Problem on electron capture process in simulated I128 decay

Hello everyone,
While simulating iodine (I) 128 decay throughout all the detector volumes (xenon TPC) to retrieve the energy deposition spectrum of EM particles, I encountered an unknown line at low energy for which I can not understand the origin.
I128 decays ~93% of the time via beta minus, and the remaining ~7% via EC to the ground state of Te128.
Looking at the decay scheme, I expected two lines from the EC process: one at ~4 keV (L-shell) and one at ~30 keV (K-shell). However, as shown in the attached plot, another line appears at ~0.9 keV.
This low energy line might be due to M-shell electron capture, but no references are available. In the RadioactiveDecay5.4 file (z53.a128 - attached in the pdf), from which GEANT4 should take the decay scheme, the energy, and the probability, the ECs information is missing. It seems that the file contains only the nuclear de-excitation.

So my questions are:

  • Where does GEANT4 take the EC BR and energy to simulate the decay?
  • Is there a way in the GEANT4 output to distinguish a beta minus decay from an EC?

i128.pdf (53.5 KB)

Thank you in advance for the help.