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The role of temperature on air fluorescence measurements

The role of temperature on air fluorescence measurements. M. Fraga 1 , A. Onofre 1, 2 , N. F. Castro 1 , F. Fraga 1 , L. Pereira 1 , F. Veloso 1 , P. Vieira 1 , R. Ferreira Marques 1 , M. Pimenta 3 , A. Policarpo 1 J. A. C. Gonçalves 4 , C. C. Bueno 4.

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The role of temperature on air fluorescence measurements

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  1. The role of temperature on air fluorescence measurements M. Fraga1, A. Onofre1,2, N. F. Castro1, F. Fraga1, L. Pereira1, F. Veloso1, P. Vieira1, R. Ferreira Marques1, M. Pimenta3, A. Policarpo1 J. A. C. Gonçalves4, C. C. Bueno4 1 LIP- Coimbra, Dep. Física, Univ. Coimbra, 3004-516 Coimbra, Portugal 2UCP, R. Dr. Mendes Pinheiro, 24, 3080 Figueira da Foz, Portugal 3 LIP-IST, Av. Elias Garcia 14, 1100-149 Lisboa, Portugal 4IPEN and PUC, S. Paulo, Brasil M. Fraga, Prague, May 17th. 2006

  2. Layout: • Theory; • Experimental set-up; • Previous measurements taken with alpha particles as excitation source (Nc versus T for r= const.); • Simulation of the chamber and correction factors evaluation; • Corrected data versus T and comparison with recent measurements; • Further tests – the need of a precise knowledge of the behaviour all the components of the experimental set up; • Conclusions and plans for the future M. Fraga, Prague, May 17th. 2006

  3. N2 scintillation2nd positive system (300-400 nm) In steady state conditions, the light yield for the v’v’’ band is given by: with The rate constant is given by: F (r) represents the fraction of the excitation processes which produce photons that arrive at the PMT window. M. Fraga, Prague, May 17th. 2006

  4. Experimental set-up and data (raw) on Dec. 2004 – Jan. 2005 gas input Cooling unit PM3 PM1, PM2 - XP2020Q to vacuum pump Excitation source: a particles (5.4 MeV) M. Fraga, Prague, May 17th. 2006

  5. Am-241 source outside the chamber, exposed to air • For a constant r, as the temperature is lowered, the energy loss outside the chamber increases: • the mean energy, <ea>, with which the a particle enters the chamber is lower for lower temperatures; • the length of the a track is also shorter for lower temperatures ; D y = 6 mm M. Fraga, Prague, May 17th. 2006

  6. Filter Transmission* : T(qi) Filter:Melles Griot, lc = 340 nm; Dl = 10 nm For smallangles of incidence,qi 0º Transmission curve as given by the manufacturer Otherwise it has to be measured: *S. Klepser, AirLight 03, Dec. 2003, Bad Liebenzell, Germany. M. Fraga, Prague, May 17th. 2006

  7. Monte Carlo simulation using GEANT4 code* • Outside the chamber: • air (273 K) • Inside: • N2(336 hPa at 20ºC) <track> = 46 mm • N2(818 hPa at 20ºC)  • <track> = 22 mm 5 events 5 events 5 events Outside the chamber: Pair < 0.1 torr Inside: Dry air (434 hPa at 20ºC) * Note: pressure effects on light yields are not included in the simulation M. Fraga, Prague, May 17th. 2006

  8. Results of simulation: typical F(r)factors with air at 1013 hPa outside the chamber 818 hPa 336 hPa dE/dx dE/dx <Nph_PM> <Nph_PM> • Uncertainties in <Nph_PM>/a : • < 2% - due to variations of atmospheric • pressure • < 1% - due temperature variations M. Fraga, Prague, May 17th. 2006

  9. Introducing the corrections to the experimental data (0-0 band) ... one gets ... M. Fraga, Prague, May 17th. 2006

  10. Light yield versus t (ºC) . Values are corrected for the geometrical factors and different energy losses inside the chamber. • Inverse of light yield versus . For constant r, one would expect that: and or M. Fraga, Prague, May 17th. 2006

  11. Dependence of Light Yield on Pressure, at room temperature For T = constant, B/A = (5.8±1.4)×10-3 hPa-1 k20/k10 Inverse of light yield versus pressure at room temperature (0-0 band at 337 nm) M. Fraga, Prague, May 17th. 2006

  12. Improvement in the experimental set-up: very low pressure in the region of the alpha source M. Fraga, Prague, May 17th. 2006

  13. Experimental data with the a source in a low pressure atmosphere M. Fraga, Prague, May 17th. 2006

  14. Correction factors : Fraction of the alpha particle energy, lost in the gas. a particle source in a low pressure environment. For P20º = 243 hPa, (#coinc/s)Patm/(#coinc/s)low P = 1.26 ± 0.03 and <Nph_PM>Patm/<Nph_PM>low P = 1.16 ± 0.08 M. Fraga, Prague, May 17th. 2006

  15. Dry Air - N2+ O2 (80:20)(H2O < 3 ppm, CnHm < 0.5 ppm)O2 – (20 ±1) % M. Fraga, Prague, May 17th. 2006

  16. Further corrections: • variation of the PMT gain with T m = - 0.121 (±0.008) #/ºC for l = 337 nm; • Variation of quantum efficiency of the photocathode with T – in progress • Variation of the transmission of the interference filter with T – in progress M. Fraga, Prague, May 17th. 2006

  17. Study of the transmission of the IF Set-up : Data from Melles Griot M. Fraga, Prague, May 17th. 2006

  18. Conclusions and plans for the future • A coherent set of results were obtained under a particle excitation . • The expected dependence on T is not clear from the present set of experimental data and further studies and tests are needed (and theyareunderway). • An important issue is to lower the temperature of the gas below -20º ; this implies improvements on the experimental set-up (studies are underway). • Simulation of the chamber will go on. • Measurements using b particles (Sr-90) (already underway) will be carried out ; M. Fraga, Prague, May 17th. 2006

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