M. Fraga, Prague, May 17th 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 1 LIP- Coimbra, Dep. Física, Univ. Coimbra, Coimbra, Portugal 2 UCP, R. Dr. Mendes Pinheiro, 24, 3080 Figueira da Foz, Portugal 3 LIP-IST, Av. Elias Garcia 14, Lisboa, Portugal 4 IPEN and PUC, S. Paulo, Brasil

M. Fraga, Prague, May 17th Layout: Theory; Experimental set-up; Previous measurements taken with alpha particles as excitation source (Nc versus T for  = 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 In steady state conditions, the light yield for the v’v’’ band is given by: with The rate constant is given by: F (  ) represents the fraction of the excitation processes which produce photons that arrive at the PMT window. N 2 scintillation 2nd positive system ( nm)

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

M. Fraga, Prague, May 17th Am-241 source outside the chamber, exposed to air –For a constant , as the temperature is lowered, the energy loss outside the chamber increases: the mean energy,, with which the a particle enters the chamber is lower for lower temperatures; the length of the  track is also shorter for lower temperatures ;  y = 6 mm

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

M. Fraga, Prague, May 17th Monte Carlo simulation using GEANT4 code * Outside the chamber: air (273 K) air (273 K) Inside:  N 2 (336 hPa at 20ºC) = 46 mm N 2 (818 hPa at 20ºC)  = 22 mm P air < 0.1 torr Outside the chamber: P air < 0.1 torr Inside: Dry air (434 hPa at 20ºC) 5 events * Note: pressure effects on light yields are not included in the simulation

M. Fraga, Prague, May 17th Results of simulation: typical F (  factors with air at 1013 hPa outside the chamber Uncertainties in /  : < 2% - due to variations of atmospheric pressure < 1% - due temperature variations 818 hPa336 hPa dE/dx

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

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

M. Fraga, Prague, May 17th Dependence of Light Yield on Pressure, at room temperature Inverse of light yield versus pressure at room temperature (0-0 band at 337 nm) B/A = (5.8±1.4)×10 -3 hPa -1 k 20 /k 10 For T = constant,

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

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

M. Fraga, Prague, May 17th Fraction of the alpha particle energy, lost in the gas.  particle source in a low pressure environment. Correction factors : For P 20º = 243 hPa, (#coinc/s) Patm /(#coinc/s) low P = 1.26 ± 0.03 and Patm / low P = 1.16 ± 0.08

M. Fraga, Prague, May 17th Dry Air - N 2 + O 2 (80:20) Dry Air - N 2 + O 2 (80:20) (H 2 O < 3 ppm, C n H m < 0.5 ppm) O 2 – (20 ±1) %

M. Fraga, Prague, May 17th Further corrections: variation of the PMT gain with T m = (±0.008) #/ºC for  = 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 Study of the transmission of the IF Set-up : Data from Melles Griot

M. Fraga, Prague, May 17th Conclusions and plans for the future A coherent set of results were obtained under  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 they are underway). 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  particles (Sr-90) (already underway) will be carried out ;