| TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 1 0 R&D on the Geant4 Radioactive Decay Physics J oint International Conference on Supercomputing in Nuclear Applications + 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 | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 2 0 Introduction Radioactive decay simulation as part of a larger MC code is important for a 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 We plan to use Geant4 to estimate the prompt and delayed background for future (X-ray) detectors (IXO WFI). The low uncertainty levels needed require a thoroughly validated radioactive decay simulation and support for long term activation | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 3 Introduction Geant4 radioactive decay simulation originally developed as part of ESA contract. Uses tabulated data to obtain decay parameters (half-life, branching, levels, intensities). These data are stored in ASCII-files, but the database does not include reference information. After decay nucleus and decay products are delegated to other Geant4 processes (photo-deexcitation). RadDecay Other processes Ground state | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 4 Introduction: Issues and Status Issue: tabulated data is poorly referenced Solution: new database based on current available ENSDF data Combined effort with international Nano5 team to create common Geant4 data model. Status: retrieval code is implemented, need to finalize data format for use in Geant4. Data files used for our simulations have been updated in old format Issue: only sporadic validation of results* Solution: comparison with experiments for variety of isotopes gamma spectroscopy at Oak-Ridge Laboratories activation and decay experiment at GSI Phelix Laser Status: gamma spectroscopy validation is ongoing, laser experiment in proposal phase Issue: no native support for long term activation current implementation can bias decay times, this removes particles from MC MEGALib and Cosima have addressed this issue, include these concepts for general use Status: early code version implemented, no validation or extensive testing done yet *usually includes adjusting detector efficiency to fit measurement i.e. Hurtado et al., 2003, Sahin and nl 2009 | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 5 Data Source Explored in 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 Status : Retrieval code for ENSDF is completed, can quickly be adapted to produce data files in new format Isotopes used in our simulations have already been updated Deviation of energy levels in keV in Geant4 database compared to ENSDF Comparison between current ENSDF and current Geant4 database shows inconsistencies | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 6 Experimental Verification Simple and Self Consistent Approach Simple and self consistent approach at Oak Ridge Labs: Measure gamma spectrum of isotopes with a HPGe detector. Self consistent means: we do not tweak the detector's geometrical properties or efficiency or source properties to fit our simulated data. What we know: measurement time isotope measured activity of isotope at a given date detector background detector geometry (uncertainty does exist for electron transport during readout, i.e. dead layer at entry window) detector efficiency detector area and volume source geometry Measured so far: 2 2 Na, 5 4 Mn, 5 6 Mn, 5 7 Co, 6 0 Co, Cs, Ba Experimental setup Geant4 geometry source source position | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 7 Experimental Validation Simple and Self Consistent Approach Current best fit simulated gamma spectrum (black) of Cs compared to measurement (gray) 20% deviation 50% deviation Qualatively good, but offsets of up to 100% not tolarable peaks have different offsets 100% deviation Fitted gaussians with underlying continuum to measured (blue) and simulated(red) peaks. Ideally they should be at same position and have same height. Possible solution is to model detector response so that peaks fit this is what we do not want to do | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 8 Effects of Geant4 Version and Physics Settings Gamma spectrum of Cs for different Geant versions compared to experimental data(gray) Tested: G4.9.1, ref04, G4.9.2 Low Energy EM physics Spectra are very similar for all Geant4 versions tested Differ in particle species produced (see next slide) All versions show deviation from experiment of ~20% in continuum True for other isotopes as well Errors on following slides below 10% G4.9.1G4.9.1-ref04G4.9.2 K-S A-D Goodness of Fit (Kolmogorov-Smirnov and Anderson-Darling) GoF tests: all OK at 90% CL | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 9 Effects of Geant4 Version and Physics Settings Spectrum of particles deposting energy in detector for Cs and different Geant versions (Low Energy) Tested: G4.9.1, ref04, G4.9.2 Low Energy EM Same physics parameters are used for every G4 version. Total spectrum is similar (previous slide) but contribution particles strongly differ. This needs to be investigated. Not critical for this validation because we compare total spectrum with experiment, but would be confusing if constituents of spectrum are of interest. For the total spectrum one must add the gamma energies to the energy deposited by each electron. gamma spectrum of and electron spectrum of and 4.9.2 | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 10 Effects of Geant4 Version and Physics Settings Spectrum of particles deposting energy in detector for Cs and different Geant versions (Std) Tested: G4.9.1, ref04, G4.9.2 Std EM Same physics parameters are used for every G4 version. Total spectrum is similar (previous slide) contributions stay the same. But total spectrum does not compare as well as Low Energy EM physics For the total spectrum one must add the gamma energies to the energy deposited by each electron. G4.9.1G4.9.1-ref04G4.9.2 G4.9.1-ref04 Low energy K-S A-D Goodness of Fit (Kolmogorov-Smirnov and Anderson-Darling) GoF tests: all OK at 90% CL | TU Darmstadt | Institut fr Kernphysik | Steffen Hauf | 11 Effects of Detector Geometry Introduction of a dead layer at detector entrance side (i.e Cs) and placing the detector in a room sensitive dead source Anode area of curved field lines w/o room with concrete room with lead room 0.1 mm dead layer 1 mm dead layer 10 mm dead layer K-S