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Shield simulation for 10 kg detector

Explore neutron shielding design for minimizing track signals in NIT using Geant4 simulation. Study shield size and material effects to achieve desired background levels. Optimization focuses on muon-induced neutrons.

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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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