1. Simulations of Advanced Compton Telescopes in a Space Radiation Environment Andreas Zoglauer, C.B. Wunderer, S.E. Boggs, UC Berkeley – Space Sciences Laboratory G. Weidenspointner CESR, France

2. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment2/15 The Advanced Compton Telescope 100× sensitivity improvement for spectroscopy, imaging & polarization (0.2-10 MeV) Advanced 3-D positioning  -ray spectrometers, 25% sky field-of-view LEO equatorial orbit, zenith-pointing survey mode (baseline mission), 80%/orbit Life Cycles of Matter Supernovae & nucleosynthesis Supernova remnants & interstellar medium Neutron stars, pulsars, novae Black Holes Creation & evolution Lepton vs. hadron jets Deeply buried sources Fundamental Physics & Cosmology Gamma-ray bursts & first stars History of star formation MeV dark matter Enable high sensitivity  -ray spectroscopy and imaging from 0.2 to 10 MeV

3. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment3/15 Principle of a Compton telescope Photons interact multiple times in active detector.The interaction sequence can be determined from redundant information (scatter angles). The origin of a single not- tracked event can be restricted to the so called “event circle”. The photon originated at the point of overlap.

4. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment4/15 Baseline ACT instrument D1: 27 layers 2-mm thick Si 10x10 cm2, 64x64 strips 3888 det., 248,832 chns -30° C, Stirling cycle cooler D2: 4 layers, 16-mm thick Ge 9.2x9.2 cm2, 90x90 strips 576 det., 103,680 chns 80 K, Turbo-Brayton cooler BGO: 4-cm thick shield ACD: plastic scintillator Realistic mass model based on ISAL and IMDC (NASA/GSFC) instrument and mission engineering studies! More details about ACT: Boggs et al. 2005 ACT mass model on GLAST bus.

5. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment5/15 Simulation & Analysis Package End-to-end simulation package for space-borne  -ray telescopes (source and background). Background predictions verified on WIND/TGRS, INTEGRAL/SPI, RHESSI (MGGPOD, Weidenspointner et al. 2005). The packages includes: Comprehensive space environment model (ACTenvir, R.M. Kippen) Flexible instrument model (ACTmodel by R.M. Kippen & MEGAlib’s Geomega by A. Zoglauer) Almost complete physics model (MGGPOD based on Geant3, written and maintained by Georg Weidenspointner) Compton imaging & analysis tools (MEGAlib, A. Zoglauer) ACTtools: http://public.lanl.gov/mkippen/actsim/act_study/acttools.html MGGPOD: http://sigma-2.cesr.fr/spi/MGGPOD/ MEGAlib: http://www.mpe.mpg.de/MEGA/megalib.html

6. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment6/15MGGPOD What is MGGPOD? Monte-Carlo suite consisting of the Fortran tools MGEANT (Geant3), GCALOR, PROMPT, ORIHET & Decay Designed for background simulation of gamma-ray telescopes Packaged, written, and maintained by Georg Weidenspointner (CESR, France), with neutron cross section updates by Elena Novikova (NRL) and contributions by Mike Harris (prompt deexcitation) Advantages: Verified, mostly working & faster than Geant4 Disadvantages: Base libraries (Geant3, GCalor) no longer supported Unstable and undebuggable (ZEBRA data structures) … Not all required physics processes, cross sections, etc. included Develop replacement based on Geant4?

7. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment7/15 MGGPOD verification Good agreement between measurement and simulation for TGRS, Integral and RHESSI (simulations ca. x2 to low). Weidenspointner et al. 2005

8. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment8/15 ACT background simulations Equatorial low earth orbit after 2 years in orbit: Between 0.5 and 3.5 MeV activation background dominates

9. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment9/15 847 keV broad line from SN Ia Activation (protons & neutrons) still second largest background component  Correct simulation critical for performance prediction

10. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment10/15 Layout of a space background simulation program Geant4 based simulation program event list High level data analysis tools Detector geometry, characteristics and trigger conditions Radiation environment & history Level 1: Handle initial particles and secondaries as well as prompt (within coincidence window) de- excitation, decay, etc. and record all longer-lived radioactive isotopes Level 2: Handle radioactive decay including all secondaries Inspired by MGGPOD Determine radioactive build-up according to irradiation history

11. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment11/15 Simulation requirements I Photon interactions (5 keV – 1 TeV) Polarized Compton scattering (including subsequent Compton scatters) with Doppler broadening ? Polarized gamma conversion (at least down to a few MeV) including conversion on electrons ? Rayleigh scattering (taking care of polarization) ? Photo effect Photo nuclear reaction (e.g. Giant Dipole Resonance) Electron interactions (5 keV – 1 TeV) Energy loss via ionization (must work for thin media!) Molière scattering (must work for thin media!) Bremsstrahlung Delta rays Møller scattering Positron interactions (5 keV – 1 TeV) see electrons Bahaba scattering instead of Møller scattering

12. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment12/15 Simulation requirements II Proton interactions (1 MeV up to 1 TeV) Ionization and scattering Bremstrahlung Spallation Capture  Interaction cross sections for ALL isotopes ?  Correct generation of radioactive isotopes ?  Generate and track secondaries ( , e +-, p, n, etc.) Alpha particles interactions See protons (ex capture) Ion interactions (up to Fe) ? See Alpha

13. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment13/15 Simulation requirements III Neutron interactions (thermal – 1 TeV) Elastic scattering Inelastic scattering  Interaction cross-sections for all isotopes ?  Handle all excitation and all channels of deexcitations ? Neutron capture  Interaction cross-sections for all isotopes  Generation of correct radioactive isotopes with the correct amount ?  Handle all channels of deexcitations and decays ?

14. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment14/15 Simulation requirements IV Spallation, proton capture, inelastic neutron scattering, and neutron capture: Correctly handle meta-stable isotopes, excitation, de- excitation, radioactive decay, daughter nuclids, etc. for each possible isotope Distinguish between PROMPT (within detectors coincidence window) and DELAYED de-excitation and radioactive decay Handle all generated secondaries Keep record of all generated unstable isotopes Generated radioactive elements: Determine build-up of radioactive elements over mission life Handle radioactive decay (again take care of prompt and delayed) including tracking of all secondaries  Correct handling of all possible decay channels!

15. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment15/15 Features not only of advantage for ACT but all current and future low-to-medium energy gamma-ray instruments: INTEGRAL Suzaku NCT (balloon-borne mini-ACT) GRI (potential European Gamma-ray lens imager) NeXT (next Japanese gamma-ray telescope) EXIST (possible successor of SWIFT) …

16. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment16/15 Backup slides start

17. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment17/15 The radiation environment LEO Expected environment in an equatorial low-earth orbit (525 km) which avoids SAA

18. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment18/15 The gamma-ray imager GRI Gamma-ray lens space craft Focal plane detector space craft

19. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment19/15 Principle of a gamma-ray lens imager Compton scatter detector Laue diffraction of gamma rays within the crystal’s volume under Bragg condition

20. Andreas Zoglauer - Simulation of Advanced Compton Telescopes in the Space Radiation Environment20/15 Simulation requirements V Interface between SPENVIS and Geant4 Direct radiation environment input from SPENVIS to Geant4 as a function of:  Orbit height  Orbit inclination  Timed SAA passages