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Radioactive Decay: Status and Plans

Radioactive Decay: Status and Plans. Dennis Wright Geant4 Collaboration Meeting 29 September 2015. Outline. Mini-workshop in March 2015 New RDM package design Recent improvements Outstanding problems Plans. Radioactive Decay Mini-workshop. Met at CERN the last week in March 2015

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Radioactive Decay: Status and Plans

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  1. Radioactive Decay: Status and Plans Dennis Wright Geant4 Collaboration Meeting 29 September 2015

  2. Outline • Mini-workshop in March 2015 • New RDM package design • Recent improvements • Outstanding problems • Plans

  3. Radioactive Decay Mini-workshop • Met at CERN the last week in March 2015 • 8-10 people attended in person or by phone • addressed all (?) radioactive decay related problems • considered future projects • planned work for next few years • Many of the items discussed at this meeting have either already been completed or are addressed in this talk • A successful meeting • more to follow?

  4. New Design Adopted • Following critique of Hauf and Kuster: • RDM decay processes now much simpler, more modularized • one class each for a, b, EC, IT • easy to add new decays • Accomplished by removing one level of inheritance • New design to be extended to biased operation • current biased code is old, and interwoven with unbiased code • will begin separating biased from unbiased code • finally, will look into using generic biasing when it is ready for use in at-rest processes

  5. Recent Improvements: Energy Conservation • Current levels • alpha decay : << 1 eV • beta-/+ decay: << 1 eV • IT: < 10 keV • EC: < 10 keV • IT, EC can be improved by including local energy deposit in RDM process • Current levels attained using Q values from database • come from atomic mass measurements, not nuclear • for fully stripped ions, investigate use of nuclear masses

  6. Recent Improvements: New Channels • Branch added for decay by proton emission • no code yet, but soon to be installed • to be followed by one for neutron emission • see talk by Luis Sarmiento on Thursday • Branch also added for double beta decay • also no code yet, just a pass-through • “Observationally stable” isotopes now decay • example: 209Bi has half-life of 1.9 x 1019 years • all these cases are either double b decay or theoretically possible a decays • Important change: all unstable nuclei now decay • user must install timing cut

  7. Recent Improvements: ARM • Atomic relaxation applied now only after EC or IC • in past was applied for all channels, but not always appropriate • What about cases which change electron configuration but produce no holes? • b- decay will create a vacancy in outer shell – how to fill it? • a decay will leave two extra electrons – how to get rid of them? • can a better model be developed?

  8. Outstanding Problems: Data Files • Inconsistencies between various decay files have been a long-standing problem • example: RadioactiveDecay files and PhotonEvaporation files come from same source (ENSDF) but often contain different levels for the same nuclide • Very low-lying excited states • some excited states appear to be only eV above ground – often mistakenly ignored as unrealistic • Mismatches in precision • two files may have same level but differ in number of digits used to represent it • Unified treatment of all files is now DONE • See Laurent’s talk on Wednesday

  9. Outstanding Problems: Reproducibility • Reproducibility seems to be a moving target: • in order to get this to work locks were added which remove most of the MT advantages • at one point this worked in MT, but is now failing again (physics is OK though) • To improve this situation, need to address • data divergences • multiple files with slightly different values for same level data • some hard-coded arrays also have differing values • loss of precision while processing levels • truncation of strings occurs in translating data from one form to another • redundant classes process level values differently • differing thresholds defining short-lived and long-lived levels

  10. Irreproducibility Remedies • Unify database files, provide sufficient precision for level energies • done • Dispense with hard-coded level tables, replace by reading in all nuclide data at initialization time • G4NuclideTable for example • Put photon evaporation and RDM databases in same file structure/directory

  11. Outstanding Problems: Missing Levels • Several bug reports to this effect • nuclide with expected level is not found, GetIon() returns null pointer, lifetime is listed as -1001 • problem appeared in 10.0 (was OK in 9.6) • Problem now understood • multiplicity of decay tables partly to blame (G4RIsotopeTable) • also due to multiple access of isotope tables in G4IonTable • fix: G4ParticleDefinition::GetIonLifeTime() no longer consults G4IonTable • G4Ions object gets lifetime from G4NuclideTable when nuclide is instantiated • also no longer instantiate nuclide just to get its lifetime • fix ready for 10.2

  12. Outstanding Problems: Branching Ratio Normalization • Currently sum of branching ratios for a decay is normalized to 1 in all cases • should not be done if there are missing strengths • if missing strength, stop and kill if parent is at rest • what to do if parent is in flight?

  13. Outstanding Problems: Biased Mode • Bug report of negative branching ratios when biased • Has not been checked for reproducibility • Convolution integral may be incorrect • used to bias decay time windows

  14. Plans: New Features • Correlation of gamma angular distributions • Jason Detweiler’s code now in toolkit • Vladimir I. is installing as part of photon evaporation code • also contains some useful utility classes (Legendre, general polynomial sampling, etc.) • Beta-delayed neutrons and spontaneous fission • Luis will implement • Local energy deposit proposed by RDM process • Improve energy conservation after ARM

  15. Plans: Testing • System tests • rdecay01 – physics comparison reference • rdecay02 – Michel has cleaned up • had06, testEm1 in good shape • Unit tests • clean up existing, but old, unit tests in radioactivedecay/test/ directory (Dennis) • develop a common set (5 decays) of simple tests – Michel, Dennis • 60Co, 133Ba, 234Th, beta+/EC, alpha, IC, etc. • good gamma spectrum, lifetime, are all expected species produced?, relaxed KS cuts

  16. Plans: Validation • A ton of data available for comparison • Begin collecting data for comparison and posting on hadronic validation web pages • start with particle spectra (b+, b-, a , etc.) - Dennis • Laurent has already begun database validation for nuclide (Z,A) plots

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