1. A NEW AND PROMISING METHOD TO MEASURE ACCURATELY THE FLUORESCENCE YIELD Ph. Gorodetzky + APC team + LAL team + PHIL team 6 th Air Fluorescence Workshop, LNGS, February 2009

2. OLD APC bench G. Lefeuvre thesis Y 1 atm = 4.23 ± 0.21 ph/m integrated on [300-430 n] + spectrum

3. Patented method to measure a PMT working in single photo-electron mode efficiency with a 1.8% accuracy

4. 0° 10°20°30° 337357 391

5. Phase 0Phase 1 Energy (MeV)610 Charge (nC)0.13 rms bunch length (ps)44 rms energy spread (%)0.3< 2 % Normalized rms emittance (  mmmrad)  1 < 20 Ready in September 2009 PHIL @ LAL lab, on the Orsay campus, south of Paris (45 mn), France

6. Faraday Accelerator Thin window AIR Spectro Jobin-Yvon L? Diameter D? D and L ?

7. We bought a new Jobin Yvon Spectrometer equipped with a LN2 cooled CCD (1024 x 256) with an image intensifier (1 background / pixel / hour). It allows the full [300 - 400 nm] range in one shot with a 0.1 nm resolution It has a movable mirror for a slit output (calibrated PMT) It has a fiber adaptor to send the light through fibers

8. Fluo yield is proportional to the dE/dx deposit (Belz @ SLAC in 2006) Under 1 MeV, dE/dx deposit = dE/dx

9. d 2 N / dTdx, the number of produced  with a kinetic energy T per unit length (MeV -1  cm -1 ), K = 4  N A r 2 e m e c 2 and is worth 0.307 MeV.cm 2, Z = 7.4, average atomic number of the gas (here, dry air without argon), A = 14.28 g.mol -1, average atomic mass of the gas, T, kinetic energy of the electron ejected (MeV) for indistinguishable particles, with T inc the kinetic energy of the primary electron. This formula is valid for I << T < T max. I is the average excitation energy of the medium, (85.7 eV for air). When T is close to I, the electron is emitted with a kinetic energy insufficient to move away from the molecule and is captured again: the formula is valid from T  1 keV. T max is the maximum energy transferable from the incident particle to the ejected . It is equal to half of incident kinetic energy (interaction of two electrons) (Particle Data Booklet)

10. PROBLEM When a delta is produced, and makes a fluorescence photon, it is part of the dE/dx - If the photon from the delta is seen by the photon counter, OK - If the photon from the delta is hidden to the photodetector, then one misses a photon and the yield is underestimated. This is why when the situation is complicated, one relies on MC. (Fluorescence photons) delta = number of created deltas x dE/dx delta

11. Number of deltas vs delta energy

12. SP is the de/dx, here for pure air at 1 atm, 20°C

13. Blow-up of the low energy part, extrapolated to E close to 0

14. Product of "number of deltas" x dE/dx, extrapolated to 0 delta energy If now we take the integral of this curve, point per point: see next slide:

15. Taking the integral of this curve to be 100%, lets look at how many % each point is: ==>

17. Range of deltas P = 1 atm

18. With a radius of 7 cm One can go to an altitude of 40 km

19. Integrating sphere basics http://www.labsphere.com/data/userFiles/A%20Guide%20to%20Integrating%20Sphere%20Theory&Apps.pdf

20. 5 keV 85 <  < 90° NIST photodiode or calibrated PMT cos  = (T e /p e )*(p max /T max ) Where p max ≈ p beam /2 = (5.49 MeV/c if T beam = 10 MeV) T max = T beam / 2 Baffles to be determined

21. Number of photons per second at the 337 nm line Previous bench: - 5 10 6 e/sec - 4 cm path - eff géom: 9 10 -5 (  = 4.6 cm @ 122 cm) - eff spectro 15% - eff PMT 20% - yield proportional to product = 54 and we had 0.16 counts (pe) /s at the 337 top With PHIL - 0.1 nC / sec @ 10 Hz = 1 nC/s = 6 10 9 e / sec - 14 cm path if 20 cm sphere - eff géom: 5 10 -7 (10 x  = 0.1 mm @ 100-110 mm) - eff spectro 60% - eff CCD 60% - yield proportional to product = 15000 ==> GAIN = 300 we will have 45 counts (electrons) / s at 337 top Resolution was  = 3 nm 3 weeks 10 fibers of 100 µm (1.1 x 0.1 mm); good resolution It will now be  = 0.12 nm (see next slide) A few minutes for the full spectrum Lower beam intensity?

23. BEAM WITH PHIL Pulse width 4 ps = 1.2 mm Pulse intensity:6 10 8 e/sec The little pulse of 1.2 mm travels in the 14 cm of the sphere ==> 500 ps = 0.5 ns. More comfortable. If 4 photons per meter, then 0.6 x 6 10 8 = 3.6 10 8 photons emitted in the sphere However, solid angle efficiency of one fiber x effficiency spectrometer x efficiency CCD = 4 10 -7 ==> in one pulse (one packet of electrons passing the sphere) we will detect 15 pe in = [300 - 400] nm However, the 337 nm line is about 25% of all light: 4 pe in a pulse. Spectro resolution (  ) = 0.12 nm. If 1000 pixels for 100 nm ==> 0.1 nm / pixel ==> 2 pixels ==> 2 pe per pulse per pixel (Max pe / pixel about 300 - 400 kilo pe) CCD externally triggered: < 40 Hz OK with 10 Hz

24. ULRICH Munich d = 2.3 g/cm 3 10 keV : 20 X 2.3 = 46 MeV/cm 1.5 keV/ 300 nm 10 MeV 2 x 2.3 = 4.6 MeV/cm = 150 eV / 300 nm 1 nC @ 150 eV = 150 x 10 -9 W = 0.15 µW Question: diameter?

25. Precision beam charge 2% (beam stable to better than 1% i in 12 hours) Light in JY3% Calibration JY: a) calib PMT in single pe 2% b) calib CCD / PMT2% Total: sqrt(4 + 9 + 4 + 4) = 4.6% (better than 5%)

26. PROGRAM - Set-up and calibration : one year from January 2009 to December 2009 - Get the yield of each line for all pressures from 1 to 0.01 atm (less than a week) - Add different pollutants, and start with H 2 O, then CH 4 - H 2 0: 1 month - CH 4 1 month - Change temperature (N 2 excited states do not behave as a perfect gas) This requires to build a kind of "cryostat" around the sphere The gas would be heated or cooled before entering the sphere Needs a post-doc, and would make a nice thesis. Open to participation

27. 10 mn for 10000 counts in 337

28. 1)Calibrate a PMT using our previous method with 2 integrating spheres ==> precision = 1.8% 2)Put this PMT on the spectro output with a slit, using the inside mirror. The slit has to be adjusted to the CCD resolution (26 µm for 1 pixel) 1)Send light in the big sphere: for instance, replace electron beam with a clear 1mm fiber, unpolished, lighted with LEDs of the correct lambdas. (or put a LED anywhere in the sphere) We see here that we NEED an extra port for a NIST (or a calibrated PMT) to control the amount of light. 4)Measure the response with the calibrated PMT. This calibrates the spectrometer. 5)Switch to CCD, rotating the mirror 6)Compare: everything is calibrated (big sphere, fibers, spectro, CCD) In this method, we just created a NIST PMT working in single pe with a  of 1.8% instead of a photodiode which has a  of 1.5%, but needs 1 nA (6 10 9 e - / sec) CALIBRATION