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MEASUREMENT OF FAST NEUTRON BACKGROUND IN SAGE

MEASUREMENT OF FAST NEUTRON BACKGROUND IN SAGE. Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia. J.N. Abdurashitov, V.N. Gavrin, A.V. Kalikhov, V.L. Matushko, A.A. Shikhin , V.E. Yants and O.S. Zaborskaia. International Workshop

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MEASUREMENT OF FAST NEUTRON BACKGROUND IN SAGE

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  1. MEASUREMENT OF FAST NEUTRON BACKGROUND IN SAGE Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia J.N. Abdurashitov, V.N. Gavrin, A.V. Kalikhov, V.L. Matushko,A.A. Shikhin, V.E. Yants and O.S. Zaborskaia International Workshop Topics in Astroparticle & Underground Physics 8 – 12 September 2001 LN Gran Sasso (L’Aquila), Italy

  2. CONTENTS • High sensitive spectrometer – brief description • Main performance data • Operation principle • Design • Data acquisition system • Calibration of the spectrometer • Base properties of the spectrometer • The results of fast neutrons flux measurements in SAGE facilities

  3. Main performance data • Energy range: 1-15 MeV • Sensitivity: 10-610-7 n·cm-2·s-1 • Detection efficiency: 0.110.01 (En>1 MeV) • Energy resolution: ~60% • Scintillator volume: 30 l • Sizes: 3636 cm3 • Masse: 50 kg.

  4. Detector structure • FEATURES: • Liquid scintillator (V=30l): • CnH2n, =0.84 g/cm3 • L.Y.=40% of anthracene • Counters (19): • Mixture: 3He+4%Ar • Pressure: 400 kPa • Geometrical cross section: • 6267,5 cm2

  5. Operation principle • Calorimeter • Combined detector: • Organic scintillator-thermalizer • 3He proportional counters • Delay coincidence technique • Pulse shape record

  6. Light Yield for NE-213 scintillator Dependences for: • Electrons • Single proton • Neutron (effective Light Yield) The main problem: nonlinear light yield  rough resolution

  7. Spectrometer of fast neutrons General view of the detector

  8. Spectrometer of fast neutrons Typical passive shield(one half of lead brick thickness)

  9. Spectrometer of fast neutrons Data acquisition system

  10. Data acquisition system

  11. Typical correlated event

  12. Calibration of the PMT channel(60Co source, -lines of 1.17&1.33 MeV)

  13. Calibration of the NC channel(Pu-Be neutron source, 2000 ns-1) 3He + n p + t + 760 keV, Ep=570 keV, Et=190 keV

  14. Time delay distribution for neutron events (Pu-Be source)

  15. Time delay distribution for background events (H2O+BPE shield)

  16. Dependence detector response function on neutron energy (MC simulation)

  17. Response function of the detector (experimental) 14 MeV neutrons source: D + t   + n + 17.6 MeV • Peak – 87 ch. (5.8 MeV of electron scale) • Threshold – 4 ch • Left – scattered neutrons • Right - saturations

  18. Efficiency dependence on neutron energy(MC simulation) E= tot(En)=thr(En)(1-out(En))

  19. Dependence between electron and neutron energy scales

  20. Fast neutrons background flux measurements RTot=RN+RRand+RBkg, RCor=RTot-RRand=RN+RBkg, Rrand=rrwnT

  21. Fast neutrons amplitude distributions – mine rock (electron scale)

  22. Fast neutrons amplitude distributions –SAGE main room(electron scale)

  23. THE RESULTS OF FAST NEUTRON BACKGROUND FLUX MEASUREMENT AT SAGE Neutron flux, 10-7cm-2s-1 (1.0–11.0 Energy range, for E=0.110.01)

  24. CONCLUSIONS • The fast neutron spectrometer created with: • high efficiency 11%, 1-11 MeV; • low internal background  high sensitivity 10-7 cm-2·s-1 • n/ discrimination (/n107) without any special technique such as PSD • Pulse Shape registration. • Measurements: • n-background for SAGE • internal background of the detector. • Possible improvements: • new fast electronics (PMT) • new NC • PSD • new spectrometer (sectioned)!

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