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T riple GEM detector at CERN n_TOF facility. S.Puddu 2,4 , G.Claps 1 , G. Croci 3 , F. Murtas 1,2 , A.Pietropaolo 3 , C. Severino 2,4 , M. Silari 2 1) LNF-INFN 2) CERN 3)IFP-CNR 4)LHEP-Bern Universität. Triple GEM detector Triple GEM detector for fast neutrons

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Triple GEM detector at CERN n_TOF facility

  • S.Puddu2,4, G.Claps1, G. Croci3, F. Murtas1,2, A.Pietropaolo3, C. Severino2,4, M. Silari2

  • 1) LNF-INFN 2) CERN 3)IFP-CNR 4)LHEP-Bern Universität

  • Triple GEM detector

  • Triple GEM detector for fast neutrons

  • Triple GEM detector for thermal neutrons

  • Conclusion

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


A triple gem chamber
A triple GEM Chamber

A Gas Electron Multiplier is made by 50 m thick kapton foil, with copper cladded on each side and perforated by an high surface-density of bi-conical channels;

Several triple GEM chambers have been built in Frascati in the LHCbMuon Chamber framework

70 µm

140 µm

GEM foil

F. SauliNIM A386 531

M. Alfonsi et al., The triple-Gem detector for the M1R1 muon station at LHCb, N14-182, 2005 IEEE-NSS

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


A standard triple gem construction
A Standard Triple GEM construction

The detectors described in this talk are built starting form the standard 10x10cm2 : only one GEM foil has been modified to have central electrodes.

G3 G2 G1

  • FAST neutrons: 128 pads 6x12 mm2~ 100 cm2of sensitive area

  • THERMAL neutrons: 128 pads 3x6 mm2~ 25 cm2of sensitive area

The GEM are stretched and a G10 frame is glued on top

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Beam contamination by gammas
Beam Contamination by gammas

Prompt g flash at ~ 600 ns

E. Chiaveri et al, CERN n_TOF facility performance report,CERN-SL-2002-053 ECT (2002)

C. Guerrero Sanchez, The neutron beam and the associated physics program of the CERN n_Tof facility, ATS seminar

108 107 106 105 104 103 102 10 (eV)

105

~12 ms

~160 ms

104

F(dg/dlnt/cm2/pulse)

~4.7 ms

~63.7 ms

103

gfrom neutrons radiative capture in the beamdump

+

102

“Slow” photons from several processes

10-7 10-6 10-5 10-4 10-3 10-2 10-1

Time(s)

Thermal neutrons

Fast neutrons

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Low sensitivity to photons
Low Sensitivity to Photons

Counts(Hz)

HV scan with n_TOF and Cs137 with a gate of 1 second

Photons

Counts(Hz)

Neutrons

Workingpoint (870V) → gain ~ 300

HV(V)

HV(V)

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


How detect fast neutrons
How detect fast neutrons

200 m

Neutrons interact withCH2, and, due to elastic scattering processes, protonsare emitted and enter in the gas volume generating a detectable signal.

Aluminium thickness ensures the directional capability, stopping protons that are emitted at a too wide angle.

S. Puddu et al., ieee record N21-4

Neutron converter 60 mm PE + 40 mm Al

Gas mixture Ar-CO2 70%-30%

Measurements near to the beam dump

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Measurements beam imaging
Measurements : beamimaging

Instantaneous counts (10 msec)

y

x

y

x

Constant: 3640 ± 40

Mean1: 5.9 ± 1.8 cm

Mean2: 5.5 ± 1.8 cm

Cumulative counts

  • Delay 2000 ns, HV 870 V, gate 10 ms

  • Two different intensity beams arrive to the facility

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Measurements mean efficiency
Measurements : mean efficiency

From proton beam monitor

49000 ± 1000

136000± 4000

Beam2

Mean efficiency 2.0 ± 0.1 e-4

Beam 1

Beam2

From GEMneutron monitor

Beam1

10 ± 3 hits

26 ± 5 hits

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Measurements energy scan
Measurements : energyscan

The FPGA can detect neutrons vs a delay in time allowing to make a time (i.e. Neutron energy) scan thatallows the efficiency vs energy to be measured (uncertainty ~0.1 ÷1%, ~20% at 10 MeV ) .

Number of neutrons acquired

3 MeV

10 MeV

Number of neutrons detected

2 x10-4

100 keV

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012

9


How to detect thermal neutron
How to detectthermal neutron

Thermal Neutronsinteract with 10B, and alphas are emitted entering in the gas volume generating a detectable signal.

Gas gap (Ar CO2)

Alphas

10B (360 nm)

Glass Support (1mm)

Thermal neutrons

Side-On detector

Alphas

Thermal neutrons

Higher efficiency ~ 5%

F. Murtaset al., ieeeworkshop record He-2-5

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Monitor for fission reactor
Monitor for fission reactor

Measurements at Triga (ENEA)Power of 1 MW

Gamma background freeWithout electronic noise

Online plot top view

Good linearity from 1W up to 1 MW

Eff. = 4%

Only Support

Support with 10B

Thermal neutrons

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


N tof thermal neutron beam spot
N-TOF thermalneutron Beam spot

online measurement

Single event

Cumulative counts

Time spectrum (1ms/bin) 150ms gate

With a scan procedure itis possible

to make an image of the neutronbeam in the thermal

region

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Conclusions
Conclusions

  • A triple GEM for fast neutrons has been tested at beam dump in n_TOFfacility at CERN

  • The GEM detector system is able to measure in real time the neutron beamspotwith almost complete rejection of gamma ray

  • The mean efficiency of this detector is 2 10-4

  • The efficiency curve vs neutron energy was measured in the range 100 keV- 10 MeV

  • With a scan procedure itispossible to obtein the beamimaging for thermalneutrons

  • A new prototipe for thermalneutrons with 50%efficiency and 9cmwindowwill be ready in 01-2013

  • Other GEM detectors was succesfully tested at ISIS spallation neutron source in UK and the Frascati Tokamak in Italy.

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012

13


Triple gem detector electronics readout
Triple GEM detector: electronics readout

FAST

THERMAL

  • FAST neutrons: 128 pads 6x12 mm2~ 100 cm2 of sensitive area

  • THERMAL neutrons: 128 pads 3x6 mm2~ 25 cm2 of sensitive area

  • 8 chip CARIOCA to set the threshold on 16 channels and reshape the signal

  • FPGA-based DAQ: 128 scaler and TDC channels, in  gate and trigger, out  signals

  • HVGEM power supply with 7 independent channels and nano-ammeter

Developed by G. Corradi D. Tagnani Electronic Group LNF-INFN

Developed by A.Balla and G. Corradi and Electronic Group LNF-INFN

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Data acquisition
Data Acquisition

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Triple gem detector
Triple GEM detector

70 mm

140 mm

50 mm

  • Particle conversion, charge amplification and signal induction zones are physically separated

  • Time resolution depends on geometry and gas: 9.7 nsfor Ar-CO2 (70-30)

  • Spatial resolution depends on geometry (up to 200 m), however is limited by readout

  • Dynamic range: from 1 to 108 particles/cm2 s

  • Effective gain is given by the formula:

F. SauliNIM A386 531

M. Alfonsi et al., The triple-Gem detector for the M1R1 muon station at LHCb, N14-182, 2005 IEEE-NSS

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


Triple gem detector1
Triple GEM detector

3mm

1mm

2mm

1mm

  • Particle conversion, charge amplification and signal induction zones are physically separated

  • Time resolution depends on geometry and gas: 9.7 nsfor Ar-CO2 (70-30)

  • Spatial resolution depends on geometry (up to 200 m), however is limited by readout

  • Dynamic range: from 1 to 108 particles/cm2 s

  • Effective gain is given by the formula:

F. SauliNIM A386 531

M. Alfonsi et al., The triple-Gem detector for the M1R1 muon station at LHCb, N14-182, 2005 IEEE-NSS

Silvia Puddu - n_TOF Collaboration Meeting - CERN 2012


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