SUDANSUDAN ACADEMYAGADEMY OFOF SCIENCES(SAS)SGIENGES(SAS)

ATOMICATOMIC ENERGYEhTERGYRESEARCHESRESEARCHES COORDINATIONCOORDII\rATI ON COUNCILCOUNCIL

- Development of Chemical Dosimeters

A dissertation Submitted in a partial Fulfillment of the Requirement forfbr Diploma Degree in Nuclear Science (Chemistry)

By

FareedFadl Alla MersaniMergani

SupervisorDr K.S.Adam

MurchMarch 2006

J - - - CONTENTS

Subject Page -I - DedicationDedication...... I Acknowledgement ... '" ...... '" ...... '" ... '" ...... 11II

Abstract ...... '" ...... '" ...... -...... III -I Ch-lch-1 DosimetryDosimefry - 1-1t-l IntroductionLntroduction . 1I - 1-2t-2 Principle of Dosimetry '" '" . 2 1-3l-3 DosimetryDosimefiySystems . 3J 1-3-1l-3-l primary standard dosimeters '" . 4 - 1-3-2l-3-Z Reference standard dosimeters ... .. " . 4 1-3-3L-3-3 Transfer standard dosimeters ...... '" . 4 1-3-4t-3-4 Routine dosimeters . 5 1-4I-4 Measurement of absorbed dose . . 6 1-5l-5 Calibration of DosimetryDosimetrvsystemsvstem '" . 6 1-6l-6 Transit dose effects . 8

Ch-2ch-2 Requirements of chemical dosimeters 2-12-l Introduction ...... 111l 2-2 Developing of chemical dosimeters ...... 12t2 2-3 Classification of Dosimetry methods.methods ...... 14l4 2-4 RequirementsRequiremsnts of ideal chemical dosimeters ,. ... 15 2-5 Types of chemical system ...... 16l6 2-6 Liquid aqueous systems.systems ...... 17t7 2-7 Prerequisites of chemical DosimetryDosimety '" ... 19t9 2-7-12-7-l Purification of water '" ". 20 2-7-2 TreatmentTreaftnent of glass ware and irradiation cells...cells ...... 20 2-7-3 TreatmentTreatrnsntof plastic irradiation cells '" '" .. . .. 20 2-7-4 Use of irradiation cells...cells ...... 212l 2-82-8 Stabilizing Agents ...... 212l 2-92-9 DefmitionDefinition of G value ...... 212l

Ch-3 Types of aqueous chemical dosimeters 3-13-I Fricke dosimeter '" '" '" .. 23 3-1-13-l-1 Principle '" '" . 23 3-1-23-l-2 Basic reactions '" ...... 24 •I

t 3-1-33-l-3 Calculation of the absorbed dose . 24 3-1-43-l-4 Influence of various factors 26 3-2 Ceric sulphate (Ceric - Cerous) dosimeter 28 L 3-2-13-2-l Principle 29 3-2-2 Calculation of absorbed dose...... dose 29 3-2-3 Influence lnfluenceof various factors...factors 30 L 3-3 Other aqueous systemsqystems 30 3-3-13-3-l Aromatic solutes Systems '" 30 3-3-2 Chlorinated hydrocarbon Solutes 31 Lf 3-4 Potential liquid dosimeters ... .. , '" 31 3-5 Gaseous chemical dosimeters ..... " 32

...h 3-6 Solid chemical dosimeters ...... 32 32

Conclusion , 34 References ... 35

LIST OF TABLESTABTES

Table (1):(1) : Various Radiation DosimetryDosimetrv standards 6 Table (2):(2) : Events in Radiolysis of aqueous solutions...solutions. .. 19t9 SE

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- To those who are donate me their livelive...... To those who are lighten my way by candlescandles.... To those who are learned me and guided meme... . Lt* To all of you ...

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tJ- Father ~I t- Mother rr Teachers I Brothers rl- Friends r11 I offer you my bit hopping thatthatit it will find even a bit of your consideration. l- Your r,- tr ~l rr

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L- ACKNOI|TLEDGE|lJ|ENTACKNOWLEDGEMENT

L I thank GOD too mushthat I could completethis L beneficial work after a lot of effort and constraints that facedme. I I deeply grateful to all those who helped me in 1' achieving this research

I Many thanks for Sudanese Atomic Energy Commission (S.A.E.C) Staff for their advises. -- Also full thanks for my supervisor Dr K.S.ADAM -- for suggested idea and orientation and for his valuable gtidance research. r guidance through out the research. 1G

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J - - Affi AOT A chemical dosimeter is a systemsysternthatthat measuresmeazuresthethe energyby virtue of chemical changes fromfrom ionizingionizingabsorbed radiation produced unit when itit L- .... isis exposed toto ionizingionizing radiation. In all chemical dosimetersradiation 1

'---L- inducedinducedchemical reaction produces at leastleastone, initially initially absent species, .... which is properties long lived enough to determine its quantity or the

'---L- change in the initial systems. Different types of chemical dosimeters were discussed such as aqueous, gaseous and solid, but the greatgreatconsideration was given to aqueous systems because of their vital role in settingmany processes. '---L--

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-"~ 'l- I-DOSIMETRYl.DOSIMETRY "I .J I .l-.-. LI ....

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1 -1 Introduction:

UUsese of ionizing Radiation has become increasingly important in a different fields, industrial processing applications such as polymer cross linking, polymerpolyrner degradation, polymer grafting, vulcanization,vulcanrzation,curing of coating, scrubbing of gaseous effluents, sterilization of medical products, sewage sludge hygienisation, delayed ripening of fruits, sprout inhibition and insect population control. The absorbed doses employed in these applications range 2 from 10 Gy - more than 100 kGy).kcy). 2

In the use of ionizing Radiation, reproducible and an accurate irradiation of the products to get desirable effects depends on having reliable dosimetry systems. Dosimetry play a vital role in setting of process parameters to meet variety of specifications, dose mapping in products, carrying out validation, commissioning procedure as well as in the day today operation of the plant.

Measuring response of dosimeter to Radiation is generally much easier and quicker to measure than any other parameter of the product that has been irradiated. Documentation of dose is often required in order to ensure 2 operational safety quality control. 2

The effects of Radiation on the matter depend on the Radiation field, as specified by the Radiation quantities and on the interactions between - Radiation and matter, as characterizedcharacterizedby the interaction quantities. Dosimetric quantities are products of radiometric quantities and interaction coefficients. Radiation interacts with matter in a series of processes in which particle energy is converted and finally deposited in matter. Measurement of 1 -

- - - ...

_ .J

the energy absorbed per unit mass IIIin a medium exposed to ionizing Radiation necessitates the introduction of a dosimeter into the medium. Dosimeter is a device that, when irradiated, exhibits a quantifiable changes in some property of the device which can be related to the absorbed dose in a - given material using appropriate analytical instrumentation and techniques. - ~, Different typestlpes of dosimeters like gaseous ionization chambers, thin films, solids and liquids are used in Radiation dosimetry. There is a considerable variation in their size and composition. Also several wall materials having - 2 varying thickness are used to contain the dosimeter. 2

1-2l-2 Principles of Dosimetry: - ... The dose in a medium is measured by replacing the medium by a dosimeter.

- ... Normally, dosimeter will differ from the medium in both atomic number and density and it therefore, constitutes a discontinuity, which will be referred to - ... as activity. The energy absorbed in the dosimeter is therefore not the same as that absorbed by the medium. Under electronic equilibrium conditions, the (2) - ... dose in the medium can be estimated using cavity (Bragg Gray)GraD theory. (2) FForor irradiations using a photo-source, the dosimeter may be considered as - ,., activity in the material of interest, and the interpretation of absorbed dose in - .. material as follows. If the sensitive region of the dosimeter is very thin compared to the range of the highest energy secondary electrons, then most of the energy deposited in the dosimeter and in the material surrounding it results from secondary electrons produced outside the dosimeter (that is, in 2 - ... the equilibrium layer of material). Thus the absorbed dose in the material 2 , Dm,Dr[, is given by: .. - H P)m Dm = (SI6l P)m Dd,n - ... (SIP)d(sI P)d

2

. ..

.. - -

(sf t')m (SlP)d WhereWhere (S/1')//1 andancl(S'/ P)d areare massmasscollision collisionstopping stoppirrgpowerpowcr forlirr thethe

surroundingsttrroundingmaterialnraterial andancl dosimeter.dosirlcter'. respectively.rcspectivel;,. Ddl)d Isls absorbedabsorbecldosedose inip thethedosimeter. dosimeter.Ilff thethesensitive sensitiveregionrcgion ofol-tlie the dosimeterclosirletcr haslras aa thickness thickncssmuchuruclr greatergreaterthanthan the therange I'angeofof thethehighest higheslenergyenergy secondarysccorrclarv electrons,clcctlnns. thenlhor mostrn11sl ofof thetheenergy energydepositedde positecl inin itit resultsresultsfrom1l'orl thethc secondary scconclarvelectronselcctrons producedproclucecl withinwithinthe thedosil11eter dosinreteritit selCsell,thus,tlrr,rs , thethe absorbed absorbeddosedose inin thethematerial rnaterizilisis given qivcn r2 by:OV:2

'----- DillI)rt == (pen/0y4!!,,PJ!!2 DdD,l (pert, J (pen/P)dP)cl (1-rcnfI))nt WhereWhere (I-ten/ P)17I andar'r4v(pen/llrcnf1')r/ jJ)d arc',,'. thethc massnrassabsorptionabsorpti.n coefficientscoelflcierrtsofof thethc /t/ medium,ntediutn,11/ andaltdthe dosimeter dosimetcrmaterialtnertcrial,/, d ,respectively.resllectively. IfIf the thc sensitivescnsitivc L..- region of thetlie dosimeterdositneterhas a thicknesstlricl

Thel'he collision stopping powerspowcrs and anclthellre energycrrcr.g),nbsorptionabsor.l)tiorr coefficientscocl-llcicnts arcar-c

J energy dependent;dependent: however forlor hoivhow atomicatornicnr.rrrrbcrnumber rrratcrialsmaterials andarrcl 1'01'f or tlrcthe ellergyenergy range 0.1 to l010 MeV.MeV, thcthe ratiosof'thcof the stol'rltirrustopping powcl'spowers lrrdand cncluyenergy absorptioncocf'llcientscoefficients clcldo I)oInot var'1,vary sigrrilicantl_1,signi ficantly as a lirnctiorrfunction ol'cncrs-r,.of energy. '------AlthotrghAlthough this defiltiliotrdefinition is givcngiven slr'ictlvstrictly lorfor irtrsorbcclabsorbed rloscdose at a poirrlpoint irrill ..... I{adiationRadiation absorbing trrater,mater, itit isis gerrerallygenerally avclagcclaveraged ol'crover a ljrritcfinite nrass mass ul'uof a given nraterial,material, thcthe absorbeclabsorbed closedose bcirrgbeing r"cacl rend b1,aby a closinrctcrdosimeter calibratccalibrate irrin termsterms of energyirnparted imparted perper r.rnitunit rnassmass of'aof a givcngiven rlatcriarl.material. lnIn l{acliatiorrRadiation 1 processitrg,processing, thethe rcferetrcereference tnateriaimaterial inin nrosl1110st calibrationcalibration isis r,vatcr,water, itit isis irnpo11alrimportant

L-'--- toto realizerealize that that thethe dosimetet'dosimeter isis intendeclintended toto givcgive nrcasurcrnerrtmeasurement ol'absor.bcclof absorbed -l-he dosedose averageclaveraged tlverover aa smallsmall volurne.volume. The signalsignal Iorrrrform this this clclsirrrctcrdosimeter carrcan '-- thereforetherefore bebe aa tneasttremeasure ofof encrgyenergy absorbccl absorbed inin thatthat volrrrnc.vulume. vvhich call be 1 vvhichcan bc 2 relatedrelated toto thethe closedose inin thethe proclLrct.product. 2 -

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1-3l-3 DosimetryDositnctrySystems:Systerns: 'l-hcy They1'heyare useduseclto measuretneasut'eabsorbedabsorbcd dose.dosc. They consist oro1-thc the dosimeters.dosirncters. measurementmeasurenrentinstrumentsinstrunrents andancl theirthcil associatedassocizrtcclrelcrencercl-crcncc standards,stanclalds. andancl procedures forIbr the system's use.r"rsc. DosimctersDosirlctcrs maynray bebc dividedclividcdinto fourforrrbasic classes according to the accuracyelccuracyof thethc dosimetryclosirlctrvsystemss1'stcnrs andancl areasarcas oritl- -r' 2 applications as follows.lollows.2

1-3-1l-3-l Primary StalllhudStarrdirrdDosimetcrs:Dosirncters:

't Primary standard dosimetersdosimelct's arc establishedestablishcclandancl maintaincdrnaintaincd by nationalnatiorral standards laboratories for calibration ofol'l{acliutiorr Radiation environmentscnvilor.rrncnts (fields)(lielcls) andancl 'l'lrc • -6 other dosimeters,dosimetcr"s. these are eithereithcrionizationionizatiorr chamberscharnbcrs or calorimeters.calorirletcrs.The '------2 overall uncertainlyltncertaitrly at thethc stagestaqcis ±1 Ilo,"o% (at(at()5ot'o 95% ercs"standard"starrclirrcl deviation").clcviatiorr"). 2

• ..A 13-2l 3-2 ReferenceltefcrcnceStandardStartdarrl Dosimetcl'sDosirnetcr's L_- 'l'hese These dosimetersclositnetersusedusecl to calibratecaliLrlatcRadiationltacliation environmentscnr,'irorrnrcnts andancl routine • -6 dosimeters,closimeters,referencerel'ct'ctrcc standardstatrclarcl dosimetersclosirnctcrs maynr[r)/

· ~ dosimeters.dosimcters.'l'hcscThese are chemicalchcnrical dosimetryclosirnctr'l,systcrn system wherervhcrc responsercsl)onsc not only to "---- RadiationItadiationbutbr-rt to otherotltcrinlluencinginllucncing factorslircturs such as temperaturetcnrl-''c1'n11rlc

• -6 is reproduciblereproclLrciblcandancl wellwcll characterized.charactcriz.ccl.'l'hcyThey arc classilied clussillccl as type11,1)c:"A" andarrcl type "13". "B".'].hcThe type "1\" "A" dosimetersclositttctct'sl()rIirr example.cxatnplc. Fricke,I;t'icl

this can bebc guaranteed,guarantcccl,certainlyccrtaittlv to withinrvithirra fewl-clr,percent,1-rcrccnt. providedproviclcd a goodgoocl chemicalchernicalpracticepracticc is followed.firllorvccl.'l-ypcType "13""ll" dosimetersrlosirnctcrsarcirrc systemssyslcnrswhichu'hiclr exhibits high precision butbu1- havehavc to lx'bc calcalibratcclibrated againstagairrst <1a standardstanclarclhigherhighcr in the series.series.'1-heilTheir Radiationltacliation responsefcsponsc cancarr not bebc predicatedprcrlicatcclpurelypLrrcl;,on on thethc ~-- basic of compositionconipositionthethc overallovcrall uncertaintyrrnccrtairrtvassociatedassocialccl withrvitlr referencercl'crcrrcc ·-! .... dosimetersdosirrretersis about ±+ 3%.3o .22

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- ..... 1-3-31-3-3TransferTransfcr StandardStandnrd Dosimetcrsl)osilne(ers

- ..... TheseTl-researe specially speciztllyselectedselcctecl dosimetersclosinrctcrs usedusccl forfirr transICrring trans{crringabsorbedabsorbccl doseclosc informationinlbrmationfromfronr accreditedaccreditcd or nationalstandardsstanclarrcls laboratorylaburirturv totcl an irradiation irracliation - ..... facilitylacilityinitr orderordcr toto establishedcstablishecltraceabilitytraccability for{or thatthal f~lcil lacilitl,.'l'lrcscity. These dosimctersclosinrctcrs shouldshoulclbe useduseclunderunclcr conditionsconclitions thatthat are carefullycarefirllv controlledcontrollccl bybir thetltc issuingissLrins ... - laboratory.laboratory. Transferf'ratrsfer standardstiurclarcldosimetersclosinrcte rs maynray bebc selected sclcctcclfrom li'onr eithercitlicr

- .... reference standardstanclarddosimeters dositlctcrs or routine routinc dosimeters closinrctcrsandancl shall have havc performanceperforutancccharacteristics suchsuclt as long shelfshcll life,lifb. easilycasilycalibrated,calitrratccl. stable,stablc. - .... rugged, portable,ltortablc, mailt-nail able, broadbroacl absorbedabsorbccl dosedosc range,langc. Radiationllacliation absorptionabsor'ption properties similarsinrilar to those of irradiationirracliationproduct,proclLrct. relativelyr'clativcly inexpensiveincxpcnsivc to - .... extremes of environmentalenvironnrentalconditionsconclitions ,correctable svstcmatic errors (e.g.(c.g. ,corrcctabIcst'stcrnatic• crrors L temperature,tetnperature,humidity,hr-rrniclity, etc),ctc). producibleproclLrciblclots,lots. reproducibler'cpnrclrrciblcresponsercsl-ronsc andancl - -'" smallsnralldimensions comparedcolxpal'ccl to distancesclistanccsoverovcr whichrvhiclr absorbedatrsori'rccl doseclosc gradientsgraclicnts 2 becomebecontcsignificant,sisniflcant. etc.ctc. 2 - -'to

- .... 1-3-4l-3-4 Routinell.outinc Dosimetersl)osinrctcrs 'they --- They maynray be useduseclforlbr qualitycpralitycontrol andarrclprocessl)r'occss monitoring.nrorritorins. RoutineI{outinc dosimeters are systemssystctnswhosewhosc pcrlirrrnancc,performance, particLrlitrlyparticularly withli,ith respectlcspcct to --- environmentalenvirontnentalinfluencinginflrtcrrcitrg lirctols,f~lctors, is not as goodgooclas thetlrc referencel'cl-crurccsystems,systcnrs. - .. but whose case ofo1-useusc andancl low cost makesnakcs themthcrn idealirlcal forlirr dayclay tolii daycla,r, --L- - ... monitoring of RadiationI{adialiorrdosescloscs duringcluring pr'occsscs.processes. Criteria('rilcria forlirr selectionsclccliorrorol' routine dosimetryclosirlctry systemsystcnr includeincluclc suitabilitysuitability'of' or thetlrt: dosimeterclosinrctcr'{irrfor thetlrc

- .. absorbeddose ratrgcrange ol'intcrcstof interest ancland lirrfor uscuse with a sl)ccilicspecific ltroclLrct.product. sta["rilitvstability L- ancland reprociLrcibilityreproducibility ol'thcof the systcnr.system, cascea5e ol'systcrnof system caliblation.calibration, traccubilitl,traceability ol'of - ... systetlsystem calibratiorrcalibration to nittionalnational stanclarcls.standards, abilitvability to corrtr'olcontrol svstcn'rsystem l'csp()lrscresponse ..... lbrfor systemunccrtaintics.uncertainties, such as tlrosct!lo5C causcclcaused b1,by 1"',.,'',.''atrrrctemperature uncl

.... -- 5 H - . ~

. ~ quantities,cluantities,overall initial andancl operational cost orsystcmcll-systcrn includingirrcluclirrq dosimetersclosirnctcrs

readout equipmentequipnretrt ,and,ancl labor required recluirccl rorfbr dosimeter cklsiurctcr readmitrcaclout andancl interpretation,interpretaticln.ruggednesst'r-rggedncss orof thethc systems1,stt-'nrresistancercsistancc to damagerlanraitcduringclrrrirrg routineroLrtinc 2 handling and useusc in a processingprocessinsenvironment,cnvironnrcnl. etcctc.. .. 2 Tablefable (1):(I): VariousVarioLrsRadiationl{adiation dosimctryclosirnclry standardsstandarcls

Dosimeters .-- --- RoutineI{outirreDosimetersDosirleters (5%)( 5?6) R"f.*,,r*--Reference StandardsStr""k,',1;PIl)r'i'1lllaryrr Standards DosimetersDosirnetcrs(3(Xl)(3%r) !)I)ososil11etersirrrctcrs(1-2(~(l)( l-2'1,1,) Plastics FrickeFricl

1-4l-4 MeasuremcntMeasurenrentof absorbcdabsorbeddosetlose or dosetloscratc

The reference sourcesoLrrce is calibratedcalibrateclby meansmcansofol-onc onc ofol'thc the primarylrrinrarystandardsstanclarcls (e.g. graphite calorimetriccalorinretricor standardizedstandarclizeclreferencerel-crcncc methodsurcthoris "Fricke" filicltc dosimetry")dosirnetry")and the dosimeterclosirnetersignal is thentherrconvertedcclnvcrlccl to absorbedabsortrccldosecJosc oror'

dosedoscratet'a(c in W\1terrvatct'lr1'('11111lrlrtrttitrttsb~' c()mputnti()n:-. bnsedt'trtscrlontrtr Cn\'i\\'('irvilv \\w\)ry,tht'rrrr'.'l'lrt'r'r'{i'lt'trci' TIl\' r\'!t'n'\\\'\'

sourcesoLll'ocis lIsedtrscclto irradiateirt'lcliatcthetltc routillet'otttinc dusillll'tl'l'rlosirrrctcr is ulldnrrrrtler idclltic,t1itlcrrticirl cUlldiliulls.corrtlitiorrs.

and the calibration is usuallyr.tsuallyexpressedcxpressccl in termstcrnrsorol'clirsc dose orur doseclclscrateratc in thet[c dosimeter medium.mecliut'n. Thefhe routineroulitrec10simeterclosilneter is thenthcnexposed cxltosccltogethertclgctltcr withq,itI thethc product in the irradiation,irracliation,facility,facilitl,. althoughaltir

1-5I-5 Calibration ofol'Dosinrctl'l Uosimctry systcmssvsle lns Calibration verificationveriflcation is perrormedpcrfonneclperiodicallypcrioclically to conllrmcorrflrruthe1hc continuedcontinrrcrl validity of the thc calibrationcalibraticlncurve. Routine[{ourtincdosimetrydosinrctry systemssl,stclnscancztn bebc

6 • ...... • ...... calibrated by irradiation at high dose Radiation dosimetry calibration .- laboratory, an in- house calibration facility whose dose rates have been

~ .. demonstrated to be traceable to appropriate nationalnationai standard or irradiation ... of reference or transfer standard dosimeters with routine dosimeters in the ...... production irradiation facility. All possible factors that may affect the .- response of dosimeters, including environmental conditions and variations of I...... such conditions within a processing facility should be known and taken in to .- ...... a count.

.- For each absorbed dose point, use number of dosimeters required to achieve

I...... the desired confidence level. The number of dosimeters, n, required to .. estimate the dosimeter response at a given absorbed- dose level is based on the determination of a two sided confidence interval that is expected to - bracket the true mean response Yo,1y6,100 00 (1-(l- a)% of the time. In order to determine the mean response, Yo,y6, within ±+ 5%5ohat aa95oh95% confidence level, the number of dosimeters required for absorbed dose level is

= t7sz " - (oLoEiC Where S.s ISis the estimate of the standard deviation of the response

t distribution within a batch of random sample of dosimeters and tr is the 1--__ t-, 2 student's distribution. 2

t The number of sets of dosimeters required to determine the calibration curve .. of the dosimetry system depends on the absorbed- dose range of utilizationutilization.. Use at least five sets or each factor of ten span of absorbed dose, or at least t_ . at

- four sets if the rang of utilization is less than a factor of ten. Position the dosimeters in the calibration curve Radiation field in a defined, reproducible

t location. The variation in absorbed dose rate within the volume occupied by the dosimeter should be withinwithin+lo/o±1% of the averageaverasevalue. - 7 --

t .. It .. .-. • - WhenWhenusing usinggamma- galnma-ray raysource sourceoror X-ray X-raybeam beamfor forcalibration calibrationsurround surroundthe the .. dosimeterdosimeterwith with aa sufficientsufficient amountamountof of materialmaterialto to achieve achieveapproximate approximate -- electronelectronequilibrium equilibriumconditions. conditions.The Theappropriate appropriatethicknessthickness ofof suchsuchmaterial material ... depends 2 - depends ononthe theenergy energyofof the theRadiation. Radiation.2 ... ForFormeasurement measurementofof absorbed absorbeddosedose inin water, water,useuse material materialthatthat have haveRadiation Radiation 60co -- absorptionabsorptionproperties properties essentiallyessentiallyequivalent equivarentto to waterwater forfor exampleexample 60CO 41 source,source'5nm5nm of of solidsolidpoly polystyrene styrene(or(or equivalent equivalentpolymericpolymeric material)material) shouldshould ~ surroundsurroundthe the dosimeterdosimeterin in allall directions.directions.Monitor Monitor andand controlcontrol temperaturetemperature ... 2 andandhumidity humidity duringduringcalibration. calibration.2 .-

... 1-61-6Transit Transit DoseDoseeffects: effects: TransitTransit dosedoseeffect effect occuroccurwhen when thethe timingtiming ofof calibrationcalibrationirradiation irradiationdose not --... dosenot taketake intointo account,account,thethe dosedosereceivedreceived duringduring thethe movementmovementofof thethe dosimetersdosimeters - into and out of the irradiation ... into and out ofthe irradiation position forfor example thethe timertimer on gamma cell­cell- type irradiationirradiation dose not start until the sample chamber reaches the fully down (irradiate) position. Some dose is received as the drawer goes down and after the irradiation as the drawer goes up that is not accounted for in the j timer setting. This transit dose can be significant for low dose irradiations and should be determinedexperimentally and incorporatedinto a formula for calculating timertimer settings. For determining transittransit dose, a series of incrementalincremental inadrationirradiation timestimes thatthat startedstarted asas closclosee toto zero selected,,selected, withwith specificspecific dosimetrydosimetry systemsystem employed.employed. FiveFive differentdifferent inadiationirradiation timestimes werewere used.used. TheThe resultsresults analyzedanalyzed using using linearlinear regressionregression analysis. analysis. A A graphgraph ofof thethe 2 resultsresults looked lookedsimilar similarto to followingfollowing diagram:diagram: 2

...

8

J -.

_A

-...

- .... 400 ~------~---,

- .... ,-. 300 >- - ... Cl (l)(.) 200 --rJ:Ja 0 - .... 0 100 ...... - ... 0 100 200 300

Time of irradiation (min)

The intercept with Y-axisY- axis gives the value of the transit dose. To provide a

.. ... correction factor for all future irradiations, convert the transit dose by the current dose rate. Subsequent timer settings can be calculated using the .. ... formula: DD'-r, T=T- --It ..... DD t

Where DD,t is the target dose and 1r is the timer setting required achieving 2. that dose 2.

Since the absorbed dose rate, D due to gammagalnmaray emission by a Radioactive l- I nuclide source also varies exponentially with the decay time 1r,, the dose rate,

~ ! .A- DD,t , at a given time,time , I,l, is given by

I l~t- rI 9 r~r- r=T- - ..

- ... D, = Dor-''' - . Where D(D,thethe dose rate is at a time,time,DoDo is the dose rate at some earlier - ... timetime(r=o).(t = 0). The timer setting,setting,ZsTS necessary to deliver the targeted central dose varies inversely with the dose rate and source activity, and is given by

_. AI (rs) /-^\ -:------11(T~)o (TS}(75 f, = e _... Where (TS)/(fs) is the timer setting necessary to deliver the required target dose

at timet,timer, (TS)o(rs), is the timer sitting at some earlier time,time,r=0 t = 0 to deliver the _. "'" 2 same targettarset dose 2

- AI

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. . - .. - .. IIAPTERTWOfltIAPTERT\VO

...... - .. 2- REQUIREMENTSRE,QUIREMENTSOF CHEMICAL DOSIMETERS

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.., .... 2-1. Introduction:

...... The first chemical dosimeters were crude systems which changed color on --- exposure to the relatively soft x- rays then being used medically. Barium platinocyanide was the primary chemical ingredient of pastilles,pastiiles,which were developed by several investigators. After irradiation, this material was found ..... to change from its normal green color to orange, and then to various shades (3) of brown. (3) ...... The main difficulty encountered with pastilles was that the color reverted to

..' .... its original green on exposure to light, further more, the color standards in the comparator charts gradually faded and thereby contributed to in accurate measurements. Most important, these systems were highly energy dependent because they used materials of high atomic number. There fore, changes in - .... the spectrum of the x-rays caused large variations in doses registered.

A few years later,Iater, other chemical systems were developed, for example, 6 Fruend 6 utilized the effect of x-rays on various iodine compounds. A mixture of iodoformiodofonn was found to be sensitive to x- irradiation and was employed in dosimetry, but the reaction was also produced by head, light 3 and spontaneous oxidation, and was not proportional to dosage. 3

According to Gruther et al inrt 1928 i928 chloroform irradiatedinadiated with x-rays librates hydrochloric acid in amounts proportional to the Radiation energy absorbed. r-- Acid formation increased in water saturated chloroform solutions, it was also L, found that irradiation of chloroform solutions by the gamma- rays of Radium 3'a resuresulted1te d Inin· aClacid'd evaevaluation.1uatlOn. . 34' LT Numerous chemical systems have been described which undergo chemical t-: changes on exposure to penetrating x- and gamma- Radiations, such as the 11t1 -t, t-: ^Ji

systems.systems' oxidation of ferrous to ferric ion compounds and other chemical used by Nearly all those chemical systems have been developed and 3 individual working in Radiation chemistry.chemistry' 3

almost Physical methods, employing ionization in gases, have been used determining the dose of the x and gammaganlmaRadiations utilized - .... exclusively for determining -- in Radiation thereby and in Radiobiological research. .... - have Because of rapid advancements in electronics, physical methods -- remained in disuse - ... dominated the field of dosimetry, and chemical systems until quite recently.recentlY.33

2-2 Development of chemical dosimetric systems: - "" 2-2 advent of Renewed interest in chemical methods of dosimetry came with the advent - "" nuclear reactions, atomic weapons,weapons'and the experimental use of increasingly de Graaff intense Radiation sources such as the betatron, telecobalt, and Van de -.- on x-ray generators, and the recent emphasis in Radiobiological researches - .... the chemical changes produced in cells and tissue fluids by ionizing

Radiations.Radiations.33 - ... capable of These developments created an urgent need for dosimeters capable x- and gamma - .... registering comparatively large doses of high- energy x- 105105r/min,r/min, Radiations, delivered at tremendously high dose rates up to .... personneluse - furthermore, the dosimeters required by the Armed forces for personnel reading, must be small, inexpensive, rugged, thermo stable,stable' direct- ,. - prompt or reproducible, and within ±X20%20% limits of error responsive to either residual bomb gamma Radiation exposure under rigorous field conditions.conditions' - .- -- 12T2 - ...

--

- .... -...... _--

ConsiderableConsiderableadvancedadvanced havehave been beenmademade towardtoward the thedevelopment developmentofof chemicalchemical dosimeterdosimeter systemssystems andand practicalpractical dosimetersdosimeters whichwhich cancan register register thesethese relativelyrelatively largelarge dosesdoses ofof x- x- andand gammagamma Radiation.Radiation. AttentionAttention hashas beenbeen redirectedredirected toto chemicalchemical meansmeans ofof dosimetry dosimetry becausebecausethe the trend trend in in dosedose evaluationevaluationis is towardstowardsthe the measurementmeasurementofof energyenergyabsorption, absorption,thethe chemicalchemical changeschangesproducedproduced inin tissuetissue equivalentequivalentmaterials materialsshould should bebe inin manymany waysways preferablepreferabletoto methodsmethodsemployingemploying ionization iontzationin in gases.gases.TheThe yieldsyields inin aqueousaqueous chemicalchemical systems,systems,for for example,example, areare notnot greatlygreatly influencedinfluenced byby ambientambient temperaturetemperaturechangeschanges oror widewide variationsvariationsin in thethe energyenergyofof thethe beambeam(0.1 (0.1 toto 1.21.2

...... -- MeV)MeV) andand furtherfurther more, largelarge integralintegral dosesdosescancan readily be measuredmeasuredwith dosimetersdosimetersofof smallsmall size.size.

The most difficult problem inin chemical dosimetry has been toto finalfinal stable,

~._- reproducible systems, which register integral doses of x- and gamma­gamma- Radiations in the range below 100Rad.the lO0Rad.the ferrous-ferric sulfate system -.....i---.- _ accepted as the best chemical method for measuring x-ray and gamma ray s in kilorontgen doses at dose rates up to 1000 Rad/min, and meets most of the requirements of ideal system. An alternative method with sodium benzoate a- or benzene has also been developed. It has advantages that the initial t--r= solutionsand the product of irradiation can be kept for longer period without spontaneousdecomposition, both thesemethods are not sufficiently sensitive i--r= to register galnma-gamma- Radiation in the lower part of the dose range that is biologically most interesting(0 to 1000r).Further more, because of gradual ~ becauseof gradual t- spontaneousoxidation; the ferrous- ferric systemis not sufficiently stableto 3 T-~ permit itsits instrumentationinstrumentation for longlong termterm use. 3 The solution of these twotwo mayor problemsproblems inin chemical dosimetry has been t:r= accomplishedaccomplished by by usingusing systemssystems which which respondrespond toto RadiationRadiation byby relativelyrelatively t-[~ long-long- chainchain mechanismmechanism andand byby developingdeveloping methods methods to to controlcontrol thethe lengthlength ofof thesestheses chainchain reactionsreactions whilewhile preservingpreserving adequate adequate sensitivitysensitivity inin thethe system.system. t-r= 1313 r_(--= t_r= --

.... - 2-3. Classification of dosimetrydosimetrv methods:

.. ..: There are three ways in which the dose received from a Radiation source .. - may be determined: A. Direct: .. - In this method the energy absorbed is measured as the heat in to which it is ultimately degraded. Since the method it self elaborate and tedious it is not -- used in routine work but only to calibrate more convenient chemical methods. Calibration is carried out by measuring the rate of change of -- temperature with time, in air free water which has reached stationary state, i.e., no net chemical range. Then the water is replaced by the dosimetric fluid and the chemical change measured. -- A suitable correction must be made for heating of the walls of the container by electrons which do not enter the solution. This method has the advantage that it can be applied to wide range of Radiations and is especially useful for very mixed Radiations such as are obtained from reactors.

B. Semi- direct: -..; This method dose not involve direct measurement of energy but of some physical quantity directly related to energy; either the charge-input or the ionization due to the Radiation.

-..; I-charge-input:

-...; If the number of particles which are completely absorbed is measured then

(number(numberf/ s) x (energy/particle)(energ,,f particle) Dose raterate: = -- volume or weight in which absorbed This method is useful for particle beams from accelerators or for B- particles -- from external Radiation source. There are however many sources of error,error. 14t4 -- ...... :.

suchsuch asas backback scatterscatter fromfrom cellcell walls,walls, absorptionabsorption inin thethe windows,windows,

• .= bremsstrahlungbremsstrahlung current-current-leakage leakageandand beambeam inhomogeneity.inhomogeneity.

...... : II-11- IonizationIonization : TheThe numbernumber ofof ionion pairpair isis measuredmeasured andand dosedose rate rate = W,Wx numbernumber ofof ionion pairspairs perper unitunit maSSmass oror volumevolume wherewhere "W:"W= meanmean energy energy toto createcreate anan ion-ion- pairpair inin thethe substanceof interest.interest."" . ....: The disadvantagesof this method are:

. ..;; a- W has often to be assumedand.and . b- The results for ionization in the gas phasemust be related to those in - -= the iiquidliquid phase, sine the ionization of liquids can not generally be measured. -r: ..;;

C-C-Indirect:Indirect: Dosimeters of this type all involved measurements of some chemical or physical effect caused by Radiation and therefore all require calibration by a method of type A) or B).

-..: 1-1- Physical effects include crystal coloration; include photo­photo- conductivity and scintillation. r II-DosimetersIl-Dosimetersinin which a chemical observed are commonly used'used 1

-~ 2-42-4 RequirementsRequirementsofof IdealIdeal ChemicalChemicalDosimeters: Dosimeters:

--- TheThe idealideal dosimeter dosimeter forfor measuring measuring high-high- energy energy x-rayx-ray or or gammagamma rayray RadiationsRadiationsinin thethe dosedoserangerange between between5050 andand 5000Y5000Y shouldshouldembody embodyseveral several -...; essentialessentialproperties properties andand havehave certaincertain conditionsconditions characteristics;characteristics;thethe firstfirst requirementrequirementofof chemicalchemicaldosimeter dosimeterisis thatthat thethe amountamountof of chemicalchemicalchange changeisis -- (r) - proportionalproportionalto to thethedose doseandand independent independentofof thethedose doserate,(J)rate

-...; 1515

.. - ""'!~...... ~...... --=~======~~======------~------

8-J ThusThus ifif GG valuevalue RadiationRadiation chemicalchemical yeldyield isis defineddefined asas thethe numbernumber ofof

• --= moleculesmoleculesof of productproduct formedformed oror reagentreagentdestroyed destroyedperper 100100 eVeV ofof energyenergyfrom from thethe ionizingionizing RadiationRadiation

,J; n( r\ n(x) TT . I .-\ G(X)O(X) -= "'"'(Jnit:--unzt :mol.j-'mo .} ...: Lri... t&

WhereWhere 4*)r(x) := numbernumber ofof moleculesmolecules or or ionsions formedformed oror destroyed.destroyed. q-j €G := thethe energyenergy importedimported toto thethe mattermatter ofof thatthat system.system. --- G-G- ValueValue shouldshould bebe independentindependent ofof dosedose and and dosedose rate. rate.

ItIt isis desirable thatthat G- value should be independentindependent of the temperaturetemperature of

-' -l Radiation, quality of Radiation and thethe presenceof air and thethe chemical -- impurities, also the chemical changesshould be readily measurable(Note.'(Note: 1000 Rad ofgamma-rays will produceconcentration change of 11.01'01 G x 110-0-6 6 ---'--- 1000 Rad of mol/LmollL in a reaction in water for which the G-value is G. In addition to, the dosimeter should be made form biological tissue equivalent materials in •. -.-; respect to its density and Radiation absorption properties,properties , should lend it self to standard production method and have sufficientsuffrcientstability to give shelf life of at leastleast one year prior toto use, thereby permitting the manufacture of accurate,accurate,highly reproduciblereproducible dosimetersdosimeterssystem. system.Finally Finally thethe chemicalchemical dosimeterdosimetershouldshould be be easyeasytoto prepareprepareandand use. use.

NotNot aa single single dosimeterdosimetermeetsmeets allall the the aboveabove mentionedmentionedrequirements.requirements. However,However,wewe cancanalways alwaysselectselect oneone whichwhich satisfied satisfiedmaximummaximum requirementsrequirements andandhas hasknown knowndependence dependenceofof onon thetheparameters parameterslikelike (LET)(LET) LinerLiner EnergyEnergy Transfer,Transfer,dosedose rate,rate, temperature,temperature, etc.etc.

2-5.2-5.TypesTypes ofof Chemical ChemicalSystems:SYstems:

DeterminationDeterminationofof Radiation Ra

..a.l~ chemicalchemicaldosimetry. dosimetry.Solid Solid systemssystemsgenerallygenerally are are tootoo insensitiveinsensitiveto to provideprovide

'.. :::: direct-direct- readingreading methodsmethods ofof dosimetry dosimetry ofof valuevalue inin RadiationRadiation biologybiology oror RadiationRadiation thereby,thereby, unlessunless thethe changeschangesincluded included inin themthem areare detecteddetectedby by

-. ..:. complicatedcomplicatedelectronicelectronic amplifyingamplifying devices.devices.

EmphasisEmphasisisis beingbeing placedplacedon on liquidliquid systemssystemsforfor severalseveralreasons.reasons. TheyThey maymay bebe preparedpreparedfrom from reagentsreagentswhichwhich areare water-water- oror tissuetissue equivalentequivalentin in respectrespecttoto densitydensityand and RadiationRadiationabsorption absorptionproperties.properties. TheThe RadiationRadiationinduces inducesreactionreaction

-~ products are relatively stablestableand can be measured directly by color changes, .. ...: or indirectlyindirectly by simplesimple analyticalanalyical procedures. Liquid chemical dosimeters

~. can be prepared inin smallsmall containers within body cavity, in tumor areas, or at positions close to high, Intensity sources. Finally aqueous chemical systems absorb Radiation of various type and energies by mechanisms more like those occurring in body tissues or fluid than do gaseous or solid systemssystems..

.. ...:

2-6. Liquid aqueous systems:systems : .. ...: Principle: In a dosimeterdosirneterof this type, solute is present which can reacts stochiometrically with one or more of the primary species whilst in sufficiently low concentration so as not to influence the rate of energy ...... : deposition. --...... To understandthe mode of action of aqueous dosimeters it is necessaryfirst to considerthe natureand distribution of the species.These differ somewhat for Radiationsof high and low linear EnergyTransfer (LET). Immediately after the passageof through water of a fast charged particle thosemolecules closed to the Radiationtrack areionized whilst thosefurther away are raisedto an excited level.

-\_ H2O -+ HzO- * e-f HzO* +_

-\- 11 II17

_t!

t* \ t- I E .

...b. .:..-: \

!, .J

\, TheThe HHzo-20+ ionion reactsreactswith with H H2o20 toto givegive OHOoH' RadicalsRadicalswhilst whilst HH2o*20* maymay

..I': ~ decomposedecomposeoror bebedeactivated, deactivated,allall withinwithin 10-121O-ttg.g. Formerly,Formerly, it it waswasconsidered considered \- thatthat thethe electronelectron reactedreactedrapidly rapidly toto formform aa hydrogenhydrogen atomatom andand aa hydroxidehydroxide

ut : ion,ion, butbut itit isis nownow knownknown thatthat thethe electronelectronpersistspersists upup toto aboutabout10-4 10-ass beforebefore --_t-_ reactingreactinginin thisthisway. way.After After notnotless lessthanthan 10-IIS 10-'1sthethe electron electronbecomesbecomes solvatedsolvated ..g: ...:. byby thethewater watermolecules moleculesandand in in thesetheseconditionsconditions isis usuallyusuallyrepresented representedby ^. by eea9aq w: HH:O*0+ ++ H 0 ~-+ H 0+ ++ OHo -~\ 2 HzO2 H2O*2 OHo ~-+ ...u: ..: HH2O*20* HOHo+ + OHoOHo 1 7 --~ InIn thethe periodperiod 10-i0-lrsJS toto 10-10-7ss therethere is is competitioncompetitionbetweenbetween combinationcombination ofof

3/ ,: RadicalsRadicalstoto givegive "molecular"molecularproducts"products" and and diffusivediffusive escapeescapefromfrom thethe spurspuror or

OHo~ ~ track.track. TheThe recombinationrecombinationreactionsreactions HOHo + * OHo-+ HHzO,20, or e- + OHo -> OH­OH t: are omitted because theythey leadleadto to no chemical change in a solute,solute,combination I reactions are: '!r r -:

e-uo*e uo---+ H2 + 2OH- lcr : Ho + Ho _-+ H2

e-ro+Hu--- H: + OH- lr,~, .:- ~ OHoOHO + OHo --' H:OzH20 2 \..: Radiation of high LET favors the formation of molecular products over diffusive escapeand also the intra -track reactions: L, .:

_....a..­

1 t,: OHo+ H2O2*H20 r -+ H2O+H20+ H2O H20 e-uq*e-aq+ HzOz--H202~ OH-+ OHo t.r SinceSince most most ofofthe the "molecular"molecularproducts" products" have have beenbeenproduced produced after after thethe lapselapse of of 10-r7s10- 17s thethe RadicalRadical combination combinationprocess process will not be interfered with by solutes r-[~ will not be interferedwith by solutes t.j whichwhich cancan reactreact withwith e-e- oror OHOH oror both,both, providedprovided thethe half-liveshalf-lives ofof thesethese latter latter 7 [-~ reactionsreactions areare largerlarger thanthan aboutabout l0-7s.10- s. These These half-liveshalf-lives varyvary withwith naturenature andand t,-". ..:: r:[~ 1818 [-~ t:, .., t:L J concentration of solute but frequently the rate constant of the bimolecular l reaction of reactive solutes with these Radicals is about 1 1010M-rs-tOloM- S-l so that, if

10 7- 10-^, l0-r0 5 10-l0_,(( (>::::,(= 10-l0_,ss solutesolute' The G value vaiue of the pnmaryprimary speCIesspeciesmay be treated as being sensibly constant. The time scale of these processes is illustrated in table (2). Therefore, we usually write the following reactions [infin stochiometry

..:: equations G "H") is commonly written for G (e-)(e ) + G (H) because HandH ande-e-uo aq 1 are frequently stochiometrically equivalents. 1

Table (2): Events in the radiolysis of aqueous solutions

Events in the aqueous solutions Time(s)

~1O--10-' Ionization and excitation,excitation.H20~H20++HrO_+HrO-+ e-s- + HH,O".2O°. 1 4 xlO-x10-''> Formation of the hydroxyl Radical; H20'HzO- + H20~H20HzO-+HzO- +OH.+ OH. ~lO-u- 10-'' Dissociation of HoH"O"0° ~---+H+OH. ~10-11-10-" Solvation of the electron;electron:e- e ~---+e-e aa. ~lO-lU/1l- 10-''/trr Relaxation time of the ion- atmosphere of e- aq in an aqueous solution of ionic strength=1lstrength:p ~1O-/-10-' Combination; (2e- aqae ~r HHz2 + 20K;2OH'; eeuo-*aq-+ H~H-+ HH22 and 20H2OH ~-- HH2O2).20 2). And Reactions (e-aq+OH~OH-andH+OH~H20)(e-uo*OH---+OH-andH+OH--HzO).reactions virtually complete in low LET systems. Intra lack reactions (OH+ H202~H2O2---+HHzO2 0 + HH2O20 and e-e-uoaq + HHzOz20 2 ~OH+ ---OH+ OH}OH-). In high LET systems will also be complete in about this time. ~lO-lU/[S]-10-'"/[s]Time in which 50%50oh of Radicals will have reacted with reactive solute S present in concentration [S].IS].

2-7. Prerequisites of chemical dosimetry: Radiolytic reactions are extremely sensitive to trace impurities. Hence water, glassware's and irradiationinadiation cells used for dosimetry must be free from 2 trace of amount of organic and inorganic impurities 2 19T9 ..

... - 2-72-7-1.-1. Purification of water: Commercially available distilled water contains traces of orgamc organic and ... inorganic impurities which have been shown to cause significant variations ... in the response of these systems. Pure water is necessary for reproducible results. Distilled water is purified by redistillation from alkaline permanganatepennanganateand from sulfuric acid followed by a third redistillation and by ... - collection of the condensed steam into closed Pyrex glass containers. This ... - procedure gives a supply of water of low conductivity which is sufficiently free of all impurities. This pure water is used in the preparation of other .... - reagents and for final rinsing of all glass wareware. .

- - 2-7-2 Treatment of glass wares and irradiation cells: Glass wares and irradiation cells used for dosimetry arearc generally made from t_ - - Borosilicate or Silica glass, they are filled with or dipped in 1:1:11 mixture of concentrated sulphuric and nitric acids for 24 hours, then washed successively with tap water and distilled water. Then they are filled distilleddistiiled

..... - water and exposed to a dose of approximately lKGylKGy. . IrradiationInadiation cells purified in this way are kept filled with distilled water or ' -. - with dosimetric solution, solution.when not in use. 2

- - 2-7-3. Treatment of plastic irradiation cells: Use of material like Teflon, Perspex, ploy ethylene, ploy styrene and poly propylene as container for a chemical dosimeter require a special procedure - - for cleaning, storage and use. The inner walls of the irradiationinadiation tube should be inert. i.e. it should not liberate any impurities during irradiation or pre and post irradiation storage of dosimetric solution. The procedure followed as follows:

20

l-

I L~I ~­E- iI ...lr- !

!F - -fhen - Cleaning:Clcaning: Plastic tubes areafc filledfilleclwithu,ith 10%l0% HN0IINIOT3 forI'or 24 hours. Then I they are arc rinsedlinscclwith tap waterwatcrandilncl then distilledclistillecl water.rvatcr'.'l'o 'ro makernal

!,-- are filledfillecl with dosimetricclosimetricsolutionsoh-rtion andancl exposedexposecl to a dosecloseofol'.10 40 Gy. L Storage:Storagc.'PlasticPlastic tubesttrbes or bags are filledIlllccl withr.r,ithdosimetricclosimctric solutionsolutiorr whenn,hcrr -- not inir-ruse. -~

-I- . 2-7-4.2-7-4.IJseUse of irradiation cells:cclls: --_ - When glass or plastic irradiationirracliatiorr cells are to be useduseclforfbr dosimetry,dosirnetry.thethc --~ old dosimetricdosimctricsolution in themthernis discarded.cliscarclecl.'fheThe cellscelis are rinsed at least -t- - two times with freshliesl-rdosimetricclosirnetric solution. They I-heyare then filledlllled withrvith thetht: 2 solution, stopper andarrcl irradiated.irracliatecl. 2 ..-- - l-

..bs - 2-8. Stabilizing Agents:Age nts: All materialsmateriiilsshouldshor,rlcl bebc reagent gradegracle or analytically purepr-rre substances, so

t statedstateclby the manufacturer.tnanulactr,rret'.FurtherIrurthcr purificationpr-rrilrcationis madenraclebyLry fractionallt'ac:ticlnal .. - redistillationreclistiilationand/orancl/or by recrystallization.rccrystallization.All reagents shouldshoLrlcl be keptlicpt in clean, dosed, closecl,PyrexI)yrex containers.containers.'I'heThe reagentrcagcrrt whichrvhich have been foundl'ouncltotcr il..\--- provide adequate aclequate thermalthernral stability and ancl simultaneouslysiurultaneously to render rcitclcr'

chloroformchloro{bnnand/ancl/ or tetrachloroethylene- dyeclye systemsystc.nr forlbr exampleexanrplerelativelyrelativcl)' l- l dose-close-rate andancl temperatureternperature independent.inciepenclent. 3

2-9 DefinitionDafinition of G value:valuc: lt - C - G value Radiationl{acliationchemicalchcnrical yieldyicld is the thc fundamental l'Lrncllnrcnlalquantitativequuntitrtivc Lt-- characteristic ofo{'l{acliation Radiation inducedinclr-rce clreactionre action in a chemicalchcmicaldosimeter.closin-re ler. The

reactionreactior-rchemicalchernical yield,yielcl, G (x)1.;ofol'an an entity, x, is the quotientc1r-rotientofof'n(X)n(X) by;"b1'r, r=r where n(x) is thetl'iemean amountamolrnt of substance of that entity produced, of sr-rbstanceof entity proclucecl, r=t"- destroyed or changed in systems1,stembyb1, thetlie energyeticrgl,imparted,inrpartecl, ct_ 212I [~r- [ r'- t

[' L,. E,e,to tothe thematter tllattel.of'thatof that systcm,systeln, thus:thus J : = lE. G(G(X)X) = n(x)/n(x)fdJnirr:(Jnit ::mol.! ntol,/I

^L OrOr itit isis definedclefineclas as thethc numberrtLrtrtbelofol'ions, ions, frcc1r'ccR~ldic~J!s,I{arlicals, ~ltoms;utonrs, moleculesr.}r()lcrrulcs formedfbrrned oror clisapPearecl disappeared when\vhcn thethc systemsyst.enrhashas ~lbsorbcdabsor-bccl100100 evev,ol-e.el.g'of energy -A 2 fromft"ornthe the ionizingionizing radiationracliation2 . . lL l- I I -A

j -r- l-- -L l-

L

~\- - J

I L,- l l

\_I

_t.-

~ -

... -

.. -

I*

,A- i\* l-L 2222 ^^IL

L. ,- l-

t.-

l.a I t.- 1-

..l_ - -I

ll- _

1-

l_ .t- IHAPTERTHAPTERTHREETHREE ~l- - --L.)- 3-3. TYPES OF AQUEOUS CHEMICAL DOSIMETERS ll- _

lt__

\_

l!- _

l.' .. -

... -

.. - . -

A-

..L.-- . LI

;:

l,r

3-1. Fricke dosimeter: This dosimeter "ferrous- ferricferric sulfate system", which described by Fricke t, and Morse then developed by Miller 5, isis presently accepted by numerous t] workers as the the best chemicalmethod for for measuring x and gammagarnmarays, and itit meets most if thethe requirements of the idealideal system-(3)system'(3) tr This dosimeter isis thethe best one forfor lowlow medium dose-rate. It is based on the

oxidation of ferrous to ferric ions in aerated 0.8N HH2SO42S04 and the ferric ion concentration may be measured as follows:- ll* .-- i) By measuring of light absorption at 3050 Aa.A'. The extinction : J l _ (2200±9)(2200t9) M-M-r at 20°C20'C and show the considerable temperature ; dependence, namely (dEI@e I E)dTe)dT =:0.007.0.007. ~t-- ii) Alternatively the ortho-phenanthroline complex with Fe Fe*2+2 may be I formed and its light absorption at 5100 Aa measured: ~11000-11000 M-Jcm- . ~ and absorptionat 5100A0 measured: M-lcm-r. t-_ iii) Other techniques involve potentiometric titration, labeling and 2 ~ measurement of the light absorption of the Fe SCN+SCN*2 complexes at t^ 4600 Aa.A0. t~ 3-1-1. Principle: r:t. When an air saturated dilute ferrous sulfate or ferrous ammonium sulfate in solution in 0.8 NNH H2SO42S04 is exposed to ionizing Radiation, ferrous ions are r:r_ oxidized to ferric ions in a series of quantitative and irreversible reactions 2* -+ 3 ~ Fe 2+ -+ FeFe3*+ it Concentration of ferric ions gives the measure of absorbed dose. The i~ concentrationis measuredby spectrophotometricanalysis means which is generally more convenient than chemical titration methods for it is rapid, i-_l~ i_~ 23

;---. t+

I t*

lL! .!! accurate,acQurate,andand expedientexpedient for for thethe analysisanalysisfor for lowlow ferricferric concentrationconcentrationandand i. _- smallsmallquantities quantitiesofof solution.solution.(1)(l)

lq 3-1-23-l-Z BasicBasicreactions: reactions:

- - 0 ~ L! es-uc+Huq-Hoaq+ H aq H (3.1(3 l))

InIn 0'8N 9 r---- 0.8N HHzSo+,2S04 , this this reactionreactionis is completecompleteinin lesslessthan than 10- s. I 10-es.InIn deaerateddeaerated I ll.! A solutionsolution atat pH

Reaction ( & ) Lf ( a ) is slow compared with the others when t=t: 0 G (Fe1..'*)o:Gu3+)0 =GH+* GGou*OH + G G H02noz In practice the half -life rI of reaction (3.4)(3.a) may be increased by using very dilute solutionssoiutionsof ferrous ferrous sulphate and thus G 1re+:)0(Fe+3)0 measured. In an aerated [ solution reaction (3.2) I (3.2) is completely superseded by reaction (3.6) followed [ by reaction(3.5) t. U + Oz -) HOz (3.6) [i Hence: G 1n.(Fe :*;-3+)00 := 3Gn3GH +Gos+3Gnozt2GHzOz+GoH+3GH02+2GH202 rt_ cG (Hz)(H2) :G=G (Hz)(H2) :GH*Gon*Gsoz r- G 1E.:*;(Fe3+) o0 =GH+GOH+GH02 rL* 3-1-3. Calculation of the absorbed dose..dose: 24 [_

- !* I -,

-- FerricFerricion ionhas hastwo two absorptionabsorptionpeakspeaks at at3004 3004nm nmand and224 224nm, nm,the theone oneat at224 224 nmnm beingbeingmore moreintense, intense,thethe sensitivitysensitivityof of thisthis analyticalanalyical methodmethodcan canbe be

l- doubleddoubledby by measuringmeasuringthe the opticalopticalunit unit densitydensityat at 224224 nmnm ferricferric ionion peak.peak. I AnotherAnother advantageadvantageofof measuring measuringat at 224224 nmnm peakpeak isis thatthat thethe molarmolar linearlinear absorptionabsorptioncoefficient coefficient increaseincreasewithwith risingrising temperaturetemperaturebyby onlyonly 0.13%0.13% C.C. However,However, atat thisthis lowerlower wavelength,wavelength,the the absorptionabsorptiondue due toto ferrousferrousis is notnot whollywhollynegligible.negligible.

InIn addition,addition, impuritiesimpurities fromfrom plasticplastic containercontainer areare reportedreported toto bebe more more 3 troublesometroublesomeatat 224nm.224nm. HenceHence304nm 304nm isis usedusedfor for measurementmeasurementofof Fe+Fe*3ionion concentration,concentration,atat temperature temperature25°C.25 oC.

I MolarMolar absorptionabsorptioncoefficientcoefficient shouldshouldbe be determineddeterminedbyby measuringmeasuringofof opticaloptical densitydensityof of solutionssolutionsofof differentdifferentknown known concentrationsconcentrationsofof ferricferric ions.ions.

! Absorbance ofof irradiatedirradiated dosimetersdosimetersisis measuredagainstagainst thethe Irradiated Inadiated - solution formform thethe standard flask, optical density of the unirradiated reference blanks in the dosimetric tubes is also measured against solution in standard I -- flask. Absorbance of the irradiated solution is corrected for reference blank reading. 2: L- reading. The absorbed dose is calculated from the following equation 2:

!" M D_D= M Gy ! Gy PeP& I Gu,G(x)

Where: : MM = thethe differencedifference inin absorbanceabsorbance (optical (optical density)density) betweenbetween thethe irradiatedirradiated and and unirradiatedunirradiated solution. solution.

€& := molarmolar linearlinear absorption absorption coefficient.coefficient. I := opticaloptical path path lengthlength 0.01 0.01 mm 3 pp := densitydensityofof solution:solution= 1024KgKg m3m- : 3 : 6 l G(',G(x) = GG(F/ 10.*')) = 1.611.61 x x10- 10-6molmol J-l.r . SubstitutingSubstituting thethe aboveabove valuesvalues gives:gives:

2525

J- w

...

0.0977 Dn =___ O.0977MLA 3 GG lFe'*+ lx e at (Fe\ )X/ £ ot25"C2SoC

3-1-4.3-l-4. Influence of various factors:factors: I) Oxygen Supply: ItIt isis necessary thatthat the -- the Fricke dosimeter should have an adequate supply of oxygen since, when when all the oxygen has been used up H can no longerlonger form HH2o0 and (Fe*3)is - 2 G (Fe+3)is correspondinglyconespondinglydiminished, when oxygen is completely exhausted ,*) ,reaction mechanism change reducing G(Fe 3+) to 0.85 Mol --rb,- 0.g5 Mol f.J-.

2* O 3 -- Fe 2+ +H+H" + H+H* --....,-+ FeFe3*+++ H 11,2 Here one atom oxidizes only one ferrous ion to ferric instead of three. { 3 :2 Therefore, G (Fe+(Fe*3)) = 2 GGH26,*H202+ GesFr OH

\ a- ... 11)II) Ferrous ion concentration: For concentration of ferrous < 4 a- ion < 10-l0-1 M reaction (3.4) becomes slow in relation to irradiation time, so that if the analyticalanalyical procedures are rapid the measured G (Fe+(Fe*3)3) 3 3 \ willwitl lie between G (Fe+(Fen3)6and)oand G (Fe+(F"*r)_.}Xl. Solutions of this concentration are are also inconvenient in that all the ferrous ion will be destroydestrov L- (r) by a dose of 7000 Rad. (1)

\, Ill)III) Sulphuric acid concentration: The concentration of O.4M0.4M is alwaysused; chemicallyall that is necessarvnecessary is that the pH of the solution shall be less than 1.5.

\,

I I L 26 t t L

Lt. - rI

-,4-

• L -L 0.40.4 MM sulphuricsulphuricacidacid solution solutionisis usedusedbecausebecause FrickeFricke consider considerthatthat the the electronelectronconcentrationconcentration ofof thisthis mediummediumwouldwould approximateapproximateto that of the • L to that of the -.L livinglivingcell. cell.

· " -.4- IV)IV) Purity Purity ofof reagentsreagentsandand cleanliness cleanlinessofof glassglassware:ware: OrganicOrganicsubstances, substances,RH,RH, competecompetewithwith ferrousferrousforfor OHOH RadicalsRadicals -./- · . ~ -.4- OHO+OHo+RHB11 - HHzO20 + + RORo AndAnd thethe resultantresultantorganicorganic Radical, Radical,RO, Ro,maymay eithereitherreact reactwith with O022 toto givegive R0Ro2'2° 3 -,/- whichwhich oxidizesoxidizesthree threeferrous ferrousions, ions,so sothat that GG (Fe(Fe'*)+) increases.increases.

.. 1

RORo '++ 02~Oz- R0ROzo2° I e.g.e .g.RHRH: = alcohol. 2* 3 r R0RO2o+Fe2o+Fe 2+ ~-) FeFe3*++R0+ROz- 2- ROOH+ FeFe2'2+ ~-+ Fe pe3+3++ROo+OH-+ROO+OH- 2* 3* r RO°ROo+ Fe 2+ ~-+ Fe 3+ +RO-~+RO--+ ROH 3 3 r Oror reduce Fe Fe3n+ when G (Fe1Fe3n)-+)oo decreases. The former predominateswhen RH is alcohol and the latter when RH is allyl thiourea,or styrene. 3- r A test of organic impurities can be made by adding chloride ion (-10(~l 0 3- M r NaCl) when the rapid reaction: -+OH- OH"OHO +Cl -~OH- +Clo

2 occur,Occur, since chloride atomsreact react much much moremore rapidlyrapidly withwith Fe2*Fe +thanthan RH,RH, any 3 changechange ofof G(Fe3*)G(Fe +) causedcaused byby additionaddition ofof chloridechloride isis indicativeindicative ofof thethe presencepresence of of organicorganic impurity.impurity. GreatGreat carecare isis necessarynecessary toto ensureensure thatthat purepure 1 waterwater andand pure pure chemicalschemicals reagentsreagents areare usedused inin veryvery cleanclean glass glass containers containers 1

V)V) EffectEffect ofof Dose-Dose- rate:rate:

2727 At dose-rate of about 101088 RadRad,4ninlinin Radicals from adjacent tract with the solute and as consequence G (Fe(Fe'*)3+) diminishes as the dose-rate is further increased. Practical a. High LET, e.g. Po particle - up to 10102020 e v 1-1 S-lS-r 26 I b. Low LET, e.g. X- or r- rays- up to 101026e v 1-11-rS-lS

VI) Effect of linear Energy Transfer (L.E.T): From the mechanism of energy loss one would be expect no great difference

in the number of e-e-uoaq , HOHo and GHOOHo produced by ionizing particles per 100 eV, as either phase or particle is changed. However, as the LET is altered by changing the energy or mass of the particle or by changing from water vapor

to liquid, also the true G-G-s26H20 is constant the fraction of e-e-,q,aq , HOHo and GHOOHo escaping will vary between limits of 100% andand 0%0o/oit is equivalent to sayingsaylng

that the molecular product yields increase, tending to 1/2112G-G-Hzo H20 whilst GGgH 3 and GG6sOH decrease to zerozero it follows that G (F+1F*3;) will decrease as LET mcrease.increase.

VII) Temperature: 3 By increasing temperature during irradiation G(F+G(F*')) increase slightly The temperature at which the spectrophotometric measurements are dose is very important as the molar linear absorption coefficient increase by about 0.69% per C for the 304 nm peak. For this reason it is important to know the temperature at which the spechrophotometric measurements are done.

3-2 Ceric Sulphate (Ceric- Cerous) dosimeter:dosimeter.' This dosimeter makes use of the reduction of ceric sulphate of by Radiation. This dosimeter is standardizedstandardtzedagainst Fricke dosimeter. With great care (1) precision of ±+ 1%lo/ocan be obtained. (1)

28 3-2-13-2-l Principle:Principle: when When dilutediluteaerated aeratedsolutionsolution ofof ceric cericsulphate sulphateinin 0.8N 0.gNH H2so42S04 is isexposed exposedtoto ionizingionizing Radiation,Radiation,ceric cericions ionsare arereduced reducedtoto cerous.cerous.DecreaseDecrease inin cericcericions ions concentrationconcentrationisis measuredmeasuredspectrophotometricallyspectrophotometrically toto evaluateevaluatethethe absorbed absorbed dose.dose. 4+ C 3+ CCe4*e ---+---) Ce3*e

TheThe basicbasicreactions reactionsdosimeters dosimetersareare about about± + 3%.3oA.AreAre dosimetersdosimetersisis aboutabout± + 3%.3%. ---) 3 HH (or(or H0HO2)2) + + CeCe ---+ H+(H*(oror H+,1n++ OOz)2) + * CeCe3*+ (3.7)(3.7) 4 ----) 3 HH2o,20 2 ++ CeCea*+ ---+ H++H*+ H0Ho22 ++ CeCe3*+ (3.8)(3.g) 3 4 OHOH +* CeCe3*+ ~-) OH-OH-+ + Cege4*+ (3.9)(3.9) 3 = GG (Ce(Ce3*)+) = GHGH ++ 2GH2GH2O2_20 2 - GOH-GOH_ (3.10)(3.10) The yield The yield ofof CeCe isis independentindependentofof oxygenoxygen sincesince HH handhand HH2o20 bothboth reducereduce ceric ions, thethe stoichiometrystoichiometryequations indicatesindicates thatthat G(Ce)G(ce) is largelylargely determined by the magnitude of 4 GGn:oz-H20r 2G2Gnzand H2 and isis therefore: a. Strongly dependent on LET b.b' Small and consequently very useful for measurement of highhieh dose­dose- rate.

3-2-2 Calculation of absorbeddose: whenWhen thethe dosimeterisis usedused for calibrationpu{pose,purpose, spectrophotometry isis 3 usedused toto measuremeasure thethe decreasedecrease inin cericceric ionion concentrationconcentration .as.as thethe startingstarting Ce*3Ce+ ionion concentrationconcentration isis high,high, bothboth unirradiatedunirradiated and and irradiatedirradiated solutionssolutions have have toto bebe diluteddiluted toto obeyobey BeerBeer Lambert'sLambert's lawlaw .ceric.ceric ionsions havehave anan absorptionabsorption 4 maximummaximum atat 320nm320nm .the.the molarmolar linearlinear absorptionabsorption coefficient coefficient e[> (ce*1)(Ce+ ) isis 2 l o 2 561mzmo1-Iat56lm mor at 25c025C e[> (ce*a)(Ce+4) atat thisthis wavelengthwavelength isis onlyonly 0.27m20.27m mol-r.so morl.so interferenceinterferenceto to cerouscerousions ions cancan bebe neglected.neglected. TheThe absorbedabsorbeddosedose is is thenthen calculatedcalculatedasas followsfollows 2:2:

2929 ------_...... ~~~======--===., --.

Dose,Dose,GyGy =- ., ( -Y,3) GCeG\Ce'.+ )t.p.l c.p.! Where:

M =: charge in absorbance. ^/^ r-\ 3 : G(Ceu\Le' +)) = Radiation chemical yield of cerous IOnsions =: O.25/lmol0.25umol rlorJ-lor {2.4(l{2.4(l00eVr-'}OOey)-I}

:molar 4 2 [;t =molar linear absorption coefficient ofCe+of ce*aions (561m(561m2mol-1morl p =density:density of the dosimetric solution, Kgm- Kg--' 3 : I = pathpathlength of the dosimetric solution within the spectrophotometric cell'cell

3-2-3 influence of various factors:

This system is influenced by the same and specific factors which alter the response of Fricke systemsystem,with,with following exceptions (a)(a)oxygen oxygen content does not effects the yield; (b) dose rate effects are minimal; (c(c)trace)trace amounts of organic impurities produced very erratic yields; and (d) the system has t. definite spectral dependence at energies below 100kvp 1.

3-3 Other systems: 3-3-1-aromatic solutes:solutes :

Many aromatic compounds such as benzene and benzoic acid undergo hydroxylation on irradiation in aqueous solution and the amount of product formed can be related to the dose . .forfor calcium benzoate in water the product is salicylic acid, the concentration of which can be measured bybv its 0 0 fluorescence at 4000A400040 excited by 2900A2900,4.0light.tignt. (l)1t; The advantage of these dosimeters is that the solution needed not to be acidic. The disadvantages include: a- G (PhOH) is low; being of the order of 1.6 b- Products other than phenol are produced. 30 ------,

c-c-G G(PhOH) (PhoH) showsshowsfairly fairlymarked markeddependences dependencesonon (PhH), (phH),LET LETand anddose dose rate.rate. d-d-The Thesystem systemisis too tooinadequately inadequatelycalibratedcalibrated toto be beof ofgreat greatuse.use.

3-3-23-3-2Chlorinated Chlorinatedhydrocarbon hydrocarbonsolutes: solutes:

TheseThesesystems systems(two(two -phase) -phase)areare better betterthermal thermalstability stabilityand andhigher higherRadiation Radiation sensitivity;sensitivity;these thesefeaturesfeatures permitpermit the thepreparation preparationofof stablestabledosimetersdosimeters capablecapable 6 ofof registeringregisteringgammagammaray ray exposuresexposures coveringcovering abroadabroad rangerange (l.0(1.0 to to 10t06Rad). Rad). TheThe chemicalchemical reactionsreactions areare complex,complex, ofof ten ten involvinginvolving chainchain reactionsreactions consequentlyconsequentlythethe G-valuesG-valuesareare high high sosothat thatthey theycan canbe beused usedto to measuremeasurelowlow doses,doses,but but theythey areare veryvery sensitivesensitiveto to impurities.impurities. ItIt hashas claimedclaimed thatthat thethe aqueousaqueoustetrachloroethylene tetrachloroethylenesystemsystem can can bebe usedused toto measuremeasuredosesdoses in in thethe I rangerange0.50.5 to to 3.03.0Rad Radwithwith20o/o 20% precision.precision. 1

3-4 Potential liquidliquid dosimeters:

Generally, there are many liquids which on irradiation generate intermediate Radicalsand excited molecules which can be reactingwith solutes having strong absorption spectra.These solutions should show indirect action and might yield useful dosimeterafter proper calibration.

Iodine can be regardedregarded as a suitable solute inin that;that; itsits concentrationmaymay bebe measuredmeasured spectrophotometrically,spectrophotometrically, butbut inin aromaticaromatic solventssolvents backback reactionreaction occursoccurs which which militatemilitate againstagainst its its use.ruse. 1

AlsoAlso DiphenylDiphenyl picrylpicryl hydrazylhydrazyl (DPPH)(DPPH) consideredconsidered asas aa suitablesuitable solute, solute, since since itit hashas aa highhigh excitationexcitation coefficientcoefficient andand GG (-DpH)(-DPH) isis independentindependent ofof (DppH)(DPPH) Radical.Radical. overOver considerableconsiderable range,range, however,however, thethe mechanismmechanism is is complexcomplex andand GG isis veryvery dependentdependenton on thethe solvent,solvent,being being 0.760.76 inbenzenein benzeneand and highhigh asas 3535 inin chloroform.chloroform. Some inorganic Some inorganic solutessolutes whichwhich mightmight bebe usedused areare (FeCl3,(FeCI3, cuCl2)CuCb) inin NN-NN­ I dimethyldimethyl formform amideamide 1 3131 3-53-5 GaseousGaseouschemicalchemical dosimeters: dosimeters: TheseTheseare are lesslessimportant importantthan than thethe liquidliquid phasephasetype,t1pe, since sincethe the dosedoserate rate inin aa gaseousgaseoussystemsystem maymay bebe obtainedobtainedfrom from ionizationionization currentcurrentmeasurement measurementandand W-valuesW-values(mean (meanenergy energytoto createcreateanan ion-pairion-pair inin thethe substancesubstanceofof interest)interest)or,or, ifif anan internalinternal particleparticle sourcesourceis is usedusedunder under conditionsconditionsthat that thethe rangerafigeof of thethe particleparticle isis considerablyconsiderablylessless than than thethe containingcontainingvesselvessel dimensions,dimensions, fromfrom thethe productproduct ofof thethe disintegrationdisintegrationraterate and andthe the meanmeanenergyenergy perper particle.particle. The most useful gaseous dosimeter is the use of nitrous-oxide; thethe mechanism of which is:

---) NNzO20 ----+ N + NO or NN22 +* 0,Q, --+ N+NN + N2O2O ----+ NNz2 +NO,* NO, -> 0+NO+N2O2O ----+ 2NO2NOorNz+OzorN2 + O2

2NO+02NO + Oz2 ----+ 2N02 oC G value is independent of temperature in the range -80 QC"C to 200 QC the

extent of reaction by measurmg measuring the amount of N0 NOz2 spectrophotometrically, the disadvantage of this dosimeter is that aback 4 1. titration becomes important at dose>dose>104 10 Rad 1.

3-6 Dosimetersbased on solids: These are all rely on the fact that some intermediateis trapped,or causes some chemical changein a solute or in the gel material itseliitself, which may be detectedcalorimetrically, either directiydirectly or after subsequentchemical development.Such systemsare easyto handle and have the possibility of being made three dimensional; furthermore,back reactions can only be slow, becauseof the immobility of the solutes. In order toto obtain reproducible results such dosimetersmust be very carefully preparedand highly standardizedprocedures.

') Ft 32

The The optical density-dose relation is linear and thus these systems have obvious potentialities as dosimeters.dosimeters.l1

33

t CONCLUSIONCONCLUSION BasedBasedonon this review onon developmentdevelopmentofof chemicalchemicaldosimeters,onedosirneters,one cancan draw the following conclusions remarks: I-Chemical1-Chernicaldosimetersdosimetcrs are still under developing,developing,butbut an aqueous chemical dosimetersdosirneters are preferable because :: 'fhey 2- They can be preparedprcparedinin small containers within body cavities caviticswhich permitspennitsthethe actualmeasurementmeasurcment of Radiationdose.dosc. 3-3-TheyThey are morenrore convenient in RadiationItadiationtherapy.thcrapy. ,'/ 4-They may~reparedrnay preparcd fromhom reagents which arearc waterwatcr or tissue equivalentseclr-rivalents in respect to densityand RadiationItadiation absorption properties.properlies. 5-5-TheThe Radiation induced reaction products are relatively stablestablc and can be measured directly by color changes or indirectlyby simple analytical procedures.

34 IHAPTERflHAPTERFOURFOUR

4- REFERENCES ------

REFERENCESII.EFtrITENCIIS

1-l- F.S Dainton: Chemical Dosimetry-Dosimctry- RadiationIladiation Dosimctry (G.W.Reed,(G.W.lteed,ed), AcademicAcadernic press, NewNerv York LondonI-ondon(1964).(1964).

2- P.G Benny: Radiation Iladiation Dosimetry,I)osimctry, Radiation TechnologyTcchnology 'l'rornbay, Development Section, BhabhaIlhabha Atomic Atornic Researchl{esearchCentre, Trombay, MumbaiMurnbai(India)(lndia)

3- Gm'danGordan L.BI-.8 and GeraldGcrald 1.1-1.:J.i-I.: Radiationltadiation Dosimetry,Dosimctry, Boston,IJoston, Massachusetts (1956).( 1956).

4- Gunther, P., Von der H FI orst, H.D.,Il.D., and Cronheim,Cronheirn,C.F.,C.lt., Z. Elektrochem.34, 6166i6 (1928).( 1928).

5- Miller, N., J :Chem.Phys.18,:Chcm.Phys.18,7979 (1950).

6- Freund, L.: Wien Klin .Wochschr.17,.Wochschr.17,412 412 (1904).( 1904).

35