Two Experimental Techniques Yielding Different Descriptions of Quenching

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1 Two Experimental Techniques Yielding Different Descriptions of Quenching a very personal view by Andreas Ulrich with real work done by: Thomas Dandl, Thomas Heindl, and Andrei Morozov * and a lot of help by Jochen Wieser ** Physik Department E12 Technische Universität München * University of Coimbra **Optimare Analytik GmbH & Co KG Air Fluorescence Workshop, Karlsruhe 2011 andreas.ulrich@ph.tum.de

2 Molecular Physics Communities Potential curves, energy levels, QM calculations, disentangle vibr. rot. spectra etc. Gas Kinetics Population and depopulation of levels, energy transfer, light emission, laser schemes etc. Particle and Astro- Particle Physics Energy loss in matter, particle tracks, particle identification, quenching factors etc. Air Fluorescence: A bit of all of these subjects!

3 Fluorescence of Nitrogen Molecules C B Effects of: A ik Lifetime Quenching by N 2, O 2, H 2 O etc. - Density Temperature Ground state

4 This picture leads to the following analysis of the fluorescence: Measurement of p using dc excitation I A R I p ik dn Rp Aik n k dt const. pumping rate const A ik n R p k q N q dn dt q N 0 q n I 0 A R ik I R p p 0 Aik kq N q 0 Just one quencher of density N q I I 0 1 kq N 1 A ik q 1 = ; p 1 p' p' I I A k ik q 1 p N q 1 k A q ik N q p N p p' const A k ik q

5 Measurement of quenching rate constants using pulsed excitation: After the pulse: dn dt t t 0 Aik n nkq N q n I n0 1 Aik k 1/τ q N q N q e A ik k p' const A ik k q q q N q A k t ik

6 However, N +* 2 N + 2 e - Ar* Energy transfer X C B cascades Recombination Quenching + chemistry + impurities Radiation trapping? A normally: 50% excitation 50% ionization N 2 O 2 NO N et al.

7 A complex gas kinetics is normally the case See rare gases:

8 172nm excimer light following a 2 ns ion beam excitation pulse This looks simple but it s not! G. Ribitzki et al, Phys. Rev. E 50,3973 (1994)

9 W. Krötz et al. Hyperfine Interactions (1994)

10 An extreme case: Recombination laser Diploma thesis C. Skrobol

11 This is, by far, too complicated for the air fluorescence data analysis? What can be done? We have to identify what is purely academic and irrelevant or relevant for our goal and focus on air instead of nitrogen?

12 So one has to identify relevant processes. My personal feeling at the moment: (based on some of the data described below) I think it is important to be aware how data were obtained! Excitation Nitrogen Air Individual particles Particle beam

13 b) Measurements with air should be more relevant than with pure nitrogen c) Recombination may be relevant d) Cascades may be important e) I would guess that Ar, N and NO are not important f) The p concept is conceptually wrong but may be ok as an approach in air g) Deviations between p and k q measurements reveal other mechanisms How can I dare to make such strong statements? Some observations:

14 70000 Intensity e-beam, 5µA Pure nitrogen, 800mbar Some information comes from emission spectrasee second presentation (nm)

15 nm NO Intensity 2000 Intensity (nm) (nm) N nm Gaydon Herman green (GHG) and Herman Infrared (HIR) Intensity Intensity nm (nm) (nm)

16 Extension into the VUV shows N I lines! (nitrogen spectrum)

17 Atomic nitrogen shows up in the VUV spectral range

18 Emission of the 337nm C-B transition from pure (?) nitrogen

19 Thomas Heindl L Aquila N 2 Absolute Fluorescence Efficiency ,1 Flourescence Efficiency * Y (3, ) 10 (90,4 6,2) MeV This work Davidson & O Neil Nagano et al. Khare & Kumar [theory] ; ; 434,8 380,4 326,1 271,7 217,4 163,0 108,7 54,3 0,0 Flourescence Yield Y [MeV -1 ] Pressure [hpa]

20 Thomas Heindl L Aquila Problem with Efficiency Data Fitting P Flourescence Efficiency * Data: Data1_B Model: Arfly1 11 Equation: y = P1/(1+x/P2) Weighting: 10 y No weighting p ~ 200 mbar Chi^2/DoF = R^2 = P ± P ± Pressure [hpa]

21 Correlation with lifetime and quenching data: p = 74.4 mbar???

22 Another test: 337nm emission intensity nitrogen vs. air Quenching rate constants of nitrogen and oxygen are involved!

23 Int. ratio nitrogen / air Ratio 337nm Int. N 2 to synt. air % 0-2,5 0,0 2,5 5,0 7,5 10,0 12,5 15,0 17,5 20,0 22,5 Concentration of O 2, H 2 (%) measured downwards measured upwards hydrogen 800 mbar pressure Impurity dependence of the intensity ratio of the 337nm line starting from pure nitrogen! Synthetic air = 1

24 How does the intensity ratio depend on p O 2 and p N 2?

25 Airfly Morozov Heindl

26 The ratio can be modeled with the p concept using different sets of p values for N 2 and O 2 quenching

27 Ratio of Intensity at 337nm Nitrogen to Air Messung vom Messung vom M.Ave et al. Dandl Airfly Pressure (mbar)

28 For the comparison of nitrogen and air the p concept fails there must be other important processes involved!! I suspect due to the factor of 2: Recombination!

29 1 Intensity 0,1 0,01 1E-3 This! 337nm line, 800mbar Nitrogen synth. Air 1E-4 preliminary 1E-6 1E-5 1E-4 1E-3 Time (s)

30 N 2 + e - Ar* Energy transfer X C B cascades Recombination Quenching + chemistry + impurities Radiation trapping? A normally: 50% excitation 50% ionization N 2 O 2 NO N et al.

31 Comment: Ar N 2 mixtures lead to 13x increase in (358nm) intensity So: going from air to Ar-N 2 means 16x13 ~ 200 x intensity increase!!!! With the same power deposition

32 Comment: how to study beam vs. single particle excitation

33 Conclusion: p is conceptionally wrong (but may be ok in air (O 2 )?) Transfer from nitrogen to air is probably too complicated for the air fluorescence data analysis. Oxygen quenching should be measured again. What type of excitation is an extended air shower??? How can p, T, humidity be included if not from first principles from nitrogen measurements??? Sorry for the long and somewhat smart-alecky presentation!

34 Happy End!!! Reading a draft of an AIRFLY paper this weekend Now, if I think I understand the problems and discrepancies I find a photon yield for air at 1000 hpa of ± 0.37 Phot. /MeV (from Y Heindl and r Dandl) Compared with the AIRFLY averaged value at 1013 hpa of 5.61 ± 0.06 Phot. /MeV

35 Thank you for your attention!

The air fluorescence yield. Fernando Arqueros Universidad Complutense de Madrid Spain

The air fluorescence yield. Fernando Arqueros Universidad Complutense de Madrid Spain The air fluorescence yield Fernando Arqueros Universidad Complutense de Madrid Spain XLIII rd Rencontres de Moriond: Electroweak Interactions and Unified Theories La Thuile, Aosta Valley, Italy. March