Baydjanov M. Turin Polytechnic University in Tashkent polito.uz

1. «Radiation-induced processes in silica core high-OH optical fibers under gamma-irradiation of 60Co» Baydjanov M. Turin Polytechnic University in Tashkent www.polito.uz Institute of Nuclear Physics, Uzbekistan www.inp.uz

2. Application of silica optical fibers • Telecommunication • Sensors • Dosimeters • Medicine • Radiation-resistant optical fibers • DESY – beam loss monitoring • Nuclear Reactors – transfer information in IR-region of spectrum • LHC CERN – detection of high-energy charged particles • UV-irradiation in medicine • Nuclear Power Plant • In the future • ITER – plasma diagnostics (400-700 nm) • Space technologies • Expansion of optical fiber application fields is continuing

3. Optical fiber samples Polymicro Technologies LLC clad polymer clad (F) SiO2 core SiO2 Buffer CCDR=1.1 (Clad to core ratio) Effective range of high-OH fibers is 400 – 500 nm

4. PURE SILICA FIBERS with High-OH group content www.polymicro.com • Why OH-groups? • OH-groups are formed during adding hydrogen gas during optical fiber drawing. • Accompanied with two main processes: • suppressing ruptured Si-O-Si bonds during fiber drawing • reducing radiation-induced defects • OH-groups are necessary to increase a radiation resistance ≡Si–O–Si ≡ → Si•+ •O–Si → ≡Si–H + H–O–Si≡ ≡Si• – electronic E′-center - absorption band 215 nm •O–Si≡ – Non-bridging oxygen hole center (NBOHC) - absorption band 260, 620 nm ≡Si–O–H •O–Si≡ – NBOHC-H - absorption band 600 nm MPNP’09

5. What happens to optical parameters of fibers under the influence of ionizing radiation? • Radiation-induced absorption(induced losses) of light caused by color centers • Radiation-induced light emission • Cherenkov’s effect – high-energy charged particles • Luminescence of color centers • Reabsorption of induced emission

6. 3 3 6 2 5 1 4 γ-rays γ-rays 7 Fig.1.Experimental setup for in-situ measurements of radiation induced losses and light emission under γ-irradiation of60Co (1.25 MeV): 1) Probing lamp; 2) Lenses; 3) connectors; 4) Transporting part of fiber5) EPP2000C Spectrometer; 6) PC; 7) Irradiated part of fiber coiled into a ring with diameter 4.5 cm.

7. Radiation induced losses of transmission In-situ measurement of losses Stable losses Unstable losses Transient color centers Unstable color centers Stable color centers - in-situ losses - stable losses - unstable losses

8. Fig. 2. High-OH fiber FVP300: Relaxation kinetics after γ-irradiation. Unstable losses are caused by unstable color centers that are created under irradiation and annealed within 10 min. Stable losses are caused by stable color centers that are created under irradiation and living longer than 10 min.

9. Low-OH FIP300 High-OH FVP300 Fig. 3. γ-induced in-situ losses: a) FVP300 at dose rate6R/s(1) 8∙106; (3) 3,5∙107Rad; at dose rate360R/s(2) 8∙106; (4) 3,5∙107. b) FIP300 at dose rate6 R/s(1) 3,5∙106; (2) 8∙106Rad; at dose rate360R/s(3) 3,5∙106; (4)8∙106 Rad. The magnitude of in-situ losses depends not-only on radiation dose but also dose rate

10. In-situ losses at dose rate 6 R/s Fig. 5. (1) 1,2∙105; (2) 3,6∙105; (3) 5∙105Rad Fig. 4. (1) 3,3∙103; (2) 2∙104; (3) 4∙105; (4) 3,5∙106; (5) 107; (6) 6∙107Rad. (1) 1.7 ∙105; (2) 1.5 ∙106; (3) 4.8 ∙106; (4) 8 ∙106; (5) 3.4 ∙107; (6) 8.45 ∙107 Rad (1) 3.6 ∙103; (2) 104; (3) 4 ∙104; (4) 4.5 ∙105

11. Optical fibers with pure silica core and F-silica clad and high-OH group content shows better radiation resistance and that optical fibers with same core and polymer clad. But the cost of silica/polymer fibers are low and diameter is higher . If the maximum annual dose is not more that 108 Rad and temperature is under 100°C in addition very long length of fiber is required then it is convenient to use silica/polymer fibers. Optical fiber with buffer (coating) Tefzel is not radiation resistant!

12. Comparing stable and unstable losses Fig. 6. In-situ (1), stable (2) and unstable (3) losses spectrainFSHA600, measured at 10 R/s. The length of irradiated part is L=5 m.

13. 8 4 FVP300 FSHA600 6 dB/m dB/m ), λ 4 ( ), 2 A λ ( A 2 0 0 5 6 7 8 8 10 10 10 10 2? 10 5 6 7 8 10 10 10 10 Dose, Rad (log. scale) Dose, Rad (log. scale) Fig 7. Dose dependency of induced losses at 610 nm in high-OH fibers. ≡ Si – O – Si ≡ → ≡ Si – O• + •Si≡ (1) ≡ Si – O – HH – O – Si ≡ → ≡ Si – O• H – O – Si ≡ + H+(2) ≡ Si – H → ≡ Si•H0orHCl(3) ≡ Si – O – H → ≡ Si – O• + HCl(4) ≡ Si – Cl → ≡ Si•HCl(5)

14. Increasing of unstable losses intensity with dose • Fig. 9. Unstable losses spectra forlow- OH FIP300 at the doses: • 1) 2,3·105; 2) 106; 3) 1,7·106; 4) 2·106; 5) 3,5·106; 6) 8·106; 7) 3,4·107; 8) 6·107; 9) 1,5·108; 10) 2·108Rad (Р=360 R/s) • Fig. 8. Unstable losses spectra for high-OHFVP300 at the doses: • 1) 9,2·104; 2) 106; 3) 4,7·106; 4) 7,9·106; 5) 3,4·107; 6) 5,9·107; 7) 8,4·107; 8) 108; 9) 2·108Rad (P=360 R/s). ≡ Si – O – Si ≡ → ≡ Si – O- + •Si≡ (6) ≡ Si – H → ≡ Si• + H+ (7) ≡ Si – O – H → ≡ Si – O• + H + (8) ≡ Si – Cl → ≡ Si• +Cl (9)

15. FVP300 FSHA600 Dose, Rad (Log. scale) Dose, Rad (Log. scale) FIP300 105 106 107 108 109 Dose, Rad (Log. scale) 105 106 107 108 104 105 106 107 108 109 Fig. 10. Dose dependency of unstable losses in high-OH fibers. Fig. 11. Dose dependency of unstable losses in low-OH fibers

16. If the diameter of the core of fiber is larger then the number of unstable color centers will be smaller, so fiber becomes more resistant to radiation. Linear dependence of unstable losses and saturation effect can be used for dosimetry purposes.

17. If unstable losses are caused by unstable color centers then where is its maximum located? What is the nature of this center? How the number of this center can be reduced?

18. UV-induced losses in high –OH fuber Fig. 12. UV-induced losses spectra in high-OH fiberFVP300: (1) right after irradiation (2) 10 min after irradiation; Fig. 13. Difference of (1) – (2) from Fig. 12. Fig. 14. UV-induced losses spectra after excitation pulses n=20 – 100.

19. 3 1.4 2 1 1 2.5 1.2 1 1.5 1 2 2 2 A(λ), dB/m 0.8 A(λ), dB/m A(λ), dB/m 1.5 1 0.6 2 1 0.4 0.5 0.5 0.2 0 0 0 0 100 200 300 400 0 100 200 300 400 0 100 200 300 400 Dose rate, R/s Dose rate, R/s Dose rate, R/s 1.4 1.6 1.4 1.4 1.2 1.2 1 1 1 1.2 1 1 1 2 0.8 0.8 2 A(λ), dB/m 2 A(λ), dB/m A(λ), dB/m 0.8 0.6 0.6 0.6 0.4 0.4 0.4 3 3 3 0.2 0.2 0.2 0 0 0 0 100 200 300 400 0 100 200 300 400 0 100 200 300 400 Dose rate, R/s Dose rate, R/s Dose rate, R/s 4,7·106 Рад 3,4·107Rad 4,7·106Rad 8·106Rad Fig. 15. Dose rate dependency of induced lossesin high-OH fiberFVP300 in wavelength range 450 nm: 1) in-situ; 2) unstable. 4,7·106Rad 3,4·107Rad 8·106Rad Fig. 16. Dose rate dependency of unstable lossesin high-OH fiberFVP300in different wavelength ranges: 1) 400 nm; 2) 450 nm; 3) 600 nm. Linear dependence can be used as a parameter to control radiation dose rate

20. γ-Radiation Induced Light Emission Radioluminescence Cherenkov’s emission Spectrometer Transporting part - L Irradiated part - lg

21. lg L Influence of reabsorption process on radiation-induced emission in fibers Intensity of Cherenkov’s emission (1) IR(λ) – Intensity of Cherenkov’s emission exposed to reabsorption within transporting (L) and irradiated (lg) lengths of optical fiber

22. a) b) IR(λ), arb. un. IR(λ), arb. un. 1 1 2 2 3 3 4 4 λ, nm λ, nm Fig. 17. Possible spectra of Cherenkov’s emission plotted by formula (1) at different given values for lgandL: a) 1 – Real spectrum of Cherenkov’s emission plotted by formula I0(λ)=k/λ3; 2 – lg=4 mandL=22 m.A(λ)forD=106Rad, P=70 R/s (МТ-22С-accelerator)); 3 – lg=3 m и L=6 m, A(λ) при D=1,5∙106 Рад, P=360 Р/с; 4 – при D=1,5∙106 Рад. b) A(λ) forD=106Rad; P=70 R/s (МТ-22С-accelerator), 1 – построенный по I0(λ)=k/λ3; 2 – L=5 m; 3 – L=22 m; 4 – L=50 m.

23. Dependence of the length of transporting fiber on reabsorption 0 5 a) Zoom a) 1 6 7 2 8 11 9 12 3 10 13 4 14 15 5 0 5 7 Zoom b) b) 8 6 9 1 12 13 2 14 10 15 11 3 4 Fig. 2. Theoretical Cherenkov’s emission spectra (curve (0)) and plotted by eq. 2) for different length of fiber samples: a) FVP; b) J-LowSol; c) J-UltraSol. Numbered curves correspond to the length of fibers as follows: (1) – 1 m; (2) – 2 m; (3) – 5 m; (4) – 10 m; (5) – 20 m; (6) – 50 m; (7) – 75 m; (8) – 100 m; (9) – 150 m; (10) – 200 m; (11) – 250 m; (12) – 300 m; (13) – 400 m; (14) – 500 m; (15) – 103 m. 5

24. From 1 to 20 m J-UltraSol sample has the best performance, 2nd FVP and 3rd is J-LowSol. At the length of 20 m for J-UltraSol the intensity magnitude is still highest while for FVP and J-LowSol it is comparably equal. At 20 < L < 75 m J-UltraSol, J-LowSol and FVP correspondingly in order of highest intensity to lowest. 100 < L < 250 m – J-UltraSol, FVP, J-LowSol. 250 < L < 1000 m – FVP, J-UltraSol, J-LowSol. 5 0 7 Zoom c) 1 c) 8 2 6 3 12 9 13 10 14 15 4 11 5 6

25. Reabsorption takes place in irradiated and transporting parts of optical fibers. Reabsorption depends on the lengths of irradiated part, transporting part and dose of irradiation. Reabsorption changes the shape of real spectrum – deformation of spectrum. Is it possible to restore the real shape of the spectra? Yes, if we measure in-situ losses simultaneously with radiation-induced emission spectrum!

26. Irradiated part of fiber l I0 Method of restoring the true emission spectra Details in Jap. J. Appl. Phys. 2008 (47) 1 301-302. Intensity of true emission with taking into account reabsorption within irradiated and transporting parts of optical fiber.

27. FVP300 false FVP300 true • Fig. 18. γ-induced light emission spectra of high-OH fibers: a) measured; b) andc) after calculations. • 1 – 7,3∙104; 2 – 1,4∙106; 3 – 5∙106; 4 –8∙106; 5 – 3,45∙107; 6 – 6∙107Рад, P=360Р/с. c)

28. Fig. 19. Difference of spectra (6) and (1) from Fig. 18 b) and c). • Fig. 20. Real spectrum(1), Cherenkov’s emission spectrum(1/λ3) (2) and their difference(3).

29. 1,5 1,5 1 1 0,5 0,5 650 650 350 350 450 450 550 550 750 750 850 850 λ,nm λ,nm Intensity arb. units 1,5 1,5 б) 1 1 3 3-1 0,5 2 0,5 1 0 0 750 750 350 450 550 650 850 350 450 550 650 850 λ, nm λ, nm a) Intensity arb. units b) 4 4-1 3 2 1 Fig. 21. γ-induced light emission of high-OHFVP300: а) at dose rates 6 (1), 65 (2), 160 (3), 360 R/s(4); b) Different of curves4-1. Irradiated by60Со source. b) a) Fig. 21. γ-induced light emission of high-OHFVP300: а) at dose rates 10 (1), 40 (2), 70 (3)R/s; b) Different of curves3-1. Irradiated by bremmhstrahlungγ-radiation of MT-22C accelerator.

30. Fig.23. Dose rate dependency of emission intensity at the wavelength 450 and650 nm. Increasing dose rate brings to the increase of the number secondary electrons responsible for Cherenkov’s emission therefore its intensity increases linearly. This linear dependence of radiation induced light emission can be used to control dose rates of radiation sources or beam loss monitoring.

31. In-situ measurements can give us full information about optical properties of radiation resistant fibers. Reabsorption causes deformation of radiation-induced emission spectra therefore it must be taken into account. Linear dependencies of unstable losses, light emission on dose or dose rate can be used in development of fiber based detectors of radiation. The method presented here probably can be used in beam loss monitoring with silica fibers.

32. Fig. 24. Dose dependencies of absorption band at(1) 610 nm, luminescence bands(2) 450 and(3) 650 nm. (norm. un.) • It was supposed that 610 nm absorption band is formed by the sum of absorption bands of two types of NBOHC: 600 nm (Si–O• H–O–Si) and 630 nmSi–O• • Difference in dose dependencies of absorption band 610 nm and luminescence bands 450 and 650 nm shows that : • some part of NBOHC are making non-radiative relaxation. • different centers other than NBOHC are also responsible for formation of 610 nm absorption band.

33. Influence of preliminary neutron irradiation on color centers creation under gamma-irradiation • Fig.25. γ-induced losses spectra of high-OH FVP300 fiber preliminary unirradiated by neutrons at the doses: • 103(1), 5·103 (2), 104 (3), 5·104 (4), 5·106 (5), 5·107 (6) and108Rad(7) • а) UV-range. • б) differences of spectra; • в) VIS-range 9 8 7 6 5 4 3 2 1

34. Fig. 26. γ-induced losses spectra of high-OH FVP300 fiber preliminary irradiated by neutrons fluence1012n·cm-2 UV-range; VIS-range. Doses: 105(1), 5·105 (2), 106 (3, 4), 5·106 (5), 107 (6), 5·107 (7), 108Rad(8).

35. Fig. 27. γ-induced losses spectra of high-OH FVP300 fiber preliminary irradiated by neutrons fluence1014n·cm-2 Doses 105(2), 5.105 (3), 106 (4), 9.106 (5), 1,5.107 (6) and6,5.107Rad(7) Fig. 28. Kinetics of change of the value of A(λ) at 610 nm in preliminary unirradiated. preliminary irradiated by 1012n·cm-2. 1014n·cm-2.

36. Si O H γ e+ γ e- e+ γ e- e-

37. Effect of high temperature heating on transmission recovery of irradiated high-OH fibers Fig.29. Spectra of γ-induced losses before Aγ(λ) (1) and after heating ΔAi(λ) after the following temperatures: 1000С (2); 1500С (3); 2000С (4); 2500С (5); 3000С (6); 3500С (7); (8) 4000С; (9) 4500С; (10) 5000С; (11) 5500С; (12) 6000С; (13) after cooling to room temperature.

38. Fig. 30. Difference of curves of Fig 29.: 1) 1-2;2) 2-3; 3) 3-4; 4) 4-5;5) 5-6;7) 7-8;8) 8-9;9) 9-10;10) 10-11;11) 11-12;6) 6-7;12) 12-13; Fig. 31. Temperature dependence of K(λ)=Ai(λ)/Aγ(λ)

39. Dankefür die Aufmerksamkeit Thank you for your attention Спасибо за внимание E’tiboringizuchunraxmat