Decay chain - Internal electron positron production

Hi all,
I will be very thankful if you could let me know about possibility to reproduce Internal electron positron production in latest version of Geant4 (released 13 Feb 2023 ), for example Yttrium 90 decay chain.
The internal pair production branching ratio of Y-90 equals to Ipair = (3.26 ± 0.04) × 10-5 pairs/decay, but seems the decay process even with high statistics (100 M decays) does not produce this pair.
Many thanks,


we have implemented internal gamma conversion to electron but do not have a process of internal gamma conversion inside nucleus. Can you post links to theory and/or phenomenology of this process?


Thanks Vladimir,

Internal pair production, a species of gamma decay, occurs when an unstable nucleus that has at least 1.02 MeV of excess energy directly ejects an electron-positron pair created within its own electromagnetic field without first producing a gamma photon. Many particles decay into particle-antiparticle pairs.

Here is an related article:
Can nuclear physics explain the anomaly observed in the internal pair production in the Beryllium-8 nucleus? ](INSPIRE)
Xilin Zhang Washington U., Seattle

and older one:
DOI: Comment on internal pair production in nuclear decay | SpringerLink

Please let me know if there is any point or idea.
Best regards.