1. Status Report of Neutron Detector Simulation Development Brian Roeder Postdoc LPC Caen 20 Sept. 2007

2. 21 June 2015B.T. Roeder - Neutron Det. Simulations2 Motivation  Development of fast neutron (1 MeV < E n < 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 – γ-rays  Challenge  detect multiple (N  2) neutron events from breakup reactions and β - multiple n decays.

3. 21 June 2015B.T. Roeder - Neutron Det. Simulations3 Recent Activities  Event Generators  7 He  6 He + 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.

4. 21 June 2015B.T. Roeder - Neutron Det. Simulations4 Event Generator – 7 He  6 He+1n  Generates “back to back” decays of 7 He in rest frame of the 7 He (isotropic) then boosts n and 6 He to beam energy (lab frame).  Relativistic dynamics.  Integrated into GEANT4, based on Fortran code from FM Marques and JL Lecouey.

5. 21 June 2015B.T. Roeder - Neutron Det. Simulations5 Acceptance – Simple Model T. Nakamura et al. – Nebula proposal - RIKEN

6. 21 June 2015B.T. Roeder - Neutron Det. Simulations6 Tests of 7 He evt. generator  GEANT4 + 7 He evt. generator reproduces maximum neutron angle expectations.  Detector acceptance needed will depend on energy of resonance AND available beam energy!

7. 21 June 2015B.T. Roeder - Neutron Det. Simulations7 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.

8. 21 June 2015B.T. Roeder - Neutron Det. Simulations8 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?

9. 21 June 2015B.T. Roeder - Neutron Det. Simulations9 GEANT4 simulation - XSDiff  A thin target simulation with a 4π, 100% efficient neutron detector.  Measures both total cross section and differential cross section of n and recoil.

10. 21 June 2015B.T. Roeder - Neutron Det. Simulations10 Neutron_El_R model  Data based model. Uses n-elastic total cross sections from ENDF.VII for H and 12 C.  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.

11. 21 June 2015B.T. Roeder - Neutron Det. Simulations11 Test Results for H and 12 C  Reproduces flat (isotropic) n-p scattering differential cross section.  Working on parameterization of 12 C 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).

12. 21 June 2015B.T. Roeder - Neutron Det. Simulations12 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.

13. 21 June 2015B.T. Roeder - Neutron Det. Simulations13 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.

14. 21 June 2015B.T. Roeder - Neutron Det. Simulations14 Kiitos to Collaborators!  F.M. Marques, J.L. Lecouey, B. Laurent, N.A. Orr – LPC Caen  M. Labiche

15. 21 June 2015B.T. Roeder - Neutron Det. Simulations15 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.

16. 21 June 2015B.T. Roeder - Neutron Det. Simulations16 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. G.F. Knoll, Radiation Detection and Measurement, Chapter 15, Pgs. 570-575 N. Boukharouba et al., Phys. Rev. C 65, 014004