A gas scintillation proportional counter for thermal neutron scattering measurements

D.Raspino, N.J.Rhodes, E.M.Schooneveld (ISIS-STFC),I.Defendi, M.Jurkovic, K.Zeitelhack (FRMII-TUM),

F.A.F.Fraga, L.M.S.Margato, A.Morozov, L.Pereira (LIP Coimbra),B.Guerard, G.Manzin, H.Niko, A.Gongadze (ILL),

R.Engels, G.Kemmerling (Jülich GmbH) andF.Sacchetti (INFN).

Outline

• Aim of the project• Detector

description• Results

– Position resolution• Electronics • Conclusions

The Project

• NMI3 – FP7 collaboration – 2009-2012• Six European institutes: FRM II, ILL, ISIS, Julich , LIP, INFN• Develop a 2D detector for thermal neutrons with:

– Position resolution < 1 mm– Efficiency > 50% for 1 Ǻ– Active area of 200x200 mm2

– Rate capability ~1 MHz• Application in the neutron scattering community in:

– Reflectometry – SANS (micro-focusing)

• Gas Scintillation Proportional Counter (GSPC)

The Detector

PMT

MSGC

~4.5∙105 γ/n at G~102

TransparentMesh (~ 5 kV)

TransparentWindow

n (E0)

3He-CF4 (~6 bar)

3H

p

γ

PMT

PMT

PMT signals

ANTS: Anger-camera type Neutron detector: Toolkit for Simulations

http://coimbra.lip.pt/~andrei/

A. Morozov et al, 2012 JINST 7 P02008.

1 cm

The MSGC• Produced by IMT• Glass: Schott S8900, 1 mm thick• Strips:

– Chromium .5 µm thick– Anode pitch: 500 µm– Anode width: 5 µm– Cathode width: 200 µm

• All anodes connected together• All cathodes connected together• Active area: 32x32 mm2 / 90x77 mm2

at 6 bar CF4

The PMTs signals• PMTs signals digitised at

400 MHz – 12 bit• Signals are filtered τ=150

ns• Amplitude (an) at the peak

of the signal is measured for each PMT

• The 2D position of the neutron is calculated using the Centre of Gravity (CoG) of the light

7 PMTs in hexagonal arrangementRaw signals

nn

nn,pmtn

a

xax

nn

nn,pmtn

a

yay

Position Resolution

• Four PMTs (Ø=38 mm) in a square array

• PMTs to MSGC 20 mm

• 1 bar 3He / 2 to 6 bar CF4

• Gain increased until not better position resolution

• Similar results with 7 PMT (Ø=29 mm) in hexagonal arrangement

0.6 mm FWHM

3H p

Electronics

ADC

ADC

FPGADSP

Peak Finderγ/n

Position

X,YPH

Position Reconstruction Algorithms • PMTs signals amplitudes as

input XY as output

• Centre of Gravity (CoG)• Maximum Likelihood (ML)• Least Square (LS)• Neural Network (NN)

Position Resolution FWHM (mm)

COG ML LS NN

0.8 0.83 0.83 0.82

Cd MaskHoles 2 mm Ø, 5 mm pitch

Gamma/neutron

Σ PMT signal

Ch

arg

e s

ign

al

nPMT signal

charge signal

γPMT signal

charge signal

Reason for slower gamma signal: Electron ionises much large volume of gas than proton + triton Takes longer for all charges to drift to MSGC Gamma signal is wider (and lower).

Full size detector • 40 x 40 cm Al vessel• fill pressure: 1 bar He + 7 bar CF4

• Entrance Al window (5 mm)• MSGC S8900 (9 cm x 7.3 cm)• 3.3 mm Borofloat glass window • 19 R5070A PMTs on 28.5 mm pitch

• Tested up to 400 kHz incident rate• Read out with the final electronic

Dx = 0.60 mm

Conclusions• The GSPC was developed in the NMI3-FP7 project• The obtained performance are the result of the precise

measurements of the detector’s physical parameters• The simulation tool (ANTS) has been crucial for the

development of the detector:– Position reconstruction– Position resolution– Rate Capability

• A real size detector is operative

Future• Try the detector on a reflectometer

Light Spectrum

A. Morozov, L.M.S. Margato, M.M.F.R. Fraga, L. Pereira, F.A.F. Fraga, Secondary scintillation in CF4; 2012 JINST 7 P02008.

Red PMTsS20 photocathodeFused Silica Window200-800 nmQE~10%

Blue PMTsBialkali photocathodeBorosilicate Window300-550 nmQE~20%