Neutron production in atmosphere Nuclear physics for Galactic Cosmic Rays in the AMS-02 era – Grenoble (38) / France Session: Neutron detectors, solar modulation and GCRs – Tuesday 4 th December 2012 A. Cheminet a,b, G. Hubert a, V. Lacoste b and D. Boscher a a The French Aerospace Lab (ONERA), PHY/DESP, 2 avenue Edouard Belin, Toulouse Cedex 4, France b Institute for Radiological Protection and Nuclear Safety (IRSN), DRPH/SDE/LMDN, Saint Paul-Lez-Durance, France

Outline Introduction – Context The Atmospheric Natural Radiative Environment Spallation process Extensive Air Showers The Cosmic-ray induced neutrons Transportation through the atmosphere: neutron spectrum Monte Carlo calculations The High Energy Range Multisphere Extended IRSN System The Neutron Monitors The measurement location: the Pic du Midi platform Some results Comparison NMs-HERMEIS A Forbush Decrease Conclusion – A link to GCRs - slide 2 – Outline

Introduction – Context - slide 3 – Introduction

Introduction – Context - slide 4 – Introduction Aircrew Dosimetry Microelectronics Reliability Space Weather Why do we need to study the atmospheric neutrons? Spectral fluence rate (cm -2 ·s -1 ·MeV -1 ) PhD Thesis (ONERA-IRNS/ ): Development of an operating neutron spectrometer extended to high energies and dedicated to the characterization of the natural radiative environment (at the Pic du Midi)

The Natural Radiative Environment - slide 5 – The NRE

The Spallation process (Nuclei fragmentation) - slide 6 – The NRE  A four-step nuclear reaction: The Natural Radiative Environment  Intranuclear cascade [Serber, 1947]  Preequilibrium [Griffin, 1966]  Evaporation/Fission [Weisskopf and Ewing, 1940] [Hauser and Feshback, 1952]  Final deexcitation

The Natural Radiative Environment Extensive Air Showers (hadronic) - slide 7 – The NRE  Primary Cosmic Radiation  Galactic Cosmic Rays  Sun’s particles  Protons (85%)  He nuclei (13%)  Secondary Cosmic Radiation  Neutrons  Protons  Muons  Pions  Photons  Electrons/Positrons

The Natural Radiative Environment Extensive Air Showers, many researches: - slide 8 – The NRE  Simulations and Theory (from CORSIKA School 2011, D. Heck)  CORSIKA (Heck et al.)  AIRES (Sciutto et al.)  COSMOS (Kasahara et al.)  CONEX (Kalmykov et al.)  …  Experiments (detector arrays)  Pierre Auger Observatory (Malargüe, Argentina)  Energy range:  eV  KASKADE-Grande Experiment (Karlsruhe, Germany)  Energy range : eV  High Resolution Fly’s Eye HIRES (Utah, USA)  Energy range : eV  … AIRES, 1 TeV proton (20 km) Pierre Auger Array

The Cosmic-ray Induced Neutrons - slide 9 – The Cosmic-ray Induced Neutrons

The Cosmic-ray Induced Neutrons - slide 10 – The Cosmic-ray Induced Neutrons  Some characteristics:  Broad energy range (meV to GeV)  13 decades  Responsible for Aircrew doses and SEE  Fluence rate dependence:  Altitude  Geomagnetic latitude

- slide 11 – The Cosmic-ray Induced Neutrons  Some characteristics:  Broad energy range (meV to GeV)  13 decades  Responsible for Aircrew doses and SEE  Fluence rate dependence:  Solar activity 24 th Solar maximum activity foreseen in SOHO probe 13/03/2001 The Cosmic-ray Induced Neutrons

The Atmospheric Natural Radiative Environment - slide 12 – The Cosmic-Ray Induced Neutrons  The Cosmic-ray induced neutrons:  Transportation & physics: Boltzmann equation (steady state) O’Brien et al., 1996 The Cosmic-ray Induced Neutrons Boltzmann operator Radioactive decay ( τ neutron = 881 s) Advection operator Absorption-Capture (n,γ) Generation of a i-type particle of energy E and direction Ω Source (for example: GCR) Stopping power for charged particle i(= 0 for neutron) Scattering-down integral Fragmentation (evaporation and cascade)

The Atmospheric Natural Radiative Environment - slide 13 – The Cosmic-Ray Induced Neutrons  The Cosmic-ray induced neutrons:  Spectral fluence rate in lethargic representation at ground level (spectrum): Gordon et al., 2004 Neutron Spectrometer extended to high energies: HERMEIS (IRSN) NRE characterization: Atmospheric neutron spectra measurements  Thermal region ( < 0.5 eV)  Epithermal plateau (0.5 eV – 0.1 MeV)  Evaporation peak (0.1 MeV – 20 MeV)  Cascade peak ( > 20 MeV) The Cosmic-ray Induced Neutrons

Natural Radiative Environment (NRE) Calculations - slide 14 – The Cosmic-Ray Induced Neutrons  Complex radiation field The Cosmic-ray Induced Neutrons  NRE simulations based on Monte Carlo method  GCR spectrum (up to ~TeV) as input  Only H and He  High Energy physics for transportation  Cross sections and models  Atmosphere modeling  Secondaries - global values:  Mean Spectral fluence Rate of the field  Some Monte Carlo NRE codes:  EXPACS (Sato et al., JAEA) based on the PHITS code, 2008  QARM (Lei et al., QINETIC) based on MCNPX and FLUKA codes, 2006  ONERA tool (in development with the Geant4 toolkit)

Natural Radiative Environment Calculations - slide 15 – The Cosmic-Ray Induced Neutrons The Cosmic-ray Induced Neutrons  NRE codes feature:  The atmosphere: Standard atmosphere: T, P and ρ versus z  The GCRs: Axford and Gleeson-force field, solar modulation potential: Φ  The magnetic field: Vertical cut-off rigidity R c : MAGNETOCOSMICS (Desorgher, 2004)  Handling with the hadron transportation: G4 HE models: QGSP_BIC/BERT  Storing the secondary trajectories: G4 flux scorers  ONERA tool (preliminary result): Goldhagen et al., 2004 Experimental data (ER-2 NASA) Φ = 405 MV, R c = 4.3 GV and z=201 g/cm² (h=11.9 km)

The High Energy Range Multisphere Extended IRSN System (HERMEIS) - slide 16 – HERMEIS

The High Energy Range Multisphere Extended IRSN System (HERMEIS) - slide 17 – HERMEIS HERMEIS:  10 polyethylene Bonner spheres  3″, 3.5″, 4″, 5″, 6″, 7″, 8″, 10″ and 12″  2 extended spheres  8″ + W shell (0.5″) & 9″ + Pb shell (0.5″)  High efficiency: 3 He pressure: 10 atm  Fluence Responses R d (E) calculated with MCNPX  130 energy groups  Realistic modeling geometry  Central detector: 2 ″ Thickness and matter of spheres and metallic shells define the detector response in a certain environment EXTENDED BSCLASSICAL BS

The Neutron Monitors (NMs) - slide 18 – HERMEIS

The Neutron Monitors (NMS) - slide 19 – The Neutron Monitors The NM-64:  NMS are used since the 50s  To study cosmic rays  Same principle as extended spheres  Polyethylene reflector (a)  Lead Producer (b)  Gas BF3 proportional counter tubes (c) :  High volume  High efficiency  Fluence Response R NM (E) to neutrons and protons calculated with Geant4  A worldwide Network (NMDB)  ≠ altitudes  ≠ geomagnetic latitudes  Real-time Count Rates available online Pioch et al., 2011

The measurement location: the Pic du Midi platform - slide 20 – The measurement location

The measurement location - slide 21 – The measurement location  Located in the French Pyrenees (5.6 GV)  Various assets:  High altitude: m above sea level  Proximity of Toulouse (2h from the ONERA)  Scientific observation of the Sun (Coronagraph)  HERMEIS operating continuously since May 2011 (GUI) Φ The Pic du Midi Observatory (OMP)

Some results - slide 22 – Some results

Some results - slide 23 – Some results Atmospheric neutron differential spectrum  Example (June 2011)  Unfolding procedure with GRAVEL (a priori spectrum given by EXPACS)  Good consistency between measured and predicted spectra Count rates corrected from pressure effects Cheminet et al., 2012

Some results - slide 24 – Some results Comparison between HERMEIS and NMs count rates  HERMEIS spectra folded with NM responses ≠ HE G4 models Cheminet et al., 2012

Natural Radiative Environment (NRE) characterization - slide 25 – The Cosmic-Ray Induced Neutrons  Comparison between HERMEIS and NMs Some results  HERMEIS  Spectrum: information about neutron energy distribution  Modular (number of spheres)  Very well characterized  Only sensitive to neutrons  SEE and dosimetry studies  Low efficiency  Complex data analysis  A few in the world  Not yet suitable for cosmic ray studies  NMS  High efficiency  Data analysis quite simple  Data available online  A powerful network (≠ R c )  Cosmic ray studies  Only count rates  Sensitive to protons and muons  Not well characterized

Solar event (4 th of August 2011) - slide 26 – Some results  CME and Forbush Decrease: Some results

Conclusion – A link to GCRs - slide 27 – Conclusion

Conclusion - slide 28 – Conclusion Neutron production in the atmosphere  A very well known and documented phenomenon  Theoretical point of view (HE and fragmentation physics)  Calculations: Monte Carlo Transport Codes  Measurements (Bonner spheres, NM, scintillators, …)  A link to GCRs  Neutron spectral fluence rate depends on GCRs  Solar modulation (eleven-year cycles)  Solar events:  Solar Event Particles (SEP)  Ground Level Enhancements (GLEs)  Coronal Mass Ejection (CME)  Forbush Decreases  Perspectives  Calculation of the Yield Function of each Bonner Spheres with the G4-ONERA tool  Study of the Forbush Decreases observed at the Pic du Midi

- slide 29 – Conclusion Thank you for your attention!