large colimator study ear2 christina weiss, cern
TRANSCRIPT
Large Colimator Study EAR2 Christina Weiss, CERN
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Introduction
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INTC approved proposals for measurements with large collimator in EAR2: 1. STEFF: CERN-INTC-2014-004 ; INTC-P-405
2. 26Al: CERN-INTC-2014-006 ; INTC-P-406
Count-rate estimations where performed with n/cm2 from EAR2 proposal, for samples:1. STEFF(235U): 50 mm in diameter
2. 26Al: 50 x 60 mm2, tilted in the beam
Study for large collimator for EAR2.
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2nd Collimator Geometries under Study
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• Smallest aperture for all geometries: r = 30 mm.
• Geometries:
• Scoring at 2 m from the floor in EAR2 (STEFF nominal sample position).
Straight Conical Double Conical Funnel
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Study Approach
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1. Study profile and flux with transport program from Vasilis – geometrical transport.
2. Choose best geometries.
3. FLUKA simulations for photon and neutron background impinging on NaI detectors of STEFF.
Results from Particle Transport Program
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Cone Collimator from EAR2 Proposal
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Initial simulations for EAR2, these results are included in the proposal
for EAR2!
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Present Collimator in EAR2
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Existing collimator in EAR2!
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Conical Geometry
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Double Conical Geometry
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Cone Geometry
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Straight Geometry
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In Comparison to EAR1
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Best Profile
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Beam Profile - cummulative
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HighestFlux
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Total Flux for different Geometries
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Total Flux for different Geometries
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Conclusions from Transport Program
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Best beam profile with conical geometry.
Highest flux with double conical geometry.
FLUKA Simulations
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Introduction
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• Neutron beam above the target as primary beam in the simulations.
• No ‘in-beam’ material implemented in the simulations.
• Conical and double conical geometry for 2nd collimator.
• Materials:
- 1 m B-PE (5%)
- 2 m stainless steel
• Materials already available. ConicalDoubleConical
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Introduction
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• For STEFF: Closest ‘sensitive’ detector are NaI at ~ 30 cm from the beam center.
• Scoring of neutron and photon spectra impinging on the ‘NaI detectors’.
• Shielding elements removed (Pb after 2nd coll., B4C + B-PE + Pb before the dump).
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Neutron Flux
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Neutron Background @ STEFF-NaI
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Neutron Background @ STEFF-NaI
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x 5x 1.5
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Photon Background @ STEFF-NaI
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Photon Background @ STEFF-NaI
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x 3.3
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Beam Profile (Conical), different Times
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Asymmetric shape for high-energy
beam profile
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Beam Profile (Conical) at 2 m Height
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Beam Profile (Conical) at 1 m Height
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Conclusions
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Best beam profile with conical geometry.
Highest flux with double conical geometry.
Less background with double conical geometry.
?Which geometry and aperture shall we choose?
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Beam Profiles
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Thank you for your attention.
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High-Energy Beam Profile at 2 m Height
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Vacuum chamber above the target