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. 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) Comparison with other photo detectors, especially Photomultiplier tube (PMT) • Large Area : > ~ 1000 cm 2 • Good position resolution : < ~ 1 mm • Easy to operation in a magnetic field • No vacuum • Low cost / area Such GPMs are better suited to Dark Matter / neutrino searches

GPMs with Bialkali photocathode Tokanai et al. in press Visible light 160  m Photo- Bialkali electron (K–Cs–Sb) Pyrex glass capillary plat (Pitch: 300  m) Bialkali: sensitive to visible light UV-sensitive GPMs  Liq. Xe / Ar scintillators ( λ <180nm)  solid VUV scintillators

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 Reflective photocathode Semitransparent photocathode

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 (CsI) 1mm +GEM +CMOS CMOS Effective area: 15 mm x 15 mm Small size Compared to other GPMs Shadow image with UV lamp Semitransparent photocathode Bellazzini et al. (2007)

large area We have already operated the 30 cm size MPGD stably for a Compton camera and an X-ray imaging detector 2-D position sensitive gaseous detector 28 cm 30cm 23cm 30cm  -PIC (micro pixel chamber) GEM (gas electron multiplier)

Concept of our new detector UV Scintillator: GPM using MPGD:  Higher detection efficiency  larger area  Low cost / area than gaseous detector in  count rate hard X / gamma-ray range  Short decay time ~10MHz / mm 2 with  -PIC+GEM @ 17.4keV ~ a few nsec New hard X / gamma-ray imaging detector 1 st step: Prototype of our GPM ( 10 cm size ) with CsI photocathode

Our gaseous photomultiplier (gaseous UV detector)

Overview of our GPM Sensitive to one photoelectron Total gas gain ~ 10 5-6 CsI photocathode •MgF 2 window We used 2 GEMs + μ -PIC (5mm thickness)  GEMs for ion blocking   -PIC for high position resolution, with Drift plane (Al) stability in high gain, large effective area GEM hv (gas electron multiplier) Electric Sauli (1997), Inuzuka et al. (2004) Thickness :50  m, 100  m field e -  pre-gas-multiplier  -PIC (micro pixel chamber)  2-D detector 10 cm

CsI Photocathode MgF 2 window Thickness : 5mm Drift plane 70mm 50mm 34mm Al vapor deposition Photocathode CsI vapor deposition 50

CsI photocathode 100 for reference QE Quantum Efficiency 10 Quantum Efficiency (QE) of R6835 (Hamamatsu) 1 Using a MgF 2 window 0.1 UV sensitive 0.01 100 200 wave length [nm] Graph by Hamamatsu

 -PIC : 2-D gaseous detector 400μm pitch Size: 10 cm x 10 cm Pixel pitch: 400  m ~ 65,000 pixels Gas gain:  ~6,000 (stable operation of 10cm anode cathode more than 1 month) Cu

 -PIC : gain and Energy spectrum We filled with Ar(90%) + C 2 H 6 (10%) gas at 1atm  E/E 30% @ 5.9 keV Ar-escape 0 2 4 6 8 10 Energy [keV] Energy spectrum ( 55 Fe) Gas gain uniformity RMS ~ 7%

X-ray imaging with  -PIC AMP-Discri. Board Based on a chip for ATLAS Thin Gap Chamber 0.8V/pC 1 mm Test chart image Position resolution: 120  m

GEM 1 4 0  m We used 2 GEMs 70  m as pre-gas-multipliers above the  -PIC Size : 10cm × 10cm Thickness (material) : 100  m (LCP + Cu) 50  m (Kapton + Cu) plasma-etched Made by SciEnergy 10 cm

VUV scintillator

Our detector : X-ray imager To detect hard X-rays with a higher efficiency, we used VUV (vacuum ultra-violet) scintillator on the GPM VUV scintillator X / gamma rays LaF 3 (Nd) Maximum emission: Electric UV at 172 nm field Light yield: e - 410  80 ph / MeV @1.5mol% of Nd Decay time: 6 nsec Density : 5.9 g / cc Yang and DeLuca (1976) Dorenbos et al. (1990) Gruwe and Tavernier (1992) 10 cm

LaF 3 (Nd) : an UV source Made by Tokuyama corporation Reflector : Gore-Tex 172 nm Counts (a. u.) Emission spectrum 20 mm 160 180 200 220 240 260 wave length [nm]

Measurement with PMT 241 Am (  source) Reflector LaF 3 (Nd) (Gore-Tex) grease (Krytox 16350) PMT LaF 3 (Nd) size: (R8778) 15 mm x 15 mm x 15 mm PMT: R8778 (2-inch) (Hamamatsu) Counts (a. u.) ~30 p.e. (photoelectron) 100 QE [%] 33% @ 172 nm PMT QE ~100 UV photons @ 5.5 MeV  ray 10 160 170 180 190 200 210 0 20 40 60 80 100 Wave length [nm] Photoelectron

Our new radiation detector = GPM (UV detector) + UV scintillator

Setup (1) GEM :  422V  -PIC: 465 V Total gain: ~ 2.6x105 Top view LaF 3 + 241 Am 241 Am (   source) LaF 3 (Nd): 15 mm x 15 mm x 15 mm MgF 2 window 15 mm Electric UV field e - E = 0.3 kV / cm 13 mm 1 st GEM 2 mm 2 nd GEM 4 mm E = 1 kV / cm  -PIC 10 cm Ar(90%) + C 2 H 6 (10%) gas at 1 atm (sealed)

Anode signals  -PIC Anode CP581 preAMP (1V/pC) X 64 ch sum Oscilloscope Clearpluse co., ltd. Pulse height : 120 mV preAMP : 1V/pC 2.6x105 Gas gain : 2.9 p.e.

Spectrum  -PIC Anode CP581 preAMP 10MHz sampling (1V/pC) X 64 ch sum ADC Clearpluse co., ltd. ~100 photons from Counts (a. u.) LaF 3 (Nd) Our detector Sensitive to 1 p.e. QE : 1-2 % QE of CsI QE ~2% @ 172nm 0 2 4 6 8 10 12 Photoelectron

Setup (2) GEM :  280V  -PIC: 490 V Total gain: ~ 7x105 Top view LaF 3 + 241 Am 241 Am (   source) LaF 3 (Nd): 20 mm x 20 mm x 20 mm MgF 2 window Electric 20 mm UV field e - E = 0.5 kV / cm 2.5 mm 1 st GEM 2.0 mm 2 nd GEM 2.0 mm E = 2.95 kV / cm  -PIC 10 cm Ar(90%) + C 2 H 6 (10%) gas at 1 atm (sealed)

Gain:  -PIC + GEMs Gas: Ar(90%) 106 gain  -PIC + double GEM + C 2 H 6 (10%) gas at 1 atm 105 (sealed) 104  -PIC : 10 cm x 10 cm 103 double GEM GEMs : 102 10 cm x 10 cm ~100 10 Total gain: 1 up to 7x10 5

Lens effect by Electric field  20 mm Electric UV field 32mm e - Lens Effect X 1.6 It is possible that this effect may enhance the position resolution of the GPM by compensating for the electron diffusion in the gas.

Rotation image 45 ° We can also obtain the image of LaF 3 (Nd) at a 45-degree rotation

Shadow images 10mm X projection 16mm 241 Am 15mm LaF 3 (Nd) 2mm Y projection polyvinyl chloride Black tape (0.1 mm thickness)

Galleries 14mm 2 mm x 15 mm slits 5 mm interval When You Wish Upon a Star….

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 : LaF 3 (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 LaF 3 (Nd) / new crystal

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