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Xe-based d etectors: recent work at Coimbra. C.A.N.Conde, A.D. Stauffer, T.H.V.T.Dias, F.P.Santos , F.I.G.M.Borges , L.M.N.Távora, R.M.C. da Silva, J.Barata, P.N.B.Neves, J.M.Escada, L.P.M.M.Carita, S.do Carmo, A.Trindade, J.Mariquito, P.J.B.M.Rachinhas. - PowerPoint PPT Presentation
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Xe-based detectors: recent work at Coimbra
C.A.N.Conde, A.D. Stauffer, T.H.V.T.Dias, F.P.Santos, F.I.G.M.Borges, L.M.N.Távora, R.M.C. da Silva, J.Barata, P.N.B.Neves, J.M.Escada,
L.P.M.M.Carita, S.do Carmo, A.Trindade, J.Mariquito, P.J.B.M.Rachinhas
Workshop on Xenon-Based Detectors 16-18 Nov 2009, Berkeley
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
Summary
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
2/21
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
Discontinuities in energy resolution
Xenon filled detectors exhibit sudden increases in energy resolution whenever a new Xe atomic-shell becomes available for photoionization
Monte Carlo
3/21
M
L
F and w-value
are discontinuous
Xe
E
2.35 rx
int
FwR
/ nEw xr
/ 2 nF n
MC simulationexperimental
Discontinuities in Fano factor and w-value
Monte Carlo
w
ph
w-value and Fano factor F
• are Exr dependent
• Reflect photoionization XS ph
/ nEw xr
F
ph
/ 2 nF n
4/21
■ MC□ experimental
Discontinuities in energy linearity & w=Exr/n
Mean number n of primary (sub-ionization) electrons produced in Xe as a function of absorbed x-ray energy Exr
Monte Carlo
5/21
Is n proportional to Exr ?
Energy resolution and Energy linearity
Exr > 4782 eV
• distributions shift to lower n:
discontinuity in w & linearity. • distributions broaden: discontinuity in F & Rint
Exr < 4782 eV (L3 ): M shell vacancy; M-photoelectron (~3500 eV) dominates; Exr > 4782 eV (L3 ): inner vacancy (L); photoelectron (few eV); various Auger electrons (30eV to ~4000eV).
Xe L3 binding energy = 4782 eV
Monte Carlo
6/21
n
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
High E0:
Photoelectrons •carry most of the photon energy E0•are scattered mostly forward. • have long trajectories in the gas
Long trajectories in the gas: energy gain/loss from the drift field is not negligible.
Deposited energy is higher (or lower) than E0.
Energy resolution degradation: drift electric-field effects
7/21
60 keV x rays
200 keV x rays
Intrinsic curve :
accounts for fluctuations in # of primary (sub-ionization) electrons (FXe=0.17; wXe=E0/n=21.5 eV).
Distributions (PENELOPE): for E/p=0.1 to 0.8 Vcm-1Torr-1:
Spreads Г vary with drift field (-function @field=0).
• drift field • photon energy
Energy resolution degradation: drift electric-field effects
Drift field effects:
Fluctuations increase with
8/21
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
ionexc
Electron scattering cross sections in Xe and CH4
9/21
10/21
Electron scattering cross sections in Xe and CF4
Electron drift velocities in Xe, Xe-CH4 and Xe-CF4
Addition of CH4 or CF4 to Xe
• increases drift velocity
Monte Carlo
11/21
0.01
0.1
1
0.01 0.1 1 10
Dri
ft v
eloc
ity
w (1
06cm
s-1
)
E/N (Td)
Vd (106 cm/s) MC XS_MT Xe
w_MC (106 cm/s) 99.99Xe+0.01CF4
w_MC (106 cm/s) 99.95Xe+0.05CF4
w_MC (106 cm/s) 99.9Xe+0.1CF4
0.01%
0.1%CF4 w
Xe
Xe-CF4
XeXe - 0.01% CF4
Xe - 0.05% CF4
Xe - 0.1% CF4
0.01
0.1
1
0.01 0.1 1 10
Dri
ft v
eloc
ity
w(1
06cm
s-1
)
E/N (Td)
Vd (106 cm/s) MC XS_MT Xe
w_MC (106 cm/s) XS_MT 99.9Xe+0.1CH4
w_MC (106 cm/s) XS_MT 99.75Xe+0.25CH4
w_MC (106 cm/s) XS_MT 99.5Xe+0.5CH4
w_MC (106 cm/s) XS_MT 99Xe+1CH4
0.1%
1%CH4
wXe-CH4
Xe
XeXe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4
0.01
0.1
1
10
0.01 0.1 1 10 100
Cha
ract
eris
tic e
nerg
ies
εkL
, ε k
T(e
V)
E/N (Td)
ekL (eV) MC_2008
ekT (eV) MC_2008
ekL (eV) MC XS_MT 99.5Xe+0.5CH4
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%
1%CH4
1%CH4
0.25%
εkT
εkL
XeXe-CH4
Xe
XeXe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4 where
Addition of CH4 or CF4 to Xe
• increases drift velocity
• decreases longitudinal and transverse electron diffusion
12/21
Monte Carlo
Electron diffusion in Xe, Xe-CH4 and Xe-CF4
0.01
0.1
1
10
0.01 0.1 1 10
Cha
ract
eris
tic e
nerg
ies
εkL
, ε k
T(e
V)
E/N (Td)
ekT (eV) MC XS_MT Xe
ekT (eV) MC XS_MT 99.99Xe+0.01CF4
ekT (eV) MC XS_MT 99.95Xe+0.05CF4
ekT (eV) MC XS_MT 99.9Xe+0.1CF4
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
0.01%
0.1%CF4
0.1%CF4
εkT
εkL
XeXe-CF4
Xe
XeXe - 0.01% CF4
Xe - 0.05% CF4
Xe - 0.1% CF4
Monte CarloAddition of CH4 or CF4 to Xe
• increases drift velocity
• decreases longitudinal and transverse electron diffusion
where
13/21
Electron diffusion in Xe, Xe-CH4 and Xe-CF4
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
0
500
1000
1500
2000
5 7.5 10 12.5 15
Xen
on
exci
tatio
ns
per
e-N
exc
E/N (Td)
5 cm drift, 1 atm
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
Nexc / e- Xe-0.05%CF4
Nexc / e- Xe-0.1%CF4
dummy Nexc Xe
dummy Nexc Xe-CH4
dummy Nexc Xe-CF4
XeXe-CH4
Xe-CF4
Xe
1%CH4
0.5%CH4
0.1%CH4
0.25%CH4
0.1%CF4
0.01%CF4
0.05%CF4
a)
Electroluminescence fluctuations in Xe vs Xe-CH4, Xe-CF4
0
100
200
300
400
5 7.5 10 12.5 15
J =
2 /
Nex
c
E/N (Td)
5 cm drift, 1 atm
J Xe
J Xe-0.1%CH4
J Xe-0.25%CH4
J Xe-0.5%CH4
J Xe-1%CH4
J Xe-0.01%CF4
J Xe-0.05%CF4
J Xe-0.1%CF4
dummy J Xe
dummy J Xe-CH4
dummy J Xe-CF4
XeXe-CH4
Xe-CF4
Xe
1%CH4
0.5%CH4
0.1%CH4
0.25%CH4
0.1%CF4
0.01%CF4
0.05%CF4
c)
• decreases EL (n. of excitations, i.e. sc.photons, produced per electron in sc. gap)
• increases EL fluctuations (CF4 has catastrophic effect …)
The addition of CH4 or CF4 to XeMonte Carlo
14/21
5 cm drift, 1 atm ↔ 5 mm, 10 atm 5 cm drift, 1 atm ↔ 5 mm, 10 atm
0%
20%
40%
60%
80%
100%
5 7.5 10 12.5 15
Atta
ched
ele
ctro
ns
N
a
E/N (Td)
5 cm drift, 1 atm
J Xe
J Xe-0.1%CH4
J Xe-0.25%CH4
J Xe-0.5%CH4
J Xe-1%CH4
J Xe-0.01%CF4
J Xe-0.05%CF4
J Xe-0.1%CF4
dummy Natt Xe-CH4
dummy Natt Xe-CF4
Xe-CH4
Xe-CF4
1%CH4
0.5%CH4
0.1%CH4
0.25%CH4
0.1%CF4
0.01%CF4
0.05%CF4b)
0
0.2
0.4
0.6
0.8
1
5 7.5 10 12.5 15
G=
J / N
exc
E/N (Td)
5 cm drift, 1 atm
Natt Xe
Natt Xe-0.1%CH4
Natt Xe-0.25%CH4
Natt Xe-0.5%CH4
Natt Xe-1%CH4
Natt Xe-0.01%CF4
Natt Xe-0.05%CF4
Natt Xe-0.1%CF4
dummy Natt Xe
dummy Natt Xe-CH4
dummy Natt Xe-CF4
Fxe
XeXe-CH4
Xe-CF4
1%CH40.5%CH4
0.1%CH4
0.25%CH4
0.1%CF4
0.01%CF4
0.05%CF4
Xe
FXe
d)
Monte Carlo
15/21
Electroluminescence fluctuations in Xe vs Xe-CH4, Xe-CF4
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
Tertiary-Scintillation Gas Proportional Scintillation Counter
TS-GPSC prototype
16/21
TS-GPSC Results
Best results obtained for
• scintillation electric fields just above Xe ionization threshold• voltage across GEM-structure below charge multiplication.
Typical spectrum 109Cd source
17/21
R
G
0
100
200
300
400
500
0 150 300 450 600 750 900 1050Channel
Co
un
ts FWHM=8.2%
22.1keV
24.9keV
ΔV GEM=140V
GEM_60
FWHM 8.2%
0
200
400
600
800
1000
2 3 4 5 6 7
E/P at Tertiary Scintillation region (V.cm-1.Torr-1)
Gai
n, G
(ar
bit
rary
un
its)
7
11
15
19
23
27
En
erg
y re
solu
tio
n, R
(%
)
G
R
Ed=0.8; Ecint2=6; Eext1=0.01;
Eext2=1.3 V.cm-1.Torr-1
22.1keVXe, 1atm
ΔVGEM=140V
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
Multigrid High Pressure Xe GPSC
(Indicated voltages are ideal values)18/21
• primary electrons are produced in the absorption/drift region
• primary electrons produce secondary scintillation VUV photons
along gap between G1 and G2
• VUV photons release electrons from CsI photocathode at backplane of detector
• electrons are collected at G4 giving the detector signal
Multigrid High Pressure Xe GPSC – Experimental results
0
2
4
6
8
10
1 1,5 2 2,5 3 3,5 4 4,5 5
Reduced electric field in the scintillation region, E s (V.cm-1.Torr-1)
Det
ecto
r ab
solu
te g
ain
1,5 bar
3 bar
5 bar
5,4 bar
Linear(5,4bar)Linear(5 bar)
Linear(3 bar)
Linear(1,5bar)
Pulse amplitude vs
G3-G4 potential barrier (V34 )
Charge gain vs
E/p in scintillation gap
19/21
300
350
400
450
500
-1200 -800 -400 0 400 800 1200 1600 2000
V3-V4 (V)
Puls
e am
plitu
de (a
rbitr
ary
untis
).
V3<V4 V3>V4 5.4 bar
5 bar
3 bar
1.5 bar
E/p (Vcm-1Torr-1)
Gai
n
Energy resolution degradation: drift electric-field effects
Tertiary-Scintillation Gas Proportional Scintillation Counter
New detectors developed at Coimbra:
Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4
Multi-Grid HP Gas Proportional Scintillation Counter
Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4
The Gridded Gas Proportional Ionization Counter
Discontinuities in energy resolution & linearity of Xe detectors
Research topics
Detector gas filling: Xe vs Xe-CH4 & Xe-CF4
The gridded GPIC: definition of multiplication volume
Grid around the anode: ideal to define multiplication volume However, grid diameter too small, unfeasible at 1 atm.
Solution:
planar microstructure where PIC conventional anode is hemmed in by a close second anode.
20/21
12
16
20
24
28
290 320 350 380 410 440 470 500
Anode voltage (V)E
ner
gy
reso
luti
on
, R (
%)
1
100
10000
Gas
mu
ltip
licat
ion
fac
tor,
M
○ R ■ M
Dual anode microstrip
Standard microstrip
0
20
40
60
80
100
120
140
0 200 400 600 800
Channel number
Co
un
ts/C
ha
nn
el
5,9 keV X-rays
E/P=0,63 V.cm-1.torr-1
Vanode= 410V
Vgrid= 150V
Ar escape peak
12,58%
P10
The gridded GPIC - Experimental results @5.9 keV
Gas Microstrip Best R
(%) Vanode (V)
Vgrid (V)
M
Xe MS2 13.4 400 100 1150
Standard 15.6 480 - 560
P10 MS2 12.6 415 150 590
Standard 13.6 480 - 490
21/21
R
M M
R
12
16
20
24
28
290 320 350 380 410 440 470 500
Anode voltage (V)
En
erg
y re
solu
tio
n, R
(%
)
1
100
10000
Gas
mu
ltip
licat
ion
fac
tor,
M
○ R ■ M
Dual anode microstrip
Standard microstrip
Experimental results with gridded GPIC
At the atomic absorption edges, an electric-field triggered discontinuity may become noticeable as the ejected photoelectron tends to have much lower energy after a new atomic shell becomes photoionizable than before. However this non-linearity is only about 4% of the intrinsic non-linearity.
Energy resolution degradation:drift electric-field discontinuities at atomic edges
Intrinsic discontinuity
0.01
0.1
1
0.01 0.1 1 10
Dri
ft v
eloc
ity
w(1
06cm
s-1
)
E/N (Td)
Vd (106 cm/s) MC XS_MT Xe
w_MC (106 cm/s) XS_MT 99.9Xe+0.1CH4
w_MC (106 cm/s) XS_MT 99.75Xe+0.25CH4
w_MC (106 cm/s) XS_MT 99.5Xe+0.5CH4
w_MC (106 cm/s) XS_MT 99Xe+1CH4
0.1%
1%CH4
wXe-CH4
Xe
XeXe - 0.1% CH4
Xe - 0.25% CH4
Xe - 0.5% CH4
Xe - 1.0% CH4
Drift velocities for electrons in Xe and Xe-CH4
Monte CarloAddition of CH4 or CF4 to Xe
• increases drift velocity