1. Notes and Summaries from the Geant4 Radioactive Decay Mini-workshop Dennis Wright 28 March 2016

2. Outline Summaries from talks – last year’s progress – handling floating levels – database improvements – RDM tests (biased and un-biased) – problems with random number generators – using Geant4 for super-heavy elements – angular correlation of cascade gammas – discussion of floating levels – photon evaporation code improvements 2

3. Outline Notes from Discussions Use Cases and Requirements for Biasing Tasks Design Teams 3

4. Summaries from Talks Progress since last year (talk by D.H. Wright) – RDM, PhotonEvaporation and ENSDFSTATE databases now consistent with one another – reproducibility problems (in both sequential and multithreading mode) have all been fixed – improved energy conservation for all RDM channels – refactoring of RDM non-biased code completed – code for angular correlation of cascade gammas nearly ready to be installed – photon evaporation code improved and updated – new channels added (decay by proton emission, neutron emission) – many lost levels found and bugs fixed 4

5. Summaries from Talks Handling Unresolved (Floating) Levels (talk by T. Koi) – a non-negligible number of decay chains are based on levels whose energies are not known – levels denoted by guessed energy level plus X, Y, Z, etc. e.g. 108 Tc[176.6+X] – currently treated in Geant4 as having energy 176.600004 in order to distinguish from known level nearby – 92 isomers identified which have this problem – agreed last year that these levels should be handled by model and propagated as a unique ion (distinct from nearby level) – proposed solution: set minimum difference between levels to be 1 meV in particle category and add character to particle name, e.g. 108 Tc [176.6X] 5

6. Summaries from Talks Handling Unresolved (floating) Levels (talk by T. Koi) – how to handle transitions from floating levels to non-floating levels (energy conservation problems) – 234 Pa[73.92+X] particularly important example 6

7. Summaries from Talks Database Improvements (talk by L. Desorgher) – levels in RadioactiveDecay4.3.1, PhotoEvaporation3.2.1 and ENSDFSTATE1.1 now consistent – some corrections for Geant4 10.2. p01 – Q values now taken directly from Qcalc – PhotonEvaporation db now has easy-to-read format – corrected use of BRICC to compute internal conversion coefficients 7

8. Summaries from Talks RDM tests (L. Desorgher) – single decay of different nuclei from example rdecay02 (gamma, x-rays, electrons from 214 Bi, alphas from 238 U, – generally good comparison to data – in biased mode, looked at activity in bunker walls from 45 MeV electrons (very good agreement) – example rdecay02: 137 Cs, 99 Mo, 226 Ra => generally good agreement (see plots) 8

9. Summaries from Talks Random number generators (A. Howard) – granularity and repetition are crucial for radioactive decay – serious issues with granularity and computation time observed – several engines tested: Ranecu, Ranlux, Ranshi, Ranlux64, Mersenne Twist, MixMax – race conditions appear in MixMax – Ranshi doesn’t produce randoms over full interval (0:1) – serious clumping observed in Ranlux – many other results plotted – see slides 9

10. Summaries from Talks SuperHeavy Elements in Geant4 (L. Sarmiento) – proton emission experiment described – very sensitive – excellent agreement of experiment and Geant4 for 53 Co – better atomic relaxation code is needed for x-ray fingerprinting of new heavy elements – high quality code is available – need to implement it rather than make work-around for current code – move away from current G4AtomicShells to G4AtomicShells_EADL 10

11. Summaries from Talks Future Plans (D. H. Wright) – see section on to-do list and assigned tasks 11

12. Summaries from Talks A Few Notes on X, Y, Z levels (M. Venhart) – floating levels (X, Y, Z,..) occur for several reasons – gamma ray spectroscopy difficult in some cases – they decay by low energy transitions (hard to measure) – states fed only by other floating states – decay only by beta decay (hard to fit) – nobody tried to measure – mistakes were made – such states are general problem of nuclear physics – we must identify critical cases and evaluate data ourselves – 92 cases known so far 12

13. Summaries from Talks Photon Evaporation Model Improvements (V. Ivantchenko) – messy design, many problems over the years – many problems fixed – 4-momentum balance – reduced memory churn and overhead – … – in order to fix many other problems, new code developed – default for 10.2 – old code still available – code used by – hadron inelastic – neutron capture – radioactive decay (with single gamma transition) 13

14. Notes from Discussions Multithreading issues – locks currently slow down RDM when reading decay tables – checking that data is there causes delay – possible solution: use double checking as done in ion table (thread-local bool) or G4LevelManager in G4PhotonEvaporation – G4NuclideTable has hard-coded data which duplicates some parts of database, takes memory space – database storage could be optimized by using less granular groupings of files (such as one file with decay data from all nuclei with same A) – convert to binary to speed up reading – users would see no changes (granular ascii files still visible) – consider using SQLite which supports multithreading 14

15. Notes from Discussions Dealing with floating levels – how do we handle transitions which are – floating to fixed – fixed to floating – check to see if any floating levels can be made fixed by evaluating existing data – when any change made, document in data file header – also any data coming from other than ENSDF (e.g. Nuclear Wallet Cards) should be documented in header – user should be able to configure data reader to set X, Y, and Z – nuclides with X, Y, Z etc. levels should be trackable objects, unique from nuclides with fixed level 15

16. Notes from Discussions Dealing with floating levels – implementation: – extra argument for ions (character representing X, Y, Z, etc.) – Get, Find, Create methods in G4IonTable must all be changed – levels represented as 108 Tc[176.6X], instead of 108 Tc[176.600004] – does this pose a problem with too many digits? – extra column (with X, Y, Z etc.) to be added to database entries – still need to work out how to do transitions (truncate?) – 234 Pa is an especially important case where floating levels are confused with fixed ones in the current implementation 16

17. Notes from Discussions Dealing with floating levels – how do we handle transitions which are – floating to fixed – fixed to floating – check to see if any floating levels can be made fixed by evaluating existing data – when any change made, document in data file header – also any data coming from other than ENSDF (e.g. Nuclear Wallet Cards) should be documented in header 17

18. Notes from Discussions Atomic de-excitation – current model is approximate and does not handle pick-up or loss of electrons into outer shells (e.g. for alpha, beta decay) – results in energy non-conservation – RDM currently uses G4UAtomicDeexcitation – should use G4VAtomicDeexcitation – detailed model of Tibor Kibedi is available as a possible replacement – currently local energy deposit is not done – implementing this may help a bit with energy non- conservation 18

19. Notes from Discussions Beta-delayed neutrons – correct model would be to invoke precompound model after beta decay to highly excited level – however, the emission of beta and neutron appears to be nearly simultaneous – also the energy levels are spread out -> do we know level density at high excitations? – decide to implement directly within RDM (no precompound) – details of decay listed in ENSDF – new entries in table will be made – use 29 Na as test case 19

20. Notes from Discussions Redesign of biased radioactive decay – large project – currently in biased mode the RDM process accumulates rates within the process – no other Geant4 process does this -> should not be allowed – attempt to re-design based on generic Geant4 biasing – can generic biasing handle all existing RDM biasing options? – is it correct for both at-rest and in-flight decays – list of use cases and requirements compiled – see slides below – an example of how to proceed is in example GB01 – /examples/extended/biasing/GB01 20

21. Notes from Discussions Redesign of biased radioactive decay – what is biasing? – allowing RDM only in certain volumes – integrating over unobserved particles (fast beta, e.g.) – emphasizing specific branching ratios – sampling rates, weights within time windows – collimation – implementation – make a non-biased version of RDM process – wrap it in biasing class – move all current biasing methods to wrapper – develop UI commands for configuring biasing 21

22. Notes from Discussions Redesign of biased radioactive decay – tallying of histories should be done by scorers – attach scorer to process – input source time profiles by macro (not data or histogram file) – must be able to collect activities using Bateman equations 22

23. Use Cases and Requirements for Biasing Activation in radiation detectors – spacecraft – in beam line shielding Decay chains in low background experiments Radioactive source simulations – specify source activity and time (DAQ) window – make UI command for this – source profiles Radiotherapy – observation of decay within energy or time windows (in beam imaging) Examine biasing options in MCNP, FLUKA 23

24. Use Cases and Requirements for Biasing Isotope production – splitting – branching ratio biasing Backgrounds due to accidental coincidences – PET – rare decays with gammas Total dose, pulse height tallies Integrating un-observed particles – fast beta decay – when neutrinos or other particles are not needed GUI for nuclide tables 24

25. Use Cases and Requirements for Biasing Weight window for branching ratio biasing – to replace existing option for equal branching ratios Specification of ranges in (A,Z) – list of (A,Z,E) – specify levels by time limit (minimum time?) Retain attachment to volumes – currently logical volumes – what about physical? – do this within process 25

26. Tasks Martin Venhart examine 92 known floating levels to see if existing data can be used to fix them contact T. Kibede to see if Geant4 may use his atomic relaxation code Laurent Desorgher add column in photon evaporation database for multi-polarity and delta add beta-delayed neutron data to database Alberto Ribon test for thread saturation in random number generation Alex Howard continue testing of random number generators 26

27. Tasks Makoto Asai add character argument to ions, as well as Get, Find, Create methods attach scorer to process (for biasing) work on binary database implementation Andrea Dotti test for thread saturation in random number generation work on binary database implementation Dennis Wright make RDM model for testing which has all biasing code removed replace G4UAtomicRelaxation with G4VAtomicRelaxation implement double beta decay using spectrum from Luciano Pandola Marc Verderi check correctness of generic biasing in both at-rest and in-flight modes 27

28. Tasks Luis Sarmiento write code for beta-delayed neutron channel Unassigned check lower limit on life time (10e-14 ?) 9 B decays develop new RDM example (rdecay03) to demonstrate new decay channels according to XEON-Phi tests Geant4 is now CPU-bound -> general improvement in coding is required allow assignment of RDM to G4Region as well as G4LogicalVolume 28

29. Design Teams Floating Levels Makoto Asai Martin Venhart Tatsumi Koi Vladimir Ivantchenko Laurent Desorgher Biasing Marc Verderi Alex Howard Luis Sarmiento Dennis Wright Giovanni Santin Makoto Asai Laurent Desorgher 29

30. Design Teams Beta-delayed neutrons Luis Sarmiento Laurent Desorgher Dennis Wright Random Numbers Alex Howard Alberto Ribon Andrea Dotti 30