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) and F.Sacchetti (INFN).

Outline Aim of the project Detector description Results –Position resolution Electronics Conclusions

The Project NMI3 – FP7 collaboration – 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 mm 2 –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∙10 5 γ /n at G~10 2 Transparent Mesh (~ 5 kV) Transparent Window n (E 0 ) 3 He-CF 4 (~6 bar) 3H3H p γ PMT PMT signals ANTS: Anger-camera type Neutron detector: Toolkit for Simulations A. Morozov et al, 2012 JINST 7 P 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 mm 2 / 90x77 mm 2 at 6 bar CF 4

The PMTs signals PMTs signals digitised at 400 MHz – 12 bit Signals are filtered τ =150 ns Amplitude (a n ) 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 arrangement Raw signals

Position Resolution Four PMTs (Ø=38 mm) in a square array PMTs to MSGC  20 mm 1 bar 3 He / 2 to 6 bar CF 4 Gain increased until not better position resolution Similar results with 7 PMT (Ø=29 mm) in hexagonal arrangement 3H3Hp

Electronics ADC FPGA DSP Peak Finder γ /n Position X,Y PH

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) COGMLLSNN Cd Mask Holes 2 mm Ø, 5 mm pitch

Gamma/neutron Σ PMT signal Charge signal n PMT signal charge signal γ PMT 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 CF 4 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  x = 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 CF 4 ; 2012 JINST 7 P Red PMTs S20 photocathode Fused Silica Window nm QE~10% Blue PMTs Bialkali photocathode Borosilicate Window nm QE~20%