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Shield simulation for 10 kg detector

Shield simulation for 10 kg detector. Felice Dipace , Valerio Gentile, Giuliana Galati. NEWSdm Collaboration Meeting, LNGS, 14/02/2018. Aim External background characterization Neutron shielding Simulation set up One material simulations Two materials simulations. Summary.

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Shield simulation for 10 kg detector

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  1. Shieldsimulationfor 10 kg detector Felice Dipace, Valerio Gentile, Giuliana Galati NEWSdm Collaboration Meeting, LNGS, 14/02/2018

  2. Aim • External background characterization • Neutronshielding • Simulation set up • One materialsimulations • Twomaterialssimulations Summary

  3. Aim: to design neutronshield to minimize the neutron-induced track in the NIT that can simulate a WIMP signal. • In particularwe are studing the shieldsizeparameters and the effects of differentmaterials to build a shieldthatlet’s to havelessthan (1 bkg track)/(10kg*y). • To make thisstudywe use Geant4simulationprogram. • Physics list used to simulate neutronsinteraction: QGSP_BIC_HP. • Optimizationperformed on muon-inducedneutronbecause of theirharderspectrum. Aim of this work

  4. In paricularwe are studing the shieldsizeparameters and the differentmaterialeffect to build a shieldthatlet’s to havelessthan (1 bkg track)/(10kg*y) Aim of this work • Fixedparameters in the simulation for shieldoptimization: • Shape of the shield: spherical • Inner radius of the sphere • Choice of materials: water (pure and borated), polyethilene and copper • Variableparameters: • Shieldthickness • Configurationat one or more (wechoicetwo) materials • Choice of materials: water (pure and borated), polyethilene and copper

  5. Gamma energyspectrum in hall B and hall C of LNGS https://agenda.infn.it/getFile.py/access?contribId=9&sessionId=2&resId=0&materialId=slides&confId=14136 Background characterizationat LNGS Differentialenergyspectrum for muon-inducedneutronsat the various underground site https://journals.aps.org/prd/abstract/10.1103/PhysRevD.73.053004 Differentialenergyspectrum for environmentalradioactivity-inducedneutrons in the underground LNGS halls

  6. Background characterization at LNGS Fraction of surviving particles in the water shield: gamma (blue) and neutrons (red) from rock and concrete radioactivity, muon-induced neutrons (green). Studyperformed by Marco Selvi for XENON1T collaboration https://inspirehep.net/record/1081857/files/IDM2010_053.pdf

  7. Three steps are involved in neutronshielding: • Slow (moderate) the neutrons • Absorb the neutrons • Absorb the γ rays Neutronsshielding This step isnecessarybecause of the gamma production in the neutronshield by neutron radiative capture and inelastic scattering. For example 2.2 MeV gamma rays are producted by neutronsabsorbing from H-1

  8. Hydrogenousmaterial are quitegoodneutrons moderator. So materialwe can consider are: water and plasticaspolyethylene • To slow down very fast neutrons some (good) heavy materials can be placed in front of hydrogenousmaterials • For neutronradiation, as gamma radiation, greater the materialdensity of the shieldgreater the attenuation of the radiation Neutronmoderation http://periodictable.com/Properties/A/NeutronCrossSection.st.log.html

  9. B 760 H 0.332 Pb 0.171 Neutronmoderation Cu 3.78

  10. Hydrogenous materials are also effective at absorbing neutrons - the cross section for neutron capture by H-1 is 0.33 barns • Boron can be used as impurity in the shield materials because of its large cross section for neutron absorption. Further it emits only low energy capture gamma ray • To slow down very fast neutrons some (good) heavy materials can be placed in front of hydrogenousmaterials Neutronabsorption

  11. B 2.4 H 0.011 Pb 0.00004 Neutronabsorption Cu 0.0021

  12. n n Neutronshieldingstrategy Hydrogenousmaterial Gamma shield Combination material e.g. borated plastic or concrete with barium. These materials are a sort of multipurpose materials in the sense that are able to slow and absorb neutrons and shield the γraysat the same time High Z moderator for fast neutrons n

  13. Plantview NIT thickness = 50 μm Density of NIT emulsion = 3.43 1 layer (36x30 x 50 μm) NIT mass = 18,522 g N (layers to arrive to 10 kg of emulsion) = 540 Base thickness = 1 mm Total height of detector composed by 540 one side coatedlayer: h = 540x0,105cm = 56,7 cm Detector placed in the origine of the simulatedspace. Shape of simulatedshield: spherical. Inner radiusfixedat 50 cm. 30 cm Simulation set up 36 cm Front view

  14. Flux of cosmogenicneutrons (E > 10 MeV) = 7.3 x Simulation set upCosmogenicneutronfluxcharacterization Theseangular and energyspctrumreproduce the flux of cosmogenicneutronshowwehave in LNGS. The spctrum are alreadybeenvalidated by othercollaborationwhoseexperiment are housed in LNGS ( in particularthese are the spectrumused for XENON1T experimentsimulations).

  15. Inner radiusfixed. • Outer radiusvaried. • Radius of neutronsgeneratingsurface = Outer radius + 5 cm MC Simulation Input: Generatedevents (primaryneutrons): variedsimulation by simulation. Generatingsurface: calulatedusing the radius of neutronsgeneratingsurface. Mass of the detector (only NIT considered) = 10 kg. Flux (of cosmogenicneutrons). Output: Bkgevents rate in range of interest (r. of i.) (100-1000 nm). Other information… One materialSimulation Rate of cosmogenic neutrons = Flux x Generating surface. Exposure time = Generated events/Rate of cosmogenic neutrons. Rate (of background events for 10 kg NIT) = bkg events in r. of i./Exposure time. Rate (for 1 kg of NIT) = Rate/ Mass of the detector.

  16. One materialSimulation: Water

  17. Borax formula: (Fraction: 0.5% borax (B10 used)-99.5% water) One materialSimulation: WaterBorax

  18. One materialSimulation: Polyethilene

  19. Inner radiusfixed • Thickness of innermaterialfixed • Materialchosen: polyethyleneasinnermaterial and copperasoutermaterial • Radius of neutronsgeneratingsurface = Outer radius + 5 cm • Twosimulationperformed: • - polyethylenethicknessfixedat 200 cm and copperthicknessvaried • - polyethylenethicknessfixedat 100 cm and copperthicknessvaried TwomaterialSimulation

  20. TwomaterialSimulation: Poly_200cm_Copper_varied

  21. TwomaterialSimulation: Poly_100cm_Copper_varied

  22. Cross-checks on gamma raysproduced by absorbedneutrons • Cross-checks on environmentalradioactivity-induced gamma and neutrons • Cross-checks on muon-inducedneutrons in the shield Future Work

  23. Thankyou

  24. Back-up Tables

  25. Exposure time = 143.879 y One MaterialSimulation: Water

  26. Borax formula: (Fraction: 0.5% borax (B10 used)-99.5% water) Exposure time = 115.103 y One MaterialSimulation: Water-Borax

  27. Exposure time = 143.879 y One MaterialSimulation: Polyethylene

  28. Exposure time = 143.879 y TwoMaterialsSimulation: Polyethylene_Copper

  29. Exposure time = 143.879 y TwoMaterialsSimulation: Polyethylene_Copper

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