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Measurement of Re-emission of Cherenkov Radiation

Measurement of Re-emission of Cherenkov Radiation. Yuri Kamyshkov / University of Tennessee Aqueous Scintillators Meeting at Temple University, January 19, 2010. Outline. Will talk about possible extension of Cherenkov radiation

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Measurement of Re-emission of Cherenkov Radiation

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  1. Measurement of Re-emission of Cherenkov Radiation Yuri Kamyshkov / University of Tennessee Aqueous Scintillators Meeting at Temple University, January 19, 2010

  2. Outline • Will talk about possible extension of Cherenkov radiation • detection due to absorption and re-emission of Cherenkov • light in wider wavelength range by the additives to water • Will illustrate this mechanism with our work performed • for organic scintillator in KamLAND that resulted in LS • response non-linearity understanding measurement and • correction • Will discuss our R&D plans for water studies

  3. Cherenkov light emission at threshold velocities Cherenkov radiation starts with UV photons J.D. Jackson, Classical Electrodynamics 3-rd edition, page 638 Cherenkov emission band Red UV PMT sensitivity range for LS 0~ 100 nm • mostly UV

  4. Cherenkov yield in Super-K (simple estimate) S. Fukuda et al., NIM A 501 (2003) 418–462

  5. Refraction index and absorption coefficient for water from book of J.D. Jackson (3-rd edition) page 315 index of refraction n  1 m  1 mm absorption coefficient [cm1]

  6. Water data are from Segelstein, D., 1981: "The Complex Refractive Index of Water", M.S. Thesis, University of Missouri, Kansas City n PMT Q.E.  Wavelength, nm

  7. Refraction index of water

  8. How Cherenkov photons with  < 300 nm can be detectable? (Yield 70-600 nm)/(Yield 300-600 nm) ~ 7.5

  9. Total energy of Cherenkov photons (for 70-600 nm) is ~ 20 times higher that 400 nm photons

  10. Common “wisdom” for organic scintillators: • light yield is quenched for large dE/dx (Birks’ phenomenological law) • therefore quenching is important for p, , C-ions ... • but not for electrons ... • Non-linearity of e-m response is essential for  detectors • related to the purpose of such precision LS neutrino experiments • like KamLAND, Double Chooz, Borexino Daya Bay, NOA, • HanoHano, SNO+, LENA ... • e.g. for antineutrino detection • measured positron KE is almost equal to antineutrino energy • which is used for determination of oscillation parameters

  11. Relative efficiency for BC505 liquid scintillator

  12. Strong non-linearity! Calibration with monoenergetic radioactive  sources in KamLAND arbitrary normalization Light yield in KamLAND ~ 270 spe/MeV with 1325 17”-PMTs (22% coverage) ~ 430 spe/MeV with + 554 20”-PMTs (34% coverage); due to non-linearity L.Y. depends on the reference energy and might also depend on other factors (verified by periodic source calibration).

  13. Direct Cherenkov contribution Reasonably expected GEANT recommended Birks’ constant • Two possible mechanisms that can produce non-linearity: • Birks’ quenching in scintillator • Cherenkov light production • within  of the PMT photocathode Initial GEANT simulations in KamLAND with two parameters reproducing non-linearity measured with 

  14. Region of solar  in KamLAND will depend on particular mechanism of non-linearity

  15. Conversion of UV to detectable light in LS Dodecane 80% PPO ~1.5 g/L Pseudocumene 20% Energy transferred by emission and re-absorption, and by molecular collisions—Forster mechanism. Detectable PPO emission UV Cherenkov incident

  16. Mixture of n-dodecane and pseudocumene PMT Mixing references: W. Heller, Physical Review vol. 68 (1945) 5-10; R. Mehra, Proc. Indian Acad. Sci. (Chem. Sci.), vol. 115 (2003)147-154

  17.  100 m

  18. UV LS re-emission flux calibration details D2 lamp Vacuum UV Monochromator Focusing elbow MgF2 window Si-photodiode (for flux calibration) Manual wavelength control Vacuum tube for Si diode volume Wavelength reading Vacuum tube to fore-pump Electrometer for current measurements Turbo-molecular pump

  19. Calibrated Si-diode (IRD/US Company) allows to measure photon beam intensity (# photons/sec) at every wavelength starting from 115 nm No voltage bias is required (internal output impedance of the diode ~ 100 M)

  20. LS chamber with PMT LS/N2 OUT MgF2 window Hamamatsu R329-02 PMT LS/N2 IN Direct protocathode coverage without reflections is ~ 0.6% of 4

  21. ~ 22% Measured Measured as (2.70.5)E+5 Measured with calibrated Si-diode Combined efficiency The goal is to measure the re-emission efficiency C() of UV photon (as produced by Cherenkov) to the “scintillation” photon emitted by PPO in LS Light collection efficiency can be studied by MC... But C() for PPO in LS is known for 300 nm as 80-100% (80% is Borexino number)

  22. Wavelengths where Cherenkov contributes KamLAND LS refractive index (80% dodecane, 20% pseudocumene, 1.5 g/l PPO). Reemission increases the number of Cherenkov photons detected at 1 MeV by factor of 3.7

  23.  10 nm

  24. NaI NaI NaI Study of electron response with Compton spectrometer Compton spectrometer scheme Test sample 1.6m Energy of recoil electron is determined by scattered photon angle and certain initial energy of the incident photon Scattering angle variation from 20 to 120 degrees. Electron energies: 29-300keV and 166.3-1000keV 22Na gamma source 0.511 MeV and 1.275 MeV

  25. 1 mCi 22Na source (511 and 1275 keV lines) inside massive lead collimator LS test sample r=2.5cm radius, h=6.35 cm quartz cylinder NaI NaI 13 cm 1.6 m arm Compton Spectrometer VME DAQ system

  26. 20 degrees Data 20 degrees MC 1.275MeV 1.275MeV E, MeV(NaI) ADC, channels(NaI) 0.511MeV 0.511MeV Backscattering in NaI Backscattering in NaI ADC, channels(scintillator) E, MeV(scintillator) 70 degrees Data+Monte-Carlo Data Monte-Carlo Data & Monte-Carlo double Compton Scattering double Compton Scattering

  27. Scintillator response to electrons Systematic errors 0.5% parameterization Oleg Perevozchikov, PhD thesis, UT 2009

  28. Conversion of deposit energy into p. e. Evis = Edep(E)  m + NCh(E) Calculated in GEANT, Birks dependent Calculated in GEANT with reemission; 4.5% contribution at 1 MeV (or ~ 20 s.p.e. / MeV) GEANT simulations Measured electron response is a ready product for electrons in GEANT: integrates Birks and Cherenkov non-linearity effects. For  and positron simulation one needs n() and Birks’ coefficient.

  29. Best fit (Monte-Carlo) N p.e./MeV best fit is (609+110–80) p.e. in agreement with direct yield measurement N p.e./MeV=643.5+/-3.8 p.e. in Compton spectrometer Number of photons/MeV (scintillation) Fitted Birks value is kB=(0.01072 +0.0012–0.0005) g/(MeV∙cm2) =0.138mm/MeV Birks,g/MeV/cm2 GEANT recommended kB =0.013g/(MeV∙cm2)

  30. Comparison with  and protons in KamLAND LS response for  and protons calculated without parameters compared with values measured in KamLAND proton quenching measurements KamLAND data(gammas) UT MC(gammas) UT Data(electrons) UT MC(electrons) proton quenching MC

  31. How LS non-linearity would contribute in NOvA? GEANT3 10 GeV muon in 6 cm liquid scintillator layer (normal incidence; KamLAND LS non-linearity)

  32. 2 GeV electron in infinite size liquid scintillator volume (KamLAND LS properties) 15% effect dependent on LS properties (if neglected)

  33. LS re-emission efficiency (PMT readout) ~ 5% PC Combined Efficiency of KamLAND LS ~ 20% PC preliminary, no WLSF C() conversion efficiency

  34. New automatic UT vacuum monochromator

  35. Our R&D Plans • In collaboration with UT chemists (Shawn Campagna, Mark Dadmun) • will identify photosensitive molecules with excitation range covering • 70-300 nm; probably with 2-3 absorption and re-emission steps. • With final emission in the visible (detector) range. • Components solubility in water, stability, concentration, composition, • removal of components, absorption competing with water, quantum • efficiency, and emission timing should be considered. • For candidate components will measure and cross compare re-emission • efficiency with our UV monochromator (integrated detector response vs • Cherenkov ). Tune composition of components based on the measured • efficiency vs . Spectral composition of re-emitted light could be very • instructive for mechanism analysis (unfortunately, we are short of ~ $60K) • After finding the optimized composition, test light amplification effect • with ~1 m3 cosmic muon water-Cherenkov detector that we have at UT. • Hope that amplification factor of 5-10 can be achieved.

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