3

0.5

200 400 600 800 ABSORBED DOSE, kGy

. 10 . CalibratioFig thicm nn diagra0 k2 blur fo me cellophane film "Tocello". The ordinates are differences of absorbance betwee unirradiatee nth d irradiatean d d film e hig.Th h and low values are obtained by rotating the measured film around the axis of the analyzing light beam in spectrophotometer.

0.6

0.4

0.2

I o 4 . a x to'5 12 CONCENTRATION OF Ce !ON, mol-T

Fig. S.3.1. Absorbancy of the Ce ion solution against the nominal concentration. Degre e intercep whico th t e s i h t close to the origin is a "quality control" of the product.

58 Fig. S.3.2. Concentration celr potentiometrifo l c measurement with the cerium sulfate dose meterelectrodest P - - 1 . un - ,2 irradiated solution suction- ,3 irradiate- ,4 d solution, 5 - knotted fiber-glass, 6 capillary.

20 LU O CL

10 20 30 40 50 ABSORBED DOSEy kG , Fig. S.3.3. Potential difference vs absorbed dose. Solid line - calculated, - o - experimental values.

59 e'BEAM Ulliilllll

Fig. S.4.1. Film positioned obliquel n absorbina n i y g material irradiated with perpendienlarly incident electrons.

Fig. S.4.2 e for Th f beamo . m image intensity versu e thicknesth s f o s irradiated material.

60 THE EFFECT OF HUMIDITY ON THE RESPONSE OF HX DOSIMETRY PERSPE RADIATIOO XT N

K.H. CHADWICK Association Euratom-ITAL, Wageningen, The Netherlands

Abstract

Perspex can take up water to 2% of its weight and it takes only 48 hours at 80 °C for saturation of water uptake to occur. At room temperature the uptak slowes i e r althoug accumulatee weighy b b n % 1 htca d within abou4 t days. Humidity levels in perspex might affect the shape of the dose respons es bee curv ha d perspexn s re founea r experimente fo d. Th s reported here show thachange th t dosn i e e respons cleaf eo r perspe hardls i x y affecte wida y eb d rang f humiditieo e s althoug driese th h t e perspeth s ha x consistently lower response. After irradiatio oxygee nth n diffusion controlled fadin dependens i g humiditn to d proceedan y s most e slowlth n yi driest perspex. Treatmen 8 hour4 r s fo f perspe to prioC wate0 n rx8 i t ra to irradiation causes a large deviation in dose response above 15 kGy. This deviatio ascribee b n muca nca o ht d reduced inductio instable th f no e optical density component previously ascribed to a free radical species. concludes Ii t d that humidity changes shoul caust dno y significan ean t cleae th dosimetr rf o perspe e us ye xerro th dosimete n i r n industriai r l radiation facilities.

Introduction One factor, identified by Olejnik (1979) as having an important effect on the dose response of red perspex dosimeters was moisture content. In fact, this effect had been recognised earlier (Whittaker, 1964) and had led routine tth o ed perspe aginre f o gx dosimeter humia n si d atmosphere prior to sealing in the aluminium backed polyethylene sachets for distribution. Olejnik (1979) demonstrates a large difference in the response of red perspex moisturw witlo ha e conten d tperspe re compare e th x o havint d ga high moisture content inducee .Th d absorbancm (optican 0 64 lt ea density , OD) being higher for the driest perspex samples. This paper reports the results of an investigation of the effects of moisture content on the dose response of clear HX Dosimetry perspex. The results indicate thaeffece th t moisturf to e conten a smalle s mord ha t ran e tolerable e doseffecth e n o trespons f cleao e r perspe d confirman x d san expands previous results publishe Barrety . b d(1981) al t e t .

61 Materials and Methods Clear perspex samples were predominantly from Batch 5 HX Dosimetry Perspex having a mean thickness of 1.8 mm although some samples of 1 mm mean thickness from Batc werh3 e also used. Optical density measurements usinm n I spectrophoto 315/31t 5 werI Zeisa ga 30 Q er d sPM madai 4an n i e - meter. Induce valueD O d s (AOD) difference ,th e th ef o betweeD O e th n unirradiate d irradiatean d d samples were correcte thicknesr dfo a o st nominal value of 1.8 mm in the case of Batch 5 and 1.0 mm in the case of Batch 3.

Results and Discussion The results of a series of experiments are presented in figures 1-6. Figur show1 e relative sth e chang weighn ei f Batc to DosimetrX H h5 y perspex samples stored at different temperatures at either 100% R.H., in water over ,o r silica gel resulte .Th s show that 1. Perspex can take up to ^ 2% by weight of water. 2. The uptake of water is strongly temperature dependent. C uptak° 0 8 et A saturate . 3 s after s slightl"8 i hour»4 d san y greater rfo the samples store waten i d r compared with those store waten i d r vapour. 4. Even at 20 c the uptake of water is relatively rapid, a 1% increase in weight takin days4 g^ . 5. Samples taken from the sachets have a relatively low moisture content, only a 0.25% reduction in weight resulting from the drying procedure. Figure 2 shows the relative weight change in Batch 5 samples stored for 1 mont different ha t relative humidit afteC y value0 r2 removat sa l froe th m sachets measuremente .Th s confir rathee packagee mth staty th rdr f eo X dH Batch 5 at ^ 35% R.H. Figure 3 compares the dose response of Batch 5 samples measured at 315 nm both 1 hour and 24 hours after irradiation. The samples were either dried over silica gel, straight from the package, or treated for 48 hours in water at 80 C. The response curve provided with the samples is shown for comparison. The results reveal: 1. The dose response of the dried and packaged samples was very similar, compared well Mrad)2 wit( response hth y ,kG thoug0 e2 curvo t hp eu showing a little less saturation at higher doses. 2. The wet sample, on the contrary, showed an extremely rapid saturation in dose response above 10 kGy (1 Mrad). 3. The difference between the dry and packaged samples measured at 1 hour and 24 hours was small, especially compared with the large fading of the wet samples shown afte hour4 r2 s storag airn ei .

62 Figure 4 presents the results of a more detailed investigation of the dose réponse of Batch 5 HX samples equilibrated for a period of 5 months at various values of relative humidity at 20 C. The relative humidity values chosen R.H.wer% 0 e^ , stored over phosphorus pentoxide R.H% ,33 . (38%), 53% R.H. (55%) (43%)% , 65 (79%) % , 78 (90%% , 90 100d )an %(thH R e values quote nominale ar d , thos n parenthesiei s were determine measurementy b d , the measured value quotee sar d furthe n thii r s paper) e hatche.Th d response curve covers the results from samples varying in relative humidity from ^ 60% to ^ 0% R.H. The driest samples showing the lowest response. No discernable difference was measured for the samples at 43 and 55% humidity. % R.HTh38 e . sample down hatchee middle sra th th n f o ed curveo .N discernable differenc measures samplee ewa th r sfo d varyin R.Hn i g . from dose th 100o et t répons%% bu 79 f theseo e sample d diffesdi r froe resth mt giving a higher response at doses up to 30 kGy (3 Mrad), and a slightly more obvious saturation abov kGy0 e3 e importan.Th t conclusion from this figure is that the response of clear HX dosimetry perspex does not show a very strong dependenc relativn eo e humidity ove rathea r r wide rangf eo values (0-60% R.H.). The dose réponse of cle'ar perspex is relatively insensitiv relativo t e e humidity. Figure 5 shows the results of 'a fading experiment using Batch 3 HX perspex measure 0 rnne result32 .Th t a d s sho dependence wth f oxygeeo n induced radiatioe fadinth f o g n induce D signaO d samplen li s equilibrated at different value f relativso e humidity prio irradiatioo t r 5 kGy2 o .t n The figure reveals that the rate of fading is dependent both on the moisture contene storage perspeth th d f o texan temperature e drie.Th e th r sample the slower the fading. This result confirms the results shown in figurd thosan e3 presente Barrety . (1981)b d al t e t. Figure 6 presents the results of a preliminary investigation to understan dose reasoe th eth d y responsnwh f sampleeo s store waten i d t a r 8 hour4 r sfo prioC irradiatioo t r0 8 n differe radicallo s d y from other samples equilibrated to almost the same moisture content in water at 20 °G or water vapour. Samples equilibraten i r o month5 C ° r wate0 n fo d2 si t ra 8 n hourr equilibratewate4 i o r r , so C rfo vapouC 0 2 wate0 n t 8 i da r t a r air were irradiated to 25 kGy together with samples in the sachets or taken out of the sachets immediately prior to irradiation. The samples were measured afte hour4 2 hou1 rd s an rpost-irradiatio n storage d the,an n were treated at 130 C for 3 min. in air. This last heat treatment post- irradiation has been shown, previously, to eliminate the unstable radical species induceradiatioe th y b d n (Chadwick, 1971) e result.Th s reveae th l following

63 1. No difference was seen between the response of samples irradiated in the sachet remover so d frosachete mth s immediately prio irradiationo t r . 2. The samples equilibrated in water or water vapour at 20 C gave the same response, whic s slightlhwa y higher tha samplee n th tha f o ts irradiated in the sachet, in accordance with the results shown in figure 4. gavr hour8 4 ai sample response a r n Th si fo . e3 C treatee 0 simila8 t a d r to the sample in the sachets. 4. The sample treated at 80 C for 48 hours in water gave a very much reduced respons agreemenn ei t wit resulte hth s presente figurn i d . 3 e These results sho wneithes i tha t watee i t th r r saturatione th r ,no 80 C treatment, but a combination of the 80 C in water which probably e reduceleadth o t sd response. 5. After 24 hours in air the fading of the sachet samples is 1.2%, that of the water equilibrated samples at 20 C is 7%, that of the air heated sample is < 1% and that of the water saturated sample at 80 °c is 16%, confirming thafadine functioa th t moisture s i gth f no e contents i t .I worth noting here that samples store waten i d r after irradiation showed exactly the same fading so that the fading is not connected with "drying out". Afte. 6 heae th rt treatmen eliminato t unstable eth e optical density component, associated with a free radical species, the stable optical density component of all the samples was almost the same. This indicates that the saturation of perspex in water at 80 C prior to irradiation leadmuca o ht s reduced inductio free th e f radicano l species whics hi reponsible for the unstable optical density. This could be checked by electron spin resonance measurement f similarlso y water saturated perspex samples.

Conclusions The most important conclusions which can be drawn from these results for radiation dosimetry in industrial facilities are as follows. e dos1.Th e réponscleae th rf eo perspex dosimete s insensitivi r e th o t e moisture content of the perspex, this in contrast to the situation found for red perspex. 2. The oxygen diffusion controlled fading of the radiation induced optical densit dependens i y moisture th n o t e contene perspexth f to e drie .Th r the perspe e slowe th xoxygee th r n diffusio slowee th fadinge d th r nan . Ver. y clea3 dr y r perspex probably offer optimae th s l for f thio m s dosimeter with e dos respece shapth eth f o responso et t e th curv d an e post-irradiation stability.

64 . Change4 ambienn si t relative humidity during irradiation, eve wetn i n - storage irradiation facilitie temperaturet morr a e o d ear C san 0 4 p su unlikel affeco t y response cleae th t th rf o eperspe x dosimeter d wilsan l t lea dosimetrio no t d c error.

Acknowledgements This pape s publicatioi r n numbe Biologe r lo?th f £o y Divisioe th f no Commissio Europeae th f no n Communities e researc.Th s alshwa o supporten i d part by the Dutch Ministry of Agriculture. The expert technical help of D» Rintjema is gratefully acknowledged.

References 1. Olejnik, T.A. 1979. Radiât. Phys. Chem. 14, 431-447. Whittaker. 2 1964. ,B . AER 336. ER . Barrett. 3 , J.H., P.H.G. Sharpe, I.P. Stuart. 1981. National Physical Laboratory . Repor52 S tR 4. Chadwick, K.H. 1971. Ph.D. Thesis, Utrecht University.

EIGHW % T

102- _ Water/8_ C 0° o———10 RH/S0% C O°

100°feRH/40°C

100°/.RH/20°C

100 100 (h) • — 0 % RH /40 °C

BATCH 5 99-

e relativFigurTh . 1 e e chang n weighi e Dosimetrf Batco X t H 5 h y perspex samples store t differena d t temperature t differena s t humidity conditions.

65 relative change weighn i ) (% t

2.0-

1.5-

1.0-

0.5-

0 10 0 8 0 6 4O H20,8O °C relative humidit) y(% 48 h

-0.5

HX BATC mont1 H5 h storage at different humidities

Figure 2. The relative change in weight of Batch 5 HX Dosimetry perspex samples storemont1 r t differena hdfo t relative humiditiet a s 20 °C.

66 batch 5 results 1 hr 24 hr dry + A 1.0- package o • wet x UK panel

0.8-

0.6-

0.4-

0.2-

dose ( Mrad)

Figure 3. The dose response of Batch 5 HX dosimetry perspex samples measured at 315 ira for samples from the sachet, after drying and after treatment in water at 80 C. Measurements were made at 1 hour4 2 houd s an rpost-irradiation .

67 A OD 1.m 8m

HX BATCH 5 315 nm 1h

1.0-

0.8- 45-6O % R.H.

80-100%R.R- 0.6-

0.4-

0.2-

0 3 0 2 10 40 dose (kGy) e dosFigurTh e . respons4 e dosimetrf Batco X e H 5 h y perspex samples equilibrated for 5 months at 20 C at various relative humidities between 0% R.H. to 100% R.H.

68 HX BATCH 3 320 nm 25 kGy

20 40 storage time in air

0.7-

0.6- ) h ( O 6 0 4 20 storager timai n i e

Figure 5. The dependence of oxygen diffusion controlled fading of the radiation induced optical densitm n f Batc o y X perspe 0 H h32 3 t a x afunctioa s f relativno e humidit d temperaturean y .

69 A OD 1.8mm BATCH 5 315 nm 25 kGy

1.0- A-in package B- out package

C- 5 mths in H2O H R „ "/ 0 mth5 10 - D n i s

E- 48 h in H2O at 80 °C mm F-48h in AIR at 80°C

0.2

1 h post 24h post 130°r Cfo irradiation irradiation 3 min.

Figure 6. The response of Batch 5 HX perspex samples given different pre- irradiatio hou1 d t ran na treatment m n y measure kG 5 31 5 2 t o a dst hour4 2 s post-irradiatio d aftean n post-irradiatioa r n heat treatmen eliminato t unstable th e e optical density valuee .Th s meane th 4 hour2 f thre aso e hou1 t d sar ean r samples erroe th , r bars shoextreme wth e values measured.

70 INTERCALIBRATIO TESTIND NAN BLUF GO E CELLOPHANED -AN CELLULOSETRIACETATE FILMS FOR THE MEGARAD DOSE RANGE

P. GEHRINGER, E. PROKSCH Institut für Chemie, österreichisches Forschungszentrum Seibersdorf Ges.m.b.H., Vienna, Austria

Abstract

The y-radiation respons f bluo e e cellophane film s i dependens n i t a rather complex way upon dose rate as well as on the relative humidity of the air to which the films are under equilibrium. Generally, the response decreases with increasing humidity. Up to about 25 % r.h. an increase in dose rate from 0.23 to 2.3 Gy/s result a respons n i s e increas y 10-1b e r.h. Abov% 5% .6 6 ether e doso n e s i rate t intermediata effec d an t e humiditie a distincs t negative dose rate effec s observedwa t .

Gamma irradiation of CTA films in air results in an absorbance change in the UV region which is higher than for electron irradiation and which is - contrary to the latter - dependent on e wateth r contene filmsth f o t. Replacin argoy b r n ai gremove s that humidity dependenc additionallyd an e e y-responsth , n i e argon becomes almost identical to that found for electron irradiations t I ma . concludee b y d from this, thae dosth te rat- e as well as the humidity effect are in fact oxygen effects. Post-irradiation coloration proceeds after irradiation under argo s wel a ns unde a l s ri cause airt I . d e reactiomainlth y b y n with some reactive intermediates of oxygen diffusing into the films after irradiation.

. 1 Introduction

Several plastic or dyed plastic films are commonly used as routine dosimeters for quality control in radiation processing. The advantages of these systems are said to be their low cost, ruggedness, ease of handling and read-out, availability in large batches and compatibility to many geometrical configurations. The main disadvantages described to be: possible systematic errors due to variation of response with dose rate and/or environmental factor d batch-to-batcan s h variations.

Blue cellophane d cellulosetriacetatan - e (CTA)-film e typicaar s l represen- tative f suco s h routine dosimeter e advantagesth wit l al h d alsan so some of the disadvantages mentioned.

71 Blue cellophane is already used since 1956 (1) and it became one e mosoth f t widel d frequentlan y y used film dosimeters althouge th h results reporte e literatur t th ver no n i yd e consistentar e . According to HENLEY and RICHMAN (1) the dosimeter was observed to be independent of dose rate when applied in a Co y-radiation source. The response produced by a given electron dose from an electron accelerator, however was found to be about 2.2 times as great as that produced by an equal dos f y-radiatioo e d thian ns findin s alswa go confirme y otheb d r . Neverthelessauthor5) - 2 ( s , CHARLESB d WOO ) founan Y (6 D d their electron and y-results almost identical, and also MAKHLIS (7) did not observe any rate dependence. Nearly the same situation occured concernin e influencth g f oxygeno e . Althoug n oxygea h n effecs wa t reported repeatedly (3, 8, 9), DAV1ES and MCQUE (10) could not find any difference e responsth n i r sirradiation fo e s performe n vacuui d m and air. Furthermore, it was usually stated that the precision of the system is rather poor (7, 11 - 13). Possible effects of the moisture e humiditth e surroundinf th o contene film f r th o y (o f so t g atmosphere) have been neglected completely until just recentlye firsth tr timeFo . , LEV1N. (14al t e E) foun a generad l reductio n sensitiviti n r increasinfo y g values of relative humidity, with some degree of instability during post-irradiation storage.

A literature review for the CTA film dosimeter shows almost the same situation concerning the inconsistency of the results. It was introduced first by PUIG et al. (15) who reported an excellent sensitivity and linearity between dose and absorbance when the measurements are . This beenm performeha s n0 confirme28 t a d y manb d y others (16-20) e mosth tw frequentlno s i m n y0 use28 d an wavelengt e evaluatioth r fo h n dosimeterA CT e th of. Although ther e somar e e ) authorusin21 , g(5 s other wavelengths for the evaluation without any evident reason. Due to . (15al PUI t e G )a dose rate dependenc s observewa e d when applying the dosimeter in a Co y-radiation source. The influence of the dose

rate was relatively small at dose rates below about 102 Gy/h, increases remarkable around 5xl0 3 Gy/h and disappears at dose rates beyond 10** Gy/h. Applying dose rates greater tha 0 Gy/1 n o hdosn e rate effect was observed neither for y- nor electron beam irradiations and these findings have been confirmed - at least in principle - by other authors (5, 19, 20, 22, 23). Nevertheless, VERHGRADSK1I (17) as well as JANOVSK It y finrat(18no an d e d )effectdi .

Also two opposite findings exist referring to a possible fading effect. A few (15, 24.) found the response stable within seven days after irradiation although a fading effect was reported repeatedly (5, 18-20, 23). Finally n influenca , f humidito e s observewa y r y-irradiationfo d s (19, 20) but the results given are rather divergent.

The present work was carried out therefore in order to eliminate - s possibla e confusior th afa s - e n produce e divergenth y b d t results reporte e literaturth n i dd moreovean e o evaluatt r e limitationth e f o s both systems for practical use.

.2. Experimental Procedures

Dosimeter systems

The blue cellophane used was DuPont 300 MSC Light Blue with a measured thicknes 6 jim2 e f earlie.o th s Mos f o t r studies concernin e dosimetrith g c propertie f bluo s e cellophane were performed with this, 3 materia , 2 , (1 l 6, 11) and therefore it was selected for the present study although it is no longer manufactured. Moreover, there is now a blue cellophane available ("Blue Cellulose Film", manufacture y Tohcellob d , Tokyo, Japan) which show n absorptioa s n spectrum similae DuPonth o t r t filmd an s both type f filmeo s e supposear s o behavt d e rather similarly.

The CTA dosimeter films used containing 15 % triphenyl phosphate and are commercially available from Société NUMELEC, France. They were supplied in long rolls 8 mm in width and 0.125 mm in thickness.

Preconditionin e filmth f so g

After findin e wateth g r absorption/desorptio f bluo n e cellophane films used completely reversibl e followinth e g procedur r realizinfo e a g well-defined moisture contene dosimeteth f o t r films achievedwa s . Firs e filmth t s were stored abou day0 1 t s over PO^ o t Creduc e th e original indefinite water conten o neat t r zeroe drieTh .d films then were store t leasa de a weeglov x on (volumn ti kbo e e abou 0 liters9 t ) having n atmosphera f exactlo e y known relative humidity obtaine y flushinb d g x witth bo a econstanh r streaai t m (abou 5 1/min0. t ) whic s beforha h e passe a dwate r bath whose temperatur e humidit th s adjuste o t wa e e y du d required. Glove box and irradiation source were in the same room whic s alwaywa h s a constankep n o t t temperatur f 25°Co e . Temperature and relativ er streaai humidit e s welma th s insida f l o ye glov x th e bo e were checked permanently usin a gTemperature/Relativ e Humidity Indicator Model HT-10 from Weather Measure Corporation, Sacrament , USACA o . Comparative tests using saturated aqueous salt solutions for producing different relative humiditie n enclosurei s s were also performed an d

73 yielded completely identical results. Relativ, 45 , e32 humiditie, 25 , 0 f o s wer% e6 8 used d 6an 6, correspondin o moisturt g e contente th f o s films of about 0, 4.1, 6.5, 8.2, 17.0 and 22.2 % by weight. At higher humidities (and even at 86 % r.h., if longer irradiation times had to be used e filmth ) s ten o becomt d e spotty d exacan , t measuremente ar s no longer possible.

Exactly the same procedure was performed for the preconditioning filmA sCT excepe oth fe storag th t e over PO^C Decause desiccatiof o n CTA dosimeter films causes a transmittance reduction. In some experiments argon instead of air was used during preconditioning.

60C„o y-irradiation

An AECL Gammacell 220 irradiator with and without- a 1 : 10.1 lead attenuator was used, the dose rates obtained were about 2.3 and 0.23 Gy/s, respectively. All dose rate calibrations were established by Fricke dosimetry e dosth ,e values give e expressear n n termi d s of dose in water. For irradiation of blue cellophane films five pieces, each separated by 15-»im polyester films were placed between 5-mm * .__.-_. .__® lavers which approximate electron equilibrium conditions.

..._ c..j—— .-...._ — ..— — ~._ ._...... pieces were preconditioned e bluth previousl es a cellophan e samy th wa en i y e e us films e Th . e polyesteth of r e s foilnecessarfounb wa so t d y because unseparated blue cellophane films tend to stick together forming colourless spots at the point of contact especially at high moisture content of the dosimeter films. To maintain the CTA dosimeter films in electronic equilibrium during irradiation packages were prepared by stacking five films between 5-mm polymethyl methacrylate front and back platelets. The polymethyl methacrylate have been preconditioned previously analogous to the dosimeter films. During irradiation all films were thermostate o 25°d t dpermanentl an C y flushed wite correspondinth h g e appropriatth t a s ga e relative humidity.

Electron beam irradiations.

e electroAth s n beam sourc e Electroth e n Processing Facilit t Seibersa y - dorf has been used which is equipped with an ICT-500 electron accelerator supplie y Higb d h Voltage Engineering; mA , 5 Burlington2 - (50V A k 0 US , 60 5 scanner with 122 cm scan width; air cooled 25 km titanium window.)

* PERTINAX vL\/ is the trade-name of a phenoplast laminate with paper as resin a bindedensit4 g/cm d 1. an f ro 3y.

74 All irradiations have been performed under "standard conditionsm c 0 (2 " below exit ° windosca15 n t wa angle ) usin a gspecifi c rate factor k = 15.7 kGy.m/mA min (25). The dose rate at maximum beam current is about 2.7 x 10^ Gy/s.

Only CTA films were irradiated with electron beams. For that purpose five CTA film pieces were fixed to a methyl methacrylate plate, this plate put into a 15-M.m thick polyester tube and then the tube sealed on both sides. This procedure were performed in the glove box where the preconditioning took plac d guaranteean e s identical conditions during preconditioning and irradiation.

During irradiation the maximum temperature of the samples increases up to about 75°C. Accordin o TAMURt go reporte. al (19wh t ) e A d almoso n t 2 temperature effect for irradiations with dose rates above about 3.10 Gy/s no corrections have been accomplished.

Evaluation of the irradiated films.

Two absorption maxima appear in the visible region of the blue cellophane spectru t theimbu r exact position s wela ss thei a l r transmittanceT s are humidity dependent (26). Therefore, all optical measurements referred to in this paper were performed with films only whose moisture content before, during and after irradiation was identical and well defined. Selecting the 655 nm wavelength, a ÄT was determined for. each dosimeter fily subtractinb m e transmittancth g e before exposure from that after exposure e thicknesseTh . e filmth f s o s were sufficiently unifort mbu n anisotropa thers e transmittancwa th e f o y e considereb e o t whic s ha hd whe ne samth measurin ed filan me on beforg d aftean e r irradiation. Wite regardu h o thest d determineD e S fact e th s d from transmittance measurement f fivo s e foils irradiated togethe. % s 5 aboui r1. i t filmA AlCT s l were read spectrophotometricall wavelengthm n 0 28 t a y . The absorbanc f evero e y single s measurefilwa m d - beforexcep d an et when stated otherwise - 7 days after irradiation and all. absorbance measurements related to exposure were expressed as the difference A A between the exposed and the unexposed film. The thicknesses of e filmth s were checke e d sufficientlfounb an do t d y uniformD 3 e Th . determined from absorbance measurements of 5 films irradiated together is about - 1 %.

A GARY model 17 spectrophotometer was used for all the measurements. Only mean values averaged over the five foils irradiated together e reporte ar e resultsth n i d .

75 3. Results - Blue Cellophane

The absorption spectre DuPonth f o at blue cellophane films have been measured under various conditions. From Fig. 1 it can be seen that in the visible region -the absorption spectrum consist a doubl f o s e peak with absorption maxima at about 655 and 610 nm. This has been reported already earlier. e firsHowever s th foun tr wa fo tim dt i , e that with increasing moisture content of the films both peaks are shifted towards longer wavelengths and simultaneously the absorbance of the 655 nm peak increase whey abou% b s 0 n1 t increasin e humiditth g y during preconditioning and irradiation from 0 % r.h. to 86 % r.h.

During irradiation, both absorption peaks decrease in intensity (Fig. 2). In agreement with what was found in the literature (10) the destruction of the 655 nm peak was found to be somewhat faster than that of the 610 nm peak. Between zero and 145 kGy, the change in absorbance e firss highei abouth % r t0 3 fo tpear k compare e latterth o t dA . tentative explanatio r thafo n t behaviou s thai e rbleachin th t g product of the dye absorbs at or near 610 nm and thereby simulates a slower disappearanc peas m consideren wa k5 e 65 ratee d Th .therefor e b o t e more suitabl r dosimetrifo e c purpose peak.m n 0 , s 61 Onltha e yth n the forme s beeha rn measured e followindurinth l al g g investigations.

No true post-irradiation effects coul e foundb d , contrar e obserth o t y- vation y LEV1N. b s(14) al t e E . Provided thae humiditth t y before, during and after irradiation remained identica d constantan l e decoloratioth , n remained stable during post-irradiation storage. Only whe e humiditth n y was changed during that storage a sligh, t chang n absorptioi e n occured, analogou o that s t observe e unirradiateth r fo d d samples (Fig. .1)

Following the most common practice for the blue cellophane system, e experimentath t firs a l al t l results have been plotte s radiationa d - induced transmittance changes A T vs dose D (Figs. 3 and 4). The resulting curves sho wa rathe r unexpected behaviour. Wherear fo s samples conditione t a intermediatd relationshiD e s v humiditie T & p e th s s i mor r leso e s linear, indeed ,o longe n thi s i sr trur morfo e e extreme humidities. At low humidities the A T vs D relationship becomes sublinear, the downward curvature increasing with 'decreasing moisture contene foils th t hig A f .o ht humidities juse oppositth t e effect occurs: the relation becomes superlinear e deviatioth ; n from linearitw no y increasing with increasing humidity.

The varying curvature of the plots may be recognized even more clearly when response values R (transmittance changes per unit dose) are

76 plotted versus dose D (Fig. 5). Whereas for low humidities R decrease with D, for high humidities it increases. At a certain humidity somewhere between 32 and 45 %, the response becomes roughly independent of dose.

e seeb ny Aalreadma s y e radiatiofroth m, 5 Figso t n 3 respons. e at both dose rates studied decreases with increasing relative humidity. Dependin n dosd doso g an ee rate considered this decrease amounts y kG d 0.2 0 an 5 y 3 t (a kG Gy/s 0 5 30 o ta )t ofacto t (a f abouo r 5 1. t and 2.3 Gy/s) over the humidity range from 0 to 86 % r.h. This is fair agreement with the findings of LEV1NE et al. (14). However, this decrease with humidity is not a uniform one. To show this more clearly, the data contained in Fig. 5 have been condensed further by plotting only the response values at 150 kGy (which is roughly in the middle of the dose range covered) versus the relative humidity (Fig. 6). For other doses, plot f similao s r shape should result.

At first sight the two curves in Fig. 6 seem to follow a rather obscure pattern morA . e thorough analysis, however, reveal a sbehaviou r which possible is' a systematic one. For each of the two dose rates, the response versus humidity curve seems to consist of three sections; a "low humidity" branch a "hig, h humidity" branch (both decreasing slowly with increasing humidity) a s transitiowela ,s a l n zone between them where there is a somewhat steeper decrease of response with humidity.

Besides this humidity effect, there is also a dose rate effect, up to now t noreporte ye e literaturet th n i d . This effeca complicate s i t d function e samplth of e moisture. Wherea t a higs h humiditie r.h.% 6 e 6 )th £ ( s response e independenseemb o t s t from dose e rat dost th leas(a een i t rate range given), at low humidities (0 - 25 % r.h.) the response definitely increases with dose ratee difference founTh % . n thi0 i d2 f sabou- o s 5 1 t regioa ten-fol r fo n d variatio n dosi n e rate e definitelar , y outsidy an e experimental errod thean ry e considereb hav o t ea reality s a d . Additionally, the positio e transitioth f o n n zon s i shiftee d towards lower humidities with increasing dose rate. The superposition of these two effects then causes the complex pattern observed, especially the occurance of an intermediate region (around 45 % r.h.) where a dose rate effect exists which has about the same magnitude as at low humidities but is of opposite sign.

This complex pattern might as well serve as an explanation for the fact that untill just recently (26 o dos)n e rate effec s beeha t n reportee th r fo d region typica f gamma-irradiationo l e humiditth f I . y conditions remain uncontrolled (as it was obviously usual practice) during attempted measure-

77 menta dos f o es rate effect e actuath , l moisture content e sampleth f o s s involved might vary considerably. Thereby the individual dose rate effects (being of different sign for different humidity regions) might cancel to a high degree.

4* Results - Cellulosetriacetate

Figs 7-9 show that there is a linear relationship between dose and absorbance for all the different experimental conditions applied. This was expected from literature datas (15 - 20). Moreover, it can be clearly seen from these figures tha a humiditt y effect only exists whe e filmth n s were y-iiradiated in air. No humidity effect .could be observed when the Y-irradiations were performed in argon or the electron accelerator - with air as well as with argon as irradiation atmosphere - was used. (Figs. 2 and 3) Concerning irradiations in air TANAKA et al. (20) has also reported an humidity effect, namely for electron beam irradiations with dose rates of about 3 x 10 Gy/s. For higher dose rates (above 3 x 102 Gy/s) no humidity effect was found. This is in good agreement with the results presented here. Bute effecth , t that using argo s irradiatioa n n atmosphere n y-sourcei s remove e humidit th t sreporte ye e t th y no n i deffecs wa t literature. Moreover t onle humiditno th y,t als e dosbu th o e- y rate effect - which was found in agreement with the literature (15, 19, 20, 22, 23) for the irradiation in air - disappears when air is replaced by argon during Y-irradiation e derive.b Thin ca sd from Figs 2 and. 3 " froe identicath m l slope r botfo s h curves, whose k-valu f 0.007o e 5 kGy~ is in fair agreement with the values given in the literature for the irradiations with dose rates above 3 x 102 Gy/s (15, 19, 20, 23) when taking into accoun e differenth t t tim f measuremento e s after irradiation.

The radiation-induced absorbance change at 280 nm was found not be stable after irradiation in accordance with most of the results given in th, 23)e20 . literatur - n absorbancThera 8 1 s i , e (5 e e increase with e influenc th e dose timth d f an e,o e dose rate, moisture contene th f o t films during irradiation and of the irradiation atmosphere on it has been studied and the results obtained are given in Figs. 10 and 11. All the samples used were stored after irradiation at ambient conditions r.h.t a abou% n darknessi 0 )r (i6 ai tn - 25°d about % I an C.0 5 t was found that variations of the dose just as of the moisture content t significantl e no film th oo f d s y influenc e fadinth e g characteristic of y-irradiated CTA films. Therefore, Fig. 10 shows the fading curves of Y-irradiated CTA films in air and argon, respectively obtained from the- averaged e valuefouth rf o sdifferen t dose 0 kGy0 kGy5 s 10 , , 125 kGy and 150 kGy at the different relative humidities 10 %, 32 %,

78 45 % and 86 % applied. From the resulting curves it is obvious that the radiation-induced signal becomes stable after about two weeks when the y-irradiatio t continues performei bu n r ai o fad t sn i de whee th n Y-irradiatio s performei n n argoi d - neve n aftex weekssi r .

e contrarOth n r electrofo y n beam irradiations varying doses juss a t varying moisture contents of the films produce different fading curves while the influence of the irradiation atmosphere is almost negligible. Generall s observewa t i y d thae higheth t e moisturth r e contene th n i t films and/or the dose applied the more intensive the fading. Regarding the influence of the dose films irradiated with a dose of 50 kGy show in all cases significantly less fading compared to films irradiated with doses of 100 kGy, 125 kGy and 150 kGy, respectively which show between only small differences in the percentage fading. Therefore, the correspon- ding values of these three doses in air as well as in argon were averagee givear n Figi d n e an 1 influencdshowin1 .th e w th no f go e moisture e fadin contene th film th o t f gso t characteristic.

Comparin e fadinth g g characteristic differeno s tw obtaine e th t t a d dose rates applied it is remarkable to note that within the period of observation only films irradiated with r Y-rayterminatai n i s o t e fade while films irradiated with electron beams in air as well as n argoi n continu o fadt e e filme th jus ss a tirradiate d with Y-rays in argon.

It was now attempted to accelerate the fading by heating the films after irradiation in order to obtain in that way a constant response value in a reasonable time. In a comprehensive study the influence of heatine fadinth o t gg characteristi a functio e temperaturs th a c f o n e (using 6 different temperatures between 60°C and 120°C) as well as the duratio e heatinth f o n g (six different intervals betwee hou1 n r houran8 e 4. dtemperaturet th eaca s f o h s applied s beeha ) n investigated. For these experiments films irradiated with electron r beamai n i s y havkG e 5 ta bee7 odos f o ne used heating them immediately after irradiation also in air.

It was found that in any case the heating procedure has caused a noticeable decline of the fading. The higher the temperature and the longer the duration of the heating the more the flattening of the fading s possiblwa curve t i o reduc t eo S e .fadin th a ever levew o t lo gy l but it did not succeed to stop it; it was still going on even seven weeks after any heating procedure.

79 Moreover e heatinth t y onle fadinb e slopno th ,g th y f o eg curvt bu e also the absolute absorbance values itself were altered. The latter increase with increasing temperatur d heatinan e g period r exampleFo . , a 5 hours heating of an irradiated CTA film causes an absorbance increase of about 10 % (at 60°C) up to about 20 % (at 120°C). Further temperature increase up to 150°C causes a considerable absorbance increment, the films get a darkbrown colour and become opaque.

It should be noted here that heating of non-irradiated CTA films was foun o caust d n absorbanca e e decrease resultinth t bu e g value remains not stable. A fading also occurs increasing the absorbance sometimes to values above that before heating.

5« Discussio d Conclusionan n s

BLUE CELLOPHANE FILMS

The results given in this paper demonstrate unambigously that 26-jj.m DuPont MSC 300 blue cellophane films at dose rates typical for Co Y-irradiations show a rather complex simultaneous dependence on dose rate and humidity. Due to this complex behaviour, the blue cellophane e considereb o systet s s mha beina d r fro fa gn ideaa m l dosimeter, at least over the dose rate range studied in this investigation (0.23 to 2.3 Gy/s). Maybe at dose rates lower than 0.23 Gy/s the situation becomes slightly better. However, in any case this system should be calibrated at exactly the same dose rate and humidity as during its service. Any extrapolation to still higher dose rates (as it would become necessary e.g. when applying the system to electron-beam dosimetry after calibratio a cobal n i n t source) e seemhighlb o t sy questionable. *

In qualitative terms, these conclusions are certainly valid also for similar dyed cellophane systems, e.ge Tohcellth . o "Blue Cellulose Film" mentioned above. Some spot checks made with this material confirm this assumption.

CELLULOSETRIACETATE FILMS

Obviousl e mosth y t importan e syste te th practica th resulf o mr e fo t us l is the fact that no dose rate effect exists in the range of about 2.0 Gy/s up to 2.7 x 10 Gy/s provided that the irradiations at the low dose rates are performed in an inert gas atmosphere. Moreover, whenever doing so there is also no humidity effect so that now a thin film dosimeter

80 syste s mrealli y available being humidity insensitiv d dosan ee rate independent froe dosth m e rat e o y-source th C typica o t r p fo u ls dose rate rang f electroo e n accelerators, y-irradiation n inera s ga n ti s atmosphere can be easily performed and implies actually no limitation. Now it has become possible to achieve the calibration of the dosimeters for dose measurements with electron accelerators in a Co y-source what is much more simple and convenient as the use of a calorimeter. Because the reproducibility of the dosimeter system was also found to be excellent most of the requirements of a film dosimeter system for e fulfilledroutinar e us e , too.

Undoubtly the main disadvantage of the system is its fading and it s i absolutely necessar o choost y e momene readinth eth f o t g very carefully. TAMUR. (19al t e )A have recommende o perfort d e measurementmth 3 o t 1 s hours after irradiation but it may be made also after longer periods provide e accoundu d s i taket f fa'dingo n . Becaus e fadinth e g curves begi o flattet n n after abou 7 dayt s this woula convenien e b d t poinf o t timr makinfo e e measurementth g s with respec o reproducibilitt t y juss a t systematic errors. Therefore, the absorbance readings in this paper have been performe 7 dayd s after irradiation. Furthermore, speciao lt cars ha e be taken in the handling of the dosimeter films, because the absorbance readings were made in the ultraviolet part of the spectrum, where surface imperfection d n dircausan ca st e large discrepancies. Touchin e opticath g l face of the dosimeter should be avoided. An efficient spectrophotometer is needed in order to guarantee that the readings were always performed t exactla e samth y e wavelength.

Observing the rules secures the full reliability and accuracy and makes this dosimeter system to a versatile and accurate one apt for a wide rang f applicatioo e n radiatioi n n processing. Therefore t i woul, e highlb d y desirable to invest some more experimental work in order to remove the small limitation referrin s fadingit o t g .

Some spot checks with 125-M.m-thick CTA films manufactured by Fuji Photo Film, Japan which also contain 15 % triphenyl phosphate have given almost identical results so that the conclusions derived from the experiments with the French films should also be valid for the Japanese films.

Paper Published on Work Done under the Contract

P.Gehringer, E.Proksch and H.Eschweiler: "The y-Radiation Respons f Bluo e e Cellophane Films under Controlled Humidity Conditions". Int. J. Appl. Radiât. Isot. 33, 27 (1982)

81 Literature

. 1 E.J.HENLE d D.RICHMANan Y . Anal. Chem. _28, 1580 (1956)

2. D.G.LLOYD cited by A.CHARLESBY in: Radiation Effects in Materials . p 106, Pergamon Press, Oxford, I960

3. R.B.OSWALD Jr., H.A.EISEN and E.E.CONRAD. IEEE Trans. Nucl. i 9 (1966NS-13Se 22 , 6_ ),

. 4 A.MILLER, E.BJERGBAKK d W.L.MCLAUGHLINan E . Int . J Appl. . Radiât. Isotopes _26, 611 (1975)

. 5 W.L.MCLAUGHLIN, J.C.HUMPHREYS, B.B.RADAK, A.MILLE d T.A.OLEJNIKan R . Radiât. Phys. Chem. U, 535 (1979)

6. A.CHARLESBY and J.R.WOOD. Int. J. Appl. Radiât. Isot. U, 413 (1963)

7. A.F.MAKHLIS. Radiation Physics and Chemistry of Polymers p. 89, Keter Publishing House, Jerusalem, 1975

8. S.OKABE, T.TABATA and K.TSUMARI. Ann. Report Radiât. Centre of Osaka Prefecture, _16, 30 (1975)

. S.OKABE9 SympK .n Radiatio o KE Proc. t 1s . n Dosimetry7 12 . p , Oho, Ibaraki, Japan, 1978

10. J.M.DAVIES AND B.MCQUE. Int. J. Appl. Radiât. Isot. 21_, 283 (1970)

11. S.A.GOLDBLITH and R.I.MATELES. Nucleonics _16, 102 (1958)

12. A.CHARLESBY. Radiation Effects in Materials, p. 106, Pergamon Press, Oxford, I960

13. W.L.MCLAUGHLIN in: Manual on Radiation Dosimetry (Edited by N.W.HOLM d J.R.BERRYan . p 163) , Marcel Dekker Yorkw Me ,, 1970

14. H.LEVINE, W.L.MCLAUGHLIN and A.MILLER. Radiât. Phys. Chem. U, 1 (197955 )

15. J.R.PUIG, J.LAIZIER and F.SUNDARI. Proc. Radiosterilization of Medical Products Bombay 1974 . p .113 , IAEA, Vienna 1975

16. Y.NAKAI, K.MATSUDA and T.TAKAGAKI. JAERI 6, 153 (1974)

82 11. O.P.VERKHGRADSKII cited in Radiation Physics and Chemistry of Polymers, p. 88, Keter Publishing House, Jerusalem, 1975

18. I.JANOVSKY. Radiochem. Radioanal. Letters _47, 251 (1981)

19. N.TAMURA, R.TANAKA, S.MITOMO, K.MATSUDA and S.NAGA1. Radiât. Phys. Chem. _18, 947 (1981)

. R.TANAKA20 , S.MITOMO, HIROMI SUNAGA, K.MATSUD d N.TAMURAan A . DosA ManuaCT e f Metero l , JAERI-M-82-033 (1982)

21. H.LEVINE, W.L.MCLAUGHLIN and A.MILLER. Radiât. Phys. Chem. U, 1 (197955 )

. R.TANAKA22 , K.YOTUMOTO, S.TAJIMA, M.KAWAI, K.MIZUHASHI. Nucl. Sei. Abstr. 31, 598 (1975)

. J.LAIZIER23 . Techn. Report Serie . 205Nr s , IAEA, Vienna 1981

24. F.SUNDARI. Majalah Batan j)(2), 2 (1976)

. E.PROKSCH25 , P.GEHRINGE d H.ESCHWEILERan R . Int . .J Appl. Radiât. Isotopes 30, 279 (1979)

26. P.GEHRINGER, E.PROKSCH and H.ESCHWEILER. Int. J. Appl. Radiât. Isotope7 (19822 , )33 s

83 80-

40-

I- 20-

70O aoo 500 Wavelength

Fig. 1 Optical absorption spectra of 26-nm-thick Du Pont MSC 300 blue cellophane films after preconditioning at different relative humidities.

8O-

_ 60

•40-

t- 20-

non-frradlated

O SO O 6O 0 70

Wavelength |nm)

Fig 2 Optica. l absorption spectr f 26-jj,m-thico a 0 30 C u PonD kMS t blue cellophane films for various exposure levels.

84 0 V.

38V.

100 200 30O

Dos« Fig. 3 Radiation-induced transmittance changes at 655 nm for samples conditioned at different relative humidities. Dose rate 2.3 Gy/s.

100 200 300 Dos* Fig. 4. Radiation-induced transmittance changes at 655 nm for samples conditioned at different relative humidities. Dose rate 0.23 Gy/s.

85 0.30 •

0,20-

0,10-

88V.-

200 300 Do«. [kGy]

Fig. 5 The influence of dose rate ( ———, open symbols: 2.3 Gy/s; —— , full symbols: 0.2f o 3m n e Gy/srespons th 5 n 65 )o t a e samples conditioned at different relative humidities.

0,20 -

13 JE O

S 0,10 •

20 4O SO a«l. HumldKy [•/.]

Fig6 Influenc . e relativth f o e e humidity during conditionine th n o g 150-kGy response at 655 nm of samples irradiated at 2.3 Gy/s (Q) ans 0.23 Gy/s (9), respectively.

86 1.4

1.2-

< 1.0 •4

• 0.8

0,8-

0,4-

0.2-

29 90 75 100 129 1SO Do««

Fig 1 Optica. s doslv f absorbanc125-p.o m e filmsn A 0 mCT 28 , t a e irradiated in air with 60Co y-rays at 25°C with a dose rate of 2.3 Gy/s, at different relative humidities (Q 10 % r.h.; -r.h.% 6 )8 r.h.% V 5 ; 4 r.h. % G 2 ;3 A

1.2-

1.0

< •4 0.8-

O.6-

0.4-

0.2-

75 100 150 D o««

Fig. 8 Optical absorbance at 280 nm vs dose of 125-iam CTA films, irradiated in argon with Co y-rays at 25°C with a dose rate 3 Gy/s 2. ot fdifferen a , t relative humidities r.h.% 0 ;1 A 32 % r.h.; 9 45 % r.h.-; Y 36 % r.h.)

87 1.2-

1,0-

0.8-

l o,«-

0,4-

0,2-

7S 100 129 190 Do«« [kGy]

Fig 9 Optica. s .dosv l f 125-üabsorbanco em films n A 0 mCT .28 t a e d argonirradiatean r ,ai respectiveln i d y witkeV-electron0 50 h s with a dose rate of 2.7 x 10 Gy/s, at different relative humidities. (Open symbols: irradiation in air; explanation of the symbols of Fig. 7. Full symbols: irradiation in argon; explanation of the symbols of Fig. 8)

< 1,18 4

1,14

1.10-

1,08-

1.02-

8 2 1 2 14 Tim« after irradiation (<**y*j

Fig0 1 Post-irradiatio. n irradiatefadinm n 0 f 125-jio g 28 film A t da mCT s in air ( Q ) and argon ( • ), respectively with Co y- t 25°a C wit a dosh e3 Gy/s 2. rat f o e.

88 < 1.18 '

1,14-

1.10-

1,02-

14 21 28 39 42 Tim« aftar irradiation [d»y»]

Fig. 11 Post-irradiation fading of 125-nm CTA films at 280 nm irradiated in air and argon, respectively with 500 keV-electrons with a dose rate of 2.7 x 10 Gy/s at different relative humidities durin r.h.)g% r.h. 6 irradiation% r.h.8 .% 2 3 O ;0 1 Q ; 9 ( .

89 ENVIRONMENTAL EFFECTS ON THE ETHANOL-MONOCHLOROBENZENE DOSIMETER SYSTEM BEFORE, DURING AND AFTER IRRADIATION

A. KOVÀCS . STENGE,V R Radiation Technology Department, Institute.of Isotopes of the Hungarian Academy of Sciences, Budapest, Hungary

Abstract

The dos.imctcrs, use r qualitfo d y contro n radiatioi l n processing hav o fulfit e a numbel f requirementso r , thue rol th f sdifferen o e t environmental effect s studiee ethanol-monochlorobenzenwa th s n o d e dosimeter system before, durin d aftean g r gamma irradiation e effecTh . t of light, temperature, storage and transport conditions, and size of dosimeter ampoul studies wa e n detaili d .

The corrected G(C e ) syste1valu th s als f o mewa o e checketh d an d applicabilit e oscillometrith f o y c evaluation metho s extendedwa d . A numbe f internationao r l intercomparison result e alsar s o discussed.

f thio Thsm ai ewor k unde e researcth r h contract No. 2389/Ro studt l clead thoss al an yp Bwa u r e environmental effects on the ethanol-monochlorobenzene dosimeter, which hav t beeno e n investigate dosimetee o farTh ds . r systen mi question gets wide wided an r r applicability s wela ,s a l increasing importanc e fiel th f radiatio o dn i e n processing and it is also one of the back-up systems, proposed by IAE r gammAfo a irradiation facilites abov kGy5 e . Therefore e investigatioth e effectsth l al , f no whic h could influence the absorbed dose results got basic importance.

. I INTRODUCTION The applicatio f ionizinno g radiatio f increasino s ni g importanc l oveal e world th o rt e . Henc e rol th f eradiatio eo n dosimetry - for the quality control of radiation processing - s alsi o increasing e numbeth til w p f methodso rU no l . ,

91 developed for dose determination in the whole range of ionizing radiations are above thousands and are still increasing. However, in contrast to the wide variety of dosimeters, in the field of radiation processing only a limited numbe method f usede ro b n ,sca partl y becausf eo the environmental effects dosimetere .Th s hav filo et la numbe requirementsf ro , par thesf to e called environmental effects. These effects can easier be taken into account in the research and pilot scale irradiators compared to the industrial scale irradiation facilities. The calibration and evaluation of the dosimeters usually takes place soon after the irradiation in the former case. In the large scale irradiators however the environmental effects have to be taken more into consideration because of the long term process. All of the possible effects have to be examined, becaushige th h f eo ris n financiai k heald lan t problems, 2 which may be a consequence of false dose information . Amon dosimeterse gth , qualite applieth r yfo d control in radiation processing chemicae ,th l dosimeters plae th y most important rol faro es majo e .Th r advantage liquif so d chemical dosimetric simple systemth e es ar preparation , accuracy and flexibility of form, while among the disadvantage e limiteth s d rang sensitivitd ean impuritieo yt s must be mentioned .

1. The ethanol-monochlorobenzene dosimeter This dosimeter system was first proposed by Dvornik and coworker 196n si consistt I 6alcoholin . a f so c solution of monochlorobenzene. The amount of monochlorobenzene can be varied in the range of 4-40 volume %. The solution

92 contain volums4 water% e , O.04% aceton benzened ean . Negligible change is caused by changing the water content by -1%. Ethanol, aceton wated solutioe an adde s th ri o dt n for their stabilization effec chloridn to e ions formed. The basic processes in the radiation induced reaction of alcoholic monochlorobenzene solutio follows a e nar : s M " ————e + + —M »• Cl

esol vC+ 6 H5C1 ———C1 sol vC+ 6H5

H-O, C-H — — C1 L s"ol— ~ —— v

HO, C-H.OH

H°' CHOH

The dose, absorbed by the dosimeter solution is evaluated by measuring the hydrogen ion concentration /alkalimetric titration with bromphenol blue indicator/

KHC03 + HC1 = KC1 + H20 4- CO2 and/or by measurement of the choride ion concentration /mercurimetric titration with diphenylcarbazone indicator/.

2+ Hg + 2 Cl" = HgCl2 Due to the reaction of the hydrogen ion with glass, the alkalimetric titration should onl usee yb doset a d s above 2 kGy. The mercurimetric method can be used over the entire 4 dose rang. e Since the evaluation of the monochlorobenzene dosimeter by conventional volumetric titration is slow, evaluation by oscillometry was introduced .

93 2. Oscillometric evaluation method According to the Kohlrausch law, the conductivity of a solution is changed by the alteration of the amount of ions presen e solutionth n ti . This phenomeno applies i n y db measuring the conductivity by high frequency oscillometry.

At high frequency conductivity measurements thero n s ei galvanic contact between the solution and the electrodes, thus this process is precise, fast and avoids such undesirable proces polarizations sa , catalytic process, corrosion, etc. The greatest advantage of the method is that with the help of oscillometry the conductivity measurement completela carriee n b i n t ca sdou y closed system, e.g sealen i . d ampoules conductivite .Th e th d yan dielectric constant can be determined by this method. During the conductivity measurement the glass or plastic tube containin e solutio gth betweet pu armatures e ni nth f so the condenser insidr ,o inductivite eth ye coith f lo instrumen measure w d voltagee tan eth , displayee th y db scale deflectio voltmete f conductivito ne Th . ' r y measurements with oscillomete carriee usiny b rar C t gA dou with frequency in the megahertz range . With the instruments type OK-302, OK-302/ conductivite 1th y measuremens ti z frequencyMH 8 4 carriet a . t ou d Oscillometric measurements employ, as a rule", a high frequency oscillator circuit solutioe .Th n under tess ti placed between the plates of the capacitive cell in case OK-302/e oth f 1 type oscillotitrator resonance .Th e frequency of the oscillator is provided by the Thompson formula /L x C where L is the inductance /H/ and C is the capacitance /F/.

94 An oscillator circuit is characterized by the Q factor as e frequencyth y welb s la . Eithe e frequencshife th rth n ti y or the change in the Q factor of the circuit is utilized in the oscillometric measurement factoQ e change th Th r n . si e - which is characteristic of the variation of conductivity

Q for solution measures i - s d through followin change gth e in conductance. g = *_ = /L/C influencee Q factob n simplese rca th y influencin b n i dy twa g the capacitive elements accompanied by the variation of the voltage/ .anode current/ which can be measured in the resonance circuit. Measurements, performe OK-302/e th y db 1 type oscillotitrator, keep track of changes in the Q factor of the oscillator circuit. Fig. 1. shows the measuring cell, employed. There are C-, and C- capacitors between the ring type electrodes and the surface of the solution. Connected in serie scapacitoe ar wit t hi constitute, o rK tw e th y db liquid surfaces and containing the solution under test with ohmic resistanc dielectria s a eR d capacitocan _ rC havin structurga e simila thao rt capacitof to . , rC

The resistance of capacitors C, and C2 is infinitely high compared with resistance R of the solution; since those capacitances are independent of the solution under test and are constant for a given cell, they can be merged into a single capacitance, the "closed capacitance" /C/.

In the course of the measurement both K and R change, which in turn affects the AC conductivity /admittance/ of the circuit, described as follows

/ C + K / + j/co /x 2 + /coC K co R 32C R ? 22 1 + uT /K + C/ R

95 The conductance of strong electrolite initially increases with concentration/ then it passes a maximum /Fig .1 thi casHC e 2./ s% th f eo 20 maximun .I t a s mi /Fig. concentratiow well-dissociateS./a lo n t i A , s i l nHC d form, its conduction is high and these properties are used for the evaluation of monochlorobenzene dosimeter. The electrical conductanc alcoholie th f eo c monochlorobenzene dosimeterconductance Th . uS ,3 monof eo 0. use s -di chlorobenzene solution irradiateS u 0 6 s i d y witkG h5 /Fig. 2.1 i.e. it is two orders of magnitude higher compared originae toth l solution relativt .A e measuremente th f so conductance with help of radiofrequency oscillotitrator, the conductance of the individual components is close to each other. Despite the near coincidence of the values of the radiofrequency inductanc monochlorobenzene th f eo e solution with those of the individual components, it is still possible to determine a dose as low as 100 Gy. The designed oscillometric circuit makes possible in a wide range to compensate for the signal given by the unirradiated monochlorobenzene solution or by the irradiated dosimeter sample, and thus to amplify the signal given by the difference in conductance.

3. Calibratio monochlorobenzene th f no e dosimeter Since the radiofrequency method gives an indirect measure conductancth r hydroclorie fo eth f eo c acid formed in the dosimeter, the dosimeter should be calibrated. The calibration must be carried out by measuring the conductance of a solution irradiated with a known dose.

96 By usin calibratioga n curv chartr eo evaluatioe ,th s ni very simple. The original Dvornik method does not require a calibration because the products formed during irradiation cameasuree nb titratioy db n metho However. ' dmors i et ,i 3 9 saf comparo et anotheo t t ei r chemical dosimetero t r ,o us well-knowea n calibrate dirradiatioe th dos n ei n chamber. Calibration for the evaluation by instruments can be wayso tw carrie:n i t dou 1. The instrument is set to zero and then deflection is measure usiny db g ampoules filled with solution irradiated with increasing doses. The data are graphically plotted. This calibratio carriee different b a n t nca dou t ranges of the measuring instrument. With the ampoules to be measured deflectio compares ni calibratioe th o t d n curvee dosth eo ,s can be determined. 2. With ampoules irradiated with small doses, calibration can be carried out in a narrow range. The deflection can be set by using compensating circuit and ampoules which corres- e loweth pon ro e uppet d /1/10th rd an //2/3 / e rangth f eo given dose range respectively. The series of ampoules are then measurescale th ed deflectiodan n recorde charta n do . The above mentioned two ampoules are saved and the corres- ponding rang repeatedln eca evaluatioe th sete yb r Fo . f no an unknowndose data from the chart can be used. It shoul emphasizede db , tha evaluatioe tth n with radiofrequency instrument does not affect the information, dosimetere storeth n i d ,suitabls i thu t i smeasurinr fo e g absorbe dos• dn subsequen i e t experiments e accurac.Th y oscillometrie oth f c evaluatio 10%- n 5 methoe ,- th s i d

97 reproducibility is +- 2 - 5% 12, thus the method is applicable, as a routine evaluation method for absorbed do.se measurements.

4. Propertie dosimetee th f so r During the introduction of this dosimeter system, some of the environmental effects have already been studied. The following favourable properties of this chemical dosi- observede b meten ca r : - the chloride ion formed from irradiated monochlorobenzene is in the form of the hydrochloric acid. It is stabl solution ei n under irradiation eve concentratiot na n of O.5 M/l; Monochlorobenzen- thermicalls ei y stabl resistand ean t to oxydation; - The solution has high HC1 yield /see Fig. 5./; Ethano- l appliesolutioe th well-knowa n di s ni n inhibitor for the oxydation chain reaction and HC1 is well dissolved in it, thereby helping the stabilization of Cl ion y solvatiosb - , ; n large th eo t proto e Du n- affinity, ethanol effectively scavenges the positive ions; t dependenno s i - G/C / n temperaturlto e rangth f en o i e 293 - 360°K; - The dose range is 40 Gy - 50O kGy; Hydroclori- c acid determinee formeb n convene dca th y db - tional volumetric titration; - The lower limit of the measurable dose range by using chemical indicator and spectrophotometer is 10 Gy;

98 G/C1~- independens i / dose 0 Gy/1 th h e f o o t rat p eu /Fig. 6., Table I./; - The value of G/Cl/"/ at a given monochlorobenzene concentration /4-40 vol.% s independeni / dose th ef to /Tabl e 2./; G/C1~- independens i / oxygee th f nto pressur; mm eg H abov 0 30 e /Fig.7./; - The solution can be stored for a long time; - The applied chemicals are cheep; dosimetee Th - r solutio easile b n ynca prepared; - By choosing suitable dosimeter solution, tissue-equivalent electron density can be set. The evaluation and handling of the monochlorobenzene dosimete eass simpled ri yan determinatioe .Th vers ni y rapid and it can be automatized. The dosimeter solution can be easily prepared, and the instrument can be set up anywhere. The other advantag applicatioe th f eo monchlorobenzenf no e dosimeter sealeds i tha t i t , therefore t affecteno s i y dt b ,i humidityappliee b n tropican ca i d t .I l climatundern i d -ean water irradiation.

dosimetee th cose Th f to negligibles ri abous i t t;i 3 whicm irradiatior e 1/10Os i hpe th f 1 Oo 0. ? n cost.

II. DESCRIPTION OF RESEARCH CARRIED OUT, EXPERIMENTAL

Accordin purpose th o f thigt eo s wor have kw e studied numbea environmentaf ro l effectmonchlorobenzene th n so e dosimeter, not examined so far, as follows: - temperature effects during irradiation, storage and evaluation; - light effects during irradiatio storaged nan ;

99 transpor- t effects; containee th - sizsolutione f th eo f ro ; - effect of phantom materials /build up dose/. We compared the absorbed dose results, got by Fricke, Si-diod nonochlorobenzend ean e dosimeter systems monoe .Th - chlorobenzene dosimeter took part in the medium- and high- dose intercomparison programm IAEe alsd th An an oi f eo other intercomparison programmes, organized by our department. Usin recentle th g y released typw ,ne e oscillotitrator /OK-302/1, Radelkis/ we investigated the possibilities of the extensio applicabilite th f no y oscillolimite th f so - metric evaluation. The introduction of a new evaluation

method - the direct conductivity measurement - was also examined. The dosimeter solutions were prepared accordine th o gt « composition mentioned earlier. The samples were irradiated with the K-120 type Co gamma-irradiation facility of the Institut nominae Th . el activit Facilite th PBq3 f yo s yi . The determination of absorbed dose was measured by oscillometry, though the results were checked occasionally by titration too. In case of oscillometric evaluation the measurement was carried out by using the OK-3O2 and/or OK-302 /I type oscillotitrators, made by Radelkis, Buda- pest. /Fig. 8./

III. RESULTS and DISCUSSION 1. Environmental effects 1.1. Temperature effects 1.1. Temperature during irradiation Accordin literature th o temperature gt th , ee th f eo irradiation does not influence the absorbed dose values

100 between 293° 363°Kd Kan orden .I completo rt e these results we studied the effect of the irradiation temperature in the 293°K - 77°K range. The ethanol-monochlorobenzene dosimeters were irradiated with 5.3, 14.0 and 25 kGy nominal doses at 293°K, 273°K, 233°K, 191°K temperatures. In order to ensure the necessary temperature ethanol /293°K/, water-ice /273°K/, monochlorobenzene-liguid N- /233 K/, acetone-solid ammonia /191°K/ and liquid N„ /77°K/ mixtures were used respectively, The irradiation conditions and the measuring device were the same at all temperatures. However, the absorption of the different cooling mixtures was different, therefore we hacorreco t d experimentar tou l results correctioe .Th s nwa mad usiny eb g Si-diode semiconducto temperature th d ran e dependenc diode th s als ewa f eo taken into consideration. result e seee th b Tabl n ni l n . sAl ca e3 /Fig / 9. . The results show, that the absorbed dose decreases continuousl loweriny yb irradiatioe gth n temperaturd ean the decrease is less, than 20% between room temperature and 77°K.

1.1.2. Temperature during oscillometric evaluation

The oscillometric evaluatio indirecn a s ni t conduc-' tivity measuremen temperature th d tan e dependence th f eo conductivit liquidf yo knowns i s . Therefor usiny eb g oscillometric evaluatio s establishedwa t ni , that significant differences can be observed in the case, when the temperature of the calibration dosimeters and the ones to be measured, differ considerably. The temperature of the dosimeter irradiates- dose th e n rangi d - 5-30f e o y 0kG

101 was changed between 258 K and 323 K, while the calibration ampoules were kept continuously on room temperature /296°K/ resulte .Th arisins- o differen least tw ga f to t effects - can be seen on Pig. 10. The difference becomes significant above 46 kGy. The conclusion can be drawn, that the temperature of the ampoules to be measured should not differ considerably /+ 4°C/ of that of the calibration ampoules. That means/ that e.g. afte lonra g term irradia- tioirradiatee nth d dosimeter skep e b r havsom tfo o et time in the place of measurement before evaluation. Considerin sensitivite gth instrumente th f yo t ,i should be permanently checked by using calibration ampoules thuaccurace sth y coul increasede db . 10°C difference between the measuring device and the environment is high but it is leveled off:after a few minutes.

It shoul mentionee db d thasolutioe tth warmes ni n du by the radiofrequency coil at a longer measurement and analytical error could thus be caused. It is, therefore, advisable to keep the ampoule in the sample holder only for the duratio measuremenf no t whic onls 5 sechi effece 1- y .Th t of warming up appears only after 1-2 min.

1.1.3. Temperature during storage

In order to check the effect of temperature on the irradiated dosimeters during storag carriee ew experit dou - ments, keeping the samples at 243°K and at 295°K. The dosimeters were irradiated with 20, 50 and 410 kGy doses and the oscillometric evaluatio s carrienwa t frodou m tim timeo et .' Of course the samples, kept at 243 K, had to warm up to room

102 temperature before evaluation e result.Th e summarizear s d in,. chango Tabl N absorbee . s foun4 th ee wa n i d d dose readings after 85 weeks storage.

1.2. Light effects

mose th tOnf eo importan t environmental effecte th s si light, causing significant changes in unirradiated and irradiated liquid dosimeters/ like in case of Fricke, ceric-cerous systems e.g. In case of the ethanol-monochlorobenzene dosi- 4 meter system the authors suggested to store the unirradiated liquid in dark bottles before use.

1.2.1. Effec lighf to t during irradiation

dosimetee Th r sample investigatee b o st d contained ZnS-Cdd ZnSan S powder. These compounds emit under gamma- visible th n i e d redan irradiatio m ,n 0 respectively55 t na . Thus we irradiated these samples together with pure monochlorobenzene dosimeters and compared the absorbed dose results evaluatioe .Th samplee th s carrief no swa bott ou dh by oscillometr titrationd an y conclusioe th t ,bu s drawnwa n titratioe th base of nth eo n results becauspossie th f -eo bilit sucf yo h chemical reaction mixturese th n si , which could change the conductivity of the system. Dosimeter samples were also irradiated havin sheeS Zn g t aroun ampoule th d e during irradiation absorbee .Th d dose results were compared with those, got from the samples, irradiated witsame hth e dose withou e sheetS th tZn l .Al results can be seen in Table 5. It is seen, that no significant chang observes casesel wa al n .i d

103 1.2.2. Effect of light during storage "=*.,. Accordin previour ou o t g s experienc irradiatee eth d dosimeter samplestoree b yearr n fo dsca darn i s k place without any change. In order to imitate the natural light effectshorteo t d e timsan n experimentth f e o appliee sw d HGMI/a D type metal-haloge irradiatioe nth lamr e fo pth f no dosimeter samples lame .Th p emits visible mainlth n i ye range with continuous and significant emission froom 35O run and it has similar spectra to the sun. The light intensity dosimete e placttW/cme 3 th th 7. f eo t s a 2 wa r ampoules. /As a comparison the natural light intensity was 0.26 mW/cm2 r laboratory/inou . Studyin absorptioe gth n spectre th f ao unirradiated and irradiated ethanol-monochlorobenzene dosimeter samples no significant absorption was found in the visible range ,absorptioV whilU e dosimetee eth th f no r solution significante seemb o t s . /Fig. 11./ We have also checked the intensity of the UV radiation at some place laboratorye th s n arouni d followsdan s ,a : On sunshine/ outside the laboratory 1.87 xlO photon/cm On sunshine/ insid laboratore th e y 2.80 photon/c1 0x m 14

The data of the light irradiation of the dosimeter sample previousl- s y gamma-irradiated with 7.6O, 19.5, 30.I/ dosy kG eO respectivel25 d an 45.0 summarizee O ar ,15 - y d i n seed more TablFigan n Th no e . . 6 e.significan 12 t change is dosimetee observe th e cas th f eo n i dr samples, irradiated with lower dose, while the formation of HCl, produced by UV

104 light irradiation, continuously increase case th f e o n si the .unirradiated dosimeter sample. Howeve stabilite rth f yo the gamma-irradiated dosimeter solutions increases with higher absorbed dose. conclusioe Th drawne b n /nca thabese tth t solutios ni to store the unirradiated and irradiated dosimeter samples in dark place. However irradiatee ,th d dosimeter abovs- e 5 kGy - can be stored at least for one year even in open shelf in a laboratory without significant change in the composition of the dosimeter solution. Neverheless the' effect of UV light should be avoided, that is the dosimeter samples exposee shoul b lighV U t o dno dt during storage too.

1.3. Transport conditions

Wit increasine hth g numbe large-scalf ro e capacity irradiation facilitie co-operatioe sth n among different laboratories gets increasing significance same th e t .timA e in certain cases the irradiated dosimeter samples are not evaluated in the place of the irradiation. In all these case transpore sth dosimetere th f to necessars i s d an y therefore we needed experience in this field aswell. Thus we have studied the effect of air and car transport on the monochlorobenzene dosimeter. Since durin technologicae gth l processes transr ,o - portation the ampoule can be broken they should be protected against damage packine .Th g shoul made db e with cotton woo plastid lan c bagampoule breat th A . produce f o kth e t to be irradiated is not contaminated because solution is retained by the wool. The alcoholic solution remains in

105 th eevaporatest i plasti r o g cba . Sinc dosimetee eth s ri contaminatet no sealed s i t ,i d from outside,

1.3.1. Effect of car transport

We have investigate effece transporr dth ca f to t both on unirradiated and irradiated samples. The unirradiated samples were irradiated after transportation together with non-carried dosimeters. The absorbed dose values were the same in case of both samples. The irradiated dosimeters were evaluated by oscillometry before and after transportation chango . N absorbe e s founth e wa n i d d dose values after transportr ca m k O .20

1.3.2. Effect of air transport

The same experiment was carried out in order to study the effect of air transport on the unirradiated and irradiated monochlorobenzene dosimeters e sample.Th s were carried Hungariae bth y n Airlines/ dosimetee MALÉVth d ,an r samples were evaluated after 10.000 km, 25.000 km, 5O.OOO km and 100.OOtransportr ai m Ok resulte .Th s provedr ,ai thae tth transport has also not effect on the unirradiated and irradiated monochlorobenzene dosimeter samples.

1.4. Size of the ampoule

Accordin experiencesr ou o gt , concernin oscile gth - lometric evaluation method of the irradiated dosimeter sample becamt i s e clear, ampoulee tha th size tf th eo , containin solutioe gth n shoul similare db . However effece ,th t of differences in size has not been studied previously.

106 investigationr Inou studiee sw effece e th dth f to differences of those 2.5 ml nominal volume ampoules, which continuoulaboratorr n i ou e Hungaryn n i i ar d e syan us . Usin usuae gth l calibration ampules /diameter 11./ 1mm measuree w absorbee th d d dose valuee samplesth f so , varying its diameter between 1O.3 and 11.2 mm and containing the same irradiated dosimeter solution. The height of the solu- same eacn th i etio s h nwa case resulte .Th s /summarizen i d Tabl show1 1. e , thachangee tth e , th e sizcause th f e o y db ampoul mors i e e significan lowet ta r absorbed dose values and beyond the range of the diameter of the calibration ampoule +0.f so . 2mm Using such ampoules the oscillometric evaluation gives reliabl accuratd an e e result thid san s variatio sizn ni f eo the ampoules is a usual standard, according to the manufac- turer. Howeve possible rth e differenc thicknese th n i e f so the wall of the ampoule - which changes the capacitance of the system - can not be taken into consideration, thus causing some error at the evaluation. We wish to note, that the use of similar ampoules to the calibration ampoules in size /that is the diameter of the calibration ampoules and the ones to be measured is the same/ gives more accurate results chapten i e -se r III/3.

1.5. Effect of phantom materials

In many cases the irradiation of the samples is carried oudifferenn i t t container alsd san o materialse b use o t d irradiated in large quantity within a box or container. Thus the significance of the build-up dose have also to be checked.

107 In our experiments we checked some ampoule holders containin- g ethanol-monochlorobenzene dosimeter mads- f eo different materials /plexiglass, PVC, polystyrene foam/ and use differeny db t laboratorie e irradiatioth r fo s f no dosimeters resulte .Th tabulatee e sar on r Tabln Fo i d . 8 e serie experimentf so time placd th se an irradiatio f eo s nwa the same. No significant change was observed at the evalua- irradiatee tioth f no d monochlorobenzene dosimeters. In the other series of experiments we changed the wall thickness of a plexiglass ampoule holder from irradiation to irradiation conditione .Th irradiatione th f so s were always the same. The results show, that by decreasing the wall thickness of the container, the absorbed dose value increases /Table 9./. However the difference between the absorbed dos eholdee valuesth n r- i d , an measure r ai n di caused probabl absorptioy yb significantt no s i n- / taking into account the experimental error.

1.6. Storage time and reproducibility concerning oscillometric evaluation

The use of ethanol-monochlorobenzene dosimeter with oscillometric evaluation is on in our laboratory for more, tha yearsO 1 n . This evaluatio advantage th n t methogo es dha of using sealed ampoules. Thulone sth g term storage th f o e irradiated dosimeter darn si k give possibilite th s e th f yo ocassional réévaluation later on. This is important from health regulations poin vief to w too. Accordin experiencer ou o t g réévaluatioe sth e th f no irradiated monochlorobenzene dosimeters can be carried out withi experimentae nth l erro 5-10%/+ / r . Tabl . contain10 e s

108 th eIAEn a dat Af ao intercompariso n fro dosir m Ou 1977-. meters were irradiated at the National Physical Laboratory, Teddington, England in 1977, but we got back these samples onl 1980n i y evaluatioe .Th dosimetere th f no s gave eth nominal dose values, given by the irradiation laboratory. The evaluatio s repeatenwa 198n i d 2 witsame th he result. nominaq PB 9 le I nth activit gamma-irradiatioo C y n facilit oscillometrie MEDICOf yo th M RDO c monochlorobenzene dosimeter systecontrole th uses r mi fo dabsorbef lo d dose e facilit Th too largese Hungarn . i th uses - e yi ton d- y mainly for the sterilization of medical products. That means, that the oscillometric monochlorobenzene dosimetric metho uses procesr di dfo s controll dosimetry unde- rin dustrial conditions operatore .Th s have recently controlled the irradiated dosimeters of the last five years and the absorbed dose results wersame previousles th ea y within + 7%. Thus the experiences, gained both in an industrial and pilot-plant irradiation laboratory are satisfactory. The most important environmental effects, investigated frame nreviousl th thi f eo n i s d researcyan h contrac collectee tar seens i t ,I Tabln i dtha. e 11 etth most important conditions to be taken into account for the determinatio absorbef no dy radiatio an dos t ea n technological processe size d temperaturth ean e sar e th f eo calibration ampouledosimeterse th d san e welth s , a s la role of UV light on the dosimeter solution.

109 2. Extension of osciHometrie evaluation method

At the work-out of the oscillometric evaluation method of irradiated monochlorobenzene dosimeter systee sth m e 4-5 th y dosuses 0kG n wa ei d rang OX-30 e meany eth b f 2so oscillotitrator. However the increasing demands concerning the irradiation of plastics /50-500 kGy/ as well as food irradiation /0.5 - 5 kGy/ brought the dosimetry in this ranges into focus. Previously we extended the oscillometric evaluation dosy kG e O rangmetho50 - e dO usin5 intOK-3Oe e gth oth 2 oscillotitrator /Fig. 13./. This oscillotitrator was not sensitive enough dostowardw w lo ne e e e rangesth th t ,bu type oscillotitrator /OK-3O2/1/ proved suitabl thir fo es purpose. However taking into consideration the demands towards accurac reproducibilitd an y e welth s ya s la disadvantage d typol e e ampoulth f so e holder w typne e,a holde constructes rwa laboratoryr ou n i d thin .I s holder the electrodes are ring type ones, built in a metal box, thus giving necessary shielding. In order to eliminate the occasional assymetr dosimetee th f yo r ampoules there betweep iga smala s electroder e lnai th wale th f l o d san the ampoule. The symmetrical position of the dosimeter ampoulholdee th s ensuren ri wa e usiny db g small spring thJf w typo splatesne e e us ampoule .Th e holder ceased such disadvantages of the previous one, like hand-capacity and' assymetr dosimetee th f yo r ampoule. By using the OK-302/I oscillotitrator and the new type ampoule holde extendee rw oscillometrie dth c evaluation of the irradiated monochlorobenzene dosimeters into the 0.4-4 kGy dose range too /Fig. 14./. This range has

110 got main significance concerning the food irradiation technology.

3. Intercompariso dosimetef no r systems

large Inth e scale applicatio radiatiof no n processing radiation dosimetry measurements during commissioning and operation offe basie qualitr th sfo y contro guaranteo lt e the safety or reliability of the irradiated product. The IAEA programme on High-Dose Standardization and Inter- compariso Industriar nfo l Radiation Processin- e d s gwa signe e implementatio th leao t do t d independenn a f no t international service aimed at providing dose assurance irradiatioe toth n facility operators o welt s , a s la select appropriate dosimetric methods. The oscillometric monochlorobenzene dosimeter system was applieframewore th n i d thif ko s project thin .I s project the different methods for dosimetry were compared after treating the dosimeter under severe conditions. The present method along with the cerium dosimeter, used by AECL /Canada/ s recommende,wa secone th d thiro dan t d d place afte alainine rth e dosimeter, develope GSFn i d , West Germany. Accordin resulte IAEe th th A o gt f High-Dosso e Inter- comparison Programm d somean e other programmes- ab e ,th sorbed dose results/ measure monochlorobenzeny db e dozi- meter with oscillometric evaluation gave about 10% higher values compare e nominath o t dl dose orden .I cleao rt r up these differences we carried out experiments investigating the possible errors.

Ill 3.1. Indoor investigations

In order to make our results probable we checked the agreement betwee absorbee nth d dose-rate resultsy b t ,go Fricke and monochlorobenzene chemical dosimeters and Si-diode detector, calibrated previously against Fricke dosimeter. The irradiations were carried out by using the K-12O gamma-irradiatiotypo C e n facilit e Institutth f yo e /Fig. 15./. However by operating this facility we had to take into accoun transie tth t dose, i.e dose .th e given dosimetee tth o r sample dowd an sn p durinmovu f e eo gth the sources. This transit tim abous ei secondsO t2 , which could be eliminated by choosing long irradiation time, but in case of Fricke dosimeters only short irradiation time can be chosen, limited by the dose-range of the system. Therefore, in order to have an exact irradiation positio dosimetee nth r samples were irradiatee th n di middle channefacilite storage th th f lo n yi e position of the sources. Thus the up and down lifting of the dosimeters /I-2 seconds s negligibl/wa e comparee th o t d irradiation time. The Fricke dosimeters were irradiated for 2 minutes, while the monochlorobenzene samples for minutesO 6 d an .0 3 During the evaluation of the irradiated dosimeters some significant observations were done and/or taken into accout. The digital UV-VIS spectrophotometer, used for the evaluation of the irradiated Fricke dosimeters has got an error caused by the reading of the instrument and this is e erroaddeth f Frickro o t d e metho l-2%/+ / d „

112 - We have changed the G/C1~/. value of the monochlorobenzene dosimeter system, i.e. instead of G/Cl / = 5.00 we used G/Cl - / = 5.641 4 according to the recent paper of the authors. - For the oscillometric evaluation of the monochlorobenzene dosimeters the OK-302/1 oscillotitrator was used with the new type ampoule holder. diametee ampoules-containine Th th - f ro irradiatee gth d monochlorobenzene dosimeter solution- and that of the calibration ampoulesamee th .s swa The results, got by the three methods are collected iTable n Th contain2 Tabl1 e . 12 e s alsresultse oth t ,go by the chemical dosimeter system and Si-diode, when the samples were irradiated in the original irradiation position of the K-120 facility /sources are up, not in storage position/. The transit dose was taken into ccount this case, s substractedwa i.e t i . seens i t ,.I thaagreemene tth s ti very good in all cases. We wish to note, that the results got by both the Frick d Si-diodean e prove e changdth f G/Ceo value• l/ , i.e. the use of G/Cl / = 5.64. This value was also proved by titratio irradiatee th f no d monochlorobenzene dosimetery sb comparison to the Fricke results. It is also promising, that the oscillometric evaluation brought into focu erron sa f ro the titration method. Namely, the absorbed dose value, got by titration of one of the irradiated monochlorobenzene dosimeter s 8.6swa 6 kGy, while oscillometric evaluation gave 9.3O kGy value. This case the titration was carried

out with 0.001 N Hg/N03/2 solution. It came out, that at

around the dose range of 10 kGy 0.01 N Hg/NO3/2 solution

113 must be used for titration because of the big final titratevolume th f eo d solution, i.e. because th f eo non-suitable complex formation.

3.2. International intercomparison

A numbe intercomparisof ro n programmes were carried out in the past five years in order to improve the applicability of the monochlorobenzene dosimeter system. Most of the dosimeters, taken part in these'programmes were kept, thu coule sw d evaluate those again have .W e checked our monochlorobenzene dosimeters, irradiated at National Physical Laboratory /NPL/, Teddington, England in 198O and 1981, at Bhabha Atomic Research Centre Bombay, India r Institute/BARGou t 198n a i / d 1an , together with the .alanine sample Gesellschaff so Strahlenr tfü d -un Umweltforschung /GSF/, München 1981n i G usiny .,B FR e th g previous calibration table - based on the G/Cl / = 5.O value - we got the same values, as sent to IAEA at that time. Howeve usiny rb G/Ce gth 5.6= l/ 4 valuee ,th OK-3O2/1 instrument witampoulw hne e holde similad ran r ampoules to the calibration ampoules in size we got corrected absorbed dose values /Table 13/ agreemene .Th t is very good again. ratione Th estimatef so d e doseL th dose NP f so o st IAEA High-Dose intercomparison Programme, carried out in 1980 and 1981 are summarized so, that both the original and the corrected values are together. /Table 14/. The results clearly show, that in order to get precise results, G/Cl" 5.6= / 4 value mus usee tb thit a d s monochlorobenzene concentration. Also in order to get

114 very accurate results the size of the ampoule have to be checke concernin- d calibratioe gth n ampouled an s- w typne e r ampoulou e holder .shoul usede b d . This case the original + 5-10% error of the method could be improved. However originally the method was developed as routine evaluation metho procesr fo d s control- in n li dustrial and pilot scale irradiators, where'the + 5-10% limit is allowed in most cases. future Finallth e suggesr ew fo y calibrato t e eth monochlorobenzene dosimeter against the Fricke system instead of titration. Als propose ow accordancn i e- e wite hth purposDosimetre th f eo y Sectionationt se o IAEf t no - A- internationad aan l l irradiation laboratories /like National Standardization Office/ in order to calibrate, compare and controll the different dosimeter systems.

4. Evaluatio direcy nb t conductivity measurement

Oscillometr speciaa s yi l typ conductivitf eo y measurements, therefore we decided to determine the conductivit unirradiatee th f yo irradiated dan d monochlorobenzene dosimeter solutions. These experiments were carried out by using the OK-1O2 type conducto- mste Radelkisf ro e found.W , thaconductivite tth f o y the solution measuree b n vera sca n yi d wide dose-range. The conductivity of the unirradiated dosimeter solution is 0.3 uS, while that of the solution irradiated with 5O Gy is 2.1 uS and of the solution, irradiated with 400 kGy is 60 mS. The dose dependence of the conductivity of irradiated dosimeter solutions is seen on

115 FigHowever. 16 . known s i t ,i , thaconductivite tth f yo any solution depends ver ytemperaturee mucth n ho . Therefore we investigated the temperature dependence conductivite oth f samplese th f yo , see Fign . no 17 . e temperaturTh e dependenc f conductiviteo e b n ca / /V y describe Nernse th y tdb equation -*£ / -i--JL, ' T T ' R Vl = V2 X e 2 -1

by means of which the correction of the measured conductivity of solutions, concerning the temperature of the data of the calibration table, can be carried out. e evaluatioxTh absorbef no d dos measuriny eb e gth conductivity of the irradiated monochlorobenzene dosi- carriee metervern b i n yt sca broadou d dose-range MGy/1 - .y G Howeve0 /1 orden ri routins applo a rt t i y e evaluation method, it must be worked out in detail. Nevertheles possible sth e application fiel thif do s metho donl t coulno y e dgamma-b electrot ,bu n beam dosimetry too.

IV. CONCLUSIONS

As a summary of the investigatons and results, car- y studyinb riet environmentae dou th g l effecte th n so monochlorobenzene dosimeter system followine ,th g conclusions can be drawn: monochlorobenzene Th . 1 e dosimeter system with oscillometric evaluation can be used in a broad dose-range /0.4 - 500 kGy/after extending its applicaliblity limits by using the recently released OK-302/1 oscillotitrator connectetypw ne e a ampoul o t d e holder.

116 2. Amon numbega environmentaf ro l effectsV U onle yth light /during storage/, the size of dosimeter ampoule and the temperature of the solution to be measured have to be taken into consideration during oscillometric evaluation. 3. On the base of careful analysis of all the intercomparison result alsd literature san oth e date aw changed the G/Cl"/ value from 5.0 to 5.64. The simultaneous application of - the corrected G/Cl / value; similaf o e us r e dosimeteth - r ampoule calibratioo st n one sizen si ; OK-302/e th d an 1 - oscillotitrator witampoulw hne e holder gave good agreement of results of all previous intercomparison programmes. However, less careful applicatio systee th f mno gives still suitable results, i.e accurace methoe .th th f dyo in this case /+ 5-lO%/ still fulfills the requirements both for research and technological irradiation processes, as routine evaluation method. 4. Beside the oscillometric evaluation method the conductivity evaluation metho s introduceddwa . This methos i d applicable in wide dose-range /10 Gy - 1 MGy/ with simple and cheap measuring technic and device. The temperature dependence of the method was also determined.

• The clearing up of all the environmental conditions, discusse e intercomparisoth d an d n resulte welth s sa s la introductio evaluatiow ne f no n method possibld san e field of applicatiooscillometrie th f o e nus make c th monoe -

117 chlorobenzene dosimeter system much more reliable and wide- spread for the absorbed dose control of radiation processing.

BIBLIOGRAPHY

l; Manual of Food Irradiation Dosimetry IAEA Vienna, 1977. Technical Reports Series No. 178.

2.. Stenge : IAErF. A Coordinated Research Meetin Hign go h Dose Standardizatio Intercomparisod nan Industriar nfo l Processing, Budapest, 12-16 November 1979.

3. Dvornik I., Zee V., Ranogajec F.: Food Irradiation, Proc. Symp. Karlsruhe, 1966 IAEA, Vienna /1966/ p.81. 4. Dvorni Manua, I. k Radiation lo n Dosimetry /Holm N.W. Berry R.J. Eds./ Marcel Dekker Jorw ,Ne k /197O/ p.345

5. Raze Dvorni, mD. Dosimetr: kI. Agriculturen yi , Industry, Biolog Medicined an y , IAEA, Vienna /1973/ p.405.

6. Horvâth Zs., Bânyai É., Foldiâk G.: Radiochim Acta 13 /1970/.p.l50

7. Oscillotitrator System Pungor Type: OK-302 /Produced by Radelkis Electrochemical Instruments, H-130O Budapest, P.O.B Hungar6 .10 y

8. Pungo Nag, rE. y S.B., Kisss - Mr Szab , : G. ôOK-302/ 1 Oscillo- titrator and Its Measuring Cells, Hungarian Scientific Instrument , /198048 s / p.35

9. Cserép Gy., Feje Foldiâ, sP. Györg, kG. Horvât, I. y h Zs., Jaka Stenge, bA. Wojnärovit, rV. Chemica: sL. l Dosimetry, Laboratory Aid, Institute of Isotopes, Budapest, Hungary, /1970/

118 10. Magat M., Bouby L., Chapiro A., Gilson N.Z.: Electro- chemistry 62 fl958l p.307. /- Hirlin. 11 Stenge, gJ. : EnergirV. Atomtechniks ae 2 a2j /1969/ p.446

12. Földiäk G., Horvâth Zs., Stenger V.: Dosimetry in Agri- culture, Industry, Biology and Medicine, IAEA, Vienna /1973/ p.367

13. Nam J.W.: Food Irradiation Newsletter 5_ /1981/ p.16.

14. Razem D., Ocic G., Janicic J., Dvornik I.: Int. J. Appl. Radiât Isotopes .32 /1981/ p.705

15. Dvornik I., Razem D., Boric M.: Large Radiation Sources for Industrial Processe, IAEA Vienna, /1969/ p.613

Papers publishe worn o d k done unde Contrace rth t

1. Kovâcs A., Stenger V., Földiäk G., Recent results wit ethanol-monochlorobenzene hth e dosimeter, Procedings of the Sevent International Congress on Radiation Research, Edited by I.I. Broerse, G.W. Baendsen Nyhof. ,M f publishers /1983/ Vol.E., No.2-23.

2. Kovâc Stenge, A. sFöldiä, V. r: G. k extensioe Th Oscillometrie th f no c Evaluation Methor dfo the Determinatio Absorbef no d Dose. Proc. of the Second Working Meeting of Radioisotope Appli- catio Radiatiod nan n Processin Industryn gi . Edited by the Central Institute of Isotopes and Radia- tion Research, Academ Sciencef yo GDRf so , Leipzig, 1982., D.120.

119 3. Stenge Kovâc, Földiä, V. r A. : s G. k Control gammf lo a irradiation technolog alkoholiy yb c chlorobenzene dosimeter, IAEA Semina High-Dosn ro e Bosimetrn yi Industrial Radiation Processing, Ris0, Denmark, 20. September-1 October 1982

4. Koväcs A., Stenger V., Földiäk G.: Dosimetry for radiation technology in the Institute of Isotopes, Consultants Meetin Promotion go Radiatiof no n Processing in Europe, IAEA, Budapest, Hungary, 14-16 December 1982.

5. Koväc Stenge, A. s: V. r Technological dosimetry, Radiation Technolog P-rospects it d an yHungaryn i s , Seminar, Hungarian Chemical Society, Budapest, Hungary, 14 September, 1983.

120 R--n-L

/ b a/ Pig.l. Dosimeter ampoules connecte capacite th o dt y cell a/ Ring electrodes b/ Plate electrodes

Fig.2. Change of conductivity of strong electrolites as a function of concentration

121 0 (HCI%5 0 4 ) 0 3 0 12 0

Fig.3. Change of the conductivity of HC1 as a- function of concentration

Fig.4. Chang concductivitf eo monochlorobenzenf yo e dosimeter solutio functioa s na dosf no e measureme MHz8 4 t ;da measurez x H O 8 t da

122 G (CD

30 £0 vo cl% e Pig . /Ref.5 Radiolyti/ 5 . c yiel chloridf do functioa s ea monf no - chlorobenzen'e concentration. Inverted triangles: evacuated samples; triangles: samples in equilibrium with air; circles; sample equilibriun si m with oxygen. Dose rat JcGy/he3 , the doses applied belo kGy5 w .

GET)

a.o 16 Mrad/h • Q.•, 3 Mrad/h

10 OOM (Mrad) Fig.6. /Ref Radiolyti/ 5 . c yield chloridf so functioa s ea dosf no e and dose-rat e sample volth O 4 n e,i d san containinO 2 , 10 / g4 CB respectively. Open circules: samples initially brought into equilibrium wit beforr hai e sealing/ dose-rat kGv/h6 3 e ; solid circles: samples in ground-glass stoppered test tubes/ dose-rate 3'kGy/h.'" For better resolution the circles for 20 vo.% CB are inscribed into squares.

123 G

20%

»0 200 300 «B 500 600 TOO

Fig.7. Radiolytic yield of chloride as a function of oxygen pressure in the samples containing 4, 10, 20 and 4O vol.% monochlorobenzene respectively. Inverted triangles: evacuated samples; triangles: sample equilibriun si m with air, Dose-rat dosee th kGy/3 es applieh d belo kGyw5 .

Fig.8. OK-302/I type oscillotitrator with separate ampoule holder

124 pA-

Si-«Hod« -Si-diod.

cooling _ -cooling mixt art mixtur«

$. l

Fig.9 arrangemene .Th Si-diodee th f to , durin measuremene gth t of the absorptionof the cooling mixtures

200-

93kCy

'00-

50-

TemperaturI »CC

Fig.10. Temperature dependenc irradiatee th f eo d ethanol-monochlorobenzene dosimeter oscillometrit sa c evaluation

125 "T" T 200 MO «00 «»VtLEMOTH Fig.11. The absorption spectra of the monochlorobenzene dosimeter solutions 1-unirradiated solution; irradiated solutions; 2-1 kGy; 3-25 kGy; 4 - 1OO kGy

s8 ^ I

1500 •

soo-

100-

500 1000 1500 Irradiatio (hours« odm ) Pig.12. Effec lighf to t irradiatio urriadiaten no irradiated dan d ethanol-monochlorobenzene dosimeter samnles

126 I s

raj

900

300

TOD

600

500

0 7 0 6 O S 0 4 0 3 0 2 10

Instouiwni Mucban, seal* Fig.13. Calibration curve OK-3O2 Oscillotitrato" r"4

10 so 100 inshumtnt dafl«etiO(\ seal» numbw Fig.14. Calibration curve OK-302/1 Oscillotitrator "32"

127 ' Fig.15. K-12O typo gammC e a irradiation facility

•-prepared solutions •-irradiated seditions

100 •

800 Absorbed dos«

Fig.16. Conductivity resultirradiatee th f so prepared dan d monochlorobenzene solutions

128 10 100 AteortMd dos« IkGyJ

Fig.17. Conductivity of the irradiated ethanol-monochlorobenzene dosimeter solution

TABLE I. COMPARISON OF THE G{C1-) VALUES AT 7 Mrad FOR EVACUATED SAMPLES AND SAMPLES IN EQUILIBRIUM WITH AIR

G*values Chiotobenzeae content 0.3Mnd/h 3.6Mnd/h (vol.*) Evacuated Alt r Ai Evacuated

4 3.55 3.S4 3.67 3.74

10 4.90 4.35 5. 02 S. 00

20 5.87 5.82 5.67 5.66

40 6.10 0 0 . 6 6.00 0 1 . 8

129 oOJ

TABL. 2 E

The G /Cl"/ values for different monochlorobenzene concentrations

CB cone. /vol. %/ G - values Present work Previous work o.l-l kGy 1 - lo kGy 1 - lo kGy 1 - loo kGy

4 4.o6 + 0.19 /23/a 3.95 + o.35 /9/ 3.97 +_ o.oS /6/ 4.oo ^ o.o5b

lo 5.o+ 0.37 3 /21/ 4.9 6^ o.3 1 /lo/ / /6 O.1S.o+ o.oS.o+ _ _ 3oSl

2o 5.66 +_ 0.28 /14/ 5.58 _+ o.21 /lo/ 5.7o +_ o.o7 /6/ 5.66 +_O .o5

4o 6.1 . o.36+ 2 /lo/ 6.2o.3^ 8 o /ll/ / 6.1/5 6.0o.o+ 8 7 0.0; 6+ 6

a numbe n paranthesei r s denote numbee th s f entriero s

value adopted for dose range 1 - lo kGy only TABL. 3 E

The effect of the irradiation temperature on the absorbed dose values, measured with ethanol-monochlorobenzene dosimeters

Temperature Absorbed dose Absorbed dose, corrected with Q£ j~ the absorption of the cooling mixture

1. 5.2 5.1 293 2. 14.0 13.7 3. 25. o 24.5

S.o 4.8 273 14.o 13.3 23.8 22.6

4.7 4.4 233 13.6 12.8

23.2 21.8

4.7 4.3 191 12.2 11.2 22.0 2o.2

4.3 4.3 77 12.1 12.2 2o.6 2o.8

131 TABL. 4 E

Effec f storago t e temperatur e irradiateth n o e d ethanol- monochlorobenzene dosimeters at 243°K

Storage time Absorbed dose of the dosimeters /weeks/ No.l. No.2. No.3.

- 2o.o So.o 41o.o 6 2o.9 So.o 41o.o lo 2o.o 49.0 41o.o 14 2o.2 49.4 41o.o 36 2o.7 49.0 41o.o 60 19.7 47.7 412.0 85 2o.5 49.5 0 . 8 4o

TABL. 5 E

The effect of light during gamma-irradiation on the ethanol monochlorobenzene dosimeter samples e a l a Evaluatiorr y titratiob n n Evaluatio y oscillometrinb c dosimeter ______method______

L conc>/MHC solutio/ Dose/TcGyn / Instr.deflec- Dose/kGy/ tion /scale/

Monochlorobenzene lo.Zxlo 22. 9 2 421. 3 Monochlorobenzene S Zn + 9.7xlo"3 21. 21 2 17.9

Monochlorobenzene 1.9xlo"2 41.7 62 41.8 Monochlorobenzene + ZnS-CdS 1. 1.9xlo~* 41.7 49 32.7 2. 1.9xlo~2 41.7 51 34.0

Monochlorobenzene 1.6xlo~2 35.1 52 34.9 Monochlorobenzene S sheeZn + t l.oxlo"2 35.1 52 34.9

132 TABLE 6.

e effecTh f ligho t t irradiatio unirradiatee th n o n d irradiatedan d monochlorobenzene dosimeter samples

Ampoule numbers 1 2 3 4 5 6 7

Absorbed dose, measured before experiments /kGy/ 7.6o 19.7 3o.8 45.0 15o 25o

Absorbed "light irradiation dose" measured during experiments /kGy/ Duratio f lighno t irradiation /hours/

So o.4o 7.6o 19.7 3o.S 45.0 15o 2So loo 0.55 7.6o 19.7 3o.S 45.0 ISo 2So 2oo 1.48 7.85 2o.5 31.1 46.5 ISo 2So 3oo 2.35 8.60 21.1 32.5 49.0 ISo 25o 65o 4,75 9.7o 21.7 33.3 49 ..4 ISo 2So loSo 7.7o ll.oo 23.2 34.9 So.o ISo 25o

135o lo.Zo o . 13 24.0 35.1 So.o ISo 2So

1675 o S . 11 13.80 24.7 35.8 So. 5. 16o 26o

133 TABL. 7 E Investigation of the size of the ampoule, containing the dosimeter solution, concerning oscillometric evaluation /The diameter of the calibration ampoules were 11.1 mm/

No. Diameter Absorbe D/kG^ yd dose /kGy/ titration /A/ oscillometry

4528 lo.3 18.5 14.8 3.7 2o.o 26.6 22.0 4.6 17.3 31.3 25.7 5.6 17.9 46.5 42.5 . 4.0 8.6 4842 lo.S 18.5 16.4 2.1 11.4 26.6 24.0 2.6 9.8 31.3 28.5 2.8 8.9 46.5 45. S 1.0 2.2 434o lo.7 18.5 17.0 1.5 8.1 26.6 24.5 2.1 7.9 31.3 3o.l 1.2 3.8 46.5 46.2 0.3 o .6 49o4 io.9 18.5 17.5 1.0 3.8 26.6 25.4 1.6 3.4 31.3 31.1 0.2 o .6 46.5 47.0 0.5 1.1 5525 ll.o 18.5 18.0 o . 5 2.7 26.6 26.o 0.6 2.3 31.3 31.4 0.1 0.3 46.5 47.0 o .5 1.1 5597 11.1 18.5 18.2 0.3 1.6 26.6 26.3 0.3 1.1 31.3 32.1 0.8 2.6 46.5 ' 47.4 0.9 1.9 5634 11.• 2 18.5 18.2 0.3 1.6 26.6 26.5 0.1 0.4 31.3 32.1 0.8 2.6 46.5 47.4 0.9 1.9 TABLE 8.

Effec phantof o t m material monochlorobenzene th n so e dosimeter samples

Measurements Wall thickness Absorbed dose /kGyn /i f ampoulo e holder r Ai Plexigla C PolystyrenPV /mms/ e foam

o S. 5.2 . 51 5.So 5.So 5.25

o l. 11.7 t o . 2 ll.oo 11.65 11.75

3. l.o - 3.0 26.0 26.0 26.3 26.5

TABL. 9 E

Effect of plexi glass on irradiation of ethanol-monochlorobenzene dosimeter samples

Wall thickness of plexi Absorbed dose glass ampoule holder /mm/ 1. 2.

5 1 9.4o 21.0

lo 21.2

5 7. 9.4o 21.1

5 9.8o 21.3

3 lo.S 21.8

2 22.3

1 11.6 22.3

In air 12. o 22.6

135 TABLE lo.

Effec f storago t e ethanol-monochlorobenzen th tim n o e e dosimeters concerning oscillometric evaluation

Ampoule Nominal dose /kGy/ Absorbed dose /kGy/ measured irradiation at INISO No. at NPLA in 1977 in 198o n 198i *2

1568 25.0 25.4 . 25.7 1553 25.0 25.7 25.2 1668 25.0 25.7 25.4 164o 25.0 26.0 26.3

ANational Physical Laboratory, Teddington, England Institut f Isotope eo Hungariae th f o s n Academ f Scienceso y , Budapest, Hungary

136 TABLE 11.

Environmental effects on the ethanol-monochlorobenzene dosimeter

Environmental conditions Observations

Previous wor y Dvornikb k Dose dependence G/C1~/ is independent of dose in o.l-loo kGy Dose rate dependence G/Cl" independens i / f dose-rato t e lo5 G h uP to ^/ Dose range y MG 1 - y SG o Stabilit f dosimeteo y r Thermically stable and resistant to solution oxydation; HC1 formed is stable in solution under irradiation even at concentration of o.S Ml"1; Temperature G/C1~ s independeni / n temperaturo t n i e the rang f 27o-36eo K o Present work Transport No effect on the irradiated and unirradiated dosimeter samples During irradiation No e rangeffecth f 273-29n eo i t 3 K.but 2oa» decreas e rangn G/Cl"i eth f 77-27o n ei / K 3 Temperature K Durin 3 32 g d storagan K 3 o effecN e25 t a t During oscillo- The temperature of the calibrated ampoules metric evalua measuree b onee o th t s- d dan mus e similab t r tion within +_ 277 K Light Onl V lighyU t change e compositioth s e th f o n dosimeter solution Size of ampoule The diameter of calibrated ampoules and the ampoules to be measured must be the same m m withi 2 0. _ + n Storage No effect in the absence of UV light

137 TABL. 12 E Dose-rate values, determined by Fricke, ethanol-monochlorobenzene /CB/ dosimeters and Si-diode detector

Number Dose-rate values /kG/ y" h of measurements Fricke dosimeter CB dosimeter Si-diode

1. 8.23 ± 0< 16 8.29 ± °.41 — 2. 8.2o — °*16 8.36 ± °.42 - 3. 20.90 - 0.42 2o .55 +_ 1 .03 21.1C ^ 3

* / G/Cl"/ - 5.64 was used /

TABL, E13 Intercompariso monochlorobenzenf no e /CB/ dosimeter with different dosimeter systems

Absorbed dose results /kGy/ CB dosimeters Alanine CB dosimeters Nominal dose Measured dose Irradiatet a d INISO Irradiatet a d NPL Evaluate t INISa d O EvaluateF GS t a d at INISO

5 4.8 0.1+ o 5 2 0. + 7 4. 4.5 0.1+ 5 5 lo 9.85 + o.3o S o. . + 7 9. o .3 o ± o S . 9 19 19. So +_ 0.60 2o.o ^ 1 .0 18.2 ^ 0.6

2o 0.6_ + 00 8 . 19 5 3o.1. _ + o o l. 29. _ + 0 3o 29.5 l.o* j o o 6 51.2. * 0 5 1. So.; + o

So l.S_ + o S . 48

Irradiatet a d BARC ' lo 9.9 + 0.3 2o 6 0. 2o. ^ 9 3o 32.5 + l.o 4o 41.8 + 1.3

NP Nationa- L l Physical Laboratory, Teddington, England;

GSF - Gesellschaft fur Strahlen- und Umweltfoschung, München,FRG; BAR Bhabh- C a Atomic Research Centre, Trombay, Bombay, India; INISO - Institute of Isotopes, Budapest, Hungary

138 TABLE 14.

Ratio o£ estimated doses to NPL-doses from NPL calibration n concerninru g monochlorobenzene dosimeter

NPL-dose Estimated dos/ e L dosNP e 8 19 AGy/ 0 1981 Previous results Recent results Previous results Recent results

5 1.19o o.96o

lo 1.145 0.985

19 - 1.111 I.o26

2o l.ooS o.99o

3o 0.98S 0.983

31 - 1.029 o.97o 1.087 l.oSS

So 0.996 o 97 o.

139 PROGRESS IN ALANINE/ESR TRANSFER DOSIMETRY

D.F. REGULLA, U. DEFFNER, 0. SCHINDEWOLF, . VOGENAUERA . WIESE,A R Gesellschaft für Strahlen- und Umweltforschung mbH München, Neuherberg, Federal Republi Germanf co y

Abstract

Reference is given to a new and precise dosimetry method as developed, withi a researcn h contract Gesellschafe th t ,a Strahlenr fü t - und Umweltforschung (GSF), Miinchen-Neuherberg witInternationae th h l Atomic Energy Agency, Vienna. Concerning terminology, this method is named free-radical'dosimetr alaninejelectror o y n spin resonance (ESR) dosimetry. Apart fro reviewa m , fundamentals, physical, chemicad an l dosimetric parameters are given together with a system description. The report deals extensively with the effect of apparative parameters and influence quantities, and considers particularly 1) analysis of ESR equipment to reduce uncertainties, 2) quality improvement and assuranc sampln i e e preparation ) softwar,3 e developmen datr fo ta evaluation, 4) calibration of the system and 5) performance tests under laboratory and field conditions. For an objective rating of the overall uncertainty and reliability of the system achievable under routine conditions of transfer dosimetry, results of an international dose intercomparison are reported with the samples mailed, and irradiated at a primary standard dosimetry laboratory.

INTRODUCTION GSP activities in the field of high-level photon dosimetry are tracable yeare th bac so t k1974197d an 3, whe pilona t plan hygienizatior tfo f no sewage sludg y irradiatioeb n (Co60, ISOkCi s builwa ) t clos Municho t e . projece Th supportes t wa Federae th y db l Ministr Interioe e th th f d yo ran Free Stat Bavariaf eo that .A t time contributeF ,GS dosimetryo t d , which discoloratioe bases th wa n do silvef no r doped metaphosphate glassed san thermoluminescenc f lithiuo e m borate, with Fricke - dosimetrre a s a y ference system resulte .Th s were reporte occasioe Internae th th n do f no - tional Symposium on the Use of High-Level Radiation in Waste Treatment, organize IAEy b dMunichn i A , 1975/1/. Nearby, researc performes hwa t a d GSF to develop a dosimetry system matching the needs in high-level dosimetry more properly .methoA d using solid organic compounds revealed- ,al earln reada n yo y stag f progresso e , most promising results; this work referred to earlier efforts of Bradshaw et al. in 1952/2/ and Bermann et 197 n 1971/3/i n i 6s . thawa al t .tI first rather accurate resulte th n i s dose range 100 Gy to 100 kGy were reported by GSF at the First Interna- tional Conference of ESNA Working Group on Waste Irradiation/4/. In 1977, GSF was invited by IAEA to join an international party on the subjec Higf to h Dose Standardizatio d Intercomparisoan n r Industriafo n l Radiation Processing e ultimatth ; e intentio provido t f IAEo ns n wa Aa e international dose assurance service. For this purpose different obviously appropriate dosimeters from different organisations should be tested aiming to find a system applicable for transfer dosimetry. In parallel, IAEA establishe coordinateda d research programme with activity concentrated among stude other th f influenc o yn o s e quantitie- saf

141 facting reliabilit d accuracy,an y n whic i F als GS ho participatede Th . commo F activitienGS IAEd an A s were bound int a Researco h Agreemenn i t 1978 and 1979; from 1980 till to now cooperation was based on Research Contracts. In November 1981, the IAEA Advisory Group on High-Dose Pilot Intercomparison quoted alanine/ESR dosimetr developes a y d performean d d F havinbGS y g achieve bese th dt results withi e inteth n r comparison programme. The group proposed to the Agency to initiate the planned pilot dose y usin assurance kG electro th g0 10 o net servicy range G th 0 1 en i e spin resonance measuremen fref to e radicals induce alaninen i d operas /a - ted by GSF, as the intercomparison dosemeter system. The state of the alanine/ESR dosimetry technique elaborated at GSF in course of the years is compiled in Table 1. Table 2 summarizes intercomparison results involving standard dosimetry laboratories. The figure giv2 Tablef sd o e an evidencprinicipa e s1 th r efo l applicabi- alanine/ESe th lit f o y R syste transfe. in m r dosimetry. Further activity referred, withi e IAEA/GSth n F Research Contract e evaluatioth o t , d an n physical interpretation of ambient parameters as well as to computational data evaluation within four major categories, i.e.: # Detector production # Influence of ambient parameters # ESR spectrometer optimization # Data processing. findinge Th reporte e followine sar th n i d g along wit shorha t description of the measuring principle.

Tab. 1 Selected chemical-physical and dosimetric properties of the GSF alanine/ESR transfer dosimetry system

Composition L-a-alanin Œ3-GHNH2-CCOH(90%), paraffine (10%) Effective atomic number Zeff =7'2, Effective specific 1,07 g/oif4 (50% alanine/50% paraffine) gravidy 1,22 g/cm"3 (90% alanine/10% paraffine) Dimension lengtsm m 0 1 h x (photonsa di m m ,9 neu4, - trons) 4,9 mm dia x 1 mm length (electrons) Dose range 1 Gy- 1 MGy (present state) 1 Gy- 0.01 MGy (linear range) 0.1 Gy- 10 MSy (objective) Time behaviour (1 - S/So) a 0.01 for 2 years, at 22°C and 40 - 60% rel. humidity Interspecimen scattering s<+- 1,5% Overall uncertainty_____ < 5 % (2s)______

142 Tab2 Selecte. d result f high-doso s e intercomparisons basen o d GSF alanine/ESR Transfer Dosimetry. Nominal absorbed doses in water give y NPLb n, Teddington d IRD-SSDLan /e d o ,Ri Janeiro. Dosemeter transport by mail. Nominal dose Evaluated dose Ratio kGy (Lab) kGy (GSF) Ev./Nom. dose 0.05 (IRD) 0.050 1.000 0.1 (IRD) 0.101 1.010 0.1 (IRD) 0.102 1.016 0.5 (IRD) 0.493 0.986 0.7 (IRD) 0.703 1.004 1.0 (IRD) 0.982 0.982 5.0 (NPL) 4.800 0.977 10 (NPL) 10.210 1.021 20 (NPL) 20.080 1.004

30 (NPL) 29.250 0.975 50 (NPL) 50.050 1.001 70 (NPL) 68.740 0.982 100 (NPL) 98.600 0.986

Fundamentals The traditional dosimetry methods are based on radiation effects in inor- ganic materials, e.g. ionizatio r (ioai n n ni chambe r dosimetry), temperature rise in graphite or metal (calorimetry), coloration of chemical solutions (Fricke dosimetry) and induction of luminescence capability (thermoluminescence, photoluminescence). In contrast, the dosimetry method described her bases i e solin o d d organic compounds particularn ,i , crystalline alanine CH3-CHNH2-CCOH r measurementFo . e generatioth , n of free radicals is used (Fig 1).

PRIMARY PROCESS SECONDARY EFFECTS OOS1METRIC EFFECTS

COLOUR OPTICAL CENTERS DENSITY

ELECTRON RADIATION* IONIZATION FREE RADICALS SPIN RESONANCE

[SOLVENT DISSOLUTION lYOLUMINESCENCE

FigDosimetr1 . y with solid organic molecules Alanin organin a s i e c compound whic s roughli h y tissue equivalent with respect to atomic composition. Additionally, the generation of free radical radiationy sb , quantitatively accessibl y electrob e n spin resonance

143 (ESR) spectroscopy, is part in the chain of cellular damage in biological materials. îhese propertie higa d h san precisio determinatioe th n ni f no the spin concentration, make alanin usefua e l detector botdosimer fo h - tric and radiobiological studies. Due to the experiences hitherto achieved at GSF, the new dosimetry method may be considered an off-line tissue equivalent (TE) chamber dosimetry.

Fig. 2 Alanine dosemeter samples of 4.9 ram diameter and different length

Fig. 3 View of the ESR spectrometer

144 System description The two major components of the alanine/ESR transfer dosimetry system are first/ the dosimetric alanine samples (Fig. 2) and second, the ESR spectrometer (Fig. 3), which at GSF is of Varian E9 type. For dose evaluation computea commerciaa usefuls F i r GS t datR ;a lES a acquisition systes i m applied with an adopted software. Data are displayed on graphic and al- phanumeric screens; hardcopie Y recorde X e mad b n o d matrien an rca s x printer. The whole system is operated in an air-conditioned lab. a laborator p u F moreovet GS se y s equipmenha r r preparatiofo t e th f o n alanine samples which will be described elsewhere. Samples The preparation of the samples is done in three steps; i.e. mechanical processing of the crystalline alanine, blending of the components (alanine/paraffine pressind pellets)e an th f go . Pure polycrystalline alanine first is grained and sieved. Afterwards the two components alanin d paraffinan e a homogeniou e blendet ar ege o t d s mixtur basis e a samplr sfo e preparation. Present samplesr o consis 0 8 f to paraffine% 10 r o 0 2 .alanin % f Besideo 90 d edifferenan e sth t sensitivity the surface qualit workabilitd yan y during preparatio leay eitheno ma dt r composition. For preparatio samplesf no ,laboratora y pres useds si , wher blendee eth d materia filles li pressina n di g forcompressed man de th manuall n i / yor early past, automatically. The sanple mass depends on radial and axial extension of the ESR measuring cavity. It was found convenient to use sam- lengthm m diametem m 0 1 9 ,d ple 4. whic ran f so h results masa int f o so t thin I s. casmg 0 e 25 ther onls ei smalya l influenc sample th f eeo length signae tth o l whic n easilhca correctede b y ; longer samples cause more problems in preparation and show less mechanical stability. The influence of specific gravid peak-to-peao yt k signal gives si Fign ni . .4

210 ••

200 - Qasa 3-105rad 190 0.9 Alanine/ 0.1 Paraffin ^*"

3 <à 180 o oo'X° 13 e x ai Jx ° 170 o^-^ a. 0. 160

isn- 1 1 1 ! 1 1.05 1.10 1.15 1.20 1.21.30 5

Specific gravidy (g-cm~3)

Fig. 4 Dependence of ESR signal height (peak-to-peak) on specific gravidy

145 Earlier tests have shown that zero-reading, respons certaia d ean n angular influenc readine th n eo g depenf preparationo y dwa o upot e e th n .Du grain size, response varies by about 10% using the peak-to-peak method, whil angulae eth r influence durin g+-4o t readou %p u relativ s e i t th o et average reading value; the response R turned out being a function of angle 6 for peak-to-peak reading, according to the equation R = a + b x cos2e where a and b are constant (Fig. 5). The angular effect can be minimized by either integral evaluation or use of proper grain size.

104-

1.02-

100 i*1% bond -

098 oPeokAmpL x. Integral 096 45 90 180 Angte9,Deg Fig Angula.5 r dependenc readinf eo g from alanine samples

0.7-

06 •0.05Gy 0 0 05-

1 1 1 012345678910 Sample No.

Fig Zer.6 o readin differen0 1 f go t alanine samples

146 The ratd magnitudan e f pressuro e e during sample preparation influence the zero reading pretending doses up to about 0.6 Gy. Fig. 6 shows the results of zero reading from 10 samples. Crystalline L-alanine from different manufacturers (Fluka, Merck, Serva) revealed no significant difference, so far, neither in response nor in angular dependenc readingf eo . Since response, zero reading, angular dependenc readinf eo d reproduan g - cibility of the ESR signal differ with the preparation procedure of the samples, standardization is mandatory. Till today, some thousand dosemeterf o s s were prepared wit a standarh d interspecimer 1.5- deviatio+ fo %= s f no n scatterin responsf o g e within a batch (Fig. 7). Interbadge scattering is equally 1.5% or less for Is. ESR spectrometer specifications Quantitative ESR measurements are affected by a number of uncertainties resulting mainly from spectrometer stability? spectrometer settings and sample positioning. It coul showe db R spectrometen ES thae tth r need swarmua p tim approf eo - ximately two hours, for high precision measurement. After this time the spectrometer sensitivity remains constant wit smalha l negative slopf o e <1% over a period of 8 hours. The gain steps marked at the spectrometer console must be calibrated, sinc converet theno o yd t linearl eaco yt h other prefactoe .Th r switcf ho amplification deviates from linearity by approximately +- 3 %, while the decade-switc Therefore. h4% deviate- + o t , p correctionsu amplie th r -sfo fication factors have been evaluated accordine th Fig d ; Fig9 an o . gt 8 . precision of the corrections are -H- 0,25%.

i T

O O o O

OQ 00 O o ___ g o O •2% bond

00° 0° S 098r>____o 35

0 4 6 3 2 3 8 2 4 2 0 2 6 1 2 1 8 4 0 Sample No.

RelativFig7 . e interspecimen scatterin alànin0 4 f go e samples

147 l i t ' 1 i l i i iii

1.05 — -

1.04 - -

1.03 - - 1.02 - -T" S 1.01- <=> - ftoo l |Q99 m _ i ii t i i t i i O i i i 0123456789 10 Switch setting

Fig Correction8 . simplificatioe th r fo s n prefactor spectrometeR ES switce th f ho r

1.05J

1.00

3 u o

••«0.95

2 1 0 Switch setting

Fig Correction9 . amplificatioe th r sfo n decade spectrometeR ES switce th f ho r

For precision dosimetry it is necessary to record the ESR spectrum as un- distorted as possible. Therefore the magnetic field modulation should not be higher than 1/5 of the line width of the central peak of the spectrum, ïhe time constant should be 1/40 of the passing time of the central peak. Amicrowavta e R poweline ES mor f alaninf re so o eth thaW em n5 begi o nt saturate and broaden. Therefore a microwave power of 2 mW was used for all measurements.

148 1.01-

-Q— 1.00 .<-O-O-O-

0.99-

0 2 8 1 6 1 4 1 2 1 0 1 8 6 A 2 0 Measurement No.

Fig. 10 Reproducibility of an individual alanine sample not removed' from sample cell beetwee readoue nth t procedures

1.01

o o o 1.00 o o ]±QA%- band

1.99-

02463 10 12 14 16 18 20 Measurement No.

Fig Reproducibilitl i . individuan a f yo l alanine sample removed frosample mth e cell after each readout procedur- in d ean serted again upside down

Reproducibilt R spectrometeES e th f s beeo y ha rn differeno testetw n i d t ways. For both tests the same sample was irradiated by a dose of 1 kGy and evaluated successivel times0 y2 tesspectrometen e .I th t1 (Fig ) .10 r settings were not changed and the sample was not taken out of the cavity. The standard deviatio measuree th 0,13%- + f no = tesn d.I s dos2 ts ewa (Fig. 11) the sample was taken out of the cavity after each measurement and inserted again upside down; furthermore the settings of the spectrometer were adjusted before each measurement e standarTh . d deviatiof o n the measured dose was s = +- 0,23%.

149 Software for dose evaluation According to the software program prepared by GSF (Fig. 12) the dose eva- performee R signab ES n luatioe lca th df no eithe doubly b r e integration R spectru ES measuriny b e or th fo m maximue th g m peak-to-peak amplitude. If the dose value is determined by integration, the computer evaluates th o eways tw dos ,n i eeithe y integratiob r n ovewhole th r e scan range (200 Gauss) of the ESR spectrometer/ or by a partial integration over the spectrum only (approximatel Gauss)0 y13 lattee .Th r procedure providen sa iirproved precision tims i ed ,savingan othee th rn .O hand peak-toe ,th - peak amplitud eithen eca assessee b r d durin integratioe th g n n timei r ,o a second way independently of integration, by the g-value of alanine. The advantage of the second approach is that there is no need to record the whol spectruR eES jus t centrae mbu tth l peak. computee Th r program contain mathematicae dose sth th e f responso t fi l e curve of alanine. For dose evaluation, the first sample of every measurement series is a calibration sample. Based on the evaluated dose of this sampl dose eth e response curv shiftes i e d accordin minoo t g r changef so spectrometer sensitivity. Furthermore, the program provides the possibilit evaluato t y zere eth o readin n unirradiatea f o g d sample, store this valu fro t followinl ei mal g measurements. The software program automatically corrects for amplification factors and sensitivity shift of the ESR spectrometer as well as for zero reading, irradiation temperatur saturatiod ean dose th e f effecno t curv highet ea r doses.

WRITE TO SCREEN RESTART: OR PRINTER? »RIT SCREEO ET PRINTERR NO ? CORK 31 ZERO SAMPLE? QUICKDOSE DETERMINATION? QUICK DOSE OETERM? DATE? FIELD SET? SCAM RANGE? FIELD MODULATION? MICROWAVE FREQUENCY? MICROWAVE POWER? CALIBRATION DOSE? NUMBER OF SCANS?

NORMAL DOSE OETERMl WICK OOSE DETERMINATION! INTEGRAL If Cal saoçl P-P CAL CURVE PART INTEGRAL P-P COHR CAL CURVE P-P CAL CURVE P-P SHIFT CORR CAL CURVE P-P CORR CAt CTRVE P-P SHIFT CORR CAL CURVE

EVALUATED SPECTRUM VALUE X CM, FAC73R - ZERO DOSE

If cal Saopl

OIS7LAX RESULTS r o l Ca f I (SCREE PRINTERR NO ) Sanpl

LISR O TF DOSEOF CONTINUER SO ?

Fig Flo2 .1 w compute e schemth r efo r evaluatioR ES f no signals (peak-to-pea integralr ko )

150 Detection limits Alanine/paraffine samples sho a zerw o reading correspondin o about g t 0, y (se6 G lowe e eTh Pigr. limi6) . dosimetrf o t determines i y e th y b d reproducibility of the zero reading value and by the noise of the spectrometer signal-to-noise .Th ezere th ratiordee o r th readin ofo rf o s i g of 10. These two limiting factors result into a scattering of the zero readinwhicy G present 1 lowee ha abouf 0, gth o r- s t + i t limi detecf to - tion. For completing the dose response curve in the high dose range GSP alanine samples were irradiated with electrons (2.y MG 5 doseo 5 t MeV f p o su ) (Pig. 13). At a dose level of 0,5 MGy the ESR signal shows saturation. For doses above 0,5 M3y the ESR signal decreases again, which holds for both reading methods, i.e. peak-to-peak amplitude and integral of the whole spectrum. The alanine/paraffine samples change structure, become softened and deform for doses higher than about 2 MGy loosing capability for precise dosimetry. At doses above 0,3 MGy precision is anyway decreasing because of the dose response curve saturating in this range. Efforts are made to overcome these problems and extend the upper detection limit.

Co-60 o§/25MeV

Error band *20% ulo.1 OJ 1 1000 Dosey ,KG

Fig Dos3 1 . e effect curv alanine/ESr efo R samplee th n si range 0.1 kGy to 5 MGy

IRRADIATION CONDITIONS Previous studies showe n increas da yiele th f fre o dn i ee radicals (spin concentration) with irradiation temperature. This increase is linear up e characteriseb n toca a 80°slopd an y f C(aS/SJ^nX^QOlSb o de 0^1. To explore whether this phenomenon dependirradiatioe th n so n atmosphere, experiments were performed as shown in Fig. 14 with the dosemeter samples exposed in pure oxygen respectively in pure nitrogen atmosphere.

151 -Thermoelement Double-wall Steelcontainer -Aianine Samples ter vThermoelement

Fig. 14 Experimental set up for the irradiation of alanine dosemeters at different temperatures and in different gas atmospheres

Tfae irradiation sourc0 s6 wero C e e a wit carrien i dosha t edou ratf o e 90 Gy/min. Bie dose effect curves obtained for these gases and air show no noticable difference (Fig. 15). Detailed result measuremenf o s e ar t becomet I . plotteFigd 17 s.an eviden Fig6 n 1 di . t that the- partial pressure of oxygen and nitrogen during irradiation has no influence on the yield of free radicals in the dosemeter samples used here. This result indicates that paramagnetic oxygen molecules from the ambient gas should not explai e increaseth n d rat f spio e n concentration e experimentTh . s will be extended to irradiation atmospheres with higher humidity.

i 1 i 1 i i ~

100

0> '3

i l l l l l i l l____l l l l l l l I I 10 100 Dose.kGy

DosFig5 1 .e effect curve different sa t temperature airn si , oxyge nitroged nan n

152 115

g 100 a 109,y 9kG "o A 54,9y 5kG c o 5,496 kGy .S'qc If) 33 * 0,546 kGy ce V) LU 20 40 SO 80 Irradiation Temperature, "C

115

110

CN CM o105 6 j- Atmosphere 2100 109,9 kGy a 54.95 kGy .2> 5.496 kGy to 0,546 kGy ce to UJ 20 40 60 80 Irradiation Temperature, °C

Fig. 16 Dependence of ESR signal on irradiation temperature at different doses in oxygen and nitrogen atmosphere

153 120 Oxygen 115

110 0«° 2 105 6 +—+- g

120 Nitrogen 115

0110 70 *C —* 56 "C —+ 5105 £ 1100 d .2» oc 01 aä to LU 10 100 kGy

Dependenc7 1 Fig. f normalizeeo d ESR signa dosn o lt ea different tenperature oxygen i s nitroged nan n atmosphere

154 Pilot dose assurance service Based on these preparatory investigations, IAEA started, in late 1983, a pilot project to the scheduled Dose Assurance Service together with GSF acting as a Reference Laboratory, The number of participating industrial irradiator plantaddin i ; projec-e s 15 th withi s f o firse twa th n ru t tion, NPL was involved for independent check of GSF dose evaluation by irradiation under calibration conditions. GSF issued the transfer dosemeter package for mailing, consisting of 10 dosemeter capsules (Fig 18) for irradiation, and one dosemeter capsule containin n unirradiatea g d sampl r zerfo eo reading contro d anothean l r sample expose a referenc o t d e dose e transfe.Th r dosemeter packags i e backed up by dry gel and a set of temperature indicators. IAEA was in charge of administration selecting the participants and mailing and collecting again the dosemeter packages. The Agency issued a handling instruction and questionaire to each participant (Annex 1) and was responsible for confidential handling of the NPL check doses and participants dose estimations. "For evaluation, GSF receives the transfer dosemeter package only together with the figures on irradiation temperature. GSF reports the dose results to IAEA which evaluate e degreth f agreemenn o eso t between local dose estimatio transfed nan r dosimetry Agence .Th y reportparticipante th o st s and is together with GSF prepared for dosimetric advice. Evaluation of Piloe thth etf o firsDos n eru t Assurance Service wil finalizee lb n i d early 1984 resulte ,th s wil reportee lb Internationae th t a d l Symposium on High-Dose Dosimetry, to be organized by IAEA at Vienna during 8-12 October, 1984.

Research Centre Munich

ESR Transfer Dosimetry Nr..iAJ.;;A-rnuo7

Fig. 18 GSF Transfer Dosemeter capsules, alanine samples and sticker for ID number

155 References /!/ Regulla, D.F., Schurmann, G., Suess, A. In: Radiation for a Clean Environment, p. 465, IAEA, Vienna (1975) / Bradshaw/2 , W.W., Cadena, D.G., Crawford, B.W., Spetzler, H.A.- ,Ra diât. Res. 17,11 (1962) / Bermann/3 Choudense d , , F. Descours , , H. Advance : In . ,S Physican si l and Biological Radiation Detectors, STI/PUB/269 . 311p , , IAEA, Vienna, 1971 / Regulla/4 , D.F., Deffner Dosimetr: megara. e ,U th n yi d rang meany eb s R spectrocopofES f freo y e radical aminn i s o acids : Radiatio.In n for Pollution Abatement (Ed .A.F: . Groneman), European Societf o y Nuclear Methods in Agriculture, Wageningen (1976)

156 Annex 1 Handling instruction and questionnaire to accompany the GSF Transfer Dosimetry Package.

INTZRHATIOKAL ATOMIC ENERGt AGENCY

Pilot Dose Assurance Servies - 1983 Participant

Instructions Each participant receives 11 numbered dosimeter capsules, 10 of which are green-labelled and 1 is red-labelled. The green-labelled capsules are for irradiation, the red-labelled capsule is for reference purposes and supposed to accompany the other capsules except .during irradiation. Attached to each capsule is a temperature indicator. Irradiate 2 green-labelled capsules simultaneously for each dose of interest. t Pleasope e capsuleno th n o dosimeter e ed Th . y s i baseunde e alaninn o dus r e samples and ESR evaluation which method is described in the reprint mailed under separate cover. Aftee irradiationth r , kindly retur l al capsulen s together with this information e mailin sheeth o t tg address below.

Serial number of dosimeters: Date of irradiation: (d) Cy) 1983 Type of radiation source: Irradiation temperature: 3C (mean) or °C (max)

Nominal absorbed dos waten ei r (kGy exposurr )o e (kR): Pai capsulef ro . sNo - dose/exposure (kGy/kR) Pai capsulef ro . sNo - dose/exposure (kGy/kR) Pai capsulef ro . sNo - dose/exposure (kGy/kR) Fai capsulef ro . sNo - dose/exposure (kGy/kR) Pair of capsules' No. - dose/exposure (kGy/kR)

(Date) (Signature)

Mailing address; Dr. J.W. Nam International Atomic Energy Agency Wagramerstrass5 e P.O.Bo0 10 x A-1400 Vienna AUSTRIA

157 DOSIMETR ELECTROR YFO N BEAM APPLICATION

. MILLEA R Accelerator Department, Ris0 National Laboratory, Roskilde, Denmark

Abstract

o aspectTw electrof so n beam dosimetr e describedyar hane on d n ,o development of thin film dosimeters and measurements of their properties, and othee th rn o hand developmen calorimeterf o t r calibratiosfo f routinno e dosimeters, e.g. thin films. Two types of radiochromic thin film dosimeters have been develope thin i d s department e propertieth d ,an f thesso d coman e - mercially available dosimeters have been measure comparablee d founb dan o t d . Calorimeters routinr fo e eus ,measurementsn i whic e ar h beine ,ar g investigated with reference to their application as standardizing instruments, and new calorimeters are being developed.

1. INTRODUCTION

Thin film dosimeters that can be used for absolute as well as relative dos« measurement at industrial electron accelerators are developed. The wide range of energ f suc o yMeV0 1 hd thei )- an accelerator V r ke hig 0 h15 dos- ( s e rates sugges applicatioe th t dosimeterf o n s whic e thid displaar han n y littl- ede pendence of dose rates. Radiochromic dye films (McLaughlin et al., 1977) seem to possess these properties (McLaughlin et al., 1979). During this work measurements have been performe n commerciallo d y available thin film dosimeters as well as on dosimeters made in this department, in part to confirm previous findings (Miller and McLaughlin, 1980) and in part to extend these measurements, which include studies of the influence of relative humidity and storage effects.

When determining various propertie f dosimeterso s importani t si emploo t y calibration procedures, which provide a fixpoint beyond dispute. In the cours f thio e s becom ha wor t i ke apparent thaproceduree th t s employer fo d calibration of electron accelerators - not only in this department, but also more worldwid mighe- facn i tdisputede tb stilt I . l remain seee b f i no st

This work was supported by IAEA Research Contract No. 2883/RB, and this report constitutes the final report under that contract.

159 suc disputha justifies i e n effora notr o dt s beebu t,ha n initiate shoo t d w the merits of electron beam calibration procedures, and if needed to improve them.

This report describes measurements mad n varioueo s type f radiochromio s e dy c films wels , a status la calorimetrir sfo c worcalibratior fo k n purposese .Th calibration procedures are not restricted to be used with thin films only, but can of course be employed for any dosimeter system.

2. PROPERTIES OF RADIOCHROMIC FILM DOSIMETERS

2.1 Types of radiochromic films

Three types of film dosimeters have been investigated:

Nylo. a n films containing hexa(hydroxyethyl)pararosaniline cyanids a e dye precursor. Commercially available (Kantz and Humpherys, 1979). Type designation: FWT-60.

b. Polyvinylbutyral (PVB) films containing hexa(hydroxyethyl)pararosaniline cyanide. Made in this department on a small scale (Miller and McLaughlin 1980). Type designation: P-15.

c. Polyvinylbutyral (PVB) films containing pararosaniline cyanide. Made in this departmen smala n to l scale. Type designation: P-15 R.

2 Preparatio2. f filmno s

FWT-60. No information has been published on the preparation of Nylon films. They are normally supplied in 1x1cmz pieces, and each batch is supplied with a calibration factor, referring to a common calibration curve. This factor is usually between 0.8 and 1.2. The thickness of the films is around 50 ym and withi batcna h varies less 5 urntha3~ .± n

160 P-15. Radiochromic dye films made from PVB are cast on flat glass as describe Milley b d McLaughlid an r n (1980) e recipfollowss .Th a s i e :

3 2-ethoxy-ethanocm 5 28 l 0.4 cm3 diocthyl phthalate 25 g PVB 1. hexa(hydroxyethyl)pararosanilin5g e cyanideW ,M 578 citrig 6 0. c acid.

This amount is enough for 6 films of - 30 cm diameter. The thickness is - 65 um. After stripping from the glass plane, the films are dried for one week in vacuum at - 50°C for removal of residual amounts of solvents. The films are then allowe weea morr r o kstabilizo fo t de r beforai n i ee measuremente sar made.

ii i i i >i] FWT60- Nov.81 X-600nm 30 20 10

1 5 Q O <3 2

Q5i

.Q2

0.0 51 15 2 50 100 200 Dose. kGy . Respons1 Fig. e curve r Nylofo s n radiochromic dosimeters (FWT-60). Irradiations were made at Cobalt-60.

R. Films containing pararosaniline cyanide, MW - 314, are made from the same recipe as above, but with a reduced amount of dye (0.8 g) according to the molecular weight. Further details about the casting of P-15 and P-15 R films have been described earlier (Mille McLaughlind ran , e 1980)ar d ,an based on earlier work at Ris0 (McLaughlin et al., 1977).

161 10 20 I I I P15R-3-9-82A 20

15- S "6 a a o o 4 10

/,... 50 100 Dosey ,kG Dos». kGy Fig . Respons2 . e curve r PVfo s B radio- Fig. 3. Response curve for PVB radiochromic dosimeters (P-15). chromic dosimeters (P-1. R) 5 Cobalt-60 irradiations. Cobalt-60 irradiations.

Respons3 2. e curves

Response curves of the three film types are shown in Figs. 1-3, and absorption spectra are shown in Fig. 4. Wavelengths of 600 nm and 510 nm are used for dose measurements with FWT-60 and P-15 dosimeters, while 551 win is used for P-15 R. When comparing irradiations with Cobalt-60 Y-rays and at 10 MeV electrons, some dose rate dependence is found above 50 kGy for .the FWT-60 dosimeter (McLaughlin et al., 1983). Measurements for the PVB dosimeters show less dose rate dependence than the FWT-60 dosimeters (ibid.). Gehringer (1979) has demonstrated dose rate dependence at very low gamma dose rates for FWT-60 dosimeters, particularly at low relative humidities.

The trend toward saturation, which is observed at high doses on the curves, is instrumental saturation rather than film saturation, which is demonstrated by measurin response th g e vi5 curvma filmf eo n thi.I s case filth em satu- rates at an AOD/mm value of - 450. This corresponds to an optical density of filmn ur .5 Saturatioe th 2.2r fo 5 n woul, um d 0 hav5 e e th 22.- bee r D nO 5fo which canno measuree tb d directly.

162 2.4 Relative humidity

The influence of relative humidity on these radiochromic dosimeter films must be taken into account e influenc.Th B (P-15PV n e)o dosimeter s beesha n studied (Mille McLaughlind an r , influence 1980)th d , an Nylo n eo n (FWT-60s )ha been studied by Gehringer et al. (1979,1982) and Levine et al. (1979). All studies used cobalt Y-ray irradiation. In the newer work by Gehringer a link between oxygen content, relative humidit dosd an ye rate seemestabe b o st - lished.

In the present study some of Gehringer's measurements have been confirmed, humidite anth d y electroV responsMe 0 1 nt ea irradiations have been measured.

' T

1.6 -OA 15 kGy Cobolt

1.4

1.2 03

1JO a a o o 03 -02

0.6

0.«

0.2

0 300- 400 500 600 700. \.nrn

. Absorptio4 . Fig n e threspectrth r e fo adifferen t types of dosimeters whose response curves are shown in Figs. 1-3.

163 Fig. 5. Glass vial used for humidity studies at cobalt irradiations. The diameter of the vial is approx, 25 mm. ,

5 Cobal2. t irradiations

In each set of measurements, dosimeters were stored over saturated salt solutions for at least 5 days. The salts used were:

12.4$ r.h.: LiCl

33.6$ r.h.: MgCl2

54.9$ r.h.: Mg(N03)2 75.5% r.h.: NaCl

The stated r.h. values are for 20°C, but they are found to change less than 30°- ° Crange 20 (Wexle th f eo n 1 i $Hasegawad ran , 1954). Normall filme th y s were stored at - 20°C and 40-60$ r.h. before conditioning. We also tried to

dosimetere drth y s ove ro influencn Psubsequene w Z0th sa S n firste eo w t t,bu measurements.

cobalt-irradiationsf Io firsa n t se t , dosimeters were irradiate smaln i d l glass vials. The dosimeters were resting on a stainless steel mesh above saturated salt solution s dose s calibrate(FigTh ewa . .5) exposiny b d g Fricke solution in similar glass vials. It is realized that transfer of dose in the Fricke dosimeter to dose in the thin film dosimeter is not readily made under these conditions, but relative measurements are significant in this case.

164 Cobalt Y-ray irradiations were made in a gamma-source with dose rate of 1.1 Gys, and also within a lead cylinder, which lowers the dose rate to 0.2

Gys"-1 1. The temperatures during irradiations were measured to be between 20° and 30°C.

FWT-60. Figure 6 shows the measurements at only 3 different relative humidities together with Gehringer's measurements (Gehringer, 1979). There is a good relative agreement, althoug absolute hth e e inaccuratb valu y ema s ea mentioned previously.

FWT-60 dosimeters have all been given a heat treatment after irradiation as suggested by Chappas (1981). We used 60°C and 5 minutes, although for cobalt- irradiations thi scarcels i s y neededtreatmene th d ,s usean twa d onlr fo y reasons of standardization.

o Gehringer 2.8 • A.M 1.1 • Gehringer Q28 AM Q17

£ Cobalt. 20 kGy à o

20 40 60 80 Relative humidit) (% y

Fig. 6. The influence of relative humidity on Nylon radiochromic dosimeters resulte Th .f thiso s stud e showar y n super- imposee resultth n Gehringey do b s . (1979)al t e r .

165 Fig. 7. Nylon block used for humidity studies at the 10 MeV linear e th d maccelerator5 m an s i d thicknesli e e Th th . f o s diameter is 75 mm.

T R 5 FWT-6P1P1 5 0

~ Cobalt-60 X _1electronV 0Me s •f 100

I 90

60- I 12 . 34 55 75 100 Rel. humidit) (% y

Fig. Dependenc8 . f relativeo edifferen3 humidite th r tfo y radiochromi e dosimetersdy c , irradiateelectronV Me 0 1 t sa d and Cobalt-60. The dose was 20 kGy in all cases.

The apparent dependence of dose rate at low rates" Is not found in all studies (McLaughlin et al., 1981) and may depend on long-terra pretreatraent of the dosimeter n irradiatioo s wels a s la n conditions.

P 15. Dosimeters made as described earlier were irradiated under conditions equal to FWT-60 dosimeters. Generally the PVB-based dosimeters show increased

sensitivity by +(0.4-0.5)* per percent increase in relative humidity, and .a 10/t lower response as the dose rate is lowered from 1.1 to 0.2 Gysec"1 (Miller and McLaughlin, 1982), which is similar to earlier findings of Levine

166 et al. (1979). Also in this case dosimeters were dried over P20S without finding any differences in response, as compared to storage at room temperature and humidity.

2.6 Accelerator irradiations

An approach similar to the one by Gehringer et al. (1979) was used in order to irradiat different a e V lineat Me humiditie0 1 r e acceleratorth t a s . Small cylindrical nylon blocks s show,a Fign wer, i n7 . ee mont storeon t a hr fo d the different relative humidities. Dosimeters, which have been stored for one e samth weee t a humiditiesk , were then e nyloe cavitplaceth th n n i i yd block, the lid tightly secured, and the blocks were irradiated, first on cobalt in order to see if the same.response would be obtained as in the experiment above facn .casee i Tha th td therebs ,an twa seemet i y d- as saf o et sume that the humidity conditions were not seriously disturbed during the 5-6 hours of irradiation in the nylon blocks, and it might thus be safe to pro- ceed with irradiation electronsV s Me wit 0 1 h .

The results are shown in Fig. 8, where cobalt and 10 MeV electron irradiation comparee sar type3 r dosimetersf o sfo d , normalize mose th t o sensit d - tive measuring point. At that point the difference, before normalization between cobalt and electron irradiations, is less than 556, which is within the precision of the dosimeters, and thus no dose rate dependence is demonstrated over this rang dosf o e e rates, accordancn whici s i h e with earlier findings (McLaughlin et al., 1979).

The parameter acceleratoe th r sfo r irradiations wer s followsea :

EnergV Me 0 1 y Pulse currenA 2 1. t Pulse lengt yse4 h c Pulse frequency 200 pps Irradiation n scanneso d bea n conveyoo m r Scan frequencz H 5 y Scan width MO cm Conveyor speed at 20 kGy: 0.8 m/min.

The dependence on relative humidity seems to be comparable for electron and cobalt irradiations. Onl casn i yf P-1 eo R ther 5 significana e e seemb o t s t

167 differenc o thas e t electron irradiatio than i n t case shows less dependencf o e relative humidity.

As previously mentioned all dosimeters were given a short heat treatment (60°C min.,5 ) after irradiation, whic founs i h accelerato t d ecoloua - de r veloping process after irradiation. This heat treatment was also found to decrease the humidity dependence for all investigated dosimeters.

2.7 Stability after irradiation

All investigated dosimeter e foun sar develoo t d p their final e colouth n i r first hours after irradiation. Thi particularls si y observed after electron irradiation, while cobalt Y-ray irradiation doegivt sno y e suc an ris ho t e effect, becauslone th g f eirradiatioo n time .brieA f heat treatmen5 f to minutes at 60°C in an oven accelerates this development of colour and leaves the films ready for reading. The long-time stability for the different dosimeter s typefollowsa s i s :

FWT-60 e optica.Th l densit thesf o y e films reache same sth e "saturation level" after heat treatment as is reached after 24 hours of storage without heat treatment. There does not seem to be any need for great accuracy in administerin e treatmentgth same ;th e resul achieves i t y timdb e variation r temperatureminute0 1 fo o frod t san 3 m 70°Co st fro° .50 m

Storin dosimetere th g lona r g fo stim e after heat treatmen givy tma e riso et some fading of the colour. For the batch used in this study it was found that 3 months storage reduced the optical density by 15Ï, but other batches may be more stable (Levine et al., 1979).

The dose response of FWT-60 dosimeters seems largely to be independent of pre-irradiation time. Repeated cobalt-60 irradiations usually give responses within ± 5% of each other.

P-15. Heat treatment (60°C, 5 min.) of these dosimeters gives rise to an optical density, which is higher than the value reached after 24 hours, or even several day storagf so e after irradiation. Variatio e temperaturth f o n e and time seems als thin i o sallowee b cas o t e d without influencin- re e th g dosimetee sponsth f eo s abovea r e stabilit.Th y after irradiatio vers i n y good. The change in optical density after storage at normal laboratory condi-

168 tions for up to half a year does not change the optical density by more than 2%. ± e dosTh e response over long-term pre-irradiation storag less i e s stable than for FWT-60 dosimeters. Variatio morf no s bee eha n tha ? observe- 20 n re r fo d peated irradiatio t Cobalt-60a n e relativ.Th e high humidity dependencf o e these dosimeters is suspected to be one of the causes of this apparent instability t investigationbu , e beinsar g n attempa mad n i eo improvt t e this.

P-15 R. This dosimeter reacts to the heat treatment in the same manner as the P-15 dosimeter e long-tim.Th e stability after irradiatio alss i n o very good with changes being leshalr sfo yeafa % tha2 r ± nstorage .

The dose response for repeated irradiations seems to be more stable than P-15 with changes of less than ± 5% for pre-irradiation storage times of 9 months, but further measurements are needed to confirm this.

2.8 Light sensitivity e sensitivitTh ligho t ys previousl twa y measure r FWT-6fo d P-1d 0an 5 dosimeters (Miller and McLaughlin, 1980). These measurements have been repeated, P-15 R included (Fig. 9). All 3 dosimeters are most sensitive around 330 nm, relative buth t e sensitivit type3 : FWT-60e sis th f o y: 100Î; P-15: 25%,d an . 2% P-1 : R 5

3- CALORIMETRIC MEASUREMENTS

e measuremenTh different ta t type f irradiatioo s n with relative dosimeters requires that the absorbed dose on the different irradiation facilities can be measured with accuracy by some common standard.

Ferrous-sulphate (Fricke) dosimetr standare th uses i ys da gammn o d a irradiation facilities t tha,bu t dosimeter canno usee tb d without correctione th t sa 10 MeV linear accelerator because of dose-rate problems (Sehested et al., 1973)• or at the 400 keV DC accelerator because of very low penetration at this energy.

169 0» 0)

> "o

280 300 320 340 360 380 X. nm

Fig. 9. Response to light for the three different radiochromi e dosimetersdy c e samTh e. arbitrary units are used for all three curves.

Kcm

32cm

r Sem i 1.7cm f T 5cm i 32cm

Fig. 10. The water calorimeter that is used for dose measurement at Riso 10 MeV linear accelerator.

170 A water calorimete s use i rs referenc a dV linea Me e Ris 0 th 1 ar t a eaccelera - tor (Fielde d Holman n , 1970calorimetea d an ) s alsha ro been designer fo d acceleratoV ke calibratio0 40 e rth (Radaf o n al.t e k , 1973). These calorimeters have been investigated and a new simple calorimeter made of graphite with potential of being used both on the 10 MeV and the 400 keV accelerators has been constructed (Miller, 1982a, 1982b). This is similar to one designed by Humphreys 4 McLaughlin (1983) at NBS for use in 10 MeV electron beams.

V electronMe 3.0 1 1 s

e wateTh r calorimeter describe dt designereferenca no here b s i eo - t d in e strument rathet procesa ,bu s ra s calorimeter. Nevertheles reasonabls i t si y accurate and precise, as will be discussed, and it seems possible to apply the water calorimete standardizen i r d measurements.

The calorimeter consists of a polystyrene Petri dish filled with water (for dimension e Figse s . 10) e dis. Th isolates i h polystyreny db e foam d tem,an - peratur measuree b n ca e meany glass-encapsulatea b d f so d calibrated thermistor. The calorimeter will normally be irradiated on a product conveyor making on-line measurement of temperature difficult. The measurements are therefore restricte beforo t d d afteean r irradiation observee th d ,an d temperature differenc measur a absorbee s i th e f eo d dose usuae .Th l extrapolation techniqu t used no temperaturet s ,bu i e e assume constanse ar b o t d- tbe fore and after irradiation. The former can be obtained if the calorimeter is in equilibrium with its surroundings, and it was determined that the temperature after irradiatio 0.5%y n b minutr y increasepe kG e0 1 ove t sa a r10-min - ute period. The temperature will increase because the plastic is heated more than the water during irradiation because of its lower specific heat. Meas- uremen usualls i t y made minute2 betwee d an s1 n after irradiation.

The calculation of absorbed dose is based on material properties only, as no calibration heater is employed. The absorbed dose D is:

(1) D -M - AT'c'm m m specifie th whers i cc e heate involve th e temperatur ,m th T dA masd san e difference. When several component absorbee heatee th sar y b d d dosequae eth - tion becomes:

(2) D

111 It is assumed that the components contributing to the total calorimeter body e followingth e ar :

Water, specific heat 0.998 Cal•g~l•°

r eacFo h calorimete watee Petre massee th e deterth th r ar rf if o so dis -d an h mined individually, whil thermistore th e e assumesar havo t d e equal masd san heat capacity. e Petr o th thas if , t o g dis d 0 6 han g Typical 0 watee 21 th mase s i rf th , so th calculatee b dosn eca : as d

D m 21,0.0.996^60.0.335 * 0.12 .Uil8 .10,

recommendes Ii t measuro t t no de doses correspondiny belokG w3 tema o t g- perature 1.0°C- ris f eo , sinc time eth e o temperaturbetweetw e nth e measurements can vary somewhat, which may give rise to unwanted temperature changes due to influence from the environment.

uncertais Ii t n whethe mas e d specifith rsan cPetre th hea if to dis h should be included calculationse fullth n i ymase d specifith somf s an i f eo r ,o c heat of the insulation should be included. The very slow temperature rise after irradiation seems to indicate that the Petri dish is in thermal equilibrium d thacontinuee ,an th t d contributio e temperaturth o t n ee risdu s i e to the insulation, which again suggests that shortly after irradiation this has a negligible effect.

Precisio2 3. n

For routine dose measurement .lineae th n rso accelerator 20-30 calorimeters o tha s unirradiaten a te us n i e ar d calorimete therman i r l equilibriun ca m alway usede sb calorimeter5 .2 s were irradiate conveyoe th Mra2 n o o dt n d i r rapid succession of each other, and the scatter of individual measurements wer e averageeth withif o % . ±2 n

172 3.3 Accuracy

The International Atomic Energy Agency is currently initiating a "Dose Assur- ance Program" (Chadwick 1982; Miller et al., 1983) for gamma irradiation plants and work is in progress to expand this service also to include electron irradiation facilities pars .A f thio t s worwatee th k r calorimetes wa r tested in intercomparisons with graphite calorimeters made at National Bureau of Standards, U.S.A.Risat a d .,an Irradiations were mad Nationat ea l Physi- l Laboratoryca , EnglandmeasurementL NP t Risea e d .Th ,an generan i s l showed good agreement between the NBS graphite calorimeters and the Risa water calorimeters, but the details are reported elsewhere (Morris, 1983; Humphreys and McLaughlin, 1983).

The measurements at Risa were made on the 10 MeV linear- accelerator, both using scanned beam on a conveyor and fixed beam in a "straight ahead" con- figuration.

The thicknesses of both kinds 'of calorimeters (water and graphite) are about 1.7 g/cmt totallno d electrotheV e 2,an Me yar 0 1 absorbin ne th beam r fo g. Stopping-power corrections for 10 MeV electrons are therefore applied for comparison of water and graphite calorimeter readings (using stopping-power value Seltzef so Berged ran r (1982)). r! dEi w vT * 777' W

n threI e separate serie f irradiationso l linacV fo Me Ris e e 0 th 1 a,th t sa lowing ratios were obtained:

1. 1.1 0.0± 1 6 Scanned beam 2. 1.09 ± 0.04 Straight ahead beam 3. 1.0 0.0± 7 2 Scanned beam

Dy is dose as measured by the Risa water calorimeter, and DQ is dose as measured by the NBS graphite calorimeter.

Following these measurement graphitU s e calorimeters were mad t Risaea , partly in order to make comparisons with the water calorimeter, and partly in order to use the graphite calorimeters as routine dosimeters for lower doses

173 lineae ath t r accelerator acceleratorV possiblf i ke O d MO ,an e th als. t oa The lower specific heat of graphite should make it possible to measure doses d assuminan y kG homogeneoua g 5 0. dow o t n s distributio caloe th heaf o n-n i t rimeter shortly after irradiation, application on the low penetrating ^00 keV electrons is possible.

e graphitTh e calorimeter disa e mad sar s k a e wite samth he ) diametecm M 1 - ( r as the water calorimeter and with the thickness (1.7 g'cm""*) also equal to the water calorimeter. The density of the graphite is measured to be 1.78 g »cm' ,-3

The dose may be calculated as for the water calorimeter, but since there is no encapsulatio graphite thermistoe th th f d no nonencapsulatea ean s i r d type with thin wires and negligible influence on the temperature measurement, eq. (reduce1) : sto

The specific heat of graphite, CQ, was measured as a function of temperature e s showtemperatura Th Fign . i n 11 . ecalorimetee risth f eo expectes i r t no d

T l l I l l l | l l l l i i i i

0.22

5°-20 LU X 0.18 o u. o 0.16 LU Q. 0.14

0 5 0 24 0 0 3

TEMPERATUREt ,

Fig. 11. Specific heat of the graphite used for construction of calorimeters at Riso.

174 to exceed 10-15°n averaga d an Ce valuf o e is accordingly chosen to 0.174 g^-o'c" 0 J-kg"73 = 1 l«°C~l.

For use at the linear accelerator the graphite disk was isolated by - 5 cm polystyrene foam.

Several series of irradiations were made on the conveyor where 1 water calorimeters were irradiated together with the 4 graphite calorimeters. The doses were generally between 10 kGy (- upper limit of graphite calorimeter) and 5 kGy (- lower limit of water calorimeter). Measurement of temperature was made 1-2 minutes before irradiation and again 1-2 minutes after irradiation.

T i 1s

w//////////, T 55 i

32cm

. Graphit12 Fig. e calorimeters with different isola-tion configurations.

175 The following ratios were found between the dose as measured by the water calorimeterdose th s measure a e e individuad th an y , b dDy s l graphite calorimeters multipliet bu , e stoppinth y b d g power ratio:

1. 1.04 ± 0.04 2. 1.04 ± 0.03 3. 1.03 ± 0.03 4. 1.0 80.0± 3

No significant variatio ratie th of no coule dos s variedth seee ewa b d s a n , and e averag tha s alsth case twa of th ei e dose rat s lowereewa shorteniny b d g e beath mf o puls1 jjtsec o et .

Thinner layers of isolation were used as shown in Fig. 12 in order to test the validit e dosth e f measuremeno y t whe calorimetee th n usee b t a do t s i r low energy electron beams significano .M t ratie chang th s found of wa o e .

The differences between individual measurements may be due to the construc- calorimeterse th tio f no particulan ,i r with respecmountine e th th o t f go thermistor likels i t i y d tha ,an valun i t e numbe abov4 r temperature th e e measurement is inaccurate.

e deviatio Th ratie th heao t of no tfroe exchangdu m e b unit y ema y betweee th n foam insulation and the graphite. The specific heat of the foam is higher than that of graphite, and the foam is therefore not heated as much as the graphite. After irradiation the temperature of the graphite therefore decreases. The decrease was measured to 0.5% per minute at 10 kGy. If a few e insulatiogramth f so takes ni n into account when calculatin dosee gth e ,th ratio wil broughe lb t clos unityo t e othe e b t ther ,bu y r e ma causeth r sfo deviations. The change in temperature with time for both the water and graphite calorimeter accouny s ma o tharatie r s abou th tfo , o2% t becomes 1.02 rather than 1.04. The remaining 2% difference seems hardly worth reducing, realizes i but i t d tha t leasa te possiblon t e sourc f oerroeo r still excists: Correction wit simplha e stopping power adequate e b rati t ono y (eq.ma .) 3 Cavity theorie electror sfo n beam irradiations have been questioned (see e.g. Horowitz possibl s i (1981)) t i d e, an that additional corrections muse tb included.

176 e momenth e havr w t Fo e assumed thawatee th t r calorimete estimatins i r a g correc readine e graphittth th dos d f o gean e calorimeters wil e calibrateb l d against the reading of the water calorimeters. It is realized that Domen finds error dosn i s e interpretation usin watea g r calorimete e ordeth f o rf o r 3-4$. Domen, however, uses low doses (1-10 Gy) and we do not feel that these findings can be extrapolated to the kGy region.

The following calibration factors have been obtained for the four graphite calorimeters:

Dose to graphite Dose to water (10 MeV.electrons)

1) 757 Gy°CTl 858 Gy0C~l Gy°C"8 85 Gy'CT7 12)75 1 Gy0 a85 C~ Gy'CT0 l3)75 1 i») 786 Gy°C-1 891 Gy°C~l

These values are used for routine determination of dose at the 10 MeV linear accelerator.

Based on these measurements there is no evidence that the water calorimeter is inaccurate. Possible sources of error include:

a) Heat defect <1$ (see section 3.5) b) Thermistor calibration error <0.2? c) Determination of masses <1J Uncertaint) d specifif yo c heat value$ s<1 e) Temperature changes not observed between readings <1£.

It seems thus acceptabl assumo t e e thaaccurace th t withis . i y 5% ± n

400 keV accelerator

Therradiatioo n s i e n measurement device availabl measurinr fo e absolutn i g e terms the absorbed dose from high-intensity, low-energy accelerators under product-irradiation conditions, as is done with water calorimeters at the 10 MeV accelerator.

177 Preliminary measurements have been made wite graphitth h e calorimetern i s order to test if this may be applied as reference dosimeter for 400 keV electrons. Aboum insulatiom 5 t n between graphite bodd acceleratoan y r windos wa w used, but measurements have also been made with a 15 urn PE-foil covering the graphite front surface. acceleratoV ke e dos O Th calculatee HO b froe y th rma m d approximately accord- methoe th inf Proksco o dt g al.t he , (1979) usin followine gth g parameters:

- JJOV k E O HE « 0.89 (voltage efficiency) H0.8* I 0 (current efficiency)

Rq - 0.0625 g«cnT (equivalent range) e z Yeq - 100 cm (equivalent scan width)

100.10*.0.89.0.8_ ^6.103 kGy(cm.sec- Req«ïeq 0.0625*100

D - k -l

At I - 6 mA and V - 5 cm/sec, the dose is calculated to be D - 15.6 • •=• » 51.7 kGy.

Measurement with Nylon radiochromi filmse cdy , which were calibratee th t da Cobalt-60 and at the linear accelerator and assumed dose rate independent, measure 50 kGy at this setting of irradiation parameters and are thus in reasonable agreement with the calculations.

e graphitTh e calorimeter measures averag calorimetee th dos n i e r bodyt .A 100 keV electrons, only a small fraction of the total body is actually irradiated, and in order to make a dose measurement it must be assumed that the temperature, is equalized over the full graphite disk. Tests have been made that indicate this bein case th ge c aftewithise r0 2 n irradiation.

In orde determino t r surface th e e dose base knowledgn o d average th f eo e dose, the depth dose curve in graphite must be known. The depth dose curve measures wa d previousl staca n dosimetef i yko r films (McLaughli al.t ne , 1975), but it was suspected that the depth dose curve might be different in electrical conducting graphite, as compared to electrically isolating dosimeter films dose s therefor.Th e wa e measured under different thicknessef so

178 conducting plastic (Fig. 13)1 but as can be seen there is no appreciable difference.

depth-dose Baseth n o d e curve ,a simpl e approximatio ns use i o (Fig t d) 13 *

integrate this curve in order to find the ratio between the surface dose D, s

average anth d fule eth l dos r thicknesfo e diske th ,f so D G>a> DS - 27.1 i,a

r i

16 Conducting plastic

Stack of films 12 o 8 0» &

0 0.02 0.04 OÛ6 008 0.1 0.12 Depth, g • cm"2

. FigDept13 . h dos electroV e ke measurement 0 n40 acceleratoe th t a s t Risa r a f measuremento t Onse e s were carrie elec n t witur d ou 0 -hstaca 5 f o k trically isolating dosimeter films, while another set of measurements was made with dosimeter films at different depths of electrically conducting plastic.

179 DG,a i3 calculated by application of eq. (U) and no stopping power correction is made becaus calorimetee th e s totalli r y absorbing e firs .Th measurew fe t - ments of this ratio, assuming D$ to be equal to the dose usually measured by film dosimeters and calculated as shown above, seem uncertain, but most val-

ues have been around 19, indicating either a too high D(j>a (measured), or a too low DS (assumed). Further investigations are being made trying to solve this problem.

Another calorimetric approac r calibratiofo h V ke dosimeter0 f o n10 e th t sa electron accelerator has been used by Radak et al. (1973), and with small modifications this method has been tried again (Miller, 1982a). The calorimeter is shown in Fig. 11. The temperature difference between the irradiated and the non-irradiated body is measured on-line for fixed irradiation times. Following calibration irradiations witcalorimetere th h , stack dosimetef so r films are irradiated under equal conditions, and calibration curves are constructed.

e calorimeteTh equippes i r d wit electrican a h l calibrationw ne heater a d ,an calibration curv mads ewa e (Fig. 15). d irradiatinan A m 0 1 gd an , 5 e calorimete , Th 2 t a V s irradiateke rwa 0 40 t a d times were varie 0 seconds6 do t fro 0 .2 m

Whee irradiatioth n n tim s increasei e signae th d l increases proportionalls a y shown in Fig. 16, but when the time is fixed and the beam current is increased, there proportionalit doee b t see sno o t m othee s showth a y rn i nhal f of Fig . Variou.16 s attempts have been mad resolvo t e e this discrepancyt ,bu without success have w ed ,thereforan e concluded that beam measurementn sca be extrapolated and interpolated in terms of irradiation time, but not in terms of beam current. Measurements at each beam current in question should therefor madee eb .

Dosimeters, whic e calibratehar t thia d s calorimeter t irradiateno e ,ar d under processing conditions, where they are going to be used, and the procedure for evaluation of the calibration curve is rather troublesome. Even with these and the previously mentioned drawbacks this calorimeter may still be the best available for low-energy electron beams, and its application as a calibration instrument is still being considered.

180 Fig. 14. Calorimeter for calibration of dosimeters irradiated at low energy electrons (Radak et al., 1973). (1) Calorimetric body; fixed part. ) Aluminiu(6 m shield. (la) Calorimetric body; exchangeable part. (7) Brass col limator. (2) Reference body. -Dumm) (8 y collimator. (3) Perspex supports. ) Bea(9 m current monitor. (4) Aluminium matrix. (10) Calibration heater. (5) Aluminium lid. (11) Copper connectors.

181 1.2

1.0

0.8

0.6

0.4

0.2

0 10 15 20 25 30 Input energy [Joulel

Fig. 15. Electrical calibration of the calorimeter of Fig. 14.

i r i i T i i i

I =10mA t » 20 sec

-3

-2

t i i i i i i i i 0 8 0 6 0 4 20 0 5 10 Irradiation time (sec] Beam current [mAj

Fig. 16. Electron beam measurements with the calorimeter of Fig. 14,

182 5 Hea3. t Defect

It has been suggested that endo- or exo-thermal chemical reactions in the water calorimeter might give ris erroneouo t e s dose readings (Fletcher, 1982) (fographite th r o chemican e l reaction e assumear s tako t d e place).

Hd 20an y irradiatioThb 2 2 eH yield, 2 0 f watef so no r have been calculatey b d a computer code developed here (Bjergbakk d Lanean g Rasraussen, e 1984)th d ,an amounts of energy consumed or released in the reactions were found. We have considered 5 different irradiation conditions:

Consumption Formation

H20 H202

Source Dose Irr, time Heat defect 1CT M 5 1CTM 5 (exothermal)

1. Cobalt 1 kGy 1 hour 1 .1 % 8.47 7.1 2. Cobalt 10 kGy 1 hour 0.16* 12.2 9.9 3- Electron 1 kGy 3.6 sec 1 .4 % 9.15 6.7 4. Electron 10 kGy 3.6 sec 0.25% 18.7 15.2 5. Electron 0.4 kGy 4 usée 2.7 % 7.07 4.95

We conside worse th t) r5 cas e wher correctioe th e e nth wilo t hige le b du h initial conditions successivy .B e pulsin correctione th g s wil lesse lb - ,de pending on the time scale.

We have considere closea d d system (the water calorimeter)t no o d e w t ,bu expect larger corrections in an open system, in particular not at the short time scales involved witelectroe th h n irradiation e therefor.W e conclude that "heat defects" will amoun leso t sr irradiation r thafo o J y 1 n kG 5 f so higher under these irradiation conditions.

183 REFERENCES

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CHAPPAS, W.J. (1981), Accelerated Color Developmen f Irradiateo t d Radiochro- Filmse miDy c . IEEE Transaction Nuclean so r Science, Vol. NS-28. 2 . ,No

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FLETCHER, J.W. (1982), Radiation Chemistry of Water at Low Dos« Rates. Empha- sis on the Energy Balance: A Computer Study. AECL-7834, Chalk River Laborato- ries, Chalk River, Ontario, Canada.

GEHRINGER Eschweiler, ,P. Prokschd an , ,H. . (1979) ,E , Dose RatHumiditd an e y Effects upon the Gamma-Radiation Response of Nylon-Based Radiochromic Dosime- ters. SGAE-3058. Forschungszentrum Seibersdorf, Austria.

GEHRINGER, P., Proksch, E., and Eschweiler, H. (1982), Oxygen Effect on the Y-Radiation Respons FWT-6f o e 0 Radiachroraic Film Dosimeters. Int Appl. .J . Radiât. Isot 1403-1407, .33 .

HOROWITZ, Y.S. (1981) Theoreticae ,Th Microdosimetrid lan c Basi Thermof o s - luminescence and Applications to Dosimetry. Phys. Med. Biol. 26, No. 4, 765-824.

HUMPHRYES, J. and McLaughlin, W.L. (1983), to be published.

184 KANTZ, A.D. and Humpherys, K.C. (1979), Quality Assurance for Radiation Proc- essing. Radiât. Phys. Chera. 1_4, 575-584.

LEVINE McLAUGHLIN, ,H. , W.L. d Miller,an . (1979),A , Temperatur d Humiditean y EffectGamma-Rae th n so y Respons d Stabilitean f Plastio y d Dyean cd Plastic Dosimeters. Radiât. Phys. Chem. 14, 551-574.

McLAUGHLIN, W.L., Hjortenberg, P.E., and Batsberg Pedersen, W. (1975), Low Energy Scanned Electron Beam Dose Distribution Thin i s n Layers. Int Appl. J . Radiât, and Isot. 26, 95-106.

McLAUGHLIN, W.L., Miller Pejtersend Fidan, an ,A. , ,S. . (1977),K , Radiochro- mic Plastic Film r Accuratfo s e Measuremen Radiatiof o t n Absorbed Dosd ean Dose Distributions. Radiât. Phys. Chem. 10, 119-127.

McLAUGHLIN, W.L., Humphreys, J.C. Radak, B.B., MillerOlejnikd an , ,A. , T.À. (1979), The Response of Plastic Dosimeters to Gamma Rays and Electrons at High Absorbed Dose Rates. Radiât. Phys. Chem 535-550, 14 . .

McLAUGHLIN, W.L., Humphreys, J.C., Levine, H., Miller, A., Radak, B.B., and Rativanich, N. (1981), The Gamma-Ray Response of Radiochromic Dye Films at Different Absorbed Dose Rates. Radiât. Phys. Chem. 18, No. 5-6, 987-999.

McLAUGHLIN, W.L., Uribe, R.M., and Miller, A. (1983), Megagray Dosimetry (or Monitorin Verf go y Large Radiation Doses). Radiât. Phys. Chera , 333~36222 . .

MILLER, A. and McLaughlin, W.L. (1980), On a Radiochromic Dye Dose Meter. Risa-M-2254, Ris0 National Laboratory, Denmark.

MILLER, A. (1982). IAEA Research Contract 2883/RB, Progress Report August Apri- 1981 l 1982. Risa-I-100, Riso National Laboratory, Denmark.

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MORRIS, W.T. (1983), High Dose Intercomparison ElectroV Me 0 1 n i s Beamt sa d Ris0NPan L , May-June 1982 ReporL .NP S (Int.R t , Nationa)72 l Physical Labo- ratory, England.

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SEHESTED Bjergbakke, ,K. Holm, ,E. , N.W. Fricked ,an . (1973),H e Reactio,Th n Mechanis Ferroue th f o ms Sulphate Dosimete Higt ra h Dose Rates "Dosimetrn .I y in Agriculture, Industry, Biology, and Medicine", 17-21 April, 1972, IAEA, Vienna. IAEA ST1/PUB/397.

WEXLER Hasegawad an . ,A , S.(195*0, Relative Humidity-Temperature Relation- ship somf so e Saturated Salt Solution Temperature th n i s e 50°Co Rangt ° .e0 JOURNAL OF RESEARCH of the National Bureau of Standards, U.S.A. 53, 19-26.

186 DEVELOPMEN TECHNIQUER ES F TO FRER SFO E RADICAL DOSIMETRY IN ELECTRON BEAMS*

R.M. URIBE Institute de Fisica UNAM, Mexico DF, Mexico

Abstract

This report describes the attempts to produce a free radical dosimete R measuremenES re baseth n o df paramag o t - netic centers induce y irradiatiob d n somi n e plastic materials which contain dye precursors as an additive. The report deals mainl R signaES y f polyvinye wito le studth th hf o y l butyral with different dye precursors namely, pararosaniline cyanide, hexahydroxyeth/1 pararosaniline, formyl violet, new fuchsin, and malachite green, and of some other plastic materials with pararosaniline cyanide s alsi ot I described. ' the preparation of nylon films with and without dye to use R measurementsES ther fo m .

Introduction f electroo e Thougus e n th hspi n resonance (ESR r radfo )- iation dosimetry by means of the radicals produced in irradiated matter has been pointed out in 1973"', only one succesful application has been reported using alanine as the irradiated medium*- '. The main difficulty in making R dosimetryES , disregardin e availabilitth g e equipmentth f o y , is to get a suitable material, water or tissue equivalent, -in which the radicals produced upon irradiation could be "freezed d consequentl"an y their recombination avoided, getting a stable ESR signal with time. Though the best method to acomplish this is to create free radicals in organic crystal matrices in which electrons are trapped in lattice vacancies

* IAEA Research Contract 2963/RB.

187 (th o calles e d F-centers) productioe ,th f suco n h crystals is not an easy .task and usually one encounters the additional problem of anisotropy and hyperfine structure of the ESR signal On the other hand solid amorphous materials are easier to a smalmak n i el laborator mosd f an theiyo t R signalES r e ar s simpler to interpret than those encounter on organic crystals. However the main problem with these systems is the mobility of the free radicals produced which will tend to recombine X * themselve d consequentlan s R signaa reductioyES e lth witn i n h time will be observed. In what follows we make a description of the attemps to create such an amorphous solid consisting polymeria f o c material wit a radiochromih e precursody c s a r an additive which upon irradiation could give a stable, eas deteco t y R signalES t . e firsTh to determin t stethi. y in sptr projeco a et s twa suitable combinatio precursore dy f o n d plastian s c matrix which gave a strong ESR signal, concluding that the .signal was due to some sort of interaction between the plastic and the dye; s founwa als R signat di oES thae lth t induce y radiatiob d n e plastith n o c wite decady h y with storage tim t rooa e m temperatur d thaan e t this proces diffussioa s i s n controlled mechanism "alse w ; o describ e worth ek don n doso e e response curves for the system of pararosaniline cyanide (PR) in PVB i nR spectr ES air e f somth ,e precursoro a dy e B irradPV n si - iate measured an d d under vacuume fabricatioth d ,an plastif no c films consisting of PR in a nylon matrix.

Description of research carried out

Previous determinations of the ESR signal of radiochromic dye films used mainly for spcctrophotometric determination of dose showed the factibility of this technique^ '. However

188 the intensity of this signal was very small. In order to o overcomt y tr e s decidethiswa t i ,o mak t d e thicker films with larger concentration of dye in them and also to try new different combination d plastian e dy c f matrio s x which could enhanc d stabiliz an eR signa ES e lth e produce y irradiationb d . These combinations included: pararosanilinc cyanide (PRn )i polyvinyl butyral (PVB)., polyvinyl alcohol (PVA) , polyvinyl acetate (PVAc) or nylon; and different dye precursors in PVB, namely: hexahidroxyethyl pararosaniline (HH), formyl violet (FV) , new fuchsin (NF), and malachite green (MG). Apar e precursortdy froe th m , certain amoun f citrio t c acid was added to the solution in order to avoid back reac- s producetionwa e s dy y irradiation b oncde th e ,a commo n problem encountered in the spectrophotometric analysis of such dye films^ '. The final formulation used in these studies was as follows:

5 ml-o5 - f ethanol - 55 ml of 2-methoxy ethanol » - 1.1036 f citrio g c acid - 20g of plastic matrix - dye: enough amount to have one molecule of dye per two molecules of citric acid in solution. Films were cast by pouring 75 ml of the above solution omirroa n r polished casting plate mad f aluminut o e le d an m it stand ove e weer r on tilthere o filmk r th l fo es were dried orden I .preveno t r t fast evaporatio e solventsth f o n , the aluminum plate was covered with filter paper (Whatman qualitative 2) and maintained at a temperature in the range o 25°Ct fro 0 2 ;m additional monitorin e relativth f o g e humi- e laboratorth dit n i y y wher e filmth e s were cas s carrietwa d out and such films cast at relative humidities higher than

189 759à were discarde n ordei d o prevent r y effecan t f trappeo t d water molecule e finath ln i sR cassignal ES te filmth . n o s After casting e filmth , s were strippee aluminuth f of dm plates and stored in a vacuum oven at 40°C till all solvent was evaporated, which took about 5 days. In this way the following films were prepared: - pararosanilin n polyvinyi e l butyral - hexahydroxyethyl pararosanilin n polyvinyi e l butyral - forrayl violet in polyvinyl butyral - new fuchsin in polyvinyl butyral - malachite green in polyvinyl butyral - pararosaniline in polyvinyl alcohol

In order to check if the ESR signal observed in irradiated e plastith o t e combinatioc th e matrie filmo du t dy s i r so x n d plastican e dy ,f o several films were prepare e samth e n i d way as described above, but without dye precursor. These films were made with the following plastic materials: polyvinyl butyral, polyvinyl alcohol, and polyvinyl acetate. An attempt to make nylon based film with and without dye was o changt d eha solvente w madt bu es thos a s e mentioned above do not dissolved the nylon resin used in our studies. Finam thic m y 5 dr lfilmk 1. werf abouo - o st ob e1 t y describewa e taineth n di d above, from which R sampleES r fo s measurements were cut in pieces, l.S x 1.5. x 1.5 mm and put in conventional ESR glass tubes (O.D. 4 mm). Dose-respons B irradiatePV n ei curveR P n air i df o s, were investigate y makinb d g solution B containinPV f o s R P g as an additive. The films were cast by pouring the solution in aluminum plates to allow the solvent to evaporate. After S m thickdayfilmm e th 1 s ,2. , coul e strippee db th f of d aluminum plate and put in a vacuum oven for 3 more days to * 190 allow complete evaporation of the solvent. The final film was cut in strips 1.5 cm long and put into quartz tubes for its irradiation o witgammC h a ray o doset s s betweed an 0 1 n y witR determi kG ES dosa h 0 e e11 th 0 kGy/hr 1 -rat r f Fo o e . nations samples were transfered to new quartz tubes and the ESR signal recorded at room temperature. The intensity of R thsignaES e s estimatelwa e peak-to-peath s a d k distance of the ESR spectrum devided by the mass of each sample. These values were corrected for d'ecay of the ESR signal with time. R spect-rES samplef o a s irradiate measured an d d under vacuum conditions, were recorded accordi e followinth o t g g • procedure: new fuchsin (NF), malachite green (MG) hexahydroxyethyd ,an l pararosaniline (HII) , were disolved in PVB as described previously and films were cast according to the procedure described above. Samples for these films were cut in strips 1.5 cm long and put in quartz tubes connected to glass tubes wit a flangh o allo t es connectio it w e vacuuth o t mn linf o e e lab th l sample.Al s wer" tor10 d e - an revacuate " 10 o t d then sealed by heat. For their irradiation the samples were a glas n i s t dewn pu d irradiatean r d o witgammC h a rayo t s a total dose of 150 kGy with a dose rate of 10 kGy/hr. After irradiation the bottom end of the tubes were annealed to allow trapped electrono escapt t i e n keepini s e samth g - e otheR signath pleES rn e i slend th recorded ,an t rooa d m temperature. In order to see if the ESR signal induced by irradiation n radiochromio e filmdy c s depende plastith n o sc matrixe ,w decide o fabricatt d nyloa e n filn additiva ms a wit n R i eP h e firsth tf o problem e itOn . s encountere e facth t s thawa d t

191 nylon was not dissolved by the usual solvents used for films prepare a suitabl d o loo r t wit fo kd hha e PVB e solvenw o ,s t to dissolve both nylon and dye precursor. The solvent chosen r thifo s purpos s 1-propanolewa e initiaTh . l formulatior fo n solutions with nylon was:

g 0 1-propano10 - l 10 g nylon .0.5518 citric acid

50 g 1-propanol - 0.472 g citric acid - 8.55 g nylon - 0.386 g of PR

The first three compounds were mixed and heated to hrs5 r . 61°fo cooo t CThe e solutiolt th nle dow o s t n nwa

192 room temperature and the dye precursor added. When the PR was dissolved completely then the solution was poured in the aluminum casting plates. Total period of drying was 8 days. After this period nylon films 6-8 mm thick with PR in them, were obtained and the ESR signal o.f unirradiated nylon films with and without PR was recorded at room temperature.

Results and discussion.

ESR signal of different precursors in PVB and of some

plastics without dye. ; Samples consistin f severao g d e precursorsoman dy l eB PV n i s plastics alone were prepared as described above and irrad- o y witgammC kG h a0 17 raysdosa iate f o o et . d After irradiatio e sampleth n s were store t rooa d m temperature R signaES e lth recorded an d als t rooa o m temperatur. e th n o e next day, on a Varian ESR spectrometer model 4500 with an X-band microwave bridge. ESR parameters were set as follows:

HQ = 3500 g Microwave power: 1.5 mW . . Modulation amplitude: 4.8 g

The results obtained in this experiment are shown in table n Figuri d . Fro1 an e1 m thi e seeb s n figur ca tha t n i ei t most of the cases where a signal was obtained this corres- ponde singlea o t d t wit o signawidtN a h . f aboug ho l 5 2 t was obtained at all from plastics without dye which suggest that the ESR signal obtained for the rest of the samples combinatioe dependth n o n som i sy e f plastiewa o n dy d an c rathe f theo re m on consideretha n i n d separatel r thao e y th t free radicals produced in the plastic matrix transfer their

193 energy moleculese completeldy e th o t .y Another interesting finding concerns the film made by the combination of formyl viole d polyvinyan t l butyra whicn i le signa th h l obtained s large wa e sample th e res rth f o t thas r fo nconsidere d here d thian s signasinglea a superpositioe b t lo bu t seem t no s n o signalstw f o , accountin e facgth t thir thafo s a larget r ; widt s obtainedwa h .

R signaES e lDecath wite timf o yf storagth h o e e after irradiation

R tube ES d irradiate n an si B wer t PV pu e n o i sampled Tw R P f o s with Co gamma rays to a dose of 150 kGy, one in air the other one under vacuum ( ~ 10" torr ). ESR signals were recorded at room temperature for both samples right after irradiation and every twelve hours on for a total period of two weeks. Between measurements the samples were also stored at room temperature. During the course of the expe- \ ° rimens noticewa t i t d thae signath t lt chang widtno d edi h i wit R signae hintensitES th s timreportee lo wa th s e f o y d only as the peak-to-peak distance of the ESR first derivative, Result f thio s s experimen e show. ar t3 n figurei n d an 2 s Figure 2 shows the spectra for the samples irradiated and recorded in air and in vacuum. As can be seen, from this figure the signals are different from each other, the vacuum sample showin presence th g vera f yo e broad e peaban(se kd n figuri c fiel; 2 e d widt h) whic g abou 5 h 12 te seemb o t s very stable. Both signals show a 15 g width peak which probably comes froe samth me paramagnetic specie since both correspon o almost d e samth te resonance fiel d theian d r rate constant paramagnetir fo s c species recombinatio e verar ny similar. This last assortment can be verified from Figure 3 in which the decay with time of each peak is shown. From

194 this figure we got a half life of 1.88 +_ 0.17 days for the sample kept in air and 1.69 +. 0.09 days for the sample kept in vacuum, which shows that both signals can be corre- lated with each other. In orde o chec t re possibilit th k y thae recombinatioth t n mechanis e paramagnetith r fo m c species produce n boti d h samples could be diffussion controlled a. plot of intensity of ESR versus the square root of storage time was made, showing tha case t th thie s i indees d (see figur. 4) e Dose-respons B irradiatePV n r ei ai curveR P n i df o s

Figur showS e e dose-responsth s n PVBi eR .P curv Fror fo em this figure it can be seen that the response of the system is linear up to about 100 kGy showing exhaustion effects above this dose.

ESR spectra of irradiated samples in vacuum

Figure 6 shows the ESR signals of the four dye precursors in PVB mentioned above. Except for FV which seems to presen complea t x structure consistin perhapf o g peak8 s e th s res dyef o t s gave singlets wit valueg h s around 1.9n i 9s a the case of those recorded in air. Table 2 shows g values r eacfo hcorrespondine samplth d an e g linee widtth f o h signal. Comparing- these values with R thosES t froe go eth m e seesignab n f sampleca o ltha t i t r snarrowe ai kep n i t r signals were obtainee cas f th signalo e r fo d s recorden i d vacuum conditions, this probably due to the effect of oxygen in the samples.

R spectruES ' f nyloo m n witd withouan h e dy t

R signaES f e nyloo lTh n without idy s presentei e n Figi d . .7a The spectrum consists of a combination of 2 doublets probably presence o th differen tw o t f o ee du t paramagnetic-species a s

195 evidence e facth t y b thad t each doublet saturate t differena s t microwave powers. The addition of the dye precursor produces a singlenyloe e centeth th nf t o a rtwithou e spectrudy t s a m can be seen in Figure 7b. This signal is easily detected in contrast e precursor wite signaldy th he th mosf o sf n o i ts PVB. The signal is probably due to a paramagnetic center locatee crystallinth n i d nyloe th para s thina f o ts i s polycrystalline material. The effect of radiation on this system will show if this is the case since the interaction of . radiation with the plastic matrix will tend to destroy the crystalline structure. Also due to the fact that the ESR signal is produced in the crystallin e plastie th par f o tc matrix this will teno t d produce more stable dose-response curves with this plastic- dye combination as the crystalline structure will prevent free radical recombination.

V: %,.» Conclusions - The new formulations to make thicker radiochromic films have shown to be succesful in what respects to provide a strong ESR signal for our purposes. Films containing plastic without dye showed no ESR signal which leads us to e conclusioth o somt R e signan ES du sor thae s f i o tlth t interaction between the plastic and the dye. This is supported by the additional finding that the intensity of the ESR signal depends on the dye-plastic combination as is shown in Table 1.

- Decay of the ESR signal with the time of storage for PR in PVB showed that this a diffussion controlled mechanism, and the absence of oxygen during irradiation and storage induces a broad ESR band which origin is not very well

196 understood at the present. This band has shown to be pretty stable with time, making it useful for dosimetry but the need to have the film in an evacuated glass tube could make it impractical. Other formulations which could be suitable for ESR dosimetry are formyl violet and malachite green in polyvinyl butyral but further stability studies need to be done in these systems in the near fu- R signalES e valuef thesg th o s turee r eTh fo s dye. n i s PVB irradiated and recorded in vacuum showed no difference with respect to those measurements made in air though in general the ESR-signals were narrower.

e dose-responsTh - B showePV e possibilitn i th de R curvP r efo y * to- use this system for dosimetry' purposes up to doses of kGy0 e disadvantag10 On . f thio e s e instabilitsysteth s i m y of its ESR signal"with storage time, so the measured intensities should be corrected to time zero after irradiation.

- Nylo e onln th filmy e onear s s whic hR signa ES giv n a el without irradiation e precurso dy e additio e Th .th f ro n e plastitth o c matrix produce a singles t superimposet a d the nyloe cente R th spectrum ES nf o r .

References

Manambelon) (1 a J.R. (1973), "Conception d'une dosimetrie physiqu e spectrl r resonance pa ed a e magnétique"n ,i Dosimetr Agriculturen i y , Industry. Biolog d Medicinean y , Proc. Int. Symp. Vienna, 1972, International Atomic Energy Agency, Vienna pp. 293-301, (IAEA-SM-160/24).

(2) Regulla, D.F., Deffner, U., Tuschy, H., C1981), "A practical high level dosimeter based on tissue-equivalent alanine", High Dose Measurements in Industrial Radiation

197 Processing, IAEA Technical Report Series No. 205, Interna- tional Atomic Energy Agency, Vienna.

(3) Uribe R.M. , McLaughlin W.L., Miller, A., Dunii, T.S. and Williams, E.E. (1981) "Possible use of electron spin resonanc polymef o e r films containing leucodye- do r fo s simetry", Radiât. Phys. Chem. 18, 1011-1016 *. f ) Buenfil-Burgos(4 , A.E., Uribe, R.M.Piedaa l , e d ,A. d McLaughlin W.L., Miller , (1982,A. ) "Thin plasti- ra c diochromi e film dy cs ionizin a s g radiation dosimeters", publishee tb o n Proci d . 4th. Int. Meeting Radiât. Proc. Dubrovnik, Yugoslavia.

Table 1.- ESR intensities expressed as the product of peak-to-peak distance and width of the signal, divided by the mass of sample in the ESR cavity for the films considere n thii d s contract.

Film ^ ^ Weight p-p distance Width Intensity (grams) (cm) (gauss) (gauss.m c grams'1)

HH in PVB 0.0281 0.6 32.5 - 693 .95 B PV 0.040n Ni F 2 5 71 5 2 1.15 .17 MG in PVB 0.025 100' 1 3 4 2 1.05 .98 B PV 0.025n Fi V 3 3.8 57 8636 .36 B PV 0.027n Pi R 5 7 68 1 2 0.9 .27

(+) Code: HH, hexahydroxyethyl pararosaniline; NF, new fuchsin; MG, malachite green; FV, formyl violet; PR, pararosaniline

198 Table 2,- Line widths and g values for several dyes in polyvinyl butyral irradiated and recorded in vacuum s compare,a d with thos n airi e .

Vacuum Air

Sample Line width gauss Line width gauss g

New fuchsin 6.73 16 1.9951 Malachite green 10 24 1.9966 j» Hexahydroxyethyl pararosaniline 1.82 32.5 2.0042

199 R signaES r differen- FIGfo l1. . t kind f filmschromio s c dyes B irradiateiPV n d gammo witC ha rays) a . hexahydroxyethyl pararosaniline; b) new fuchsin, c) formyl violet; d) malachite green; and e) pararosaniline.

200 FIG. 2.- ESR signals for pararosaniline in polyvinyl butyral irradiate n r (spectrud storei ai an d d n an i d ) mA vacuum (spectruwidte d Th an peakf o h . a smB) abous i 5 g'approx. 1 t t i s r peai fo bc kd ,an 125 g. Resonance fields for peaks a and b are 3430 g and 3444 g respectively.

201 vacuum 1 . «id a b s

2F 1 i 5 10 s t srago 'jtrc.diys

R signaDeca- ES FIG 3. f .o yl wit e systehth timr m fo eparar o sanilin polyvinyn i e l butyral R intensitieES . s were measure peae peao th t k s ka d distance th f o e * signals.

202 v a c u u n

30-

20-

10-

1/2 square root tf storage time, aayo

FIG. 4.- Plot of ESR intensity versus tz for the system pararosaniline in polyvinyl butyral irradiated and stored in air to check if the recombination mechanism of paramagnetic species is diffussion controlled.

203 0 5 10 100 Dose in kGy.

FIG. 5.- Calibration curve of the ESR intensity versus dose r pararosanilinfo e cyanidB irradiatePV n i e d an d t rooa measure mr ai temperature n i d . Recording conditions were as follows: center field = 3405 g, time constant - 0.25 sec, mod. amplitude = 2.5 g, 4 gain = 6.3 x 10 , microwave power = 0.15m W, microwave frequency = 9.515 GHz.

204 FIG. 6.- ESR signal of different dyes in PVB irradiated to vacuumn i y kG . 0 Recordin15 g conditions wers a e follows :

25g

) Formya l viole PVBn i t , centerfield (Ho )324= , g 0 gaimicrowav, n0 1 (S.L. x 8 e )= frequenc ) (v y • - 9.013 GHz, time constant (T.C.) =0.25 sec, microwave power (M.P.) = 0.15 mW.

12.5g w fuchsiNe ) PVBb n 322= i n S.L, o ,4g H = 10. S, v = 9.010 GHz, T.C, = 0.5 sec, M.P. = 0.01 m W

205 c) Malachite green in ?V3, Ho = 3224 g, S.L. = x 10 8 = 9.014 ,v 0 GHz ,5 secT.C0. P ,.M. = . W m 1 0. =

2.5g

d) Hexahydroxycthyl pararosaniiine in ?V3, Ho 214 g, S.L. - 6.3 x 104, v = 3. 016 GHz, T.C. = O.b . secÏ/ ,m M.P0 2 .•

l caseIal n s C.3R ign.is ls wer e recorde t rooa d m temperature in vacuum with a -modulation amplitifde of Ig and modulation frequency of

:06 FIGURA 7 E

. 25g

FIGUR3 7 E

25g

FIG. 7.- ESR signals of nylon without dye (a) and nylon with dye precursor (pararosaniline cyanide) in air at room temperature (b)• Recording conditions were as follows: center fiel = 322d , timg 5 e constan= t 5 sec0. , modulation amplitud , g gai5 1 = n= e 4 microwav, 0 1 . Microwav IV x m e 1 powe0. e = rfrequenc y equals 9.004 GHz for nylon an 9.007 GHz for nylon wit. PR h

207 RADIOCHROMI DOSIMETRE CDY Y USING TRIPHENYLMETHANE LEUCOCYANIDES IN NYLO POLYVINYR NO L BUTYRAL*

W.L. McLAUGHLIN, J.C. HUMPHREYS Radiation Physics Division, National Burea Standardsf uo , Washington, DC, United State Americf so a

Abstract

The use of commercially-available radiochromic plastic films (nylon or polyvinylbutyral) containing the leucocyanide of hexa (hydroxyethyl) pararosani1ine is well established in radiation processing dosimetry (dose range: 10 5 ]Gy)-10 , especiallr fo y o gamma-raC y applications. These thin-film systems when' analyze y spectrophotb d y providr t e om a conveniene d routinan t e means of dose assessment and dose-distribution mapping, as long s thee a properlar y y calibrate n standari d d gamma-ray fieldd an s as long as suitable corrections are made for systematic error. e presenth n I t work e followinth , g contribution o uncertaintt s y in making absorbed dose evaluations with radiochromic film dosimeters were studied: variations in absorbed dose rate, photon energy, temperature, relative humidity, immersio n vacuui n r o m gases other thar (oxygen-ai n , nitrogen, nitrous oxide) during irradiation and during storage. These influences on radiochromic dosimeter respons d stabilitan e y have been studie n detaii d l experimentally, and suggestions are made for minimizing the resulting uncertainties in practice.

Introduct ion The leucocyanides of para-amino substituted triphenylemth-

anes n particulai , r U.^'.^" hexaki hydroxyethy1( s ) triamino- tr i p h e n y l a cet o n i t r i le (called hydroxy-ethyl pararosani l i ne cyanide e compatiblar ) e wit a largh e numbe f plastio r c media,- which can serve as film dosimeters d-^l. the films are cast from polymeric solutions, usin e sucs hosa gdy he t th medi r fo a

* This work was carried out under Research Agreements 2177/CF, 2433/DF, 3061/CF betwee e Internationath n l Atomic Energy Agency S NationaU e th d l an Burea f Standardso u e identificatioth ; f o n commercial product e sak f th clarito e r s d fo doet her an ys no si e imply endorsemen r recommendationo t s ovey othean r r products.

209 polar plastic s nyloa s r polyvinyo n l butyral (PVB) containing polyvinyl acetat d polyvinyan e l alcohol (PVA). Thicknesses range . Upoym n0 irradiatio70 o t 0 fro1 - m n they turn from colorless to a deep blue color. A plo*t of the increase in optical

absorbance (*max - 600 nm) with absorbed dose* serves as a

calibration in the dose range 10-1o1 5 Qy t thicker films being r e n e loweth use n i r d par f thio t s range. These film e commerciallar s y availabl n largi e e batches^5^, and are widely used for routine dose monitoring in radiation processing applications. Once calibrate a standardize n i d d field of gamma radiation, in terms of increase in optical absorbance at a given wavelengt r unipe h t film thickness (AA/mm) versus dose, e placeb a producthen n i ca dy t being processed unde a widr e range of conditions. In this way, they can provide a useful mean f o qualits y contro r determininfo l g absorbed dose distributions throughou e productth e treliabilit Th . f o y

radiochromic film dosimetry depend n takino s g certain precautions

o minimizt e systematic source f erroro s . We report her n comprehensivo e e studie f o thess e sourcef o s

systematic uncertainty in making dose assessments by readings from the two types of radiochromic film dosimeters, nylon and o suggest d PVBan ,t optimum condition n r radiatioi thei fo e s us r n processing applications with gamma radiation.

Experimental Conditions

The radiochromic films use n thesi d e studie e listear s n i d Table 1, along with their elemental compositions, thicknesses, typical wavelength r spectrophotometryfo s d useablan , e absorbed dose ranges. These films may be cast from alcohol solutions e oneaccordinth t s bu e,f-r u J t 4 3o , a method t g r e t i l s e giveth n i n

In this paper, except where otherwise indicated e termth , s "absorbed dose" and "dose" refer to the absorbed dose to water.

210 used in this work are commercially available types* supplied as FWT 60-0 63-00T (nylonFW 2 d (PVB-PVA)an ) , eithe s individuaa r l square films1 cm 2 s cmx a 2 sheet 2 1 x r ,,2o e ,2 b whic2 s n ca h

cut into the smaller size for spectrophotoraetry. Studies were made in order to examine variations in

radiochromic response as a function of gamma-ray dose rate and photon energy s wela ,s environmentaa l l e effectgamma-rath n o s y response characteristics and stability between irradiation and spectrophotometry. Description e .conditiond ^°Cth an f o o - s x f o s gamma-ray irradiation and of storage (dose rates, photon energies, temperatures, relative humidities, and environmental gases) are given in several previous papers C6-15J.

Experimental Results ( a) Dose rate dependence The two radiochromic film types of different thicknesses were administered absorbe y witkG h5 3 d6°C o doset o p gammu s a radiation t dosa , e rates ranging from 7 Gy-s"0.002. e o t 8Th 1 . results are shown in Fig. 1-4 for the nylon-base film (FWT 60-00) e polyvinyth r fo ann Figsi dl3 5- butyral-acetate-alcoho. l film (FWT 63-02), in terms of response curves, that is, increase in optical absorbance (at the indicated wavelengths) per unit

thickness (AA/mm a functio s a ) f absorbeo n d dos o watet e r ^6]^A low-intensity rate dependenc s observei e d particularly wite th h thinner films (see Figures 1 and 5), and particularly at low relative humidity during irradiation (stronge t 12Îa re Figse , . 1, than at 60J r.h., see Fig. 5), which substantiates earlier findings of Gehringer et al. Cl7] with hydrophilic radiochromic dosimeters e nylon-bas, th suc s a h d PVB-basan e e films e doseTh . - rate dependence occurs e highemainlth t a ry dose level0 1 > ( s

Far West Technology, Inc., 330D S. Kellogg. Goleta, CA, 93117, USA.

211 kGy), as indicated by the greater curvature of response curves e resultinanth d g tendency toward saturatio e loweth t ra n dose levels, which is more pronounced for the lower dose rates. Apparently thi o mort s e eeffec du efficien s i t t radiât ion-induced bleachin e tha s dy competitivi t f o g e formatiody e o t th e t a n lower dose rates and at the lower relative humidities. It is

especially prevalent in the absence of oxygen C6i17d3 j_ an 3 a diffusion-controlle o t e du e likelb o t y d oxygen-cad ie rr recombination mechanism. By employing an enrpirlcal eorrection factor based on the difference in the extent of competitive bleaching (difference in maximum optical absorbance at higher doses), the response curves of the thin nylon films at the different dose rate d differenan s t relative humidities shoa w linear response, at least up to 35 kGy, and no rate dependence (see Fig. 2). This radiolytic bleaching effect is apparently much less severe at very high dose rates, as with electron

beamsL7] anct £n the absence of oxygen C18J, the response curves being nearly linea d ratan r e independen o vert p yu t high doset a s

high dose rates 1-113. j t case of the thicker nylon and PVB- n e n PVA films e low-intensitth , y rate dependenc s relativeli e y small (see Figs. 3, 1, and 8). (b) Energy dependence Figure 9 shows the relative response of the FtfT-60-00 nylon film, irradiated bare, to various narrow spectral bands of x and gamma rays, expressed in terms of absorbed dose to water and

normalize e valuth t 1.2o a et dV (^°C5Me o Y-rays). Shown also are curve f maso s s energy-absorption coefficients (u/p)f o , en nylon and water and their ratios, which are seen to fit the experimental results over the energy range - 10 keV to 100 MeV"£1J43. These results indicate e nylothath t n film dosimeter may tend to underestimate relative absorbed dose to water in a photon spectrum containing an appreciable low-energy component.

212 l m i dosimete-f n i h t e th r (e.gf I . nylon s i irradiate) d with °OCQ gamma rays while surrounded with polymethyl methaorylate

(PMMA) layers thick enough for approximate electron equilibrium

conditions (- 5 mm), most of the effect of interest in the film o t secondar e du s i y electrons e froPMMAth m . Therefore,

according to Bragg-Gray cavity-theory conditions, the response of e filth m relativ s it surrounding o t e s depend n degradeo s d

secondary electron spectra e e masratith th d thu f sn o an oo , s collision stoppin ge file th powesurroundino t thosth m f o f ro e g

PMMA. These stopping powers and their ratios are plotted in Fig. 10, illustrating no appreciable energy dependence of response of

a nylon dosimeter in PMMA over a broad spectral region of electrons C163. These data were calculated according to Burlin's

cavity theory L19,20 n orde^ ] o t approximatr e energth e y dependenc f o response f o dosimetere s irradiated with gamma rays in simple geometric arrangements. ) (c Temperature dependence

Bot e FWT-60-0th h 0 nylo d FWT-63-0an n 2 PVB-PVA films were

irradiated in air with 60c0 gamma rays at various temperatures between -78°C and +100°C. The conditioning period at the

particular temperature prior to irradiation wa-3 one hour. The relative humidity during irradiation was - 50$. For the two •batches of nylon film containing hexa(hydroxyethyl)

pararosaniline (HPR-CN), Fig. 11 shows an increase in optical absorbanc r unipe e t thickness (AA/mra a give r fo n ) dose with increase in temperature during irradiation L &1. Figure 12 shows' that, amon e threth g e batche f PVc-PVo s A film,the older batch exhibit e leasth s t severe temperature dependence

particularly whe wavelengthnm n measure 0 60 t a d . These results illustrate the importance of knowing approximately the mean

temperature of irradiation when using the radiochromic film

dosimeters.

213 (d) Humid 11y dependence Both film types were irradiatet differena r ai n i td relative humidities d betwee97%,an e conditionin* th 12 n g period prioo t r irradiation e temperaturbein6 hoursth 1 d - g an , f irradiatioo e n

24°cl-8] 7h result. e shown termi ar s n Figs."1, f i no s 14 d an 3 e differences in values of optical absorbance per unit thickness f n absorbea r fo d0 kGy3 a functiodos f s o a e, f relativo n e humidity during irradiation e opticaTh . l absorbance readings were e indicateth mad t a e d wavelengths, afte e threth r e different periods of storage at a relative humidity of 5H%. In general, the respons t higa e h relative humiditie e cas s th f lesi o esn i s the nylon film type and greater in the case of the PVB-PVA film type than that at 51J relative humidity. The effect of a surface deposi f moisturo t t higa e h relative humiditie s showi s n Figi n . v 1M. (This effect may also explain the higher values for the PVB- PV ? Ar.h 96 filn Fig i t .a m , 13). When the films are irradiated at intermediate relative humidity (565 r.h.) d thee an store,ar n t varioua d s relative «• humiditie r differenfo s t periods (se d 16)ean Figs ,5 ther'1 . s i e very little effec n valueo t f o AA/mms , excep t a vert y high

relative humidity (> 97% r.h.).

In orde o studt re effecth y f relativo t e humidit n gammao y - • ray dose-rate dependence, FWT-60-00 nylon films and two batches f Riso d P-15 PV3-PVA films (Jan., 197 d Julyan 9 , 1979) were irradiate t threa d e relative humiditie ? r.h., 75 3Ï 2 i( d 1 ( >)an s , and at two absorbed dose rates to water (0.17 and 1.1 Gy-s"1}'-^ • e results(FigTh sho) 17 .w agreement wite earlieth h r resultf o s Gehringe . Cal 1 ?t e ]r with nylon film n thai e respons, th t f o e the nylon film type is rate dependent at the lower relative humidities, and that the rate dependence and humidity dependence e PVB-PVth f o A film type e dependbatcth n ho s used. These

214 results illustrate the fact that in radiochromic film types, a differenc e b ther y ma en environmenta i e l effects froe batcon m h to another. (e) Dependence on Surrounding Gases The two film types (FWT-60-00, nylon and FWT-63-02, PVB-PVA) were subjecte e houd o theon vacuut an d r r n fo werm e either irradiated with ^Co gamma radiation in vacuum or were y conditionedr , e hou n on differeni rr.h. r % fo d 5Q t ta gaser (ai s •oxygen y nitrogendr ,y nitroudr r o , s oxide) before irradiatioo t n different 8 showdose .1 e respons n thes. th i ss Fig e . egaseI15J s curves of the FWT 60-00 nylon.-base film irradiated in vacuum and e differenith n t atmospheres d e analyze an th e ,pea th f o k t a d on-inducei t a i d ra d absorptio a wavelength)nr n 5 ban(60 e d Th . responses in air and oxygen .are slightly greater than in the oxygen-deprived environments. Fig. 19 shows response curves of the FWT-63-.02 PVB-PVA film irradiated in vacuum and in the different gases, and analyzed at 600 nm wavelength. In this case, thera muc s i he greater differenc n responsi e e betweee th n * different environments, particularly at the higher doses. These results indicate the importance of calibration under atmospheric

conditions approximating those of eventual use.

(f) Stability Following irradiatio e differenth n i n o tfil tw gase me th s d 23°an C. r.h type ? 50 s t wera r e ai e darstore n th i kn i d temperature d weran , e read spectrophotometricall t differena y t time s 0 show2 afte . srFig irradiatio e , monton o C15] ht p u n that, whereas the nylon films irradiated in air and in oxygen are quite stable, there is some degree of instability during the firs y followinda t g irradiatio f thoso n e irradiate n vacuumi d , e PVB-PVth r 1 showFo 2 A . fil ' a sgenera fig m^2® n i l d an 2 iÜ n trend toward a slight increase in optical density throughout the

215 30-day storage period r irradiationfo , s unde l al fivr e

atmospheric conditions.

In another study ^8]m typefn ^ o tllstw e were irradiaten i d air to an absorbed dose of 25 kGy and were stored in the dark in J r.h50 d 23° t .an a C r temperatureai d weran ,e read

spectrophotom cal i t r threa et ly e wavelength0 60 t timea o s t p u s hours after irradiatio . n Wherea e opticath s l absorbance0 51 t a s r e 603quit(o ar 5 m an)n e 60 d stable, thosn t a a peae f o k absorption band in the near ultraviolet (360 nm wavelength) show « ** a marked increase hour4 afte2* - sr storage., These results indicate that for most practical applications in radiation processing, the two radiochroraic film types are suitably stable. There have been, however, some indications that occasional batche y tensho. ma sto dw somewhat less stability than those tested here ^213. Therefore eacw batcne hf filo h m should be tested for its stability between irradiation and spectrophotometric analysis. Summary The gamma-ray response characteristics of two widely used radiochromic dosimeter film typesa nylo e e otheon n,th fild r an m a polyvlnyl butyral-acetate-alcohol film, have been tested under various condition f irradiatioo s d storagean n . 1. The response of the thicker films shows no rate dependenc f responseo e ethinne th t bu r, films indicatn a e appreciable rate dependence, particularly at higher dose levels. The thin nylon-base film shows low-intensity rate dependence when irradiated at lower relative humidities. In the case of the PVB- PVA films, there appearà differenc e b o t s n rati e e dependence between different batches o matten , r whae moisturth t e contenf o t the films. 2. The energy dependence of the film response to x and gamma rays relative to photon absorption in water is appreciable

216 only if there is a relatively large component of photon energies less than -100 keV. Whee film th e nuse ar s d between electron equilibrium layer f plastico s , ther s i neglible e energy

dependence for irradiations with broad gamma-ray spectra, such as those used in radiation processing with large ^°Co sources. t 3. Temperature dependenc f responso e f boto e h film types i s sufficient to require correction for differences of temperature during calibration and irradiation, and there is generally increas n responsi e e with temperature rise, excepr fo t temperature m analysin e 0 th e 60 cas > f 60°Cth f o so en si , PVB-PVA film. \ e humiditTh . 4 y dependence results sho n effeca w t mainly during irradiatio t extremea n f relativo s e humidity, with very little effect of humidity during storage, except in the casa of very high relative humidity (> 95% r.h.). e nylon-basTh . 5 e filma irradiate n n i vacuui d d an m different environments do not show a gre-at difference in response, whereas the PVB-PVA films differ greatly when irradiated in different gases. Both films are relatively stable for long-term storage up to at least one month after irradiation, although the Nylon film shows a slight instabi-lity during the firs y afteda t r irradiation, particularly when irradiaten i d vacuum, nitrogen, or nitrous oxide.

From these results one may conclude that when the films are user dosimetrfo d n radiatioi y n processing, they require careful calibratio f o eacn h batch preferably under conditions approximating those of eventual use, and they require protection against extreme environmental conditions (temperature, moisture, gases) particularly during irradiation . The results ex?.lain difficulties that may arise when these dosimeters are used i r. extreme climates.

217 References

[1] McLAUGHLIN, W.L., "Microscopic visualization of dose distributions," Int. J. Appl. Radiât. Isotopes 1 7 (1966) 85.

[23 KANTZ, A.D., HUMPHERYS, K.C., "Radiochromics: A radiation monitoring system, "Radiation Processing (Trans.1st Int. Meeting,Puerto Rico,1976) (SILVERMAN, J.,VAN DYKEN, A. D., Ed.); Rad. Phys. Chera. 9, (1977) 737.

] McLAUGHLINC3 , W.L., MILLER , FIDANA. , , PEJTERSENS. , , K. , BATS8ERG PEDERSEN, W., "Radiochromic plastic films for accurate measurement of radiation absorbed dose and dose distribution, Radiât. Phys. Chem 0 (19771 . ) 119.

[43 BUENFIL-BURGOS, A.E., URIBE, R.M., DE LA PIEDAD, A., McLAUGHLIN, W.L., MILLER , "ThiA. , n plastic radiochromic dye film s ionizina s g radiation dosimeters,11 Radiation Dosi- metry, Vol. 2 (Trans. 4th Int. Meeting, Dubrovnik, Yugoslavia, 1982) (MARKOVIC, V.,Ed.); Radiât. Phys. Chem. 22 (1983) 325. ] [5 KANTZ, A.D ., HUMPHERYS, K.C. A direc," t reading exposure monito r radiatiofo r n processing" Trend n Radiatoi s n Processing, Vol .3 (Trans d Int3r . . Meeting, Tokyo, 1980) (SILVERMAN , Ed.)J. , ; Rad. Phys. Chem. JJM198O 937.

C6] McLAUGHLIN, W.L., HUMPHREYS, J.C., LEVINE, H., MILLER, A., RADAK, B.B., RATIVANICH, N., "The gamma-ray response of radiochromi e film dy t c differena s t absorbed dose rates," Trend n Radiatioi s n Dosimetry, Vol .3 (Trans d Int3r . . Meeting, Tokyo, 1980) (SILVERMAN, J., Ed.); Radiât. Phys. Chem 8 (19811 . ) 987.

[7] McLAUGHLIN, W.L., HUMPHREYS, J.C., RADAK, B.B., MILLER, A., OLEJNIK, T.A., "The respons f o plastie c dosimetero t s gamma rayd electronan s t higa s h absorbed dose rates," Advances in Radiation Processing, Vol. 2 (Trans. Int. Meeting 1978A , US Miami ), (SILVERMANFL , , J. Ed.), ; Radiât. Phys. Chem. 1 4 (1979) 535. [8] LEVINE, H. McLAUGHLIN, W.L., MILLER, A., "Temperature and humidity effecte gamma-rath n o s y respons d stabilitan e f o y plasti d dyean cd plastic dosimeters," Advance n Radiatioi s n Processing, Vol. 2 (Trans. Int. Meeting,, Miami, FL, USA, 1978) (SILVERMAN, J., Ed.); Radiât. Phys. Chem. 1 4 (1979) 551.

[9] MILLER, A. BJERGBAKKS, E., McLAUGHLIN, W.L., "Some limitations in the use of plastic and dyed plastic dosimeters," Int . ApiJ . . Radiât. Isototpe 6 (19752 s ) 6,11.

[10] McLAUGHLIN, W.L., "Solid-phase chemical dosimeters" Sterili- zation by Ionizing Radiation (Proc. Int. Conf., Vienna, 1974) (GAUGHRAN, E.R.L, GOUDIE, A.J., Eds.) M u 11 i s c i en c s , Montreal (1974) 219.

[113 McLAUGHLIN, W.L., URIBE, R.M., MILLER, A., "Megagray dosimetry (or monitoring of very Large radiation doses)" Radia- tion Processing, Vol. 2 (Trans. Int. Meeting, Dubrovnik, Yugoslavia, 1982); Radiât. Phys. Chem. 22 (1983) 333-

218 [12] MILLER, A., McLAUGHLIN, W.L., "High-dose measurements in industrial radiation processing," IAEA Technical Reports Serie . 205No s , Intern ionaat l Atomic Energy Agency, Vienna (1981) 119. [131 MILLER CHADWICK, A. , , K.H., NAM, J.W., "Dose assurancn i e radiation processing plants," Radiation Processing (1th Trans. Int. Meeting, Dubrovnik, Yugoslavia, 1982) (MARKOVIC, V., Ed.); Radiât. Phys. Chem. 22 (1983) 31.

[14] McLAUGHLIN, W.L., MILLER URIBE, A. , , R.M., "Energy dependence of radiochromic dosimeter response to x and gamma rays," to be presented at IAEA Symposium on High-Dose Dosi- metry, International Atomic Energy Agency, Vienna (198*0.

C15] CHEN, W., HUMPHREYS, J.C., McLAUGHLIN, W.L., "Response of radiochroraic film dosimeters to gamma rays in different atmospheres e publisheb o t " n Radiâti d . Phys. Chem. [16] MILLER, A., McLAUGHLIN, W.L., "Calculation of the energy dependence of dosimeter response to ionizing photons," Trend n Radiatioi s n Dosimetry (MCLAUGHLIN, W.L., Ed.) (Pergamon Press, Oxford, l982);-Int . ApplJ . . Radiât. Isotope 3 (19823 s ) 1299.

[17] GEHRINGER, P., ESHWEILER, H., PROKSCH, E., "Dose-rate and humidity effects on the gamma-ray response of nylon-base radiochromic film dosimeters," Int. J. Appl. Radiât. Isotope (1980_ 3J s ) 595.

B [18] GEHRINGER , IntercalibrP. , d testinan n f cellulosio o agt e triacetat e emegara th film r fo ds range," Proceedingf o s Coordinated Research Meetin n High-Doso g e Standardization and Intercoraparison for Industr-ial Radiation Processing, IAEA, Vienna (1983) (these proceedings). [19] BURLIN, T.E., "Cavity-chamber theory," Radiation Dosimetry, . (ATTIXEd d 2n ,Vol , F.H.1 . , ROESCH, W.C., Eds.) Academic Press w Yor Ne ,. 331 kp (1968, 8 . . )Ch

[20] CHRISTENSEN, E.G., MILLER, A., "A program in- BASIC for calculation of cavity theory corrections," RLsa Report M- 23^5 (1982). [21] MILLER, A., "Properties of thin-film dosimetry for radiation processing,: Proceeding f Coordinateo s d Research Meetinn o g High-Dose Standardizatio d Intercomparisoan n r Industriafo n l Radiation Processing, IAEA, Vienna (these proceedings).

219 Table 1

Nylo d Polyvinylbutyraan n l Radiochrotnic Film Dosimeters

Approx. Approx. Wavelengths Absorbed Film Type Batch Thickness of Analysis Dose R a n 5 e Code ) m ( Date (nm) (Gv)

FWT 60-00a 0 Ma'8 r 1 1 605 104-105

FWT 60-00a Mar '80 44 605 ,540 ,510 I03-1u5 FWT 60-00a Dec '72 700 605 ,540 ,510 102-104

FWT 63-02b 0 Ma'8 r 13 600.540 ,510 10U-105 ' FWT 63-02b Aug '79 53 600 ,540 ,510 1 03-1 O5 FWT 63-02b 0 Fe'8 b 120 600 ,540 ,510 102-105

FWT 63-02b Dec '78 580 600 ,540 ,510 102-1J5

fractional elemental composition by weight: H:0.104; C: 0.6^8;

N: 0.100; 0: 0.148

^Fractional elemental composition by weight: H: 0.086; C: 0.6^6

0: 0.297

220 FWT-60-00. NYLON, 0.011 mm 1 60 O 2.7 Gys- 30 + 0.36 Gys'1 U 0.008 Gys-1

} 605nm,60% r.h. 20 540nm,60% r.h. in

^ __•»• 605 nm, 12% r.h. — ' O in Ê 10

20 30 40

ABSORBED DOSE IN H20 kGy

Fig. 1 Response curves of 0.011 nm-thick FWT-60-00 nylon film at three gamma-ray absorbed dose rates and measured at three optical wavelengths [6]. Irradiations were made at two relative humidities s a indicated, .

SO i i r i FWT-60-00, NYLON, 0.011 mm

50 O 2.7 Gys-1 + 0.36 Gys-1 Q 0.008 Gys-1 }60X 40 Corrected for m radiolytic O bleaching 30 12 % r.h.

< 20

10 20 30 40 ABSORBED DOSE IN H20, kGy

Fig 2 . Effec f radiolytio t - percen60 cd an tbleachin - 12 t a g relative humidity. The dashed and s.olid lines marked $ r.h12 $ . r.hd 60 respectivelan . e samth s a ee ar y those shown for readings at 605 nm in Fig.l. After correctio r radiolytifo n c bleaching (see line s marked)a s , rate dependence is seen to disappear.

221 l I i FWT-60-00, Nylon , 0.044 mm 7 Gys-2. O1 30 15 + 0.36 Gys-' x 0.018 Gys-1 ' G 0.00s- • y G 8

20 io2

O iO

10 -20 30

ABSORBED DOS y HN EI 2 0kG , Fig. 3 Response curve f o 0.044-airs a thick FWT-60-00 nylon film at four gamma-ray dose rates, measured at three optical wavelengths [6]. Irradiations were made at 60? relative humidity.

FWT-60-00,NYLON, 0.70mm 2.5 O 2.7 Gys-< * 0.36 Gys-' 605 nm x 0.018 Gys"* 1 I 2'° Q 0.008 Gys' o in I 1.5 o m

« 1.0 O tO S m n 0 51 0.5

4 6 10

ABSORBED DOS N HI E2 0,kGy

Fig Response curves of 0.70-mm thick FWT-60-00 nylon film at four gamma-ray dose rates, measured at three optical wavelengths [6]. Irradiations were made at 602 r.h.

222 FWT-63-02.PV8-PVA ,0.013mm

10 20- -"" 30 ABSORBED DOSEINy HRG 20, Fig. 5 Response curves of 0.013-mra thick FWT-63-02 PVB-PVA film t a three gamma-ray dose rates, measureo optitw t - -a d cal wavelengths [6], Irradiations were made at 60? r.h.

I I I FWT-63-02, PVB-PVA,0.05m 3m

O 2.7 * 0.36 Gys-' Q 0.008 G y s-(

0 3 0 2 10

ABSORBED DOSE IN H20,KGy

Fig. 6 Response curves of 0.053-ram thick FWT-63-02 PVB-PVA film at three gamma-ray dose rates, measured at three optical wavelengths [6], Irradiations were madt a e 602 r.h.

223 FWT-63-0 -PV8 , m 0.1APV 2 . m 2 20 7 Gys2. O- + ~ 0.3s • y 6G x 0.01" s • y 8G Q 0.008 Gy • s' 15 E c E O 3 <= O O U) in 10 S nrr0 60 i

0 1 ' 5 15

ABSORBED. OOS N HEI 2 0,XGy Fig. 7 Response curves of O..12-mm thick FWT-63-02 PVB-PVA film at four gamma-ray dose rates, measureo opticatw t a dl wavelengths [6]. Irradiations were made at 60$ r.h.

FWT-63-02, PVB-PVA, 0.58mm • y G 7 2. O + 0.3• y G 6 x O.OI8 Gy s-1 j « Q s 0.00 • y G 8 -i in e" 13 m 600 i c O 2 O to £

0 10

ABSORBED DOS HN I E 2y 0,kG Fig. 8 Response curves of 0.58-mm thick FWT-63-02 PVB-PVA film t a four gamma-ray dose rates, measure t a thred e optical wavelengths [6]. Irradiations were made at 60* r.h.

224 _ 1.0

•0.1

NYLON

0.0t QOI 0.1 1.0 10 100 PHOTON ENERGYV e M ,

Fig 9 . Energy dépendanc e phototh f no e respons T 60-0FW f 0o e nylon film (experimental points d ratian )f maso o s energy-absorption coefficents of nylon and water (computed). Left ordinate: Mass energy-absorption coefficient r nylofo s n film dosimete d wateran r . Right ordinate: Rati f maso o s energy-absorption coefficients, nylon-to-water [14],

6 u r o» c. o '5. .34 i ut e o

Q01 0.1 10 EnergyV Me .

Fig. 10 Energy dependnce of the ratio of mass collision stopping power f o nylod an s PMMn A (Computed). Left ordinate: Variations with electron energy of mass collision stopping powers for (1) nylon film dosimeter and (2) polymethyl methacrylate.Right ordinate: Variatiof o n rati f o stoppino g powers on-to-po1 y n , metly l hy methacrylate [16].

225 \ i i i i i i i i r HPR-CN in NYLON 30 • BATCH I (1974)

26 + BATCH 2 (1978)

6 E 22 .X « 605 nm

10 i i i i i i i i i 0 10 0 8 O 4 0 O -4 0 -8 TEMPERATURE DURING IRRADIATION ,°C

i i i i i r

HPR-CN in NYLON

60 • BATC I H(1974 ) + BATCH 2 (1978)

m n 0 54 X* 20

j__i -80 -40 0 40 80 100 TEMPERATURE DURING IRRADIATIOC N,°

Fig. 11 Changes in optical, absorbance (600 nm and 540 nm) r unipe t thickness o batche(AA/mmtw r f O.OHo fo s) m m 4 thick FWT-60-00 nylon filmsas a function of temperature during irradiation C8]. Top: Absorbed dose - 15 kCy, Bottom: Absorbed dos 0 kGy2 e .

226 l l t l I l I l 1 t

- HPR-CN in PVB

- 600n\ m E 15 S • BATCH I (1974) <3 10 A BATC (1976H2 ) - 4 BATC H3 (1977 )

\*5IOnm

t f l 0 10 0 8 -80-60-40-20 6 0 4 0 2 0 0 TEMPERATURE DURING IRRADIATION ,"C

Fig. 12 Changes of optical absorbance (600 nm and 510 nm) per unit thickness (AA/m

227 HPR-C NYLOn i N N 40

m n 5 60 X«

20 £ E v.

m n 0 51 X*

l J_ 20 40 60 80 IOC RELATIVE HUMIDITY DURING IRRADIATION, %

HPR-CN in PVB r h l O Q 24 hr 50 r h 4 16 A

X * 600 nm

< 30

10 X ' 510 nm

I______l______I______I I______I 20 40 60 , 80 IOC RELATIVE HUMIDITY DURING IRRADIATIO% N ,

3 1 Top . :Fig Change — opticaof s l absorbancr pe ) nm 0 e 51 (60 d 5an unit thicknessCAA/m r O.OHU-tnfo m) m thick FWT-60-00 nlyon film as a function of relative humidity during irradiation. Bottom: Change f opticao s l absorbance (600 and 510 nm) per unit thickness (AA/mm) for 0.12-mm thick FWT-63-02 PVB-PVA films, as a function of relative humidity during irradiation [8]. Absorbed dose 30 kGy. Optical absorbance readings were made after storageae th t different humidities for the indicated storage periods. 4 hours)6 1 d an . , (12H ,

228 HPR-C8 PV Nn i

X « 600 nm

< r.5

5.0

2.5

20 40 6O 80 IOC RELATIVE HUMIDITY DURING IRRADIATION% ,

HPR-C8 PV n Ni o .aar h s r h 7 4 O r h 0 17 A

S >. < X' SIO nm <

— l

l l 20 40 . 60 30 100 RELATIVE HUMIDITY DURING IRRADIATION,'%

Fig. 14 Changes of optical absorbance (600, 510 and 360 nm) per unit thickness (AA/mm) for 0.053-mm thick FWT-63-02 PVB-PVA filma functio s a , f relativo n e humidity during irradiation [8]. Absorbed dose -30 kGy. Optical absorbance readings were made after storage at the different humidities for the indicated storage periods (0.25, 47, and 170 hours). The dashed lines represent result r filmfo s s havin a surfacg e deposit, which when cleaned with lens paper gave the results shown by the solid lines.

229 HPR-CN in NYI.ON 30 X'SOSnm

r h 5 0. O D 25 hr A 165 hr

l l l 0 8 0 6 0 4 20 100 RELATIVE HUMIDITY AFTER IRRADIATION,%

HPR-CN in NYLON O 0.5 hr 0 23 hr 165 hr 10

S 8 S •«* 510 nm « 6

\'3SO nm

l l 20 40 60 30 IOC RELATIVE HUMIDITY AFTER IRRADIATION, %

Fig. 15 Changes of optio-al absorbance (605, 510, and 360 nm) per unit thickness (AA/rara r O.OHU-mrfo ) a thick FWT-60-00 nylon film,as a function of relative humidity during hour5 storag16 sd r betweean 0.5fo e, ,25 n irradiation and reado-ut [8]. The films were irradiated with gamma rays at 25°C and 56? r.h. to an absorbed dose of 25 kGy.

230 HPR-CN in PV8

r h 5 0. O Q 28 hr 12.5 A ISO hr

• 10.0 X « 600 nm

< < 7.5

5.0

2.5-

I J_ J_ 20 4O 60 80 IOC RELATIVE HUMIDITY AFTER IRRADIATION, %

HPR-CN in PVB

O 0.5 hr Q 28 hr r h O IS A

4 -

- <3 < ^ m n 0 51 X* -O-

2 ~~

X»360nm

I I I_____I 20 40 60 SO 100 RELATIVE HUMIDITY AFTER IRRADIATION,4/«,

Fig 6 1 Change. f opticao s l absorbance (600) nm ,0 51036 d ,an per unit thickness (AA/mm)for 0.053-mm thick FWT-60-00 PVB-PVA film a functio s a , f relativo n e humidity during storage for 0.5, 28, and 150 hours between irradiation and readout [8]. The films were irradiated with gamm a % n r.habsorbea ray56 t o 25°.d a t s an C d dose of 25 kGy.

231 1 1 1 ^,A

40 „*-'" 4

s n .— , _ n / *i 1 c 30 O >ô 0 o

E £ 8 £ 20 - l-sJP^^ -^

<3 FILM D(Gys'') ORDINATE SYMBOL <

l K LEFT NYLO1 N 1 0.17 —— —° — LEFT ——• — to ~" RIS 0I I. P-1 f 5 LEFT ——H —— 1 0.11 7JAN 9 .'7 LEFT ——X —— RIS0 P-15 f I.I RIGHT — A —— 0.1X 7 JUL 9 '7 . — I —C — RIÖH T'

0 II -I 0 cD 12 34 75 UDO RELATIVE HUMIDIT% Y,

7 1 FigVariatio. f responso n e (chang n opticai e l densitr pe y unit thicknes r absorbefo s d dos 0 kGy2 e f threo ) e types f radiochromio c film dosimeters (FWT-60-00 nylon film thickness 0.057 mm; 3isrf P-15 PVB film thicknesses 0.052 and 0.055 mm)a functio s a , f relativo n e humidity during irradiation at two different gamma-ray dose rates [6].

232 50

HPR-CN S 30 in Nylon £ >N Q o < 20 IRRADIATION — CONDITION • — Air o —Vacuum 10 V -N2 A -02 o -NZ0 I______. 0 4 O 3 0 2 0 1 . 50 ABSORBED DOSE IN WATER, kGy

Fig. 18 Response curves, in terms of increase of optical absorbance (optical censity r unipe ) t thickness (AOD/ram) for 0.01 1 - m m thick FWT-60-00 nylon film, as a functio f o absorben d dos n i watee r (temperature during irradiatio s 24^C)wa n . Gamma-ray irradiations were mad n n i vacuudiffereni e d an m t gases d spectrophotoan , - metric analysis was at 605 nm wavelength [15].

IRRADIATION CONDITION HPR-CN • -Air B iPV n ° —'Vacuum 1 30 -T -N2 A -02 O -N20 600 nm

20 £ £ ^ Û O

O IO 0 5 ISO ABSORBED DOSE IN WATER, kGy

Fig. 19 Response curves, in terms of increase of optical absorbance (optical density) per unit thickness (AOD/mm)for 0.013-ram thick FWT-63-02 PVB-PVA film, a functio s a f absorbeo n d dos n watei e r (temperature during irradiation was 24°C). Gamma-ray irradiations were mad n n i i vacuudifferene d an c t gasesd an , spectrophtotmetric analysis at 600 nm wavelength [15].

233 HPR-CN '" Hft.OH «05 nm 3 IRRADIATED m AIR a7— — 38kG19 ko,y Z • — 9.6 kCr ———. — O Q ————— Q —— ——. Q 1

0 1 1 1

3 IRRADIATED in VACUUM 7— 2 Q— ^ ————— Q ———— O kG7 »9. — •

0 1 1 1

> 3 IRRADIATED —- —V • ——— —' — * in M tn V— 5 2 l9kG— Q y Q a~ ——0^-— — o—a ^ • — 9.S kGj s . H- • Q. °n 1 ! I

3 IRRADIATED mo, 7— 3« fcG» 2 O— I 9 kGy o- ——— o ———— o ——— Q • — 9.5 kCr ,

0 ! I 1 - -„__ __ 3 IRRADIATED in N,0 7— 38 »G» 2 Q— !9kGT a———— — — - ° a —— —a • — 9.9 kGr

0 i i i OJ 1.0 IO OO TIME APTER IRRAOIAT10N, DAYS

Fig0 2 Stabilit. f O.OM-raro y a thick FWT-60-00 nylon film- ir , radiated in vacuum and in diffepent gases with gamma pays at 24° o thpet C e absop'aed n i dose d p stopean ai s n i d th e ? p.he dap 53 p pepiodt on 23° . a d kfo o t an C p u a month [15].

234 HPR-CM in PV8 SOOnm 3 IRRAOlATtO in AIH

0 — 144 xGT u— 67 «Gr 2 r kü 8 3 — 7 O— iSkGr •— 9.S»C» 1 O —————— O —————— O ———— Q 0 [ 1 1

3 IRRADIATED in VACUUM I44k0— 0 r Z A— S7xGj 7— 38 »G> a— i» ko? »G7 9i r — •

51 ———— ————û ———û 3. 0 i 1 1

> 1.0 IRRADIATED >— in N, 35 Z 0— !42kGy a S7kG— A j _,as •7— 38I.G, Q— OkGy ,1 • •—S. 5 »G» t- a. 0 n 1 t 1

1.5 IRRAOtATCO in 0, l42kG— o r 1.0 u— S7kG, 7— 38 kG, a— i9kor as • — äs «G, ~£T=5-—— —o —— - —o

0 ! 1 1

1.2 — - - IRRADIATED in N,0 o —142 kGr 0.8 » kG 6 $ — d £_—— —4 ———— i—— —i <7— 38 kGy

Q— 19 kGT 0.4 T kG S 9. — • ————o " o ———— —— o — q

0 1 1 ! 0.1 1.0 10 100 TIME AFTER IRRADIATION, DAYS

1 Fig2 Stabilit. f 0.053-ao y a thick FWT-63-02 PVB-PVA film, irradiated in vacuum and in different gases with gamma ray t 24°a so fivt C e absorbed dosed storean sn i d ? r.he dar 50 r t th period 23°.a d kfo ai n i an Cr p u s to one month [15].

235 1.6 HPR- CN in Nylon Ê

LU 00 £ 0.8 LU ££ =36X m a 0n LU x X = 510 nm o X = 605 nm

LU CC 0 0 10 10 1000 TIME AFTER IRRADIATION, hours

Fig2 2 Stabilit. f O.OM-mo y m thick FWT-60-00 nylon film- ir , radiated with gamma rays at 2JJ°C in air and stored in air at 23°C up to 600 hours [ 8 ]. Absorbed dose to water:' 25 kGy. Values of optical absorbance increase per unit thickness (AA'mm) at the indicated wavelengths f analysio e normalizear s o thost d e obtained h afte 1 2* r storage time.

r i l i l 1.6 HPR-C n POLYV1NYNi L BUTYRAL

m n 0 36 = X a LU > 0.4 o X = 510 nm m n 3 60 « X x cUcJ 0 10 10 1000

TIME AFTER IRRADIATION.hours

Fig. 23 Stability of 0.057-ac thick R i sd P-15 PVB-PVA film, irradiated with gamma rays at 24°C in air and stored in air at 23°C up to 600 hours [8]. Absorbed dose to water: 25 kGy. Values of optical absorbance increase r unipe t thickness e (AA'mmindicateth t a ) d wavelengths of analysis are normalized to those obtained after 24 h storage time.

236 . IV LIS PARTICIPANTF TO S

Chadwick, K.H. Association EURATOM-ITAL 8 4 P.Ox .Bo Keyenbergseweg 6 Wageningen The Netherlands (Commissio Europeae th f no n Communities, Brussels) Ettinger, K.V. Universit Aberdeef yo n Fores terh1 i1 AberdeeD 2Z 9 nAB Scotland U.K. Gehringer, P. Österreichisches Forschungszentrum Seibersdorf Ges. m.b.H. Lenaugass0 1 e A-1080 Vienna Austria i McLaughlin, W.L, National Burea Standardf uo s Cente Radiatior rfo n Research Washington, O.G. 20234 U.S.A. Miller. ,A National Laboratory 9 4 P.O x .Bo DK-4000 Roskilde Denmark Radak, ,B Boris Kidric* Institute of Nuclear Sciences P.O. Box 522 YU-11001 Belgrade Yugoslavia Regulla, D.F, Gesellschaf Strahlenr fü t d -un Umweltforschung m.b.H. Ing oStädtel r Lands tral e ss D-8042 Neuherberg Federal Republic of Germany Stenger. ,V Institute of Isotopes of the Hungarian Academ Sciencef o y s 7 7 P.O x .Bo Budapes t Hungary

Uribe, R.M. Institute de.Fisica UNÂM • Apdo. Postal 20-364 Mexico 20, D.F. Mexico

237 Observer

Deffner, U. Gesellschaf Strahlenr fü t d -un Umweltforschung m.b.H. Ingolstädter Landstrassel D-8042 Neuherberg Federal Republic of Germany

Schindelwolf, 0. Wieser. ,A Vogenauer. ,A

Consultant Bills, S.C. National Physical Laboratory Teddington, Middlesex TW11 OLW. U.K.

Secretariat Nam, J.W. International Atomic Energy Agency Wagramerstrasse5 0 10 P.Ox Bo . A-1400 Vienna Austria

T a(O

238