Rdecay02 Decay Emission Spectrum

Dears G4 experts
I use a geant4.10.04 on Ubuntu 20.
when launching the extended example (rdecay02) and make a Co-60 as a gamma radiation source using commands:

/gun/particle ion
/gun/ion 27 60
/analysis/setFileName Co-60Spectrum
/analysis/h1/set 1 100 0. 1500 MeV #Energy Deposited in detector
/analysis/h1/set 2 100 0. 1500 keV
/analysis/h1/set 3 100 0. 2000 keV
/analysis/h1/set 4 100 0. 2000 keV
/analysis/h1/set 5 100 0. 2000 keV
/analysis/h1/set 6 100 0. 2000 keV # Decay Emission Spectrum
/run/beamOn 10000

And when open the existed root file I see that there is a cut in the decay emission spectrum (around 300 keV) and I don’t know why is this cut (I will attach a screenshot )