A Novel Position-Sensitive Radiation Detector Using a Gaseous - - PowerPoint PPT Presentation

A Novel Position-Sensitive Radiation Detector Using a Gaseous Photomultiplier and an UV Scintillator

Shunsuke KUROSAWA

Hidetoshi Kubo, Toru Tanimori, Kojiro Taniue (Kyoto Univ.), Hiroyuki Sekiya (ICRR, The Univ.

• f 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 photocathode

Tokanai et al. in press

Bialkali

(K–Cs–Sb) Visible light

Pyrex glass capillary plat (Pitch: 300m)

160 m

Photo- electron

UV-sensitive GPMs

• Liq. 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 photocathode Shadow image with UV lamp

Bellazzini et al. (2007) Semitransparent Photocathode (CsI) +GEM +CMOS

CMOS Effective area: 15 mm x 15 mm Small size Compared to

• ther 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 sensitive gaseous detector

Concept of our new detector

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

GPM using MPGD:

larger area Low cost / area count rate

~10MHz / mm2 with -PIC+GEM @ 17.4keV

UV Scintillator:

Higher detection efficiency than gaseous detector in hard X / gamma-ray range Short decay time ~ a few nsec

New hard X / gamma-ray imaging detector

Our gaseous photomultiplier (gaseous UV detector)

Overview of our GPM

CsI photocathode

• MgF2 window

(5mm thickness) with Drift plane (Al)

GEM

(gas electron multiplier)

Sauli (1997), Inuzuka et al.(2004)

Thickness :50 m, 100 m

• pre-gas-multiplier

Electric field

hv

e- -PIC

(micro pixel chamber)

• 2-D detector

We used 2 GEMs + μ-PIC

• GEMs 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 plane Al vapor deposition Photocathode CsI vapor deposition

50

70mm 50mm 34mm

MgF2 window

Thickness : 5mm

CsI photocathode

for reference Quantum Efficiency (QE)

• f R6835 (Hamamatsu)

Using a MgF2 window

100 200 wave length [nm] 100 10 1 0.1 0.01 Quantum Efficiency

QE

Graph by Hamamatsu

UV sensitive

-PIC : 2-D gaseous detector

10cm

Size: 10 cm x 10 cm Pixel pitch: 400 m ~ 65,000 pixels Gas gain:  ~6,000 (stable operation of more than 1 month) 400μm pitch anode cathode

Cu

-PIC : gain and Energy spectrum

Gas gain uniformity RMS ~ 7% Energy spectrum (55Fe)

E/E 30% @ 5.9 keV Ar-escape 0 2 4 6 8 10 Energy [keV]

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

X-ray imaging with -PIC

Test chart image Position resolution: 120 m

AMP-Discri. Board Based on a chip for ATLAS Thin Gap Chamber 0.8V/pC

1 mm

GEM

Size : 10cm×10cm Thickness (material) : 100 m (LCP + Cu) 50 m (Kapton + Cu)

plasma-etched

Made by SciEnergy 10 cm

We used 2 GEMs as pre-gas-multipliers above the -PIC

1 4  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 rays

LaF3 (Nd)

Maximum emission: at 172 nm Light yield: 41080 ph / MeV @1.5mol% of Nd Decay time: 6 nsec Density : 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

160 180 200 220 240 260 wave length [nm]

Made by Tokuyama corporation

Emission spectrum

172 nm

Counts (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) 10 100

33% @ 172 nm

Photoelectron 0 20 40 60 80 100 Counts (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 V Total 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 mm LaF3 (Nd): 15 mm x 15 mm x 15 mm

LaF3 + 241Am

Top view

Anode signals

Oscilloscope

Pulse height : 120 mV preAMP : 1V/pC Gas 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.

Photoelectron 0 2 4 6 8 10 12 Counts (a. u.)

Setup (2)

2.5 mm 2.0 mm 2.0 mm

Electric field

e-

UV

GEM : 280V -PIC: 490 V Total 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 + GEMs

Gas:

Ar(90%) + C2 H6 (10%) gas at 1 atm (sealed) -PIC + double GEM double GEM

~100

Total 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

• f 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 projection 10mm 15mm 2mm

polyvinyl chloride Black tape (0.1 mm thickness) LaF3 (Nd)

241Am

16mm

Galleries

When You Wish Upon a Star…. 2 mm x 15 mm slits 5 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