Xe-based d etectors: recent work at Coimbra

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









Research topics


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.


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


Drift field effects:

Fluctuations increase with

8/21









Research topics


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)


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 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





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


• 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



ekL (eV) MC XS_MT Xe

ekL (eV) MC XS_MT 99.99Xe+0.01CF4



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


• decreases longitudinal and transverse electron diffusion

where

13/21

Electron diffusion in Xe, Xe-CH4 and Xe-CF4









Research topics


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-1%CH4

Nexc / e- Xe-0.01%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









Research topics



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









Research topics


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









Research topics


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)



w_MC (106 cm/s) XS_MT 99.75Xe+0.25CH4


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


Documents

Xe-based d etectors: recent work at Coimbra