R&D on the Geant4 Radioactive Decay Physics Monte Carlo 2010

1. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 1 R&D on the Geant4 Radioactive Decay Physics Monte Carlo 2010 Steffen Hauf, Markus Kuster, Philipp-M. Lang, Maria Grazia Pia, Zane Bell, Dieter H.H. Hoffmann, Georg Weidenspointner, Andreas Zoglauer Credit: CNES, NASA

2. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 2 Introduction • Radioactive decay simulation as part of larger MC code important for variety of applications. • Examples of GEANT4 dosimetry • Biophysics • Medical physics • Accelerator physics (i.e. LHC) • Manned space mission (i.e. ISS, Moon, Mars) • Unmanned probes (i.e. JIMO), observatories (i.e. IXO) • National Security • ...

3. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 3 Introduction • Geant4 radioactive decay simulation originally developed as part of ESA contract. • Uses tabulated data to obtain decay parameters (halflife, branching, levels, intensities). • After decay delegates nucleus and decay products to other Geant4 processes (photo-deexitation) . Other Processes RadDecay Ground State

4. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 4 Introduction • Problem: Tabulated data is poorly referenced • Solution: New database based on current available ENDF data •  Combined effort with international nano5 collaboration to create common GEANT4 data model. • Problem: Only sporadic validation of results • Solution: Comparision with experiments for variety of isotopes. •  gamma ray spectroscopy at Oak-Ridge Laboratories •  activation and decay experiment at GSI Phelix Laser • Problem: No native support for long term activation •  can bias decay times, this removes particles from MC •  MEGALib and Cosima have adressed this, include these concepts into nano5

5. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 5 Problem 1: Data Source • As part of nano5: common GEANT4 data model • Should include references to data origin • Should allow generic unit testing • Should be „easy“ to update • Common superstructure but adaptable for physics process needs Deviation of energy levels in keV in Geant4 database compared to ENSDF

6. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 6 Problem 2: Experimental Verification • „Simple and General“ approach at Oak Ridge Labs: • Use GEANT4 to decay various isotopes in front of Ortec HPGe detector. • We know: • measurement time • isotope • background • detector geometry to certain extent systematics under control We do not want fit using efficiency Measured so far: 2 2Na, 5 4Mn, 5 6Mn, 5 7Co, 6 0Co, 1 1 6In, 1 3 3Ba

7. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 7 Effects of Geant4 Version and Physics Settings Gamma spektrum of 1 3 7Cs for different Geant versions compared to experimental data(gray) Tested: G4.9.1, 4.9.1* w. Compton mod, G4.9.2 Spectra are very similar for all Geant4 versions tested Differ in particle species produced (see next slide) Same trends for deviation from experiment True for other isotopes as well

8. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 8 Effects of Geant4 Version and Physics Settings Gamma spektrum of 1 3 7Cs (black) compared to experimental data(gray) G4.9.1 low energy physics G4.9.2 low energy physics Spectrum is very similar but contributing particles (e- blue, photon yellow) change

9. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 9 Effects of Geant4 Version and Physics Settings Gamma spektrum of 1 3 7Cs (black) compared to experimental data(gray) G4.9.1 low energy physics G4.9.2 standard em physics Spectrum is very similar but contributing particles (e- blue, photon yellow) change

10. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 10 Effects of Detector Geometry Introduction of a „dead“ layer at detector entrance side (i.e. 1 3 7Cs) sensitive dead source d Continuum and high energy peak representation improves, low energy peak worsens

11. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 11 Effects of Detector Geometry • Most energy is deposited in front part of HPGe crystal and at outer and bore edge. • In real world detector this area will have strongly curved electric field lines causing non-trivial charge transport and collection • Dead layer shows that selectivly changing efficiency of this region can positively influence modelling of continuum

12. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 12 Effects of Detector Geometry • Majority of energy is deposited in frontal detector regions • Holds true in continuum and peak areas of spectrum Cumulative energy deposition in respect to location in detector entrance window detector rear

13. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 13 Laser Accelerated Protons for Testing Activation and Decay Simulation Proton Spectrum Target Normal Sheath Acceleration M. Schollmeier, PhD Thesis TU Darmstadt 2008 M. Roth TU Darmstadt Parameters Laser intensity: Proton flux: Pulse duration: pico seconds Simulation Verification Activation of shielding material Interaction of MeV protons with detector and shielding materials

14. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 14 Laser Accelerated Protons for Testing Activation and Decay Simulation • Due to beam problems so far only one preliminary shot on 2.25mm Sn. • Beam time proposal for additional 18 shots at GSI PHELIX laser was handed in • Stacks are halfed: one side Sn target, other side: radiochromatic films and copper absorbers • After shot: gamma spectroscopy in HPGe detector Sn RC- Stack

15. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 15 Laser Accelerated Protons for Testing Activation and Decay Simulation Courtesy: K. Harres

16. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 16 Laser Accelerated Protons for Testing Activation and Decay Simulation Comparison between cosmic and laser accelerated proton spectrum • Analysis of radiochromatic films results in input spectrum for GEANT4 simulation (solid) • Input in General Particle Source (GPS) • Adequate similarity to cosmic proton spectrum (dotted)

17. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 17 Laser Accelerated Protons for Testing Activation and Decay Simulation • Activation and decay measurement in one run • Simple geometry, add complexity if needed • Physics as used for IXO/Simbol-X simulations (LowEn-EM, hadron) • Only particles with parent process „Radioactive Decay“ are registered. • Protons are „killed“ at boundry Sn-Detector. HPGe Sn p+

18. 08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 18 Summary and Outlook • Radioactive decay database needs to be checked for consistence • New data model which includes references would aid updating and validation • Simple experiment with HPGe detector can be qualatively modelled but simulation isn't completely accurate • HPGe simulation is not sensitive to Geant4 version or physics setups (within modest parameter changes) • HPGe simulation is sensitive to geometrical changes near detector. Further investigation underway • Additional experiment with laser accelerated protons proposed