Dose rate effects in the radiation damage of the plastic scintillators of the CMS Hadron Endcap Calorimeter
PP repared for submission to JINST
Dose rate effects in the radiation damage of the plasticscintillators of the CMS Hadron Endcap calorimeter
V. Khachatryan a A.M. Sirunyan a A. Tumasyan a A. Litomin b V. Mossolov b N. Shumeiko b , M. Van De Klundert c H. Van Haevermaet c P. Van Mechelen c A. Van Spilbeeck c G.A. Alves d W.L. Aldá Júnior d C. Hensel d W. Carvalho e J. Chinellato e C. De Oliveira Martins e D. Matos Figueiredo e C. Mora Herrera e H. Nogima e W.L. Prado Da Silva e E.J. Tonelli Manganote e A. Vilela Pereira e M. Finger f M. Finger Jr. f S. Jain f R. Khurana f G. Adamov g Z. Tsamalaidze g , U. Behrens h K. Borras h A. Campbell h F. Costanza h P. Gunnellini h A. Lobanov h I.-A. Melzer-Pellmann h C. Muhl h B. Roland h M. Sahin h P. Saxena h V. Hegde i K. Kothekar i S. Pandey i S. Sharma i S.B. Beri j B. Bhawandeep j R. Chawla j A. Kalsi j A. Kaur j M. Kaur j G. Walia j S. Bhattacharya k S. Ghosh k S. Nandan k A. Purohit k M. Sharan k S. Banerjee l S. Bhattacharya l S. Bhowmik l S. Chatterjee l P. Das l R.K. Dewanjee l S. Jain l S. Kumar l M. Maity l G. Majumder l P. Mandakini l M. Patil l T. Sarkar l A. Saikh l S. Sezen m A. Juodagalvis n S. Afanasiev o P. Bunin o Y. Ershov o I. Golutvin o A. Malakhov o P. Moisenz o , V. Smirnov o A. Zarubin o M. Chadeeva p R. Chistov p M. Danilov p E. Popova p V. Rusinov p Yu. Andreev q A. Dermenev q A. Karneyeu q N. Krasnikov q D. Tlisov q A. Toropin q V. Epshteyn r V. Gavrilov r N. Lychkovskaya r V. Popov r I. Pozdnyakov r G. Safronov r M. Toms r A. Zhokin r H. Flacher s A. Baskakov t A. Belyaev t E. Boos t M. Dubinin t , L. Dudko t A. Ershov t A. Gribushin t A. Kaminskiy t V. Klyukhin t O. Kodolova t I. Lokhtin t I. Miagkov t S. Obraztsov t S. Petrushanko t V. Savrin t A. Snigirev t V. Andreev u M. Azarkin u I. Dremin u M. Kirakosyan u A. Leonidov u A. Terkulov u S. Bitioukov v D. Elumakhov v A. Kalinin v V. Krychkine v P. Mandrik v V. Petrov v R. Ryutin v A. Sobol v S. Troshin v A. Volkov v A. Adiguzel w N. Bakirci w , S. Cerci w , S. Damarseckin w Z.S. Demiroglu w C. Dozen w I. Dumanoglu w E. Eskut w S. Girgis w G. Gokbulut w Y. Guler w I. Hos w E.E. Kangal w O. Kara w A. Kayis Topaksu w U. Kiminsu w M. Oglakci w G. Onengut w K. Ozdemir w , S. Ozturk w , A. Polatoz w D. Sunar Cerci w , B. Tali w , H. Topakli w , S. Turkcapar w I.S. Zorbakir w C. Zorbilmez w B. Bilin x B. Isildak x G. Karapinar x A. Murat Guler x K. Ocalan x , M. Yalvac x M. Zeyrek x E. Gülmez y deceased also Joint Institute for Nuclear Research, Dubna, Russia deceased also California Institute of Technology, Pasadena, USA also Tokat Univesity, Tokat, Turkey also Adiyaman University, Adiyaman, Turkey also Piri Reis University, Turkey also Gaziosmanpasa Univesity, Tokat, Turkey also Adiyaman University, Adiyaman, Turkey also Adiyaman University, Adiyaman, Turkey also Tokat Univesity, Tokat, Turkey also Necmettin Erbakan University, Konya, Turkey a r X i v : . [ phy s i c s . i n s - d e t ] S e p . Kaya y , O. Kaya y , E.A. Yetkin y , T. Yetkin y , K. Cankocak z S. Sen z A. Boyarintsev aa B. Grynyov aa L. Levchuk ab V. Popov ab P. Sorokin ab A. Borzou ac K. Call ac J. Dittmann ac K. Hatakeyama ac H. Liu ac N. Pastika ac O. Charaf ad S.I. Cooper ad C. Henderson ad P. Rumerio ad , C. West ad D. Arcaro ae D. Gastler ae E. Hazen ae J. Rohlf ae L. Sulak ae S. Wu ae D. Zou ae J. Hakala a f
U. Heintz a f
K.H.M. Kwok a f
E. Laird a f
G. Landsberg a f
Z. Mao a f
J.W. Gary ag S.M. Ghiasi Shirazi ag F. Lacroix ag O.R. Long ag H. Wei ag R. Bhandari ah R. Heller ah D. Stuart ah J.H. Yoo ah A. Apresyan ai Y. Chen ai J. Duarte ai M. Spiropulu ai D. Winn a j
S. Abdullin ak S. Banerjee ak F. Chlebana ak J. Freeman ak D. Green ak D. Hare ak J. Hirschauer ak U. Joshi ak D. Lincoln ak S. Los ak K. Pedro ak W.J. Spalding ak N. Strobbe ak S. Tkaczyk ak A. Whitbeck ak S. Linn al P. Markowitz al G. Martinez al M. Bertoldi am S. Hagopian am V. Hagopian am T. Kolberg am M.M. Baarmand an D. Noonan an T. Roy an F. Yumiceva an B. Bilki ao , W. Clarida ao P. Debbins ao K. Dilsiz ao S. Durgut ao R.P. Gandrajula ao M. Haytmyradov ao V. Khristenko ao J.-P. Merlo ao H. Mermerkaya ao , A. Mestvirishvili ao M. Miller ao A. Moeller ao J. Nachtman ao H. Ogul ao Y. Onel ao F. Ozok ao , A. Penzo ao I. Schmidt ao C. Snyder ao D. Southwick ao E. Tiras ao K. Yi ao A. Al-bataineh ap J. Bowen ap J. Castle ap W. McBrayer ap M. Murray ap Q. Wang ap K. Kaadze aq Y. Maravin aq A. Mohammadi aq L.K. Saini aq A. Baden ar A. Belloni ar S.C. Eno ar , C. Ferraioli ar T. Grassi ar N.J. Hadley ar G-Y Jeng ar R.G. Kellogg ar J. Kunkle ar A. Mignerey ar F. Ricci-Tam ar Y.H. Shin ar A. Skuja ar M.B. Tonjes ar Z.S, Yang ar A. Apyan as K. Bierwagen as S. Brandt as M. Klute aq X. Niu as R.M. Chatterjee at A. Evans at E. Frahm at Y. Kubota at Z. Lesko at J. Mans at N. Ruckstuhl at A. Heering au D.J. Karmgard au Y. Musienko au , R. Ruchti au M. Wayne au A.D. Benaglia av T. Medvedeva av K. Mei av C. Tully av A. Bodek aw P. de Barbaro aw M. Galanti aw A. Garcia-Bellido aw A. Khukhunaishvili aw K.H. Lo aw D. Vishnevskiy aw M. Zielinski aw A. Agapitos ax J.P. Chou ax E. Hughes ax H. Saka ax D. Sheffield ax N. Akchurin ay J. Damgov ay F. De Guio ay P.R. Dudero ay J. Faulkner ay E. Gurpinar ay S. Kunori ay K. Lamichhane ay S.W. Lee ay T. Libeiro ay S. Undleeb ay I. Volobouev ay Z. Wang ay S. Goadhouse az R. Hirosky az Y. Wang az on behalf of CMS-HCAL collaboration a Yerevan Physics Institute, Yerevan, Armenia b National Centre for Particle and High Energy Physics, Minsk, Belarus c Universiteit Antwerpen, Antwerpen, Belgium d Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil e Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil f Charles University, Prague, Czech Republic g Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia h Deutsches Elektronen-Synchrotron, Hamburg, Germany i Indian Institute of Science Education and Research, Pune, India j Panjab University, Chandigarh, India k Saha Institute of Nuclear Physics, Kolkata, India l Tata Institute of Fundamental Research-B, Mumbai, India also Marmara University, Turkey also Kafkas University, Kars, Turkey also Istanbul Bilgi University, Turkey also Yildiz Technical University, Turkey also CERN,European Organization for Nuclear Research, Geneva, Switzerland also Argonne National Laboratory, Argonne, USA also Erzincan University, Erzincan, Turkey also Mimar Sinan University, Istanbul, Turkey corresponding author also Institute for Nuclear Research, Moscow, Russia Kyungpook National University, Daegu, South Korea n Vilnius University, Vilnius, Lithuania o Joint Institute for Nuclear Research, Dubna, Russia p National Research Nuclear University Moscow Engineering Physics Institute, Moscow, Russia q Institute for Nuclear Research, Moscow, Russia r Institute for Theoretical and Experimental Physics, Moscow, Russia s University of Bristol,Bristol, United Kingdom t Moscow State University, Moscow, Russia u P.N. Lebedev Physical Institute, Moscow, Russia v State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia w Cukurova University, Adana, Turkey x Middle East Technical University, Physics Department, Ankara, Turkey y Bogazici University, Istanbul, Turkey z Istanbul Technical University, Istanbul, Turkey aa Institute for Scintillation Materials of National Academy of Science of Ukraine, Kharkov, Ukraine ab National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine ac Baylor University, Waco, USA ad The University of Alabama, Tuscaloosa, USA ae Boston University, Boston, USA a f
Brown University, Providence, USA ag University of California, Riverside, Riverside, USA ah University of California, Santa Barbara, Santa Barbara, USA ai California Institute of Technology, Pasadena, USA a j
Fairfield University, Fairfield, USA ak Fermi National Accelerator Laboratory, Batavia, USA al Florida International University, Miami, USA am Florida State University, Tallahassee, USA an Florida Institute of Technology, Melbourne, USA ao The University of Iowa, Iowa City, USA ap The University of Kansas, Lawrence, USA aq Kansas State University, Manhattan, USA ar University of Maryland, College Park, USA as Massachusetts Institute of Technology, Cambridge, USA at University of Minnesota, Minneapolis, USA au University of Notre Dame, Notre Dame, USA av Princeton University, Princeton, USA aw University of Rochester, Rochester, USA ax Rutgers, the State University of New Jersey, Piscataway, USA ay Texas Tech University, Lubbock, USA az University of Virginia, Charlottesville, USA
E-mail: [email protected] bstract : We present measurements of the reduction of light output by plastic scintillators ir-radiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show thatthey indicate a strong dose rate e ff ect. The damage for a given dose is larger for lower dose rateexposures. The results agree with previous measurements of dose rate e ff ects, but are stronger dueto the very low dose rates probed. We show that the scaling with dose rate is consistent with thatexpected from di ff usion e ff ects.K eywords : Radiation-hard detectors, Scintillators and scintillating fibres and light guidesA r X iv e P rint : 1608.07267 ontents Co source 64 Comparison to previous results 75 Conclusions 7 Plastic scintillators are widely used in detectors for experiments in high energy physics experimentsdue to their high light output, low cost, and versatility. However, they are also known to su ff erfrom radiation damage (for a detailed review, see [1]). Typically, the light output of the scintillatordecreases exponentially with the dose received, as in Eq. 1.1: L ( d ) = L exp( − d / D ) (1.1)where L ( d ) is the light output after receiving a dose d , L is the light output before irradiation,and D is the exponential constant. The exponential constant D depends on the materials used in theconstruction of the scintillator and on its environmental history. Several results have also shown adependence on dose rate [1–8]. The lowest dose rates probed by these measurements were a fewkrad / hr.In this paper, we present results from scintillators used in the CMS hadron endcap calorimeter(HE) [9] irradiated at dose rates between ≈ − krad / hr that indicate that theradiation damage can have a very strong dose rate dependence. We also present a measurementfrom an irradiation at a Co source at a dose rate of 0.28 krad / hr.Plastic scintillators consist of a plastic substrate, often polystyrene (PS) or polyvinyltoluene(PVT), into which wavelength shifting (WLS) fluors have been dissolved, usually a primary and asecondary fluor. When a charged particle traverses the scintillator, the molecules of the substrateare excited. This excitation can be transferred to the primary fluor radiatively in the deep UV atlow concentrations or via the Förster mechanism [10] at higher concentrations. The primary fluortransfers the excitation radiatively to the secondary fluor. De-excitation of the secondary fluorgenerally produces light in the visible range, to match well with currently available photodetectors.The light must traverse the scintillator to reach the photodetector, and can be absorbed by “colorcenters” along its path.Dose rates e ff ects have been associated with oxygen di ff usion [4, 11, 12]. The rate of di ff u-sion depends on the substrate material and has a weak dependence on dose and on environmental– 1 –actors [11]. For unirradiated plastic, the di ff usion rate for oxygen is 13 times slower for PVT thanfor PS [13]. Oxygen can increase the mobility of radicals created during irradiation when chem-ical bonds in the polymer of the substrate are broken, and can interact with radicals to a ff ect theformation of color centers, which absorb light [12]. When oxygen is not present, cross linking isenhanced, and gel formation is reduced [11]. These processes can a ff ect the energy levels of thesubstrate, thus a ff ecting the transfer mechanisms of the initial excitation produced by the chargedparticles being measured. When radicals are more mobile, they are more likely to reform goodbonds, reducing their ill e ff ects. (For a detailed review of radicals in polymers, see [14]). Thosecolor centers that go away after a recovery period, whose length depends on temperature and theconcentration of oxygen, are referred to as temporary damage. Color centers that remain afterrecovery are referred to as permanent damage. Oxygen tends to decrease temporary damage butincrease permanent damage [1].When the concentration of radicals is low, the penetration depth of oxygen into the substrategoes as [11] z = GR (1.2)where G = VS P Φ , (1.3) R is the dose rate, V is the di ff usion constant of the gas, S is the solubility constant of oxygen, P is the oxygen pressure, and Φ is the specific rate constant of active site formation. G is roughlyindependent of dose [4, 11].For a simple configuration consisting of a piece of plastic scintillator with an alpha source onone side and a photodetector on the other, assuming the fraction of the thickness of the scintillatorpenetrated by the alpha is small, the light produced will traverse first a region penetrated by oxygenof depth z , then a region the oxygen does not reach, of thickness t − z where t is the thickness ofthe piece of scintillator, and finally another region with oxygen, before reaching the photodetector.If the inverse of the light absorption length when color centers are formed in the presence of oxygenis µ and that formed independent of the presence of oxygen is µ , the light output will be L = L exp ( − µ (2 z ) − µ t ) . (1.4)The inverse absorption length µ is related to the density of color centers Y and the cross sectionfor absorption of the light by the color center σ by µ = Y σ. (1.5)When the color center density Y is low, it depends on the chemical yield g , the density of thescintillator Q , and the dose d as Y = gQd . (1.6)The light output is then – 2 – ( d ) = L exp − g Q σ √ G √ R d − ( g Q σ t ) d (1.7)and so the functional form of the dependence of the exponential constant on the dose rate is D = √ RA + B √ R (1.8)where A = g Q σ √ G and B = g Q σ t .For a more complex arrangement, the dependence will not be as simple, but still might beexpected to show a √ R dependence at low dose rate and to approach a constant value at high doserate. The HE is part of the CMS detector [15] at CERN’s Large Hadron Collider (LHC). It is a samplingcalorimeter that uses brass as its passive material and scintillating tiles as its active material. Ithas 18 layers of active material, denoted layers 0 through 17, over most of its rapidity coverage.The zeroth layer of scintillator uses BC-408, a PVT-based scintillator from the Bicron division ofthe Saint Gobain corporation , while the other layers use SCSN-81, a PS-based scintillator fromKuraray . Figure 1 shows a schematic of the HE calorimeter.The tiles are trapezoidal in shape. They contain a sigma groove that holds a 0.94 mm Y-11(Kuraray) WLS fiber, mirrored on one end. Fig. 2 shows a schematic of the tiles, arranged in a“mega tile” that holds individual tiles. The calorimeter spans the pseudorapidity region from 1.305to 3. The tiles are labeled by their pseudorapidity by “tower number”, starting with 16 for the onesat lowest pseudorapidity and going to 29. Due to the geometry of the detector, layers 0 through4 contain tiles corresponding to towers 17 through 29. Layers 5 through 17 do not have tower29. Only Layers 5 through 10 contain tower 16, and layers 14 through 17 do not have tile 17 aswell. The megatiles are inserted into the brass absorber of the HE. The tile thickness is 0.9 cm inlayer 0 and 0.37 cm in the rest of the layers. The sizes range from roughly 10 cm ×
10 cm to about20 cm × − , and was estimated as described in [18]. The timewas estimated three di ff erent ways: using LHC 2012 run performancy summaries that includedinformation on total delivered luminosity and hours in stable beam, using detailed CMS Web BasedMonitoring records for each fill parameter including delivered luminosity and time in fill, and usingthe peak luminosity, luminosity lifetime, and fill length values to correlate average lumi rate withpeak lumi. All three methods delivered very similar results. The instantaneous luminosity wasfairly constant during the run.The light was measured using a laser calibration system, consisting of a triggerable nitrogenlaser, a system of neutral density filters, and a light distribution system that delivers the UV light Saint-Gobain Crystals, Courbevoie, France. Kuraray Corporation, Otemachi, Chiyoda-ku, Tokyo 100-8115, Japan. – 3 – igure 1 . Schematic of the CMS hadron endcap calorimeter. to the scintillator tiles in layers 1 and 7 via quartz fibers. Light was also injected directly into theHPDs. The laser light was injected during the run at times without collisions, between fills of theaccelerator with protons.Plots of the light output relative to the initial light output as a function of the accumulatedintegrated luminosity during the run are shown in Fig. 3. They show an exponential decreasein light output with integrated luminosity. After the end of the run, a few percent recovery wasobserved for the tiles with the largest damage. The data are not corrected for this e ff ect.Cross checks of the results from the laser calibration from calculations of the jet energy scale,a calibration using a Co source after the end of the run, and a measurement looking at the energydistribution in the towers using data taken with a single electron trigger as a function of integratedluminosity give similar albeit less precise results.To convert the exponential constant in terms of integrated luminosity to an exponential con-stant in terms of dose, the dose received by the tile per unit integrated luminosity is needed. Pre-dictions of the absorbed dose in HE scintillator layers were obtained using the Monte Carlo codeFLUKA 2011.2c [19, 20]. The FLUKA predictions for collisions use a model that represents the– 4 – igure 2 . Schematic of the CMS hadron endcap calorimeter scintillator megatiles tiles for tiles in layer 11through 13. The numbers below the tiles represent the tower number. The megatiles in layers 0 through 4have an additional tower at large η (tower 29). The megatiles in layers 5 through 10 contain tile 16 at low η .Layers 14 through 17 do not have tile 17. − R e s p o n s e d e g r a d a t i o n i n H CA L E nd c a p Layer 1Response=exp( − Lumi[fb − ]/D) CMS 8 TeV data, 2012 η =1.99, D= 270fb − η =2.11, D= 206fb − η =2.25, D= 172fb − η =2.41, D= 123fb − η =2.58, D= 111fb − η =2.76, D= 65fb − (a) Layer 1 − R e s p o n s e d e g r a d a t i o n i n H CA L E nd c a p Layer 7Response=exp( − Lumi[fb − ]/D) CMS 8 TeV data, 2012 η =1.99, D= 651fb − η =2.11, D= 573fb − η =2.25, D= 446fb − η =2.41, D= 346fb − η =2.58, D= 281fb − η =2.83, D= 108fb − (b) Layer 7 Figure 3 . Ratio of light output to initial light output for tiles as a function of integrated luminosity, withextracted dose constant, for CMS hadron endcap calorimeter scintillators in Layer 1 (a) and in Layer 7 (b).
HE in detail, with brass, Dural (Aluminium, Cu, Mg, and Mn), Tyvek, air, and scintillator layers.The absorber regions are represented as 80 mm thick brass ’LK75’ layers (with the exception of thelast which is <
20 mm), with a density of 8.4 g / cm and a fractional mass composition as follows:Cu 75%, Zn 24.533%, Si 0.3%, P 0.01%, Fe 0.1%, Sb, 0.005%, Pb 0.05%, Bi 0.002%. Layer 0is a 10 mm thick polyvinyltoluene layer modelled with a density 1.032 g / cm and fractional masscomposition: H 8.5292% and C 91.4708%. Other scintillator regions (layers 1-17) are 4 mm thickand represented with a polystyrene plastic scintillator of density 1.05 g / cm and fractional masscomposition H 7.7423% and C 92.2577%. Since the energy loss per mass per unit area is morethan a factor two higher for hydrogen than for most other materials, the spatial resolution used in– 5 –he calculation was defined so that the dose estimates were not averaged over regions containingmaterials other than scintillator layers. For towers 28 and 29, the amount of material in front ofthe HE varies with azimuthal angle due, primarily, to to the rectangular shape of the crystals in theelectromagnetic calorimeter. This irregularity is not yet simulated, and the dose is calculated forthe average instead. The dose was calculated using an R-Phi-Z mesh, independent of the geometry,overlaying the HE region. The resolution was selected assuming a phi symmetry and aligned inorder to obtain dose values within the scintillator regions only. For the HE there was one phi bin intotal, a one mm resolution in Z, and a one cm resolution in R. Predictions for the 4-TeV-per-beam’2012’ run use a “Run1” CMS FLUKA model, with a central beam pipe and muon endcap regionwhich is modelled to reflect the configuration at that time.Since the dose received varies over the surface of the tile, the rapidity-averaged value is used.Using a value averaged over the radius of the tile gives similar results. For layer 1, the dose receivedby a tile ranged from 0.01 to 0.2 Mrad. For layer 7, the dose received ranged from 0.00005 to0.03 Mrad.The doses and dose rates are highest for the tiles closest to the beam line. If the exponen-tial constant D does not depend on dose rate, we would expect the tiles to have the same ex-ponential constant, regardless of dose. Monte Carlo studies based on the optical transport codein GEANT4 [21] shows that the exponential constant does not depend strongly on the tile size.Measurements confirm the results of the simulation. Prior to LHC turn on, tiles constructed ofSCSN-81 with dimensions of 5 cm × × ×
20 cm were irradiated ata Co source at Argonne National Laboratory at a relatively high dose rate of 100 krad / hr. Theresulting dose constants were 1.9, 1.4, and 0.9 Mrad, respectively. The variation with size is muchsmaller than that seen with the in situ measurements [22]. The extracted dose constants are notcorrected for this e ff ect.The extracted exponential constant in Mrad is shown in Fig. 4. The di ff erent points, at di ff erentdose rates, correspond to di ff erent tiles in layers 1 and 7. We see a strong dependence on dose rate,with the tiles with the lowest dose rate having the lowest exponential constant and thus su ff eringmore damage for the same dose than the tiles with higher exponential constants.We fit the extracted D values from the laser results to a power law with an exponent of 0.5.The results of the fit are included in Fig. 4. The agreement is good. Co source A rectangular tile with WLS fiber, whose construction was similar to those used in the HE (SCSN-81, and with dimensions of 10 cm by 10 cm, with a 50 cm long mirrored fiber) was irradiated inair using the Michigan Memorial Phoenix Co source at the University of Michigan, Ann Arbor,MI. The integrated dose was 300 ±
30 krad accumulated over an irradiation time of 1080 hours, fora dose rate of 0.28 krad / hr. The light output when the tile is exposed to a (di ff erent) Co sourcewas measured before and after irradiation using a Hamamatsu R580-17 PMT coupled to a Keithleypicoammeter. An unirradiated identical tile was used to check the stability of the measurement sys-tem. The tile was allowed to recover for 6 days between the exposure and the “after” measurement,so as to measure only the permanent damage. – 6 –he resulting exponential constant is shown in Fig. 4. The dose rate for this measurementwas larger than that for any tile in the in situ measurement, and the resulting exponential constantis larger than that obtained from the in situ measurements but much smaller than values obtainedfrom high dose rate reactor exposures discussed in the next section. Its value agrees well with theextrapolation of the trend from the in situ measurements to its dose rate.
We compare our results to those from Ref. [2]. The authors studied both SCSN-81, which is PS-based, and Bicron-499-35, which is PVT-based. They irradiated disks with a 0.4 cm thickness anda 1” diameter with a gamma source. The light output was measured using an alpha source, afterallowing time for recovery of the temporary damage. The exponential constant D was obtained, fordose rates below 14 krad / hr, where measurements were made for only one dose value, by readingthe values of their data from their graphs of light output, and using Eq. 1.1 to solve for D . For higherdose rates, where measurements were made for multiple values of the total dose d , the values ofthe light output versus dose rate are obtained from the functional form in their Table 1. Values withthe same dose rate but di ff erent dose are then fit with an exponential to obtain D .The values from Ref. [2] have exponential dose constants of tens of Mrad at high dose rate,much higher than the values of a few hundredths of a Mrad at the low dose rates probed in theHE. However, even though the geometry and construction of the scintillators studied in the in situmeasurement and the measurements in Ref. [2] are quite di ff erent, and the dose rates quite di ff erent,the functional dependence is similar. We have looked at the dependence of the light loss for scintillator tiles installed in the CMS endcaphadron calorimeter as a function of both dose and dose rate. We see a power law dependenceconsistent with that predicted by di ff usion of oxygen (or other gas) into the scintillator. We see thefunctional form is in reasonable agreement with results from gamma source irradiations both by usand by the authors of Ref. [2]. Acknowledgments
We would like to thank the CMS BRIL group for doing the FLUKA calculation and the sta ff s atthe Michigan Memorial Phoenix source and the Argonne source for their help. We congratulateour colleagues in the CERN accelerator departments for the excellent performance of the LHC andthank the technical and administrative sta ff s at CERN and at other CMS institutes for their contri-butions to the success of the CMS e ff ort. In addition, we gratefully acknowledge the computingcentres and personnel of the Worldwide LHC Computing Grid for delivering so e ff ectively the com-puting infrastructure essential to our analyses. Finally, we acknowledge the enduring support forthe construction and operation of the LHC and the CMS detector provided by the following fund-ing agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ,and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS– 7 – ose rate (krad/hr) -4 -3 -2 -1
10 1 10 D o s e C on s t an t ( M r ad ) -2 -1
10 110 CMS Preliminary (fixed exponent)
D = 1.35 * RCMS in-situ 8 TeV, laser Layer 1CMS in-situ 8 TeV, laser Layer 7Co Co, Biagtan 1996 (PS) Co, Biagtan 1996 (PVT) Figure 4 . Exponential constant as a function of dose rate. Results from scintillators based on PS are shownin blue, while those based on PVT are shown in red. Results from Layer 1 (7) of the CMS HE scintillatorare indicated by filled squares (open squares). Each point corresponds to a di ff erent tile pseudorapidity.Results from the Co irradiations discussed in Biagtan [2] are indicated with circles. The label “ Co,CMS” (cross) refers to the measurement first presented in this paper, which was taken using irradiation froma gamma source. A fit to the in situ data to a power law is shown, where the power is set to 0.5. (Colombia); MSES and CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUTand ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS / IN2P3(France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAEand DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea);LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, andUASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT(Portugal); JINR (Dubna); MON, RosAtom, RAS and RFBR (Russia); MESTD (Serbia); SEIDIand CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST,STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC(United Kingdom); DOE and NSF (USA).
References [1] C. Zorn, Plastic and liquid organic scintillators, in: F. Sauli (Ed.), Instrumentation in High EnergyPhysics, 2nd Edition, World Scientific, 1993, Ch. 4, pp. 218–279. – 8 – oi:10.1142/9789814360333_0004 .[2] E. Biagtan, E. Goldberg, R. Stephens, E. Valeroso, J. Harmon, Gamma dose and dose rate e ff ects onscintillator light output, Nucl. Instrum. Meth. B 108 (1996) 125. doi:10.1016/0168-583X(95)00874-8 .[3] U. Holm, K. Wick, Radiation stability of plastic scintillators and wave-length shifters, IEEE Trans.Nucl. Sci. 36 (1989) 579. doi:10.1109/23.34504 .[4] K. Wick, D. Paul, P. Schröder, V. Stieber, B. Bicken, Recovery and dose rate dependence of radiationdamage in scintillators, wavelength shifters and light guides, Nucl. Instrum. Meth. B 61 (1991) 472. doi:10.1016/0168-583X(91)95325-8 .[5] B. Bicken, U. Holm, T. Marckmann, K. Wick, M. Rohde, Recovery and permanent radiation damageof plastic scintillators at di ff erent dose rates, IEEE Trans. Nucl. Sci. 38 (1991) 188. doi:10.1109/23.289295 .[6] B. Bicken, A. Dannemann, U. Holm, T. Neumann, K. Wick, Influence of temperature treatment onradiation stability of plastic scintillator and wave-length shifter, IEEE Trans. Nucl. Sci. 39 (5) (1992)1212. doi:10.1109/23.173180 .[7] A. Bross, A. Pla-Dalmau, Radiation damage of plastic scintillators, IEEE Trans. Nucl. Sci. 39 (5)(1992) 1199. doi:10.1109/23.173178 .[8] N. Giokaris, M. Contreras, A. Pla-Dalmau, J. Zimmerman, K. Johnson, Study of dose-rate e ff ects onthe radiation damage of polymer-based scsn23, scsn81, scsn81 + y7, scsn81 + y8 and 3hf scintillators,Radiat. Phys. Chem. 41 (1993) 315. doi:10.1016/0969-806X(93)90069-7 .[9] The CMS hadron calorimeter project, Technical Design Report CMS, CERN, Geneva, 1997.[10] T. Förster, Zwischenmolekulare energiewanderung und fluoreszenz, Annalen der Physik 437 (1947)55. doi:10.1002/andp.19484370105 .[11] T. Seguchi, S. Hashimoto, K. Arakawa, N. Hayakawa, W. Kawakami, I. Kuriyama, Radiation inducedoxidative degradation of polymers–i: Oxidation region in polymer films irradiated in oxygen underpressure, Radiat. Phys. Chem. 17 (1981) 195. doi:10.1016/0146-5724(81)90331-9 .[12] W. Busjan, K. Wick, T. Zoufal, Shortlived absorption centers in plastic scintillators and theirinfluence on the fluorescence light yield, Nucl. Instrum. Meth. B 152 (1999) 89. doi:10.1016/S0168-583X(98)00974-4 .[13] P. C. Trimmer, J. B. Schleno ff , K. F. Johnson, Spatially resolved uv-vis characterization ofradiation-induced color centers in poly(styrene) and poly(vinyltoluene), Radiat. Phys. Chem. 41(1993) 57. doi:10.1016/0969-806X(93)90042-S .[14] N. Emanuel, A. Buchachenko, Chemical Physics of Polymer Degradation and Stabilization, VNUScience Press, 1987.[15] S. Chatrchyan, et al., The CMS experiment at the CERN LHC, JINST 3 (2008) S08004. doi:10.1088/1748-0221/3/08/S08004 .[16] P. Cushman, A. Heering, A. Ronzhin, Custom HPD readout for the CMS HCAL, Nucl. Instrum.Meth. A 442 (2000) 289. doi:10.1016/S0168-9002(99)01236-X .[17] T. Shaw, A. Baumbaugh, A. Boubekeur, J. Elias, J. Ho ff , S. Holm, S. Los, C. Rivetta, A. Ronzhin,J. Whitmore, T. Zimmerman, R. Yarema, Front end readout electronics for the cms hadroncalorimeter, in: Nuclear Science Symposium Conference Record, 2002 IEEE, Vol. 1, 2002, p. 194. doi:10.1109/NSSMIC.2002.1239297 . – 9 –
18] C. Collaboration, Absolute calibration of the luminosity measurement at cms: Winter 2012 update,CMS Physics Analysis Summary CMS-PAS-SMP-12-008.[19] A. Ferrari, P. R. Sala, A. Fasso, J. Ranft, FLUKA: A multi-particle transport code, cERN-2005-010,SLAC-R-773, INFN-TC-05-11 (2005).[20] T. T. Bohlen, F. Cerutti, M. Chin, A. Fasso, A. Ferrari, P. Ortega, A. Mairani, P. Sala, G. Vlachoudis,The fluka code: Developments and challenges for high energy and medical applications, NuclearData Sheets 120 (2014) 211.[21] S. Agostinelli, et al., Geant4–a simulation toolkit, Nucl. Instrum. Meth A 506 (2003) 250. doi:10.1016/S0168-9002(03)01368-8 .[22] CMS IN-2008 /022, private communication.