Status Report of Neutron Detector Simulation Development

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Status Report of Neutron Detector Simulation
Development

• Brian Roeder
• Postdoc
• LPC Caen
• 20 Sept. 2007

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Motivation

• Development of fast neutron (1 MeV lt En lt 150
  MeV) detector simulations with GEANT4 for EURISOL
  DS.
• Envisioned detector would have
• High detection efficiency
• Good energy and angular resolution
• Able to discriminate between neutrons ?-rays
• Challenge ? detect multiple (N ? 2) neutron
  events from breakup reactions and ß - multiple n
  decays.

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Recent Activities

• Event Generators
• 7He ? 6He 1n decay. A simple 1n-decay model
  with relativistic dynamics.
• Test detector acceptance at various energies.
  Model fully included into GEANT4!
• n-scattering model development
• Developed a data-based n elastic model in
  GEANT4 for hydrogen and carbon.

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Event Generator 7He ?6He1n

• Generates back to back decays of 7He in rest
  frame of the 7He (isotropic) then boosts n and
  6He to beam energy (lab frame).
• Relativistic dynamics.
• Integrated into GEANT4, based on Fortran code
  from FM Marques and JL Lecouey.

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Acceptance Simple Model
T. Nakamura et al. Nebula proposal - RIKEN
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Tests of 7He evt. generator

• GEANT4 7He evt. generator reproduces maximum
  neutron angle expectations.
• Detector acceptance needed will depend on energy
  of resonance AND available beam energy!

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Continuing Work evt. gens.

• 1n generator
• Add momentum-kick to account for how the
  unbound nucleus is produced.
• Generalize so that user can use to generate
  events for any fragment 1n.
• Develop multiple-n event generator
• Code exists (FM Marques et al.) will integrate
  code into GEANT4/C framework.

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N-scattering models

• Problems/Limitations of existing n-scattering
  models in GEANT4 see poster, previous task 10
  meetings.
• Can I do better with a home-grown model based
  on total and differential cross section data?

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GEANT4 simulation - XSDiff

• A thin target simulation with a 4p, 100
  efficient neutron detector.
• Measures both total cross section and
  differential cross section of n and recoil.

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Neutron_El_R model

• Data based model. Uses n-elastic total cross
  sections from ENDF.VII for H and 12C.
• Parameterized differential cross sections based
  on published data (may be improved)
• Rotation to account for directional
  multiple-scattering.
• Relativistic kinematics. Tested up to 100 MeV.

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Test Results for H and 12C

• Reproduces flat (isotropic) n-p scattering
  differential cross section.
• Working on parameterization of 12C differential
  cross section. Gaussian not bad.

N. Boukharouba et al., Phys. Rev. C 65, 014004
T. Kaneko et al., Phys. Rev. C 46, 298 (1992).
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Improvements to Sims.?

• Efficiency looks good, but now need to look at
  inelastic reactions in more detail.
• Cross-talk looks good, but is the elastic
  scattering cross-talk over-estimated? Need to
  look at inelastic reactions.

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Upcoming development

• Event Generators -
• Integrate fragment - multiple-n event generators
  into GEANT4.
• Develop ideal detector for 1n to 4n breakup.
• Use also to study experimental issues (crosstalk,
  etc.).
• N-scattering models -
• Develop inelastic models for scattering on
  carbon and key detector materials. Leads to
  realistic efficiency and cross-talk simulations.

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Kiitos to Collaborators!

• F.M. Marques, J.L. Lecouey, B. Laurent, N.A. Orr
  LPC Caen
• M. Labiche

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Efficiency and Cross-talk Sims.

• Efficiency of n-events detected over
  threshold (0.5 MeVee)
• Cross-talk Number of coincident events in
  detector M1/Number of Events in detector M0.

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Custom model in GEANT4

• n-p elastic scattering known to be isotropic in
  center of mass for fast neutrons at low energies
  (between 1 MeV and 30 MeV).
• Developed a discrete process in GEANT4 that
  scatters neutron on the proton in center of mass
  and then converts to final energy and scattering
  angle in lab.
• Calculate mean free path in model according to
  known n-elastic scattering cross sections from
  ENDF/B-VII.0.
• Results In thin-target simulation, total cross
  section and experimental angular distribution
  reproduced by simulation.
• Also fixes problem with DEMON detection
  efficiency simulation between 1 and 5 MeV.

N. Boukharouba et al., Phys. Rev. C 65, 014004
G.F. Knoll, Radiation Detection and Measurement,
Chapter 15, Pgs. 570-575