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Radiation damage in scintillating fibers

-Preliminary literature study-

I am no expert in the field consume results with care

Michael MollCERN, Geneva, Switzerland

Sorry for the bad quality of the scanned figures!

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Polystyrene (Fiber core)

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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

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Fiber dopants

H.Leutz, NIMA364(1995) 422

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Attenuation length in PS

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Photon detection efficiencies

P.Buzhan et al. NIMA 504 2003 48

Silicon Photomultiplier

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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/cm2

a) 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)

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Radiation damage – What is damaged?

• formation of color centers in the fiber coredecrease of light transmission

• chemical degradation of the added scintillatorsreduced light emission of the scintillators

• degrade quality of the cladding layersincreased reflection losses

• together with infiltrated gases radiation might produce radicalswhich change the chemical structure

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Parameters that are influencing radiation damage

• 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

Influence of the following parameters has been reported:

VERY COMPLEX TOPIC !!

difficult to disentangle the different contributions to the overall damage

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Pion irradiation of Kuraray fibers

• 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 π/cm2)

J.Baehr et al., NIMA449(2000)260 (HERA-B)

Result: No damage seen within 10% error of experiment.First hint that scintillating mechanism is relatively radiation hard

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…..

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Reactor neutrons: Irradiation damage

A.Asmone et al. NIMA338(1994)398

Bicron

Kuraray

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“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

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Radiation damage - Attenuation length of 3HF fibers (Kuraray)

K.Hara et al. NIMA 411 1998 31

using the fit formula above:• after 50 Krad: λ/λ0 = 0.56• after 1 Mrad: λ/λ0 = 0.37• (after 1 Grad: λ/λ0 < 0)

Attenuation loss:• e.g.l=100 mm fiber length• attenuation length: λ0 = 4.5 m

– exp(-l/ λ0): 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%

])[(log144.080.0 100 KradD⋅−=/λλ

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Annealing at room temperature

• very strong annealing

K.Hara et al. NIMA 411 1998 31

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CERN -RD25

•fiber length: 2m fiber diameter: 1mm

• mounted inside lead calorimeter module

• 0.5 GeV electronsLIL – LEP Injector Linac1010 electrons/burst – 100Hz

• measurement of lightoutput during irradiation….. up to 5Mrad

•

CERN/DRDC/93-26 and 93-38

Table: after irradiation unclear annealing state (?)

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PolymethylmethacrylatePMMA (Cladding)

Fluorinated Polymethylmethacrylate

PMMA (Cladding)

“radiation hard”

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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

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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

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Kuraray 3HF fibers – Aging (without radiation)

K.Hara et al. NIMA 411 1998 31

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Kuraray SCSF-78M fibers – Aging (without radiation)Temperatue dependence

A.Suzuki et al., NIMA453(2000)165

• Arrhenius Plot of “10% efficiency-loss time”

• Keep your fibers cold!

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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-γ, 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

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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)

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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

x

y

z

p-beam

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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?

Beam 1.5 cm

Fiber