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Radiation Damage in Scintillating Fibers

Preliminary literature study on radiation damage in scintillating fibers, including factors influencing damage, photon detection efficiencies, and attenuation lengths.

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Radiation Damage in Scintillating Fibers

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  1. Radiation damage in scintillating fibers-Preliminary literature study-I am no expert in the field  consume results with careMichael MollCERN, Geneva, Switzerland Sorry for the bad quality of the scanned figures! M.Moll –15.10.2003 - 1

  2. Polystyrene (Fiber core) M.Moll –15.10.2003 - 2

  3. Scintillating process • PS (Polystyrene) • excited by ionizing particles • poor fluorescence yield • needs scintillator to enhance light yield • p-Terphenyl • scintillator : Foerster transition, non radiative energy transfer • POPOP • wavelengthshifter (into transparent region of PS) • Absorption/Emission overlapp self-absorption • PMP (1-phenyl-3-mesityl-2-pyrazoline) • one component system • large stokes shift • low self absorbtion M.Moll –15.10.2003 - 3

  4. Fiber dopants H.Leutz, NIMA364(1995) 422 M.Moll –15.10.2003 - 4

  5. Attenuation length in PS M.Moll –15.10.2003 - 5

  6. Photon detection efficiencies Silicon Photomultiplier P.Buzhan et al. NIMA 504 2003 48 M.Moll –15.10.2003 - 6

  7. Expected radiation levels • 100 Gy/yr (low luminosity run)  10Krad/year • 105-6 Gy/year (full luminosity run)  107-8 rad/year Per’s talk (values to be confirmed): Questions: a) What will happen after 50 Krad/500 Gy of ionizing radiation? (5 yrs low L)b) What will happen after 100 Mrad/1 MGy of ionizing radiation? (1 yr high L) • Very rough conversion: 3x10-10 Gy particle/cm2a)50 Krad = 500 Gy = 2x1012 particles/cm2 (less than 10 minutes in T7 PS beam) • b) 1 Grad = 10 MGy = 8x1016 particles/cm2 (8 weeks of high intensity run) M.Moll –15.10.2003 - 7

  8. Radiation damage – What is damaged? • formation of color centers in the fiber coredecrease of light transmission • chemical degradation of the added scintillatorsreduced light emission of the scintillators • degrade quality of the cladding layers increased reflection losses • together with infiltrated gases radiation might produce radicals which change the chemical structure M.Moll –15.10.2003 - 8

  9. Parameters that are influencing radiation damage Influence of the following parameters has been reported: • dose and dose rate • ambient temperature during irradiation • recovery (annealing effects); storage after irradiation • coloration of the basic matrix • chemical structure and molar fractions of added dopants • nature of surrounding gas during irradiation • polymerization time during production • temperature and atmosphere during transport, storage and machining • oxygen content in fibers VERY COMPLEX TOPIC !! difficult to disentangle the different contributions to the overall damage M.Moll –15.10.2003 - 9

  10. Pion irradiation of Kuraray fibers J.Baehr et al., NIMA449(2000)260 (HERA-B) • Kurary SCSF-78M fibers (0.5mm, 450nm, double cladding) • 146 MeV/c pions stopped inside fiber detector • ~10KGy(1Mrad) deposited in center of detector (1.7e13 p/cm2) Introduction of paper reflects nicely the multitude of different / contradicting observations:radiation:…. damages are observed in some cases already at some 10 krad [9,10] other studies show considerable efects only above 1Mrad [11,12]…..annealing:…. Very often a recovery of the light output of the irradiated material has been reported after the irradiation. Recovery times of some days [4,6,14], of several weeks [12] or even months [9] have been observed. However, for the same material, total [12] and no recovery [11] are reported….. Result: No damage seen within 10% error of experiment. First hint that scintillating mechanism is relatively radiation hard M.Moll –15.10.2003 - 10

  11. Reactor neutrons: Irradiation damage Bicron Kuraray A.Asmone et al. NIMA338(1994)398 M.Moll –15.10.2003 - 11

  12. “Radiation Hard” fibers3-Hydroxyflavone (3HF) doped fibers • smaller permanent radiation damage than other fibers • large Stokes shift (one component system) 530nm • Only 40% lightoutput compared to PMP • e.g. Kuraray SCSF-3HF(1500) • Two step scintillating process: • PS (activation) – 99% • P-Terphenyl (primary Fluor) - 1% • 3HF (secondary Fluor) - 1500ppm L = 10,30,100,300 cm M.Moll –15.10.2003 - 12

  13. Radiation damage - Attenuation length of 3HF fibers (Kuraray) K.Hara et al. NIMA 411 1998 31 using the fit formula above: • after 50 Krad: l/l0 = 0.56 • after 1 Mrad: l/l0 = 0.37 • (after 1 Grad: l/l0 < 0) Attenuation loss: • e.g.l=100 mm fiber length • attenuation length: l0 = 4.5 m • exp(-l/ l0): before irr : 98% • after 50 Krad: 96% • after 1 Mrad: 94% -1 year full lumi 100 Mrad: 76% -2 year full lumi 200 Mrad: 55% M.Moll –15.10.2003 - 13

  14. Annealing at room temperature • very strong annealing K.Hara et al. NIMA 411 1998 31 M.Moll –15.10.2003 - 14

  15. CERN -RD25 CERN/DRDC/93-26 and 93-38 • fiber length: 2m fiber diameter: 1mm • mounted inside lead calorimeter module • 0.5 GeV electrons LIL – LEP Injector Linac 1010 electrons/burst – 100Hz • measurement of light output during irradiation ….. up to 5Mrad Table: after irradiation unclear annealing state (?) M.Moll –15.10.2003 - 15

  16. Polymethylmethacrylate PMMA (Cladding) Fluorinated Polymethylmethacrylate PMMA (Cladding) “radiation hard” M.Moll –15.10.2003 - 16

  17. Kuraray 3HF fibers – Mechanical damage • S-parameter • characteristic index for the orientation of polystyrene chains along fiber axis • large S-parameter(chains aligned along fiber axis)- fiber softer, more flexible - shorter attenuation length • small S-parameter(chains not aligned)- fiber less flexible - longer attenuation length • Difference in attenuation length before irradiation up to factor 2 K.Hara et al. NIMA 411 1998 31 M.Moll –15.10.2003 - 17

  18. Kuraray 3HF fibers – Mechanical damage • Bending fibers on - 1 cm radius- 2 cm radius • Degradation appears 1 to 10 days after bending of fibers !! K.Hara et al. NIMA 411 1998 31 M.Moll –15.10.2003 - 18

  19. Kuraray 3HF fibers – Aging (without radiation) K.Hara et al. NIMA 411 1998 31 M.Moll –15.10.2003 - 19

  20. Kuraray SCSF-78M fibers – Aging (without radiation)Temperatue dependence • Arrhenius Plot of “10% efficiency-loss time” • Keep your fibers cold! A.Suzuki et al., NIMA453(2000)165 M.Moll –15.10.2003 - 20

  21. Kuraray fibers - Summary • Attenuation due to irradiation is the same in scintillating and clear fibers (up to 500 Krad measured) • Within the errors of the experiment scintillating dyes P-TP and 3HF are not damaged (up to 500 Krad measured 60Co-g, pions) • Strong annealing effects after irradiation (in certain cases attenuation length fully recovered) • Bending fiber can cause degradation (that appears with a delay of 1 to 10 days) be careful with irradiation test  always use a reference sample that is not going to be irradiated in exactly the same way to rule out mechanical damage!! • Aging of fibers was observed M.Moll –15.10.2003 - 21

  22. Conclusion • Radiation damage should not be a problem for the “low luminosity” operation of a fiber tracker. • Giving predictions for a “high luminosity” operation is difficult and needs experimental tests and more literature research. • What do we want ? --- preliminary status from radiation hardness point of view --- • 500ppm - 3HF square fiber from Kuraray • Fluorinated PMMA cladding • High S-value (for mechanical stability) M.Moll –15.10.2003 - 22

  23. y z x p-beam Irradiation – CERN PS – T7 – 24 GeV/c protons • Still one run this year; Period P3B (20.10 – 10.11); dedicated run for RD50 • Fibers could be mounted on the Shuttle System (no access to beam area needed) • usable space 200x200 mm2 (x-z - plane) • beam spot 15x15 mm2 • scanning possible in y-direction • 1 spill = 5x1010 p/cm2 = 15Gy M.Moll –15.10.2003 - 23

  24. Beam 1.5 cm Fiber Irradiation – CERN PS – T7 – 24 GeV/c protons • Which fibers to use? • Which fluences? • Length of fibers to be irradiated? • Minimum bending radius? • Required homogeneity of irradiation? M.Moll –15.10.2003 - 24

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