A NEW AND PROMISING METHOD TO MEASURE ACCURATELYTHE FLUORESCENCE YIELD

Ph. Gorodetzky + APC team + LAL team + PHIL team

6th Air Fluorescence Workshop, LNGS, February 2009

OLD APC bench

G. Lefeuvre thesis

Y1 atm = 4.23 ± 0.21 ph/m integrated on [300-430 n]

+ spectrum

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

0° 10° 20° 30°

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337

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357 391

Phase 0 Phase 1

Energy (MeV) 6 10

Charge (nC) 0.1 3

rms bunch length (ps) 4 4

rms energy spread (%) 0.3 < 2 %

Normalized rmsemittance (mmmrad)

1 < 20

Ready in September 2009

PHIL @ LAL lab, on the Orsay campus, south of Paris (45 mn), France

Faraday

Accelerator

Thin window Thin window

AIR

SpectroJobin-Yvon

L?

Diameter D?

D and L ?

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

Fluo yield is proportional to the dE/dx deposit

(Belz @ SLAC in 2006)

Under 1 MeV, dE/dx deposit = dE/dx

d2N / dTdx, the number of produced with a kinetic energy T per unit length (MeV-1cm-1),

K = 4NAr2emec2 and is worth 0.307 MeV.cm2,

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 Tinc the kinetic energy of the primary electron.

This formula is valid for I << T < Tmax. 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. Tmax 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)

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/dxdelta

Number of deltas vs delta energy

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

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

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:

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

Range of deltas

P = 1 atm

With a radius of 7 cmOne can go to an altitude of 40 km

Integrating sphere basics

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

5 keV85 < < 90°

NIST photodiode or calibrated PMT

cos = (Te/pe)*(pmax/Tmax)

Where pmax ≈ pbeam/2

= (5.49 MeV/c if Tbeam = 10 MeV)

Tmax = Tbeam / 2

Baffles to be determined

Number of photons per second at the 337 nm linePrevious bench:- 5 106 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 = 54and we had 0.16 counts (pe) /s at the 337 top

With PHIL- 0.1 nC / sec @ 10 Hz = 1 nC/s = 6 109 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 = 300we 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?

BEAM WITH PHIL

Pulse width 4 ps = 1.2 mm

Pulse intensity: 6 108 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 6 108 = 3.6 108 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

ULRICH Munich

d = 2.3 g/cm3

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 nm1 nC @ 150 eV = 150 x 10-9 W = 0.15 µW

Question: diameter?

Precision

beam charge 2% (beam stable to better than 1% i

in 12 hours)

Light in JY 3%

Calibration JY:a) calib PMT in single pe 2%b) calib CCD / PMT 2%

Total: sqrt(4 + 9 + 4 + 4) = 4.6%(better than 5%)

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 H2O, then CH4

- H20: 1 month- CH4 1 month

- Change temperature (N2 excited states do not behave as a perfect gas)This requires to build a kind of "cryostat" around the sphereThe gas would be heated or cooled before entering the sphere

Needs a post-doc, and would make a nice thesis.

Open to participation

10 mn for 10000 counts in 337

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 mirror1) 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 (6 109 e- / sec)

CALIBRATION