Energy deposition is higher than the primary source energy!

I simulated a simple code that contains 2"x2" NaI. 1 cm away from the detector window, mono-directional and mono-energetic gamma source (E=0.662) was simulated. I recorded the primary particle energy deposition in crystal and it shows that the photo-peak is around 0.705 MeV. However I scaled the yield factor in physics list to 0.08 (SetScintillationYieldFactor(0.08)) and it shows that the peak on the expected energy axis(0.662MeV).
Any ideas why I got higher energy deposition than source energy if I set scintillation yield factor to 1 ? ( I’ve noticed that all geant4 examples has the value of 1 in yield factor)

if you run example TestEm1 with attached macro, you can see that total energy deposited do not exceed beam energy.
photon.mac.txt (435 Bytes)

Thanks Maire!
I got a similar spectrum for my simulation ( the photpeak energy is 0.662 MeV). However, once I added the scintillation properties to NaI (e.g. RINDEX, ABSLENGTH , FASTCOMPONENT…etc), I got the photopeak shifted to higher energy unless I scaled down the scintillation yield factor to 0.08. I’m just wondering is this correct or I have to change some physics lists or properties in order to get the correct spectrum?. Any genat4 scintillation codes is appreciated (other than geant4 examples).

To add to Michel’s answer, optical photons are produced without regard to energy conservation.