FLUKA simulations of DT shielding
options
Moritz Guthoff (CMS/BRIL)
7th April 2014
General Muon Meeting
Overview
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Short introduction to CMS in FLUKA
Objectives of study
Geometry implementation of shielding options
Results for
–  Particle fluence inside outer most DT layer
–  Particle energy spectra hitting muon chambers from the
cavern.
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FLUKA simulations of DT shielind options - Moritz Guthoff
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FLUKA for CMS
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BRIL Radiation Simulation maintains FLUKA geometry and provides
results to collaboration
–  www.cern.ch/cms-fluxmap
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Currently results for version v1.0.0.0 available (v2.0.0.0 will arrive shortly).
Study presented here based on v1.0.0.0.
Features of v1.0.0.0: “Prior to LS1 geometry”, Phi symmetric, no cavern
elements, no YE4, no CASTOR.
Phi symmetry implies: simulation corresponds to situation at the top of
CMS. Sides and bottom shielded are by balconies, racks, floor, nut
implemented in this FLUKA geometry version.
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Objectives for the study
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Particles leak trough forward shielding, scatter around in the cavern and
reflect back into muon systems. (Collision induced background, CIB)
Increased CIB rates (due to higher luminosities) require shielding on top of
outer most layers of DT chambers.
Not more than 3cm of polyethylene and 7mm of lead is possible due to
weight issues.
Simulation of different suggested shielding materials and comparison of
shielding effectiveness.
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Geometry
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Shielding layer covers full length of barrel, all around. Averaging over Phi to
improve statistics of results.
Scoring of particle fluxes and energy spectra of particles entering muon
chambers from the top.
Shieling volumes introduced, 2 cm above muon barrels, covering full length of
DTs. Phi symmetry maintained to improve statistics in results.
Geometry options:
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v1.0.4.0: Shielding volume filled with AIR.
v1.0.4.1: Shielding volume filled with poly-ethylene (PE).
v1.0.4.2: Shielding volume filled with borated poly-ethylene (B-PE). (5% natural boron)
v1.0.4.3: 7mm of lead shielding.
Shielding (lead+Air, v1.0.4.4: 7mm of lead shielding + 3cm B-PE.
lead+BPE) Shielding (Air, PE ,B-­‐PE) Spectral scoring plane (par9cles crossing from top to down) 7th April 2014
FLUKA simulations of DT shielind options - Moritz Guthoff
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1-D particle fluxes
725cm < R < 730cm, All Particles
Flux @ nominal lumi
Ratio of flux w.r.t. no shielding
•  General reduction of particle flux with any installed
shielding
•  Shieling at maximum efficient with ~2m overlap.
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1-D particle fluxes
725cm < R < 730cm, Neutrons
Flux @ nominal lumi
Ratio of flux w.r.t. no shielding
BPE: factor 4
With lead: no effect
7th April 2014
FLUKA simulations of DT shielind options - Moritz Guthoff
PE: factor 2
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1-D particle fluxes
725cm < R < 730cm, Photons
Flux @ nominal lumi
No lead: no effect
But: no increase!
7th April 2014
Ratio of flux w.r.t. no shielding
only lead:
factor 2
FLUKA simulations of DT shielind options - Moritz Guthoff
Lead + BPE:
factor 5
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Particle spectra, |Z| < 406cm
Thermal (<1eV):
•  PE inefficient
•  BPE highly
efficient
“Fast”:
•  PE & BPE likewise
efficient
Lead (green & orange):
•  No influence on neutrons
7th April 2014
PE & BPE: low influence on general
spectrum, but visible capture photon
peaks: PE (2.2MeV), BPE (480keV)
Lead (green & orange):
•  Significant shielding below 500keV
•  Capture peaks reduced.
FLUKA simulations of DT shielind options - Moritz Guthoff
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Particle spectra
406cm < |Z| < 661cm
•  Same qualitative result as scoring of spectra in the center.
•  Shielding less efficient due to particles leaking in from the side.
•  Recommendation to extend shielding further than DT
chambers.
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Summary
•  Significant reduction of neutron fluence with shielding PE
shielding. (assuming full coverage)
–  With PE factor ~2, with B-PE factor ~4.
–  PE and B-PE have the same shielding efficiency above 1eV neutrons
energy.
–  Below 1eV only B-PE with significant shielding potential.
–  Lead shielding has no influence on neutron fluence.
•  Photon rates significantly reduced with lead shielding.
–  Shielding mostly efficient below 500 MeV.
–  With PE sharp peak at ~2.2MeV (neutron capture at H), with B-PE sharp
peak at ~480MeV (neutron capture at B).
–  Capture peaks well reduced by lead shielding.
•  Too low statistics for proper conclusion on charged particles.
In any case: no observable increase.
•  Shieling less efficient at the sides -> maximize overlap if
possible or fold shielding around chambers.
•  Will write up this work as internal note asap.
–  If specific representation of the data is desired, please let me know
(certain plots, comparing numbers,…)
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THANK YOU
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All particle flux
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Charged particle flux
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Neutron flux
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Photon flux
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1-D particle fluxes, 725cm < R < 730cm
Charged Particles
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Particle spectra, charged
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