Radiation damage and recovery Radiation damage and recovery of PWO - PowerPoint PPT Presentation

Radiation damage and recovery Radiation damage and recovery of PWO crystals of PWO crystals R.W.Novotny PANDA-EMC GSI 2010 0222 1

quantitative studies 1 1 1 1 1 light intensity = 6.1·10 16 ph/s 1 LED, I= 0.54*10 17 ph/s light intensity=2.4·10 17 ph/s 1 min. after irr. 1 min. after irr. 1 min. after irr. 0,9 Α 1 = 0.25 τ 1 = 24 min. 0,9 blue light (464 nm) 0,9 0,9 0,9 IR light (940 nm) Α 2 =0.54 τ 2 = 260 min. IR light 1060nm 31 min. after irr. 31 min. after irr. dk @ 420nm / m -1 0,8 31 min. after irr. 0,8 0,8 0,8 0,8 2 LED, I= 1.2*10 17 ph/s 2 min blue light illum. 4 LED, I= 6.1*10 16 ph/s 4 LED, I= 6.1*10 16 ph/s 10 min. light illum. Α 1 =0.31 τ 1 = 20 min. 0,7 Α 1 =0.41 τ 1 = 55 min. 0,7 180 min blue light illum. 0,7 0,7 Α 2 =0.46 τ 2 = 244 min. 10 min infrared light 0,7 Α 1 =0.41 Α 2 =0.36 τ 1 = 55 min. τ 2 = 748 min. dk / m -1 340 min. light illum. illum. 0,6 0,6 0,6 light intensity=5.8*10 16 ph/s 0,6 Α 2 =0.36 τ 2 = 748 min. 4 LED, I= 2.4*10 17 ph/s 0,6 160 min infrared light Α 1 =0.37 τ 1 = 16 min. 0,5 0,5 0,5 0,5 illum. Α 2 =0.43 τ 2 = 220 min. 0,5 IR light 1060 nm 0,4 0,4 0,4 IR light (940 nm) 0,4 0,4 0,3 0,3 0,3 0,3 0,3 0,2 0,2 0,2 0,2 0,2 0,1 0,1 0,1 0,1 0,1 0 0 0 0 0 0 20 40 60 80 100 120 140 160 180 200 0 50 100 150 200 250 300 350 400 300 400 500 600 700 800 900 300 400 500 600 700 800 900 300 400 500 600 700 800 900 time of illumination / min wavelength / nm Time of 90% recovery: 9000 min. @spontaneous; 23 min. @ 464 nm Time of 90% recovery: 1150 min.@1060 nm Time of 90% recovery: 370 min.@940nm R.W.Novotny PANDA-EMC GSI 2010 0222 2

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4 implications for final EMC operation PANDA-EMC GSI 2010 0222 R.W.Novotny

stimulated recovery of PWO @ T=-25 o C PWO-II crystal photomultiplier γ -source LEDs • measurement at T=-25 o C • irradiation with 30Gy ( 60 Co) • damage and recovery characterized by light yield ( 60 Co) • illumination with LEDs of different color • crystals of different radiation hardness (dk) R.W.Novotny PANDA-EMC GSI 2010 0222 5

6 stimulated recovery of PWO @ T=-25 o C PANDA-EMC GSI 2010 0222 R.W.Novotny

understanding of the mechanism recovery is a thermodynamical process = − − = − i i ∑ n n exp( w b I ) t w A exp( E / kT ) with i 0 T j j T i TA j which can be accelerated by: • significant heating • photons: optical bleaching (ionization of color centers) stimulated recovery (intra-center resonant transition) initiated by minimum photon energy (IR) necessary conditions: • at least one energy level above the radiating state • re-trapping should be strongly suppressed (small number of centers) R.W.Novotny PANDA-EMC GSI 2010 0222 7

ionization and stimulation processes in PWO photons: CB UV to visible 1 4 2 IR photons 3 5 VB 1 ionization of FTD o , 2 radiative/non-radiative recombination, 3 intra-center absorption in FTD o , 4 non-radiative relaxation, 5 radiative/non-radiative recombination of FTD o . R.W.Novotny PANDA-EMC GSI 2010 0222 8

first attempt of recovery of damage due to protons in collaboration with F. Nessi-Tedaldi et al. total fluence of 24 GeV/c protons: (9.87 ± 0.69)·10 12 p/cm 2 620nm 360nm 420nm R.W.Novotny PANDA-EMC GSI 2010 0222 9

stimulation with blue light (464nm) τ short = 400 min. (6h. 40min.) τ long = 44460 min. (741 h.) R.W.Novotny PANDA-EMC GSI 2010 0222 10

irradiation with 30Gy ( 60 Co) and subsequent recovery with blue light spontaneous recovery stimulation with 464 nm τ short = < 1 min. before repeated τ long = 30 min. γ -irradiation R.W.Novotny PANDA-EMC GSI 2010 0222 11

irradiation with 30Gy ( 60 Co) and subsequent recovery start of illumination start of illumination 949 nm illumination: τ 1 = 1 h 464 nm illumination: τ 2 = 28h τ 1 <1 min. τ 2 =20-40 min. before γ -irradiation before γ -irradiation all data are normalized to the measurement before irradiation at CERN R.W.Novotny PANDA-EMC GSI 2010 0222 12

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ongoing studies 1. EPR studies of 1. PWO-II and PWO-I crystals before irradiation 2. Studies of irradiation with photons or protons 3. Impact of stimulated recovery 2. Direct measurement of optical transmission of cooled crystals 1. Before/after irradiation 2. Measurement of recovery times 3. Impact of stimulated recovery 3. Determination of optimum wavelength and photon flux R.W.Novotny PANDA-EMC GSI 2010 0222 15

radiation center @ Giessen up to 5 γ -sources 60 Co (~1.25MeV) dN = ⋅ 13 2 . 7 10 Bq dt emission of PWO integral dose: photo- 15.5Gy spectrometer T = -10 o C irradiation and recovery of cooled crystals R.W.Novotny PANDA-EMC GSI 2010 0222 16

17 (MoO 4 ) 3- PANDA-EMC GSI 2010 0222 radiation induced absorption Δ k R.W.Novotny