1. Geant4 Radioactive Decay
Highlights from the
Geant4 Radioactive Decay
Mini-workshop
Dennis Wright
25 May 2016

2. Outline Summaries from talks Notes from discussions
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
improvements in PhotonEvaporation code
Notes from discussions
multithreading issues
discussion of floating levels
atomic deexcitation
beta-delayed neutrons
use cases and requirements for biasing

3. Progress Since Last Year (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. Handling Unresolved (Floating) Levels (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. 108Tc[176.6+X]
Currently treated in Geant4 as having energy in order to distinguish from known level nearby
92 isomers have no listed ground state at 0; 79 of these are 0+X levels; 13 have no information for ground state
Agreed last year that these levels should be handled by model and propagated as a unique ion (distinct from nearby level)

5. Handling Unresolved (Floating) Levels (T. Koi)
Proposed solution: set minimum difference between levels to be 1 meV in particle category and add character to particle name, e.g. 108Tc [176.6X]
How to handle transitions from floating levels to non-floating levels (energy conservation problems)
234Pa[73.92+X] particularly important example (floating levels confused with fixed)

6. 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

7. Database Improvements (L. Desorgher)
Levels in RadioactiveDecay4.3.1, PhotoEvaporation3.2.1 and ENSDFSTATE1.2 now consistent
some corrections for Geant 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

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

9. 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

10. SuperHeavy Elements in Geant4 (L. Sarmiento)
proton emission experiment described – very sensitive
excellent agreement of experiment and Geant4 for 53Co
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

11. PhotonEvaporation 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)

12. 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
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

13. 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

14. 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 108Tc[176.6X], instead of 108Tc[ ]
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?)

15. Atomic Deexcitation
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

16. 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 29Na as test case

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. Backup Slides

24. Tasks Martin Venhart Laurent Desorgher Alberto Ribon Alex Howard
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

25. Tasks Makoto Asai Andrea Dotti Dennis Wright Marc Verderi
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
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

26. Tasks Luis Sarmiento Unassigned
write code for beta-delayed neutron channel
Unassigned
check lower limit on life time (10e-14 ?) 9B 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

27. Design Teams Floating Levels Biasing 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

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