A Novel Position-Sensitive Radiation Detector Using a

Gaseous Photomultiplier and an UV Scintillator

Shunsuke KUROSAWAHidetoshi Kubo, Toru Tanimori,

Kojiro

Taniue

(Kyoto Univ.),

Hiroyuki Sekiya

(ICRR, The Univ.

of Tokyo), Kentaro Fukuda, Sumito

Ishizu, Noriaki

Kawaguchi,

Toshihisa

Suyama

(Tokuyama Corporation), Akira Yoshikawa, Takayuki Yanagida, Yuui

Yokota

(IMRAM,Tohoku

Univ.)

PD09 June 25, 2009 @ Shinshu Univ., Matsumoto, Japan

Contents

• Introduction – Other groups’ works

• gaseous photomultiplier(gaseous UV detector)

• VUV (vacuum ultra-violet) scintillator• Our new radiation detector• Summary

Advantage of Gaseous Photomultipliers (GPMs)

• Large Area : > ~ 1000 cm2

• Good position resolution : < ~ 1 mm• Easy to operation in a magnetic field• No vacuum• Low cost / area

Comparison with other photo detectors, especially Photomultiplier tube (PMT)

Such GPMs are better suited to Dark Matter / neutrino searches

GPMs with Bialkali photocathodeTokanai et al. in press

Bialkali(K–Cs–Sb)

Visible light

Pyrex glass capillary plat (Pitch: 300m)

160 m

Photo-electron

UV-sensitive GPMsLiq. Xe / Ar scintillators (λ<180nm)solid VUV scintillators

Bialkali: sensitive to visible light

GPMs with CsI photocathode

Semitransparent photocathode Reflective photocathode

• CsI + MPGDs (Micro Pattern Gas Detector) have been developed by other groups. – Cascade GEM / MHSP/ THGEM with rim and so on– ex) Chechik et al. NIM A 595(2008) 116 and its refs

GPMs with CsI photocathode• CsI + MPGDs (Micro Pattern Gas Detector)

have been developed by other groups. – Cascade GEM / MHSP/ THGEM with rim and so on– ex) Chechik et al. NIM A 595(2008) 116 and its refs

Semitransparent photocathodeShadow image with UV lampBellazzini et al. (2007)

Semitransparent Photocathode (CsI)+GEM +CMOS

CMOSEffective area:15 mm x 15 mmSmall size Compared to other GPMs

1mm

large area

28 cm

23cm

GEM (gas electron multiplier)

We have already operated the 30 cm size MPGD stably for a Compton camera and an X-ray imaging detector

30cm

30cm-PIC (micro pixel chamber)

2-D position sensitivegaseous detector

Concept of our new detector

1st step: Prototype of our GPM ( 10 cm size )with CsI photocathode

GPM using MPGD:larger areaLow cost / areacount rate~10MHz / mm2 with-PIC+GEM @ 17.4keV

UV Scintillator:Higher detection efficiencythan gaseous detector inhard X / gamma-ray rangeShort decay time ~ a few nsec

New hard X / gamma-ray imaging detector

Our gaseous photomultiplier (gaseous UV detector)

Overview of our GPMCsI photocathode•MgF2 window(5mm thickness)with Drift plane (Al)

GEM(gas electron multiplier)Sauli (1997), Inuzuka et al.(2004)Thickness :50 m, 100 mpre-gas-multiplier

Electric field

hv

e-

-PIC(micro pixel chamber)2-D detector

We used 2 GEMs + μ-PICGEMs for ion blocking-PIC for high position resolution,

stability in high gain,large effective area

10 cm

Sensitive to one photoelectron Total gas gain ~ 105-6

CsI Photocathode

Drift planeAl vapor deposition

PhotocathodeCsI vapor deposition50

70m

m

50m

m

34m

mMgF2 window Thickness : 5mm

CsI photocathode

for reference

Quantum Efficiency (QE)of R6835 (Hamamatsu)Using a MgF2 window

100 200 wave length [nm]

100

10

1

0.1

0.01

Qua

ntum

Effi

cien

cy QE

Graph by Hamamatsu

UV sensitive

-PIC : 2-D gaseous detector

10cm

Size: 10 cm x 10 cmPixel pitch: 400 m

~ 65,000 pixelsGas gain:

~6,000

(stable operation of more than 1 month)

400μm pitch

anode cathode

Cu

-PIC : gain and Energy spectrum

Gas gain uniformityRMS ~ 7%

Energy spectrum (55Fe)

E/E 30% @ 5.9 keV

Ar-escape

0 2 4 6 8 10Energy [keV]

We filled with Ar(90%) + C2 H6 (10%) gas at 1atm

X-ray imaging with -PIC

Test chart imagePosition resolution:120 m

AMP-Discri. BoardBased on a chip for ATLAS Thin Gap Chamber0.8V/pC

1 mm

GEM

Size : 10cm×10cm

Thickness (material) :100 m (LCP + Cu)50 m (Kapton + Cu)

plasma-etchedMade by SciEnergy

10 cm

We used 2 GEMsas pre-gas-multipliers above the -PIC

140 m

70 m

VUV scintillator

Our detector : X-ray imager

VUV scintillator

Electric field

e-

To detect hard X-rays with a higher efficiency, we used VUV (vacuum ultra-violet) scintillator on the GPM

X / gamma raysLaF3 (Nd)Maximum emission:

at 172 nm Light yield:

41080 ph / MeV @1.5mol% of Nd

Decay time: 6 nsecDensity : 5.9 g / cc

UV

Yang and DeLuca (1976)Dorenbos et al. (1990)Gruwe and Tavernier (1992) 10 cm

LaF3 (Nd) : an UV source

20 mm

160 180 200 220 240 260wave length [nm]

Made by Tokuyama corporation

Emission spectrum

172 nm

Cou

nts

(a. u

.)

Reflector : Gore-Tex

Measurement with PMT

Wave length [nm]

QE

[%]

160 170 180 190 200 210

PMT: R8778 (2-inch)(Hamamatsu)

PMT(R8778)

LaF3 (Nd)Reflector(Gore-Tex)

241Am (

source)

grease(Krytox 16350)

10

10033% @ 172 nm

Photoelectron0 20 40 60 80 100

Cou

nts

(a. u

.) ~30 p.e. (photoelectron)

~100 UV photons@ 5.5 MeV

ray

PMT QE

LaF3 (Nd) size: 15 mm x 15 mm x 15 mm

Our new radiation detector

= GPM (UV detector) + UV scintillator

Setup (1)

13 mm

2 mm

4 mm

Electric field

e-

UV

GEM : 422V-PIC: 465 VTotal gain: ~ 2.6x105

1st GEM

2nd GEM

-PIC

E = 0.3 kV / cm

E = 1 kV / cm

Ar(90%) + C2 H6 (10%) gas at 1 atm (sealed)

MgF2 window

241Am (

source)

10 cm

15 mmLaF3 (Nd): 15 mm x 15 mm x 15 mm

LaF3 + 241Am Top view

Anode signals

Oscilloscope

Pulse height : 120 mVpreAMP : 1V/pCGas gain : 2.6x105

2.9 p.e.

-PIC Anode

X 64 ch sum

CP581 preAMP(1V/pC) Clearpluse co., ltd.

Spectrum-PIC Anode

X 64 ch sum

~100 photons from LaF3 (Nd)

Our detector QE : 1-2 %

QE of CsI

QE ~2% @ 172nm

10MHz sampling ADC

CP581 preAMP(1V/pC) Clearpluse co., ltd.

Sensitive to 1 p.e.

Photoelectron0 2 4 6 8 10 12

Cou

nts

(a. u

.)

Setup (2)

2.5 mm

2.0 mm

2.0 mm

Electric field

e-

UV

GEM : 280V-PIC: 490 VTotal gain: ~ 7x105

1st GEM

2nd GEM

-PIC

E = 0.5 kV / cm

E = 2.95 kV / cm

Ar(90%) + C2 H6 (10%) gas at 1 atm (sealed)

MgF2 window

241Am (

source) LaF3 + 241Am

10 cm

20 mm

LaF3 (Nd): 20 mm x 20 mm x 20 mm

Top view

Gain: -PIC + GEMsGas: Ar(90%)

+ C2 H6 (10%) gasat 1 atm(sealed)

-PIC + double GEM

double GEM

~100Total gain:up to 7x105

106

105

104

103

102

10

1

gain

-PIC : 10 cm x 10 cm

GEMs :10 cm x 10 cm

Lens effect by Electric field

Electric field

UV

e- Lens Effect

It is possible that this effect may enhance the position resolution of the GPM by compensating for the electron diffusion in the gas.

20 mm

32mm

X 1.6

Rotation image

We can also obtain the image of LaF3 (Nd) at a 45-degree rotation

45°

Shadow images

Y projection

X projection10mm

15m

m

2mm

polyvinyl chlorideBlack tape(0.1 mm thickness)

LaF3 (Nd)

241Am

16mm

Galleries

When You Wish Upon a Star….

2 mm x 15 mm slits5 mm interval

14mm

Summary• We have developed a novel radiation detector

– Gaseous UV detector :Semitransparent CsI photocathode (3.4 cm ) 2 GEMs, -PIC (10 cm x 10 cm)

– VUV scintillator : LaF3 (Nd) • We obtained images

– Lens effect, magnification : 1.6

Future work• Measurement of collection efficiency /

ion feedback• Test of a reflective CsI photocathode• Test of large-area window• Development of large-area LaF3 (Nd) / new crystal

Thank you for your attention