Neutron measurements in the LNGS Underground Laboratory

2° year PhD Seminar:Neutron measurements in theLNGS Underground LaboratoryCandidate:Dr. Antonio BonardiSupervisor:Prof. Piero GaleottiAssistentant Supervisors:Dr. Walter FulgioneDr. Marco Aglietta15 January 2009 1Antonio Bonardi - 2° year PhD Seminar - Neutron measurement in theLNGS Underground Laboratory

Neutron background for undergroundlaboratories experimentsNeutron background is troublesome for:• Neutrino experiments• Dark Matter experiments• ββ-decay experimentsbecause neutron interaction signal is able to mimic the expected signal of all ofthese kinds of experiment.Neutron background comes from:a) Natural radioactivity due to radioactive isotopes decay or to (α,n)reactions on elements that are present inside underground laboratory’sfacilities or inside the experimental apparatus itself.b) Muon hadronic interactions in the rock or in the experimental apparatusitself (e.g. a lead γ-rays shielding).Antonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 2LNGS Underground Laboratory

Neutron background for undergroundlaboratories experiments:- Natural radioactivity neutrons• The energy is low: E neutron

Neutron background for undergroundlaboratories experiments:- Muon-induced neutrons• Total flux is 2÷3 order of magnitude less thanprevious ones• There are 2 different classes:1. “evaporation neutrons”:‣ produced by photo-nuclearinteractions‣ low energy (E neutron

LVD: Large Volume Detector- OverviewLVD is located in the hall A of INFN NationalLaboratories of Gran Sasso, under about 3500m.w.e.LVD has acquired data since 1992 and it hasbeen in the actual configuration since 1999:nowaday the active mass is 1 Kton of organicliquid scintillator (C nH 2n, ρ ~ 0.8 g cm -3 )Antonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 5LNGS Underground Laboratory

LVD: Large Volume Detector- Overview• The main goal is to observe and to study neutrino bursts due togravitational collapse of massive objects in the Milky Way and the nearestgalaxies.• LVD takes part of SNEWS (SuperNova Early Warning System) projecttogether with ICECUBE, Super-K.• LVD works also as CNGS beam monitorCrab NebulaSN1987AAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 6LNGS Underground Laboratory

LVD: Large Volume Detector- Overview3 totally independent towers35 (+3 switched off) modules sorted on 5columns and 7 levels8 counters (1.5 m x 1 m x 1 m) filled with 1.2tons of liquid scintillator3 PMTs (6” photo-cathode) for light’s collectionplaced on the top surfaceAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 7LNGS Underground Laboratory

LVD: Large Volume Detector- OverviewActive MassDuty CycleAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 8LNGS Underground Laboratory

LVD: Large Volume Detector- Neutron’s measurementn + p 1 n + p 1E vis=E(p 1)+E(p 2)+...+E(p n)ε~50%τ~190 μsΕ γ= 2.2 MeVn + p 2 n + p 2n + p n n + p nn + p d + γIf E vis> E Threshold= 4 MeV (HET)E threshold~ 1 MeV (LET) , Δt = 1msIt’s possible to discriminate neutrons from other background sources by looking for protonrecoil signal followed by a neutron capture signal.Antonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 10LNGS Underground Laboratory

LVD: Large Volume Detector- Neutron’s measurementRecoiling protons are strongly non-relativistic!!For E

LVD: Large Volume Detector- Neutron’s measurementn + A Gd A+1 Gd + γ sε ~ 70%ε~50%τ~190 μsΕ γ= 2.2 MeVLS + 0.1% Gdτ ~ 25 μsΣΕ γ~ 8 MeVAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 12LNGS Underground Laboratory

Neutron’s measurement-GdR&DIn 2005 we have doped with 0.1% Gd a LVD counter (T3131) and another one (T40) usedfor test located in the LNGS mounting hall (on-the-ground laboratory)It is possible to perform natural decay neutron’s measurement by triggering for neutroncapture signal and then looking for a previous signal due to proton recoilWe have to use a new electronics instead of LVD standard electronicsSingle tank measurementAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 13LNGS Underground Laboratory

Single tank measurement:- The veto apparatus constructionA veto apparatus moduleVeto apparatus assembling phaseAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 14LNGS Underground Laboratory

Single tank measurement:- OverviewT40 + veto:•On-the-ground laboratory•High background•No radioactivity neutrons•Atmospheric neutrons, E n>10 MeV•Trigger , DAQ and Data Analysistechniques improvement•Trigger on proton recoil signalT3131:•Underground laboratory•Very low background•Radioactivity neutrons•Trigger on neutron capture or on protonrecoil signal•Data acquisition is still ongoingAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 15LNGS Underground Laboratory

Single tank measurement:- T40+veto first resultsAtmospheric neutronsNext Step Geant4 MC simulationAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 16LNGS Underground Laboratory

Single tank measurement:- T40+veto first resultsAtmospheric stopping μStopped vs. Passing trough ratio ~3.0%Next Step New data acquisitionAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 17LNGS Underground Laboratory

Muon-induced neutrons inside LVDEnergy range: 20 MeV < E neutron< 450 MeVMuons target countersVeto countersNeutron detector’s counterNot considered countersThis work had been repeated for vertical muons passing trough any LVD columnAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 18LNGS Underground Laboratory

Muon-induced neutrons inside LVD:- Selection criteriaMuon target volume:1.Δt=250 ns;2.E released≥50 MeV for L=1 && L=7;3.N counters(E released≥50 MeV) ≥ 5;Veto volume:1.Δt=250 ns;2.NO counter E released≥100 MeVAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 19LNGS Underground Laboratory

Muon-induced neutrons inside LVD:- Preliminary results• What is the real detection efficiency?• Why the knee?• What energy corrections are to be applied?Geant4 MC simulationAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 20LNGS Underground Laboratory

Neutron propagation inside LVD• LVD has 1 kton of liquid scintillar good neutron moderator• LVD is a modular experiment• LVD is a good muon detectorIt is possible to obtain a very low background facility for Dark Matter experimentinside the central part of LVD LVD_CF (LVD Core Facility)Antonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 21LNGS Underground Laboratory

Neutron propagation inside LVD:- First resultsNatural radioactivity neutron flux attended insideGran Sasso underground Laboratories.H.Wulandari et al “Neutron Flux at the Gran SassoUnderground Laboratory Revisited” hepex/0312050Simulated neutrons arriving at LVD_CFAttenuation factor for E n >1MeV ~ 37Φ(E n>1 MeV) = 5.8 10 -7 cm -2 s -1Φ(E n>1 MeV) = 1.6 10 -8 cm -2 s -1H.Wulandari, et alAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 22LNGS Underground Laboratory

2° year PhD Seminar:Neutron measurements in theLNGS Underground LaboratoryAntonio Bonardi - 2° year PhD Seminar - Neutron measurement in the15 January 2009 23LNGS Underground Laboratory