Polycast Acrylic Sheets.

Transcription

1 ) Introducton: Polycast Acrylc Sheets Davs Earle, Ron Deal and Earl Gaudette SNOSTR3042 revsed and epanded Jan, 4 One hundred and seventy sheets of acrylc have been purchased by SNO from Polycast Polycast has performed varous C measurements on these sheets and n addton * by 4" coupons from each sheet have been shpped to CRL where addtonal C measurements have been performed Polycast has shpped the sheets to Reynolds Polymer Technology (RPT) n Calforna who wll be thermoformng and machnng the sheets pror to shpment to Sudbury for vessel fabrcaton Ths report contans the detals of the measurements performed by Polycast and by CRL on coupons from the sheets and the assumptons made about the sheets from these results Reports of the optcal!) and radoactve 2) qualty of the frst 2% of the sheets have already been dstrbuted In addton most of the contents of ths report have also been reported3) 2) Sheet Inventory: The sheet nventory s summarzed n Table Polycast has cell cast twelve batches of 22" materal and three batches of 4" materal The 22" batches comprsed 4 or 20 sheets and the 4" batches comprsed up to 0 sheets Table lsts only those sheets purchased and shpped to RPT The gaps n the table represent sheets rejected by Polycast as falng to meet the SNO specfcatons Based on sheet qualty, each sheet has been assgned to the vessel (), the qualfcaton program () or as a vessel spare (S) Batches 47 4 and 3 were nferor from an optcal pont of vew and batch 0 from a Th content pont of vew 3) Polycast ualty Control Results Polycast has provded us wth copes of ther test results 3 Thckness They made thckness measurements at 2 postons n each 22" sheet and 2 postons n each 4" sheet The specfcatons requred all measurements to be between 2" and 233" or 47" and 473" Snce

2 Table Sheet Inventory Sheet Batch S 3 4 S S S 7 S S S S 0 S 2 3 S 4 S 7 20 Page

3 Table 2 Mnmum Thckness of each Sheet bat she Page

4 the bucklng forces on the vessel are greater at the top than at the bottom t may be advantageous to placed the thcker panels n the upper hemsphere Table 2 lsts the mnmum thckness measurement of each sheet as reported by Polycast The dstrbuton of these thcknesses are shown graphcally n Fgure 32 Mechancal They have made fve mechancal measurements on one sample from each batch These measurements, summarzed n Table 3, are all better than the specfcatons whch are also ndcated n Table 3 The mechancal propertes measured were tensle strength, tensle elongaton tensle modulus, compressve deformaton under load and resdual monomer Table 3 Mechancal Propertes Batch Ten Str Spec Ten Eton % Ten Mod Def Res Mon % tot ar parts nclus 03 / mcron 2M / K / / 42 3 / / 37 0 / 2 2 / 2 0 / 273 / 2 72 / 7 2 / / 0 0/7 2 / 7 7, / 2 3/4 33 Inclusons They nspected each sheet for fber nclusons and vods and documented the number of each sze from <" to " n fve ncrements The total number of nclusons n each batch s lsted n Table 3 Most batches had no nclusons greater than 0" The detal breakdown of the ncluson data s on fle SNO dd not nsst that Polycast adhere to the ncluson specfcaton, choosng nstead to rely on the radoactvty measurements

5 34 Ar ualty They measured the panculate densty n the ar near the castng machne when t was beng assembled for each batch The densty n partcles per cubc foot above 03 and mcron are lsted n Table 3 where mamum values of 2 0 for 03 mcron and 03 for mcron were the hopedfor lmts These lmts were eceeded for a number of the batches It was not practcal for Polycast to stopped producton durng hgh dust levels and so the batches were made under potentally adverse condtons A correlaton wth the partcle densty and the Th/U content would confrm that dust s the domnate source of radoactvty n the acrylc 3 Optcal Absorpton They measured the optcal absorpton coeffcent as a functon of wavelength of samples from each sheet Measurements were made on as cast materal, on condtoned materal and on materal whch had been heated to thermoformng temperatures and subsequently annealed Smlar measurements were made on samples from every sheet at CRL and the detals of the Polycast results wll be presented below wth the CRL results The optcal qualty of the acrylc deterorates wth every heat treatment but snce the vessel must be made from thermoformed and annealed acrylc t wll be those results whch wll be prmarly of nterest 4) Th and U Content The Th and U content n the acrylc was measured by the three technques 4) reported n SNOSTR20 or AECL074 Prmarly the technque of neutron actvaton followed by gamma ray countng of the Np and Pa was used, as ths technque had been shown to be least susceptble to handlng contamnaton 2) Mass spectrometry measurements ) were also made on samples from all batches and alpha spectroscopy measurements ) were made on a few samples, to check for decay chan dsequlbrum 4 Neutron Actvaton Results Eght hundred gram blocks of acrylc were rradated n the NRU reactor/the nonoptcal or saw cut surfaces were mlled off so as to remove surface handlng contamnaton and the block was vaporzed to a resdue whch was then counted for Np and Pa 2) Typcally four blocks from each batch were measured Table 4 lsts the results and Fg 2 shows them graphcally Table 4 lsts the CRL dentfcaton number (col ), the

6 Table 4Neutron Actvaton Results ID Sample days hours Th n coolnq of count fl done Mar 7 3 to 0 done Dec core core core core pg/g < <00 < <002 <004 < < < U n <0 <03 <0 <03 <03 <03 <03 <3 pg/c <0 <04 <0 < <0 < <03 <03 < <03 <0 <4 < <03 <00 <0 <07 <04 <0 <03 <0 <0 <00

7 Table 4Neutron Actvaton Results R ??0 3 4?4f) 7?0?n??03?04??? ?3 232? C <003 <003 <00 < <007 < < < <004 <00 <0 <00 <03 <03 < <0 < <0 < <0 <04 < <03 <03 <03 < < <04 <007 <00 < < <04 < <4 <03 <0 < < <04 < <0 < <04

8 batch and sheet number (col 2), the duraton between rradaton and countng (col 3) the duraton of the count (col 4), the Th concentraton as a two sgma lmt or wth a one sgma error (col ) and the U concentraton as a two sgma lmt (col ) In col 2 the frst two dgts are the last two dgts of the batch number and the last two dgts are the sheet number In four cases (core) the optcal surfaces were mlled away before vaporzaton The 22 ke Np peak was not seen n any of the spectra and so the U concentratons n the samples are reported as a two sgma upper lmt The lmt vared from 0 pg/g for samples counted wthn a few days of rradaton to pg/g for samples counted several weeks after rradaton The specfcaton s 7 pg/g If there was any suggeston of a 30 ke Pa peak then a Th concentraton was recorded wth a one sgma error If a peak was not dscernble then a two sgma lmt was reported Ecept for batch 0 the Th concentraton of all batches s less than 0 pg/g The specfcaton s 2 pg/g Batch 0 appears to be a sgnfcant ecepton n that the frst four samples were above 0 pg/g Subsequently samples from four other sheets from batch 0 were also hgh confrmng that ths batch s eceptonal The Th concentraton n the frst samples from 702, 402, 20, 30 and 40 were all above 0 pg/g but second samples from the same sheets were all below 0 pg/g, ecept for 30 whch was 04 pg/g Ether there was a local concentraton of Th n these sheets or handlng contamnaton resulted n a readng hgher than the average 42 Mass Spectrometry Results A large quantfy of acrylc has been vaporzed and the resdue analyzed for Th and U by mass Spectrometry The results are lsted n Table and shown n Fg 3 In most cases the acrylc from two coupons (or sheets) was combned so as to get kg samples for analyss These mass Spectrometry results are sgnfcantly hgher than the neutron actvaton results suggestng handlng contamnaton of the mass Spectrometry samples at CRL 2) Even so, almost wthout ecepton, the results are less than the acrylc specfcatons of Th at 2 ppt and U at 7 ppt 43 Alpha Spectroscopy Results Only two dsequlbrum measurements were performed Over 20 kg of acrylc from batch 47 and from batch 7 were vaporzed A porton of the resdue was analyzed by mass Spectrometry and a known amount of Th was added to the remander whch was then separated nto Th, 4

9 Table Mass Spectroscopy Res Batch Sheets 7, 4, 2,2 2,3, 4 4 7, 3,232 4,0 27 3,, , ,3 2 0, ,4,0 2,,3, Weght kg Th oq/q (MS) U pg/g (MS) Page

10 U and Ra usng on echange columns The radosotopes were electroplated out of soluton and the planchettes alpha counted for several weeks There was no evdence for dsequlbrum n the Th/U chans and the levels of Th and U were consstent wth the mass spectrometry results 44 Dscusson of Th/U Results: The mass spectrometry results are well below the specfcatons but they are also sgnfcantly larger than the neutron actvaton results For reasons already reported 2) we should rely on the neutron actvaton results and assume that the saw cuttng at CRL contamnates the cut surfaces We conclude, wth the ecepton of batch 0 that the Th and U n the sheet acrylc s at least an order of magntude better than the specfcatons of 2 and 7 pg/g respectvely Because they contan sgnfcantly hgher levels of Th the sheets from batch 0 have been ecluded from the vessel ) Optcal Absorpton Coeffcents SNO Specfcatons The optcal requrements and specfcatons of the acrylc were detaled n an earler report 7) In that report a weghtng functon was defned whch folded n the Cerenkov spectrum, the transmsson through the DO and H20 and the PMT quantum effcency The lght detected n SNO s the ntegral of the product of the acrylc transmsson tmes the weghtng functon The report also contaned the acrylc optcal absorpton coeffcents requred These coeffcents were based on multple measurements of samples provded by supplers Table lsts the weghtng functon, the absorpton coeffcent specfcaton and the product of the acrylc transmsson for 22" and 4" acrylc tmes the weghtng functon as a functon of wavelength Even though the weghtng functon s sgnfcant at 300 nm, 22" of acrylc attenuates 3% of the lght Whereas at 400 nm only % of the lght s attenuated by the 22" acrylc A fgure of mert s defned as the rato of lght detected wth the acrylc to lght detected wthout acrylc e the sum of column 4 () dvded by the sum of column 2 The specfcatons requre a fgure of mert of 07 for 22" materal (0 for 4" materal)

11 Table Optcal Standards Wavelength Weghtng Abs Coeff trans wegh trans wegh cm 22" materal 4" materal / total 4 4 The C on the optcal absorpton coeffcents showed that the Polycast producton acrylc was not as good as earler samples n that t faled to meet the specfcaton at 300 nm SNO decded to accept ths materal snce most of the lght at ths wavelength was lost anyway but to nsst that the specfcatons be meet at each of the other wavelengths Some materal dd not satsfy the specfcaton at 340 nm n partcular and was rejected 2 Optcal Bulk Absorpton Coeffcents There s a lot of optcal data on fle at CRL but only eamples of t wll be shown n ths report Optcal measurements have been made by Polycast and CRL on over 400 samples Polycast reported the absorpton coeffcent of samples from each sheet at 300 to 440 nm n 20 nm steps and at 00 and 00 nm CRL made measurements n nm steps The Polycast and CRL values for the absorpton coeffcent at 340 nm for all sheets are shown n Fgs 4, & An ndcaton of the measurement uncertanty n the CRL values may be seen from the multple measurements on samples from two sheets one n batch 0 and the other n batch 2 For most of the batches the spread n values wthn the batch s epermental uncertanty The spread between batches, wthn batch 47 4 and 3 and sheet n batch 2 are real Almost all of the 2 2" sheets n batches 47 & 4 and the 4" sheets n batch 3 fal the specfcaton (007) at ths wavelength (340 nm) These sheets wll not be used n the vessel but wll be used by RPT for the fabrcaton qualfcaton process 3 Fgure of Mert Results A plot of the fgure of mert of each sheet may be of more relevance to SNO than the absorpton coeffcents at varous wavelengths and was used to select sheets for the vessel and as nput to the Monte

12 Carlo programs determnng detector response Table 7 lsts the calculated fgure of mert for the 22" and 4" batches Fg 7 and are plots of these values for the two thcknesses In the case of (he 4" materal the fgure of mert was calculated from the absorpton coeffcents as though the materal was 22" thck Ths allows a drect comparson of the qualty of the bulk acrylc Actually, as can be seen from Table 30% of the sgnal s lost by absorpton n 22" acrylc meetng the specfcatons and 42% n the 4" materal Materal for the qualfcaton program should be selected usng these data Batches 47 4 and 4 and sheet n batch 2 are the poorest qualty 22" materal, followed by selected sheets n batches 0 and 7 Batch 3 s the poorest qualty 4" materal Unfortunately the other two batches are not much better Thrteen samples from sheet of batch 0 were measured and the fgure of mert calculated The spread n the absorpton coeffcents at 340 nm s shown n Fg 4 The fgure of mert from batch 0 coupons s shown n Fg The standard devaton of the 3 measurements on sheet s 004 and ths s consstent wth the epected uncertanty n the optcal measurements We conclude that no sgnfcant dfferences between the sheets of batch 0 ests, the spread n Fg s consstent wth epermental uncertantes A detaled eamnaton of the fgure of mert of the varous batches as plotted n Fgs 7 & shows that almost all of the spread wthn batches s epermental Sheet n batch 2 and sheet 7 n batch 3 are clearly worse than the averages of those batches and the spread n the rejected batch 4 s larger than the epermental uncertanty Otherwse less than a dozen sheets are more than 2 standard devatons from the batch average However the dfferences between batches as emphaszed by the averages plotted n Fgs 7 & are real 4 Dscusson of Optcal Results Wth the ecepton of some sheets n the frst two batches of 22" materal (47 & 4) and the frst batch of 4" materal (3) the acrylc satsfes the optcal specfcaton However because of our tests on Polycast materal pror to the purchase order and because of Polycasts assurances n wrtng we epected to get materal 4% better than the specfcatons In fact Polycast epected the materal to have a fgure of mert of 073 but guaranteed 07 Some of ther materal dd sgnfcantly surpass ther epected qualty but many sheets were below that grade and for that reason we have stuck to the letter of the specfcatons and rejected all sheets whch dd not meet the specfcatons at 340 nm even

13 though ntegrated over the frequency spectrum the fgure of mert was not worse than 07 The 4" materal s unformly poor but there are only 0 panels of that materal and they are so thck anyway that much of the sgnal s absorbed The large varablty of the 22" materal may be a problem for the data ftters Ths has yet to be determned Consderaton has to be gven to the dstrbuton of sheets throughout the vessel The current plan s that the good and poor sheets wll be randomly dstrbuted and not be concentrated at specfc locatons RPT are machnng the sheets Acknowledgments: We thank Dr Emmanuel Bonvn for hs contnung nterest n acrylc qualty and n the CRL work All of the fgure of mert values were calculated by hm All of the CRL optcal measurements were made on a spectrophotometer ably operated by Candy Everall The neutron actvaton samples were prepared for rradaton by Roanne Collns and Trsh Robnson and the mllng was done by Carey Grahl The mass spectrometry was performed by Nancy Ellot and Monque Campbell The alpha planchettes were prepared and counted by Shela Kramer Tremblay Wthout ecepton these people worked competently and dlgently for the SNO project We partcular thank John Lee Patty Sheahan and other members of Polycast for ther nterest n our project and ther cooperaton n attemptng to provde SNO wth the best possble acrylc consstent wth ther corporate constrants Polycast shut down for four days to vacuum ther facltes just before our producton runs They purchased a partcle detector and repeatedly measured dust levels They sgnfcantly epanded ther normal C procedures to obtan for us the best possble monomer They ncurred sgnfcant epense n alterng ther procedures so as to provde us wth better acrylc

14 References: ) Optcal ualty of Polycast 27" Acrylc, Batches 47 4 & 4 ED Earle, RJE Deal, E Gaudette CJ Everall & E Bonvn SNOSTR320 2) Th & U levels n Polycast Stage II Acrylc, Batches 47, 4 & 4 ED Earle, RJE Deal, E Gaudette, R Collns N Ellot, S KramerTremblay & E Bonvn SNOSTR30 3) Polycast Acrylc Sheets, a progress report E D Earle, R J Deal and E Gaudette SNOSTR042 4) Measurements of Th and U n Acrylc for the Sudbury Neutrno Observatory E D Earle and E Bonvn AECL074 and SNOSTR20 ) Thermal lonzaton Mass Spectrometrc Analyss for the SNO Project by N L Ellot, General Chemstry Branch SNOSTR20 ) Ultra Trace Analyss of Acrylc for 232Th and 23U Daughters GM Mlton, SJ Kramer, RJE Deal & ED Earle SNOSTR32 & submtted to Appled Radaton & Isotopes 7) Evaluaton of Optcal Propertes of Acrylc Samples from Dfferent Supplers E Bonvn and E D Earle SNOSTR20 Fgures: Mnmum Thckness of Each Sheet 2NAA Results 3MS Results 4,, Absorpton 340 nm 7, Fgure of Mert Fgure of Mert of Batch 0

15 2fc 2 fc U Fg Sheet Thckness at Thnnest Pont a a a D A S s \:r A A *00, t A A,?» * < * *? +, A A o 4 a 7 o A 2 3 A sheet #

16 000 I Fg 2 Th & U cone by NA \ \ : ; ; : ; Th sgma error Th 2 sgma lmt + U 2 sgma lmt ; : I Batch : I ; : : 0) 0) I I + +4 I+,,, f < I I : +! I+ + \! fy A +" ; [ + ; : ; ; ; ; + + ; \ ; r +! :ff! ++ IT +++ * tl IIT rt " ; ; ; :T + + ;: ( :; < on [ <:! n sample # ll ; 00 <l T "< l I I < I 4 + ~

17 < 4 Fg 3 Th & U cone from MS ll ; Ill! h >?! ; I ) 4X I ; v / v /N >$< X r v y\/\ Y >k X k <,,, I*! I IXX X ; : : ;! ; ; ; : th l h " sample #

18 CRL Fg 4 Absorpton Coeffcents for 340 nm Xy X A/\w( Wy \ X X» > X)X» A X A XXy M, Aft I : Polycast v :! Y\ y y! XYN X yy v X y I /<AX~ f\ e \) Sample # 00 20

19 " Fg Absorpton Coeffcents for 340 nm u uv c batch CO ( ) Polycast 007 (0 * C0) l CRL * <D " 04 (0 D (0 nna < y X :: «XX wx Xy X*/ / y «X y A ; X: / y N A / I Sample # 220 0

20 CRL Fg Absorpton Coeffcents for the 4" Batches 00 E c o 00 r CO \ f 007 (A *C<D o 00,? * 0)00 00 c 0 a (0 A (0 003 : XyX XX 200 Sample # batch s s l I rt /? XX Polycast 20

21 0) ) 072 a Fg 7 Fgure of Mert for 2" Batches SsaB ffl a j * a» A,» XX gdf A * * + 0 A 0 s * 0 0 v *» * A y a o 47 4 o 4 A A 3 s 4 a o average 0 20 sheet #

22 Fg Fgure of Mert for the 4" Materal normalzed to 22" o " o 0 o average sheet #

23 Fg Fgure of Mert of Batch D e ' o 072 o o 07 L sheet #