The  Geant4  Collaboration  Meeting  and  workshops  

Andrew  Green    

Manchester  Accelerators  Monday  Meeting    

Geant4  

•  Monte  Carlo  framework  for  

particle  interaction  with  matter  

•  Stands  for  “GEometry  ANd  

Tracking”  

•  Grew  from  an  RD44  project  at  

CERN  20  years  ago.  

•  Based  on  Geant3  –  a  FORTRAN  

code  from  the  70’s  

•  Now  a  large  international  

collaboration.  

The  Meeting  

•  Huge  number  of  talks  (~125)  

•  Organised  as  parallel  sessions    

•  Slightly  biased  view  

•  Tried  to  include  some  interesting  things  

Okinawa  

•  Island  ~1000  miles  

south  of  Tokyo  

•  Sub-­‐tropical  climate  

•  Excellent  weather  

•  Many  things  to  kill  you  

Headlines  

•  Multi-­‐threading:  

–  Reproducibility  is  broken  

–  Some  features  need  

moving  

–  Very  good  scaling  with  

threads    

–  Much  less  memory  

required  

•  High  Energy  Physics:  –  ATLAS  sticking  with  9.6  

and  ST  mode,  CMS  using  

10.00  in  ST  mode  

–  Exploring  MT  

–  Movement  to  C++11/14  

–  Improvements  in  

navigation.  

–  USolids  library  

Headlines  

•  Medical  Physics:  

–  Better  G4Analysis  tools  

–  Validations,  particularly  

MCS  and  Bremsstrahlung  

–  Geant4  DNA    

–  New  proton  therapy  

examples  

•  Space  Physics:  –  Better  biasing  

–  Reverse  MC  

–  Physics  uncertainties  

•  Generally  2D  simulation  

is  preferred.  

Rationale  for  MC  in  Medicine  

•  Several  good  reasons:  

– Physics  is  usually  better  -­‐  validation.  

– Able  to  look  at  e.g.  LET  &  RBE  

– Out-­‐of-­‐field  dose  characterisation  

•  Speed  is  the  major  limitation  

Medical  Applications    

•  Similar  demands  to  everyone  

else  –  Speed  and  Accuracy  

•  Vastly  different  use  case  

•  Only  one  talk  on  Proton  

Therapy  –  Accuracy  

•  Several  talks  generally  on  

Medical  Physics  

•  Many  general  talks  on  speed  

Proton  Therapy  

•  “Redacted”  model  of  IBA  

beamline  

•  Semi-­‐Realistic  

simulations  possible  

•  Validates  well…  

•  …provided  you  get  the  

physics  right.  

Proton  CT    

•  Would  be  a  very  useful  

tool  

•  Simulation  now  

reasonable  

•  Still  takes  ~90  days  on  a  

single  core!  

X-­‐Ray  radiotherapy  

•  Significant  Neutron  flux  

above  14MeV  

•  Not  well  characterised  

•  Probably  a  good  reason  

for  that…  

•  MT  should  help.  

Multi  Threading  

•  Wrapper  around  PTHREADS  

•  Makes  manipulating  them  much  

easier  

•  10  threads  uses  20%  of  the  

memory  10  processes  use  

•  10  threads  are  slower  than  10  

processes  –  locking  and  

overheads  

•  Scales  well  with  number  of  

threads.  

High  Energy  Physics  

•  50%  of  LHC  computing  time  is  

simulation  

•  Even  “small”  improvements  

make  a  big  difference  

•  EM  and  hadronics  treated  

separately  

•  Significant  efficiency  savings!  

•  6x  speedup  in  hadronics,  

10-­‐15%  in  EM  

HEP  –  An  interesting  Physics  Case  

•  Re-­‐Acceleration  of  charge  at  rest  

•  Proposed  for  frictional  muon  cooling    

•  Physics  case  shaky  –  frictionally  cooled  muons  

don’t  stop  

•  Would  this  be  something  we  might  be  

interested  in  having?  

Other  interesting  stuff  

•  Beam  collimation  with  

bent  crystals  

•  Now  implemented  in  

Geant4  (next  release  

probably)  

•  Looks  really  cool  

C++  11/14  •  Lots  of  new  features  

–  “auto”  keyword  –  really  useful  

–  Range  based  for  loops  

–  Native  threading  

–  Thread-­‐safe  STL  (for  a  given  definition  of  “thread-­‐safe”)  

•  Most  compilers  now  support  it  –  No  excuse!  

•  Plan  for  Geant4-­‐10.02  to  be  last  C++03  release  

GeantV  •  Hypothetical  successor  to  Geant4  

•  Vectorised  programming  model  

–  Already  got  a  lot  of  

implementations  in  USolids  

–  Difficult  to  vectorise  the  Geant  

style  tracking  algorithm  

–  Some  of  the  work  can  be  

backported  to  improve  Geant4  

•  Much  faster!  

•  Many  codes  will  benefit  from  this  

kind  of  optimisation  

Thank  You!