Characterization of CFCharacterization of CF44 primary primary

scintillationscintillation

Andrey Morozov

What, why and how?What, why and how?

Light emission and photon yield

Effect of applied electric field

Effect of He admixture

Quenching effects (gas aging)

Spectral studies Photon flux measurements

Time resolved measurements

CF4 primary scintillation:

Spectral studiesSpectral studies

Spectral studies: SetupSpectral studies: Setup

MonochromatorPMT

Am-241α-source

Al reflectorR=0.80 ± 0.08

Excitation volume

Quartz window

Grid (0 – 6 kV)

Second order filter

Photon counting

CF4

CFCF44 primary scintillation: Raw spectra primary scintillation: Raw spectra

!Spectra have to be

corrected for:

1) Response of the monochromator and PMT

2) Geometrical factor of the detection

3) Gas aging

Monochromator+PMT response measurementsMonochromator+PMT response measurements

MonochromatorPMT

ES: Entrance slitIF: Optional interference filtersL: LensNF: Neutral filter(s)D: Diaphragm

Tungstenstrip lamp(1900 K)450 – 850 nm

Tungstenhalogen lamp400 – 850 nm

Deuterium lamp200 – 400 nm

ES IF L

NF

D

Spectra corrected for the instrumental responseSpectra corrected for the instrumental response

Spectra from different pressuresare not to scale!

200 300 400 500 600 700 8000.0

0.1

0.2

0.3

0.3

0.4

0.5

0.6

0.7

0.8

0.8

0.9

1.0

Inte

nsity

, a.u

.

Wavelength, nm

0.5 bar 1 bar 2 bar 3 bar 4 bar 5 bar

Need directphoton fluxmeasurements

Absolute photon flux measurementsAbsolute photon flux measurements

Absolute photon flux measurements: setupAbsolute photon flux measurements: setup

PMT

Extension tubes:PMT-to-source distanceis adjustablefrom 80 to 300 mm

Broad band filter (UV or visible)

Light source is ahalf-sphere, radius:~3 mm at 5 bar~13 mm at 1 bar~26 mm at 0.5 bar

Optional interference filter

Extensiontubes

At the limitgiven by the cellgeometry!

Point-light-source approximation:

If valid, no numerical simulations (unknown error bars!) are needed.

Photon fluxes:FOBSERVED ∞ NSOURCE / R2

then FOBSERVED∙R2 should be constant!

Flux vs. PMT-to-source distanceFlux vs. PMT-to-source distance

RLight sourceDetector

Flux vs. PMT-to-source distanceFlux vs. PMT-to-source distance

PMT can “see” the whole light emitting volume!

VISIBLE componentUV component

80 120 160 200 240 2800.00

0.02

0.04

0.06

0.08

0.10

0.12

Fig.2

5 bar4 bar

3 bar

2 bar

1 bar

Cou

nt_r

ate

x R2 , 1

09 m

m2 /s

R, mm

80 120 160 200 240 2800.0

0.5

1.0

1.5

2.0

2.5

3.0

5 bar

2 bar

3 bar

4 bar

1 bar

Cou

nt_r

ate*

R2 , 1

07 m

m2 /s

R, mm

Flux vs. PMT-to-source distanceFlux vs. PMT-to-source distanceMissing double-event photoelectrons are taken into account!

VISIBLE componentUV component

Point source approximation is definitely valid for R > 140 mm for all pressures! No scattering!

80 120 160 200 240 2800.0

0.5

1.0

1.5

2.0

2.5

3.0

5 bar

2 bar

3 bar

4 bar

1 bar

Cou

nt_r

ate*

R2 , 1

07 m

m2 /s

R, mm80 120 160 200 240 280

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Fig.2

5 bar4 bar

3 bar

2 bar

1 bar

21%

16%

8%

10%Cou

nt_r

ate

x R2 , 1

09 m

m2 /s

R, mm

30%

6%

12%

Fluxes for the UV and VIS componentsFluxes for the UV and VIS components

Two lines of fluxmeasurements:

Using broad-band filters andinterference filters.

Photon detection probability vs. wavelength?

XP2020QR1387

PMT

Halogen or deuterium lamp

Neutral filters

Optical beam-line (2 m long) with diaphragms

Interference filter

Photon detection probabilityPhoton detection probability

Interference filters:

200 300 400 500 600 700 8000.0

0.5

1.0

Relative detection probabilitiesRelative detection probabilitiesUV component

PMT: Photonis XP2020Q

Visible component

PMT: Hamamatsu R1387

Max uncertainties (main contributors: the filters and lamps):

25% 35%

CFCF44 emission spectra emission spectra

(all corrections are applied)(all corrections are applied)

Flux measurements have been used to scale the spectra from different pressures

200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

Pho

ton

flux

, a.u

.

Wavelength, nm

1 bar 2 bar 3 bar 4 bar 5 bar

Fig.1

Photon yieldPhoton yield

Photon yield calculationPhoton yield calculation

Y = Number_of_photons / (α-Rate ∙ Average_Energy)

From photon flux

measurements

Number of α-particles entering the gas per second multiplied by the average deposited energy

Photon yield: Number of photons (in 4π) produced per MeV of energy deposited in the gas.

Photon yield (Photon yield (UVUV component, integrated) component, integrated)

Uncertainties

Broadband:

16% sum in quadrature

(40% sum)

IF-300 nm:

21% sum in quadrature

(55% sum)0 1 2 3 4 50

500

1000

1500

2000

2500

3000

Fig.3

Broadband (UG11) IF (300nm)

Pho

ton

yiel

d, p

h/M

eV

Pressure, bar

Photon yield (Photon yield (visiblevisible component, integrated) component, integrated)

Uncertainties

Broadband:

19% sum in quadrature

(50% sum)

IF-300 nm:

5 → 1bar:

26% → 72% sum in quadrature

(67% → 120% sum)

0 1 2 3 4 50

1000

2000

3000

4000

5000

6000

7000

Fig.4

Broadband (UV-block) IF (610nm)

Pho

ton

yiel

d, p

h/M

eV

Pressure, bar

Photon yield: cross-checkPhoton yield: cross-check

P

bar

Yield ratios

UV / vis

Spectral ratios

UV / vis

1 2.8 ± 1.0 ~2.5 ± 0.8

2 0.70 ± 0.25 0.76 ± 0.15

3 0.34 ± 0.12 0.50 ± 0.10

4 0.22 ± 0.08 0.35 ± 0.07

5 0.17 ± 0.06 0.23 ± 0.05

The ratios of yields in the UV and visible are comparedwith the flux ratios from the calibrated emission spectra

Overlap! 200 300 400 500 600 700 800

0.0

0.5

1.0

Time spectraTime spectra

Time spectra: setupTime spectra: setup

PMT

Optical filter

Silicon detector(PIPS Canberra)

0 – 300 V

Photon: “Stop”

α-particle: “Start”

Alpha source (Ortec)

Electronics:Start and stop → fast preamps → CF triggers → Time-to-amplitude converter → Multi-channel analyzer

Time spectra: UV componentTime spectra: UV component

Two distinctive decay structures (both ? exponential)

Indications of a very weak non-exponential tail

Weak pressure dependence

Time spectra: Visible componentTime spectra: Visible component

Strongly non-exponential decay

Very likely there is a strong contribution from recombination Clear pressure dependence

Effect of the electric fieldEffect of the electric field

Electric field: SpectraElectric field: Spectra

No effect for low pressures!

For medium-high pressures:Very strong reduction of the visible component and an increase of the UVcomponent with the field!

At 5 bar:Strong reshaping of the UVcomponent with the field!

Electric field: UV componentElectric field: UV component

1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

Inte

grat

ed p

hoto

n flu

x, a

.u.

Pressure, bar

220-500 nmrange 0 V/cm 370 V/cm 560 V/cm 1100 V/cm 2200 V/cm

Electric field: Visible componentElectric field: Visible component

1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

Inte

grat

ed p

hoto

n flu

x, a

.u.

Pressure, bar

500-800 nm range 0 V/cm 75 V/cm 280 V/cm 560 V/cm 1900 V/cm

Electric field: Electric field: Time spectra of the UV componentTime spectra of the UV component

Very small difference!

E-field dependence: Visible componentE-field dependence: Visible component

0 20 40 60 80 100 120 1401

10

100

1000 3 bar 0 kV/cm 0.5 kV/cm 3 kV/cm

Cou

nts

Time, ns

Very different behavior at high and low pressures!

0 20 40 60 80 100 120 140

10

100

1000 1 bar 0 kV/cm 1 kV/cm

Cou

nts

Time, ns

3 bar 1 bar

E-field dependence: Why UV and visibleE-field dependence: Why UV and visible behave differently? behave differently?

CF3+

CF4+

Recombination UV emission

CF3*Direct excitation

QuenchingVisible emission

Electric field suppressesrecombination UV emissionbenefit from thatwhilevisible emissionshould be reduced

Effect of helium: spectra and flux measurementsEffect of helium: spectra and flux measurements

Visible component(pressures are in bar)

3 CF4 + 2 He: same as 3 CF4

2 CF4 + 3 He: same as 2 CF4

1 CF4 + 4 He: same as 1 CF4

UV component(pressures are in bar)

3 CF4 + 2 He: same as 3 CF4

2 CF4 + 3 He: 20% higher than 2 CF4

1 CF4 + 4 He: 40% higher than 1 CF4

Absolute flux measurements:

Gas aging studies: Time spectraGas aging studies: Time spectra

UV component Visible component

Both components show significant aging!

NN22 quenching quenching

UV component

No effect!

Visible component

Strong effect!

Visible component is strongly affected by nitrogen admixtures!Bad news, since CF4 purifiers (effective) do not remove nitrogen.

Thank you!