Download light1Santos

Filomena P. Santos,
C. A. N. Conde, A. D. Stauffer, T. H. V. T. Dias, F. I. G. M. Borges, J. M. Escada, S. J. C. do Carmo,
A. M. F. Trindade, A. N. Garcia, P. J. B. M. Rachinhas
LIP Coimbra - Portugal
ANT2013 - Sunnyside-Tahoe City 10-12 May 2013
1
2-0v
2-2v
decays
decays
Rate
No backgrounds
above Q-value
Energy
Q value
Neutrinos are puzzling elementary particle with unique properties:
very low (but non-zero) mass
may be identical to its own anti-particle
no charge
(LQN violation)
Two neutrinos are emitted in standard double beta decay (2-2)
( A, Z )  ( A, Z  2)  2e -  2 e
already observed for 11 isotopes (from the 35 allowed) with T1/2 from 1018 to 1021 yr).
If neutrino is its own anti-particle, a neutrinoless version (2-0) may occur,
a most sensitive method to assess neutrino nature and mass.
Experimental signature of 2-0 is a line at Q
2
NEXT – Neutrino Experiment with a Xenon TPC
Very promissing experiment under development:
Expected energy resolution R ≤ 1% FWHM @ Q (~2.460 MeV)
Background reduction from event topology (2 blobs at the ends)
ELECTROLUMINESCENCE
layer
Readout plane
- energy (PMT)
TPC
HP Xe – gas detection medium
proportional scintillation - amplification mechanism.
Readout plane
- Position (SiPM)
3
Why HP Xe?
Why proportional scintillation?
Several experiments (different detection media and techniques) currently search for 2-0.
A sole claim (from Heidelberg-Moscow group) is still unconfirmed
Xe gas
• detection medium and source (136Xe isotope)
•136Xe enrichment easy and inexpensive
• 136Xe is the only long-lived Xe isotope
• very good energy resolution
• efficient background rejection from event topology
HP Xe
• scalable, pressure/size
•better energy resolution than LXe
• easier handling/purification procedures
Proportional Scintillation
• much lower fluctuations than charge multiplication.
4
Noble gas scintillation
 Excimer formation and decay:
e-  X  X *  e-
X* (
X *  2 X  X 2*  X
X 2* ( 1  u ,1  u );
X 2*  2 X  h
3
P1 , 3 P2 )
(VUV scintillation)
5
Noble gas scintillation - from recombination
Radiative recombination:
e-  X  X   2eX   X  X 2
X 2  e-  X **  X
electron impact ionization
dimer ion formation
recombination
X **  X *  heat
X *  2 X  X 2*  X
X 2*  2 X  h
excimer decay / scintillation
6
Xe emission continua
Two VUV continua:
•1st continuum (peaked at ~150 nm)
from vibrationally excited molecular states,
disappears at few hundred Torr
•2nd continuum (peaked at ~170 nm)
from vibrationally relaxed molecular states
7
Gas Proportional Scintillation Counter - GPSC
photon
n primary
electrons
detection medium
drift region
proportional
scintillation
scintillation
region
photomultiplier
tube
Amplification stage: scintillation produced in the deexcitation of electron
impact excited atoms of the medium
8
Xenon scintillation in GPSC/TPC
 Two types of scintillation
 Primary scintillation,
electric field independent
 Secondary/proportional scintillation - Electroluminescence,
@ reduced electric field E/P from 1 to ~6 V cm-1 Torr-1
Proportional* scintillation, also called ELECTROLUMINESCENCE (EL)
is produced while electrons drift for a distance D under an uniform electric field
which allows excitation but not ionization of the gas atoms.
*proportional to
number of e-,
drift distance D
(also ~ to electric field).
9
Primary scintillation
Source - when/why?
Xe excitation by electron impact in the detector absorption region;
recombination.
Amplitude
Weaker than secondary scintillation (EL) because
ionization wins over excitation above ionization threshold;
solid angle is smaller for primary scintillation detection than for EL
10
Experimental w-value for primary scintillation
Average energy to produce a primary scintillation photon
ws=111  16 eV
5.9 keV x-rays in Xe
measured from primary pulse
(we-~22 eV )
GPSC, ~1 atm.
Primary pulse:
- measured by triggering the
osciloscope with EL pulse
at low threshold;
- averaged over 128 pulses.
primary
secondary
The technique averages out
noise level to ~zero.
Experimental pulse shapes
(note different scales).
11
Electroluminescence (EL)
 EL is produced under appropriate uniform electric field
 Field is such that electrons excite, but do not ionize,
the atoms of detector gas filling.
 EL efficiency very high in noble gases.
 High purity noble gas required.
12
Electroluminescence in pure xenon
Reduced EL yield (photons electron-1cm-1Torr-1)
Monte Carlo simulation and experimental results
Excitation & EL efficiencies
Monte Carlo simulation
Q exc
QEL
F.P.Santos et al., J. Phys. D 27(1994)42.
Y/p (cm-1Torr-1)= - 0.1325 + 0.1389 E/p p(Torr), E/p (Vcm-1Torr-1)
Y/N(10-17 cm2) = - 0.4020 + 0.1389 E/N N(cm-3), E/N (Td)
C.M.B.Monteiro et al., JINST 2(2007)P05001.
Y/N (10-17 cm2) = - 0.474 + 0.140 E/N
A. Bolozdynya et al, NIM A 385 (1997) 225
Y/p (cm-1 bar-1)= 70*(E/p-1) p(bar), E/p(kV cm-1, bar-1),
13
Electroluminescence simulation – Monte Carlo flowchart
n. of electrons
gas density
electric field
Electron from sample
energy
Initial direction
Initial position
Electron path
final direction
final position
final energy
time 
Elapsed time 
Next electron
No more
electrons
Electron from
sample
No more electrons
in sample
null
Drift and scintillation parameters
Collision type
End of simulation
excitation
Scattered electron
energy
direction
Count number
of excitations
Real collision
elastic
Scattered
electron
energy
Direction
ionization
Secondary electron
energy
direction
position
time
Scattered electron
energy
direction
14
Why EL efficiency is high in Xe
1000
100
cross sections (10-16 cm2)
elastic
10
total
1
0.1
exc
0.01
0.001
0.01
0.1
1
10
Electron energy (eV)
ion
100
1000
10000
Absence of inelastic energy losses for electrons below electronic excitation threshold;
ionization and excitation thresholds are well separated.
15
Electrons in Xe
Xe
8.32 eV
E/p = 5 Vcm-1Torr-1
(E/N = 15 Td).
Energy of one electron drifting across EL region.
Arrows indicate Xe electronic excitation collisions.
16
EL amplification
high gain:
a single primary electron produces ~ 500 EL VUV photons in Xe
along D=1 cm EL region at ~1 atm. and E/p ~ 5 V cm-1Torr-1,
low fluctuation:
GPSC energy resolution approaches intrinsic limit
H
n = number of primary e- per absorbed event
H - number of EL photons per electron
2
F =  / n (Fano factor) relative variance in n
J= 2 / H - relative variance in H
17
Pure xenon / xenon mixtures
Xenon
• Best energy resolution,
• low drift velocities
• high diffusion coefficients
These may be severe drawbacks
in high dimension detectors when tracking capabilities required.
Molecular additives may be a solution
• to increase drift velocities
• to decrease diffusion coefficients
• BUT EL yield is reduced
and fluctuations increased
The best balance will determine the choice of additive
Candidates are CH4, CF4, TMA…
18
Electron scattering cross sections in Xe and CH4
exc
ion
19
Electron energy in Xe and Xe-0.5%CH4
Xe
Xe-0.5%CH4
8.32 eV
E/p = 5 Vcm-1Torr-1
(E/N = 15 Td).
Energy of one electron drifting across EL region.
Arrows indicate Xe electronic excitation collisions.
20
Electron scattering cross sections in Xe and CF4
21
Electron energy in Xe and Xe-0.5%CF4
Xe
Xe-0.5%CF4
8.32 eV
E/p = 5 Vcm-1Torr-1
(E/N = 15 Td).
Energy of one electron drifting across EL region.
Arrows indicate Xe electronic excitation collisions.
22
Mean electron energy and excitation efficiency
Monte Carlo
Gas medium
em
Qexc
Xe
3.715
92.0%
Xe-0.1%CH4
3.7
87.5%
em
Xe-0.5%CH4
3.65
74.0%
Qexc excitation efficiency
Xe-1%CH4
3.575
58.1%
Xe-10%CH4
2.498
0.1%
Xe-0.1%CF4
3.723
80.3%
Xe-0.5%CF4
3.717
45.6%
Xe-1%CF4
3.648
20.8%
Xe-10%CF4
2.178
0.0%
mean electron energy
p = 760 Torr
E/p = 5 Vcm-1Torr-1 (E/N=15 Td).
23
Electron drift velocities in Xe, Xe-CH4 and Xe-CF4
Monte Carlo
Addition of CH4 or CF4 to Xe
• increases electron drift velocity
1
1%CH 4
w
Vd (106 cm/s) MC XS_MT Xe
1w_MC (106 cm/s) XS_MT 99.9Xe+0.1CH4
0.1%
Xe-CF4
w_MC (106 cm/s) XS_MT 99.75Xe+0.25CH4
0.1
w
0.1%CF 4
w_MC (106 cm/s) XS_MT 99.5Xe+0.5CH4
Xe
Xe
Xe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4
0.01
0.01
0.1
1
E/N (Td)
10
Drift velocity w (106 cm s-1)
Drift velocity w (106 cm s-1)
Xe-CH4
w_MC (106 cm/s) XS_MT 99Xe+1CH4
0.01%
0.1
Xe
Xe
Xe - 0.01% CF4
Xe - 0.05% CF4
Xe - 0.1% CF4
0.01
0.01
0.1
1
10
E/N (Td)
24
11/21
Electron diffusion in Xe, Xe-CH4 and Xe-CF4
Monte Carlo
10
εkT
Xe
0.1%
0.5%
1%
Addition of CH4 or CF4 to Xe
εkL
Xe
ekT (eV) M C XS_M T 99.9Xe+0.1CH4
ekT (eV) M C XS_M T 99.5Xe+0.5CH4
• decreases electron diffusion
ekT (eV) M C XS_M T 99Xe+1CH4
1
1%
εk (eV)
ekL (eV) M C XS_M T Xe
ekL (eV) M C XS_M T 99.9Xe+0.1CH4
ekL (eV) M C XS_M T 99.5Xe+0.5CH4
ekL (eV) M C XS_M T 99Xe+1CH4
ekT (eV) M C XS_M T Xe
0.1
10
εkT
Xe-CH4
Xe
a)
0.1
1
E/N (Td)
10
εkL
0.1%
1
100
Xe
εk (eV)
0.01
0.01
0.01%
0.05%
0.1%
0.1
Xe-CF4
a)
with
0.01
0.01
0.1
1
E/N (Td)
10
100
25
Monte Carlo simulation results: EL Yield
this work
2500
[15]
[21]
Xe
Xe-CH4
Xe-CF4
D=0.5 cm,
p = 1o atm
T=293 K
0.01%CF4
2000
0.1%CH4
Xe
1500
Nexc / e-
Xe
Nexc / e-
Xe-0.1%CH4
Nexc / e-
Xe-0.5%CH4
Nexc / e-
Xe-1%CH4
Nexc / e-
Xe-0.01%CF4
Nexc / e-
Xe-0.05%CF4
Nexc / e-
Xe-0.1%CF4
H jm em D
H
H fs em D
#REF!
Rint2
0.05%CF4
1000
0.5%CH4
0.10%CF4
500
1.0%CH4
0
5
10
15
{
 (1/n ) (F + Q)
traço Xe-CH4
traço Xe-CF4
F = n 2/n
Q =J/H
J = H 2/H
série 13 dots para jm
série 14 black ball Xe
Linear (Nexc / e-
Xe-0.1%CH4)
Linear (Nexc / e-
Xe-0.5%CH4)
Linear (Nexc / e-
Xe-1%CH4)
Linear (Nexc / e0.01%CF4)
Linear (Nexc / e0.05%CF4)
Linear (Nexc / e-
XeXe-
Xe-0.1%CF4)
20
E/N (Td)
EL yield H (UV photons /electron) produced under uniform reduced electric fields E/N,
when one electron drifts across the EL region in Xe and in Xe-CH4 and Xe-CF4 mixtures
with the indicated CH4 and CF4 concentrations.
26
Monte Carlo simulation results: EL fluctuations
100%
0.10%CF4
1
0.10%CF4
80%
0.8
G
Xe
G
Xe-0.1%CH4
G
Xe-0.5%CH4
G
G
0.05%CF4
60%
0.6
Q
Xe
Xe-CH4
Xe-CF4
Xe-0.01%CF4
G
Xe-0.05%CF4
G
Xe-0.1%CF4
Fxe
Traço Xe
Traço Xe-CH4
z
Traço Xe-CF4
Expon. (G
40%
0.4
0.01%CF4
FXe
Xe-1%CH4)
Poly. (G
Xe-0.01%CF4)
Poly. (G
Xe-0.05%CF4)
Log. (G
0.2
0.05%CF4
Xe-CF4
Xe-1%CH4
Xe-CH4
0.01%CF4
Xe-0.1%CF4)
1.0%CH4
20%
0.5%CH4
1.0%CH4
0.5%
0.1%
Xe
0
5
10
15
20
0.1%CH4
0%
5
E/N (Td)
10
15
20
E/N (Td)
Fluctuations parameter Q=J /H of the EL yield H ,
where J=H 2/H is the relative variance of H.
The bar FXe marks the Xe Fano factor.
Rint2  (1/n ) (F + Q)
Fraction z of electrons that become
attached to CH4 or CF4 molecules in
the EL region.
27
Experimental system
GPSC
Molecular
gas
purifier
Pressure
gauge
GPIC
Noble gas
purifier
HP gas
container
28
Experimental spectra for Xe and Xe-1.5% CH4 GPIC
600
25
500
400
p= 800 Torr
5.9 keV x rays
20
R
R (%)
Channel
GPIC
300
R
200
G
100
15
G
0
10
1.3
1000
1.4
1.5
1.6
1.7
1.8
1.9
2
V (kV)
Vanode= 1,75 kV
900
800
Vanode =1,85 kV
700
Counts
600
Xe – 1.5% CH4 and 100% Xe
500
400
300
200
100
0
0
50
100
150
200
250
300
Channel
350
400
450
500
29
Experimental spectra for Xe and Xe-1.5% CH4 GPSC
Xe - 1.5% CH4 and 100% Xe
3500
45
R
3000
p= 800 Torr
5.9 keV x rays
35
2500
Y
2000
30
25
1500
20
R
1000
15
500
Y
10
0
5
1
700
Centroid - 27
FWHM - 12,2
R - 44,7%
Amplification - 22
Acq. Time - 500s
600
Counts
500
3
4
5
6
7
8
E/P scint.
Xe – 1.5% CH4 and 100% Xe
800
2
Centroid - 185
FWHM - 25,2
R - 13,6%
Amplification - 2,75
Acq. Time - 600s
400
300
200
100
0
0
20
40
60
80
100
120
140
Channel
160
180
200
220
240
30
R (%)
Channel
GPSC
40
TMA - N(CH3)3
TMA - next molecular additive to be tested
mildly toxic, foul smell…
Expectations:
• improves electron drift parameters
• Penning ionization (decreases Fano factor, not crucial)
• Xe VUV emission quenched
• TMA fluoresces in 275-330 nm - wavelength shifter
• may produce EL in alternative to xenon
• symmetric molecule (non-electronegative)
31
Xe exc 8.32 eV
TMA IP
TMA IP 7.85 eV
32
Part of the work presented here has been funded by FEDER, through the
Programa Operacional Factores de Competitividade- COMPETE
and by National funds through
FCT- Fundação para a Ciência e Tecnologia in the frame of project .....
33
Part of the work presented here has been funded by FEDER, through the
Programa Operacional Factores de Competitividade- COMPETE
and by National funds through
FCT- Fundação para a Ciência e Tecnologia in the frame of project .....
34
35
36
37
14/21
Electroluminescence fluctuations in doped xenon
The addition of CH4 / CF4 to Xe
Monte Carlo
• decreases EL (n. sc.photons, produced per electron in sc. gap)
• increases EL fluctuations (CF4 has catastrophic effect …)
5 cm drift,
atm ↔15atm
mm, 10 atm
5 cm1 drift,
5 cm drift,5 cm
1 atm
↔ 15 atm
mm, 10 atm
drift,
400
2000
c)
Xe
Xe-CH4
Xe-CF4
1500
Xe
Nexc / e-
Xe
Nexc / e-
Xe-0.1%CH4
Nexc / e-
Xe-0.25%CH4
Nexc / e-
Xe-0.5%CH4
Nexc / e-
Xe-1%CH4
Nexc / e-
Xe-0.01%CF4
300
0.1%CH4
0.25%CH4
J = 2 / Nexc
Xenon excitations per e- Nexc
a)
0.01%CF4
0.5%CH4
Nexc / e-
Xe-0.05%CF4
Nexc / e-
Xe-0.1%CF4
0.05%CF4
Xe
Xe-CH4
Xe-CF4
0.01%CF4
0.1%CF4
200Xe
dummy Nexc
1000
dummy Nexc Xe-CH4
dummy Nexc Xe-CF4
1%CH4
100
500
0.05%CF4
0.5%CH 4
1%CH4
0.25%CH4
0.1%CH 4
Xe
0.1%CF4
0
0
5
7.5
10
E/N (Td)
12.5
15
5
7.5
10
E/N (Td)
12.5
15
38
Electroluminescence fluctuations in doped xenon
Monte Carlo
5 cm drift, 1 atm
5 cm drift, 1 atm
100%
1
0.1%CF4
0.05%CF4
b)
Xe-CH4
Xe-CF4
0.8
60%
G=J / Nexc
Attached electrons
Na
80%
0.1%CF4
d)
0.01%CF4
40%
J
Xe
J
Xe-0.1%CH4
J
Xe-0.25%CH4
J
Xe-0.5%CH4
J
Xe-0.05%CF4
J
Xe-0.1%CF4
0.05%CF4
Xe
J Xe-1%CH4
Xe-CH4
J Xe-0.01%CF4
Xe-CF4
0.6
dummy Natt Xe-CH4
dummy Natt Xe-CF4
0.4
0.01%CF4
20%
FXe
0.2
1%CH4
1%CH4
0.5%CH4
0.25%CH4
0.1%CH4
0.5%CH 4
0.25%CH4
0.1%CH4
0%
5
7.5
10
E/N (Td)
12.5
Xe
0
15
5
7.5
10
12.5
15
E/N (Td)
39
15/21
Electron energy in Xe and Xe-10%CF4
40
41
Drift velocities for electrons in Xe and Xe-CH4
Monte Carlo
Addition of CH4 or CF4 to Xe
• increases drift velocity
1
1%CH 4
Drift velocity w (106 cm s-1)
Xe-CH4
w
Vd (106 cm/s) MC XS_MT Xe
w_MC (106 cm/s) XS_MT 99.9Xe+0.1CH4
0.1%
w_MC (106 cm/s) XS_MT 99.75Xe+0.25CH4
0.1
w_MC (106 cm/s) XS_MT 99.5Xe+0.5CH4
Xe
w_MC (106 cm/s) XS_MT 99Xe+1CH4
Xe
Xe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4
0.01
0.01
0.1
1
10
E/N (Td)
42
Noble gas scintillation - from recombination
 Recombination with participation of a neutral
(high pressure effect)
X   e-  X  X  X
X   e-  X  X *  X  X  X  h
X   e-  Y  X  Y
At high pressure a 3rd partner is likely to take away
the energy released and no scintillation will occur
43
Electron diffusion in Xe, Xe-CH4 and Xe-CF4
Monte Carlo
Addition of CH4 or CF4 to Xe
•
increases drift velocity
•
decreases longitudinal and transverse electron diffusion
Characteristic energies εkL, εkT (eV)
10
εkT
Xe-CH4
Xe
0.1%
1%CH 4
ekL (eV) MC_2008
εkL
ekT (eV) MC_2008
ekL (eV) MC XS_MT 99.5Xe+0.5CH4
Xe
1
0.25%
1%CH 4
ekT (eV) MC XS_MT 99.5Xe+0.5CH4
ekL (eV) MC XS_MT 99Xe+1CH4
ekT (eV) MC XS_MT 99Xe+1CH4
ekL (eV) MC XS_MT 99.9Xe+0.1CH4
ekT (eV) MC XS_MT 99.9Xe+0.1CH4
ekL (eV) MC XS_MT 99.75Xe+0.25CH4
ekT (eV) MC XS_MT 99.75Xe+0.25CH4
0.1
Xe
Xe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4
where
0.01
0.01
0.1
1
10
100
E/N (Td)
44
12/21
Electron diffusion in Xe, Xe-CH4 and Xe-CF4
Monte Carlo
Addition of CH4 or CF4 to Xe
•
increases drift velocity
•
decreases longitudinal and transverse electron diffusion
Characteristic energies εkL, εkT (eV)
10
εkT
Xe-CF4
Xe
εkL
0.1%CF4
0.01%
1
ekT (eV) MC XS_MT Xe
ekT (eV) MC XS_MT 99.99Xe+0.01CF4
ekT (eV) MC XS_MT 99.95Xe+0.05CF4
Xe
ekT (eV) MC XS_MT 99.9Xe+0.1CF4
0.1%CF4
ekL (eV) MC XS_MT Xe
ekL (eV) MC XS_MT 99.99Xe+0.01CF4
ekL (eV) MC XS_MT 99.95Xe+0.05CF4
ekL (eV) MC XS_MT 99.9Xe+0.1CF4
0.1
Xe
Xe - 0.01% CF4
Xe - 0.05% CF4
Xe - 0.1% CF4
where
0.01
0.01
0.1
1
10
E/N (Td)
45
13/21
Xe doped with CH4 e CF4 - w and ekT, ekL
10
10
εkT
εkT
Xe
Xe
0.1%
0.5%
1%
εkL
Xe
ekT (eV) M C XS_M T 99.9Xe+0.1CH4
0.01%
0.05%
ekT (eV) M C XS_M T 99.5Xe+0.5CH4
1
1%
ekT (eV) M C 99.99Xe+0.01CF
ekT (eV) M C XS_M T 99.95X
0.1%
ekT (eV) M C XS_M T 99Xe+1CH4
1
εkL
ekT (eV) M C 99.9Xe+0.1CF4
εk (eV)
εk (eV)
ekL (eV) M C XS_M T Xe
Xe
ekL (eV) M C XS_M T 99.9Xe+0.1CH4
ekL (eV) M C XS_M T Xe
ekL (eV) M C 99.99Xe+0.01CF
ekL (eV) M C XS_M T 99.5Xe+0.5CH4
0.1%
ekL (eV) M C XS_M T 99Xe+1CH4
ekL (eV) M C 99.95Xe+0.05CF
ekT (eV) M C XS_M T Xe
ekL (eV) M C 99.9Xe+0.1CF4
0.1
0.01
0.01
0.1
0.1
1
Xe-CH4
Xe-CF4
a)
a)
10
100
0.01
0.01
0.1
1
10
ekT (eV) M C XS_M T Xe
100
E/N (Td)
E/N (Td)
1
1
w
1%
0.1%
0.5%
w_M C (106 cm/s ) 99.99Xe+0
w_M C (106 cm/s ) XS_M T 99.9Xe+0.1CH4
0.05%
w_M C (106 cm/s ) 99.95Xe+0
0.1%
w (106 cm s-1)
w (10 6 cm s -1)
w_M C (106 cm/s ) 99.9Xe+0.
w_M C (106 cm/s ) XS_M T 99.5Xe+0.5CH4
0.01%
Vd (106 cm/s ) M C XS_M T
w_M C (106 cm/s ) XS_M T 99Xe+1CH4
0.1
Xe
0.1
Xe
Vd (106 cm/s ) M C XS_M T Xe
0.01
0.01
0.1
1
E/N (Td)
Xe-CH4
Xe-CF4
b)
b)
10
100
0.01
0.01
0.1
1
10
100
E/N (Td)
46
Electroluminescence: cylindrical versus parallel geometry
H number of scint. photons per electron
fluctuations J=  2/H
cylindrical geometry 
parallel geometry ∥
Calculations were made for a gap distance yielding the same H as cylindrical geometry
47
Dopagem de Xe com CH4 e CF4 - Efeito em H e em Q
m = 5000
H
2
J H /H
p = 10 atm
E
z
- Rendimento de eletroluminescência (EL)
- Variância relativa no nº de fotões H
F   2n n - Variância relativa no nº n de eletrões primários
O
Q J /H
D = 0.5 cm
2
2
Rint  2.35 (1 / n )( F  Q)
b)
b)
atual
atual
2500
[23]
[23]
[24]
[24]
1
1
Xe
Xe-CH4
Xe-CF4
0.10%CF4
Nexc / e-
Xe
Nexc / e-NexcXe-0.1%CH4
Xe
/ e-
Nexc / e-
0.8Nexc / e0.8 Nexc / e-
0.01%CF4
2000
Xe-0.5%CH4
Xe-1%CH4
Xe-0.01%CF4
Nexc Xe
dummy
0.1%CH4
Xe
Nexc / e-
Xe-0.05%CF4
Nexc / e-
Xe-0.1%CF4
0.05%CF4
dummy Nexc
Xe
Filomena
H
QQ
1500
Xe
0.6
0.6 dummy Nexc Xe-CH4
dummy Nexc Xe-CF4
FilomenaCristina
Xe-CH4
Xe-CF4
Cristina
0.4Série13
0.4 Série14 Série13
0.05%CF4
1000
Série15
0.5%CH4
0.10%CF4
500
0
[23] T.H.V.T. Dias et al. 1993
[24] C.M.B. Monteiro et al. 2007
10
10
15
15
E/N (Td)
Xe-0.1%CH4)
Linear (Nexc
/ eSérie14
Xe-0.5%CH4)
Linear (Nexc / e-
Xe-0.01%CF4)
Linear (Nexc
/ eSérie15
Xe
Xe
Xe-0.05%CF4)
Linear (Nexc / e-
Xe-0.1%CF4)
0.01%CF4
0.2
FXeXe-1%CH4)
/ e0.2 Linear (NexcF
Xe
1.0%CH4
5
Linear (Nexc / e-
20
20
0
0 5
5
1.0%CH4
0.5%
0.1%
10
10
E/N (Td)
E/N (Td)
15
15
20
20
48
Dopagem de Xe com CH4 e CF4 - Discussão
Xe *(1s5; 1s4) + 2Xe → Xe2* + Xe;
Xe puro
Xe2* → 2Xe + h (~172 nm)
1 exc → 1 fotão VUV
Y – CH4 ou CF4
i)
fração x de eletrões que são capturados por moléculas
Xe*(1s5; 1s4) + Y → produtos
Xe*(1s5; 1s4) + Xe + Y → produtos
100%
0.10%CF4
ii)
< pXe
0.05%CF4
iii)
exc. vib. → < em → < exc. Xe
iv)
capt. e- < exc. Xe
Xe-CF4
Xe-CH4
80%
x (%)
60%
40%
0.01%CF4
20%
1.0%CH4
Contribuições para a perda de H, para E/N = 15 Td
Meio gasoso
(i)
(ii)
(iii)
(iv)
Total
Xe-0.1%CH4
22.0%
0.1%
3.6%
1.2%
26.9%
Xe-0.1%CF4
0.0%
0.1%
7.0%
75.6%
0.5%
0.1%
82.7%
0%
5
10
15
20
E/N (Td)
49