Characterization of CF4 primary
scintillation
Andrey Morozov
What, why and how?
Spectral studies
Photon flux
measurements
CF4 primary scintillation:
Light emission and photon yield
Effect of applied electric field
Effect of He admixture
Quenching effects (gas aging)
Time resolved
measurements
Spectral studies
Spectral studies: Setup
Quartz window
Second order filter
CF4
PMT
Monochromator
Am-241
α-source
Photon counting
Al reflector
R=0.80 ± 0.08
Grid (0 – 6 kV)
Excitation volume
CF4 primary scintillation: Raw spectra
6000
!
1bar
3bar
5bar
5000
Spectra have to be
corrected for:
Counts
4000
1) Response of the
monochromator
and PMT
3000
2000
2) Geometrical
factor of the
detection
1000
0
200
300
400
500
Wavelength, nm
600
700
800
3) Gas aging
Monochromator+PMT response measurements
ES
IF L D
Tungsten
strip lamp
(1900 K)
450 – 850 nm
PMT
Tungsten
halogen lamp
400 – 850 nm
Monochromator
ES: Entrance slit
IF: Optional interference filters
L: Lens
NF: Neutral filter(s)
D: Diaphragm
Deuterium lamp
200 – 400 nm
NF
Spectra corrected for the instrumental response
1.0
0.5 bar
1 bar
2 bar
3 bar
4 bar
5 bar
0.9
0.8
Intensity, a.u.
0.8
0.7
0.6
Spectra from
different pressures
are not to scale!
0.5
0.4
0.3
0.3
0.2
0.1
0.0
200
300
400
500
Wavelength, nm
600
700
800
Need direct
photon flux
measurements
Absolute photon flux measurements
Absolute photon flux measurements: setup
Extension tubes:
PMT-to-source distance
is adjustable
from 80 to 300 mm
Extension
tubes
PMT
Optional interference filter
Broad band filter (UV or visible)
Light source is a
half-sphere, radius:
~3 mm at 5 bar
~13 mm at 1 bar
~26 mm at 0.5 bar
At the limit
given by the cell
geometry!
Flux vs. PMT-to-source distance
Point-light-source approximation:
If valid, no numerical simulations (unknown error bars!) are needed.
Detector
R
Light source
Photon fluxes:
FOBSERVED ∞ NSOURCE / R2
then
FOBSERVED∙R2 should be constant!
Flux vs. PMT-to-source distance
UV component
3.0
0.12
1 bar
5 bar
4 bar
2 bar
0.06
3 bar
0.04
4 bar
5 bar
2
0.08
Count_rate*R, 10 mm /s
2
2.5
0.10
9
2.0
3 bar
7
2
0.02
2
Count_ratex R , 10 mm /s
VISIBLE component
1.5
2 bar
1.0
1 bar
0.5
0.0
0.00
80
120
160
200
240
280
80
120
160
R, mm
Fig.2
PMT can “see” the whole light emitting volume!
200
R, mm
240
280
Flux vs. PMT-to-source distance
Missing double-event photoelectrons are taken into account!
UV component
VISIBLE component
3.0
1 bar
0.08
5 bar
4 bar
2.5
30%
0.06
2 bar
21%
3 bar
16%
4 bar
5 bar
0.04
12%
0.02
2.0
3 bar
7
6%
10%
2
2
2
0.10
Count_rate*R, 10 mm /s
2
8%
9
Count_ratex R , 10 mm /s
0.12
1.5
2 bar
1.0
1 bar
0.5
0.0
0.00
80
120
160
200
240
280
R, mm
80
120
160
200
240
R, mm
Fig.2
Point source approximation is definitely valid
for R > 140 mm for all pressures!
No scattering!
280
Fluxes for the UV and VIS components
1.0
Two lines of flux
measurements:
UV-block
CF4 3bar
UG11
Filter transmission/
Photon flux
0.8
Using
broad-band filters
and
interference filters.
0.6
0.4
IF-610
0.2
0.0
200
IF-300
300
400
500
600
700
800
Photon detection
probability vs.
wavelength?
Wavelength, nm
XP2020Q
R1387
Photon detection probability
Optical beam-line (2 m long) with diaphragms
PMT
Neutral filters
Interference filter
Halogen or deuterium lamp
1.0
0.5
0.0
200
Interference filters:
300
400
500
600
700
800
Relative detection probabilities
UV component
Visible component
PMT: Photonis XP2020Q
PMT: Hamamatsu R1387
D2 (10%+10%)
D2 (10%+10%)
D2 (1%)
Halogen (1% + 10%)
QE(manufacturer)
QE(published in IEEE)
DP approximation
FluxCF4-3bar-UG11
0.27
Detection probability
0.24
0.21
0.18
0.15
0.12
0.09
0.11
Halogen
Halogen, higher treshold
QE*0.4 (manufacturer data)
DP approximation
Photon flux from CF4 (3bar, UV_block)
0.10
0.09
Detection probability
0.30
0.08
0.07
0.06
0.05
0.04
0.03
0.06
0.02
0.03
0.01
0.00
0.00
250
300
350
400
450
Wavelength, nm
500
550
600
400
500
600
Wavelength, nm
Max uncertainties (main contributors: the filters and lamps):
25%
35%
700
800
CF4 emission spectra
(all corrections are applied)
1.0
1 bar
2 bar
3 bar
4 bar
5 bar
Flux measurements
have been used to
scale the spectra
from different
pressures
Photon flux, a.u.
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
Wavelength, nm
Fig.1
700
800
Photon yield
Photon yield calculation
Photon yield: Number of photons (in 4π) produced per MeV
of energy deposited in the gas.
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 (UV component, integrated)
3000
Uncertainties
Broadband (UG11)
IF (300nm)
Photon yield, ph/MeV
2500
Broadband:
16% sum in
quadrature
(40% sum)
2000
1500
1000
500
0
0
1
2
3
Pressure, bar
Fig.3
4
5
IF-300 nm:
21% sum in
quadrature
(55% sum)
Photon yield (visible component, integrated)
Uncertainties
7000
6000
Photon yield, ph/MeV
Broadband:
19% sum in
quadrature
(50% sum)
Broadband (UV-block)
IF (610nm)
5000
4000
IF-300 nm:
5 → 1bar:
3000
2000
1000
0
0
1
2
3
Pressure, bar
Fig.4
4
5
26% → 72%
sum in
quadrature
(67% →
120% sum)
Photon yield: cross-check
The ratios of yields in the UV and visible are compared
with the flux ratios from the calibrated emission spectra
P
bar
1
Yield ratios
UV / vis
2.8 ± 1.0
Spectral ratios
UV / vis
~2.5 ± 0.8
2
3
4
0.70 ± 0.25
0.34 ± 0.12
0.22 ± 0.08
0.76 ± 0.15
0.50 ± 0.10
0.35 ± 0.07
5
0.17 ± 0.06
0.23 ± 0.05
1.0
0.5
Overlap!
0.0
200
300
400
500
600
700
800
Time spectra
Time spectra: setup
α-particle:
“Start”
Photon:
“Stop”
PMT
Silicon detector
(PIPS Canberra)
Alpha source (Ortec)
Optical filter
0 – 300 V
Electronics:
Start and stop → fast preamps → CF triggers →
Time-to-amplitude converter → Multi-channel analyzer
Time spectra: UV component
UV component (XP2020Q + UG11)
1000
Counts (0.5ns bin)
Two distinctive
decay structures
(both ? exponential)
0.5bar
3bar
100
0
5
10
15
20
25
Indications
of a very weak
non-exponential
tail
10
Weak pressure
dependence
0.5bar
1bar
3bar
1
0
10
20
30
40
50
60
70
Time, ns
80
90
100 110 120 130
Time spectra: Visible component
Visible component (UV block filter)
Counts (0.5 ns bins)
1000
3bar 0 V/cm
2bar 0 V/cm
1bar 0V/cm
Strongly
non-exponential
decay
Very likely
there is a strong
contribution from
recombination
100
10
Clear pressure
dependence
1
0
20
40
60
80
Time, ns
100
120
140
Effect of the electric field
Photon yield, ph/MeV/nm Photon yield, ph/MeV/nm
Photon yield, ph/MeV/nm
Electric field: Spectra
30
1 bar,
no effect of the field
20
No effect for low pressures!
10
0
200
300
30
400
500
600
700
800
3 bar, 0 kV/cm
3 bar, 2 kV/cm
20
10
0
200
300
400
500
600
700
800
For medium-high pressures:
Very strong reduction of the
visible component and an
increase of the UV
component with the field!
30
5 bar, 0 kV/cm
5 bar, 2 kV/cm
20
10
0
200
300
400
500
Wavelength, nm
600
700
800
At 5 bar:
Strong reshaping of the UV
component with the field!
Electric field: UV component
Integrated photon flux, a.u.
1.0
0.8
0.6
0.4
0.2
220-500 nmrange
0 V/cm
370 V/cm
560 V/cm
1100 V/cm
2200 V/cm
0.0
1
2
3
Pressure, bar
4
5
Electric field: Visible component
Integrated photon flux, a.u.
1.0
0.8
500-800 nm range
0 V/cm
75 V/cm
280 V/cm
560 V/cm
1900 V/cm
0.6
0.4
0.2
0.0
1
2
3
Pressure, bar
4
5
Electric field:
Time spectra of the UV component
UV component (UG11 filter)
UV 3ar 0kV/cm
UV 3bar 4kV/cm
1000
Very small
difference!
Counts
100
10
1
0
20
40
60
80
Time, ns
100
120
140
E-field dependence: Visible component
1000
3 bar
1000
1 bar
0 kV/cm
0.5 kV/cm
3 kV/cm
0 kV/cm
1 kV/cm
100
Counts
Counts
100
10
10
1 bar
3 bar
1
0
20
40
60
80
Time, ns
100
120
140
0
20
40
60
80
Time, ns
Very different behavior at high and low pressures!
100
120
140
E-field dependence: Why UV and visible
behave differently?
CF4+
Recombination
Direct excitation
Quenching
CF3+
UV emission
CF3*
Visible emission
Electric field
suppresses
recombination
UV emission
benefit from that
while
visible emission
should be reduced
Effect of helium: spectra and flux measurements
1.0
1.00
CF4-3bar
CF4-3bar + He-2bar
CF4-1bar + He-4bar
CF4-1bar
0.8
Photon flux, a.u.
Photon flux, a.u.
0.80
0.60
0.40
0.5
0.3
0.20
0.00
200
300
400
500
600
700
800
0.0
200
250
Wavelength, nm
300
350
400
450
Wavelength, nm
Absolute flux measurements:
UV component
(pressures are in bar)
3 CF4 + 2 He:
same as
Visible component
(pressures are in bar)
3 CF4
3 CF4 + 2 He: same as 3 CF4
2 CF4 + 3 He: 20% higher than 2 CF4
2 CF4 + 3 He: same as 2 CF4
1 CF4 + 4 He: 40% higher than 1 CF4
1 CF4 + 4 He: same as 1 CF4
500
Gas aging studies: Time spectra
UV
component
UV component, aging overnigt (~16 hours)
CF4 3 bar
Fresh
After 20h
CF4 3 bar
Fresh
Recorded over 20h
Recorded after 70h
1000
Counts (0.5 ns bin)
1000
Counts (0.5ns bins)
Visible
component
Visible component, 3 days agingtest
100
10
100
10
1
1
0
10
20
30
40
50
60
70
80
0
25
50
Time, ns
Both components show significant aging!
75
Time, ns
100
125
150
N2 quenching
Visible component
UV component
UV component, N2 quenching test
1bar
1bar CF4 + 16mbar N2
1bar CF4 + 32mbar N2
1000
100
~15 ns
1000
Counts (0.5 ns bins)
10000
Counts (0.5 nm bins)
Visible component, N2 quenching tests
3bar CF4 pure
3bar CF4 + 16mbar N2
3bar CF4 + 32mbar N2
100
~6 ns
10
10
1
1
0
10
20
30
Time, ns
No effect!
40
50
60
0
20
40
60
Time, ns
Strong effect!
Visible component is strongly affected by nitrogen admixtures!
Bad news, since CF4 purifiers (effective) do not remove nitrogen.
80
100
120
Thank you!