Command </grdm/BRbias 1> not found

I’m trying to bias a Cf-252 radioactive decay simulation to boost the spontaneous fission rate. When I try

/grdm/BRbias 1

I get the error:

command </grdm/BRbias 1> not found

I can see this command in the source code I built, but quite a few grdm commands do not show up in the help:

Command directory path : /grdm/

Guidance :
Controls for the Radioactive Decay Module.

 Sub-directories : 
 Commands : 
 1) nucleusLimits * Set the atomic weight and number limits for the RDM.
 2) selectVolume * Suppply a logical volumes name to add it to the RDM apply list
 3) deselectVolume * Suppply a logical volumes name to remove it from the RDM apply list
 4) allVolumes *  apply RDM to all logical volumes. No parameter required.
 5) noVolumes *  RDM is not applied to any logical volumes
 6) applyICM * Command not active; kept for backward compatibility.
 7) applyARM * True: ARM is applied; false: no
 8) decayDirection * Supply the direction vector for decay products
 9) decayHalfAngle * Supply maximum angle from direction vector for decay products
 10) verbose * Set verbose level: 0, 1, 2 or 3
 11) setRadioactiveDecayFile * Supply user-defined radioactive decay data file
 12) setPhotoEvaporationFile * Supply user-defined photon evaporation data file

Any ideas what could be going wrong?

Alternatively, is there an easy way to set the spontaneous fission branching ratio of my Cf-252 to 100%?

In order to use biasing for Radioactive Decay, you need to use the class G4Radioactivation, and not G4RadioactiveDecayBase (the latter does only the analog mode).

The Guide for Application Developers shows the BRbias option being used with a G4RadioactiveDecay object. Is this out of date?

Yes and no!
For Geant4 10.7 (and earlier version), it is indeed out of date, sorry about that!
But for the next release, Geant4 11 (expected in December this year), the plan is to get back with G4RadioactiveDecay which should be able to handle both analogue and bias mode.

Aha, thanks. I am on 10.6 right now. I look forward to this feature! In the meantime, I will churn some cpu cycles overnight.

As an interim measure, you could use a hacky SteppingAction. For the Cf-252 primary, look to see if the secondary contains an alpha and Cm-248. If it does, change the track status (using a const-cast, which is why this is hacky) to fKillTrackAndSecondaries. It’s not a perfect solution, but at least you don’t waste the time following the whole decay chain in 96% of events.

1 Like